Ten-Tec 1254 User guide

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Page 1

74477

No. 1254

COMPLETE KIT WITH CASE,

HARDWARE

SSB-CW-AM

RECEIVER

Microprocessor-controlled,

15 Memories, dual conversion,

tunes 100 kHz to 30 MHz

KIT

by TEN-TEC

INSTRUCTION

MANUAL

America’s Best!

Page 2

Table of Contents

Section l: GETTING STARTED

A. General Introduction to Receiver Design and Features B. About this Manual and T-KIT C. Working with the Kit Parts Before Assembly D. Detailed Kit Parts List E. Checklist of supplies and tools needed for assembly F. Component Identification Information G. Building Electronic Kits: The Essent ials H. Overview of Kit Assembly Phases

Section ll: Kit Assembly and Alignment

Detailed Table of Contents Installing Parts on the Boards Phase 1.0 Display Board Assembly Notes on Main Board Assembly Phase 2.0 Logic Section and Display Drivers Phase 3.0 VCO's and PLL ("Phase-Locked Loop") Phase 4.0 Receiver Audio, AM and Product Detectors, 455 kHz IF Amplifier, AGC system Phase 5.0 2nd Mixer, 2nd LO, Clarifier control Phase 6.0 RF Input, 1st Mixer, 1st LO amplifier Phase 7.0 Final Assembly and Alignment

Section III: Reference Information

Detailed Table of Contents Specifications: T-KIT Model 1254 Model 1254 Operating Instructions

Primary Controls

Circuit Description

Model 1254 Receiver Block Diagram

Practical Operating Information

GLOSSARY: Terms and Abbreviations Component Reference Index Troubleshooting Guide

including Chart of Significant Test Voltages

Checking for Solder Bridges

Page 3

Table of Contents

Primary Controls

Circuit Description

Model 1254 Receiver Block Diagram

Section l: GETTING STARTED

Section ll: Kit Assembly and Alignment

Detailed Table of Contents Installing Parts on the Boards Phase 1.0 Display Board Assembly Notes on Main Board Assembly Phase 2.0 Logic Section and Display Drivers Phase 3.0 VCO's and PLL ("Phase-Locked Loop") Phase 4.0 Receiver Audio, AM and Produc t Detectors, 455 kHz IF Amplifier, AGC system Phase 5.0 2nd Mixer, 2nd LO, Clarifier control Phase 6.0 RF Input, 1st Mixer, 1st LO amplifier Phase 7.0 Final Assembly and Alignment

4 5 6

8-13

14 15-17 18-19

1 2

3-10

11-12 14-24 26-35

36-46 48-55 56-63 64-72

Section III: Reference Information

Detailed Table of Contents Specifications: T-KIT Model 1254 Model 1254 Operating Instructions

1 . Functions of

2. Storing Frequencies in Memory

3. Recalling or Tuning Memory Frequencies

4. Tuning AM signals

5. Tuning SSB signals

6. Tuning CW signals

7. Microprocessor RESET

8. Memory Battery Te st

Practical Operating Information

DC Power Supply, Audio, Antennas, Special installations, SWL basics and more

GLOSSARY: Terms and Abbreviations Component Reference Index Troubleshooting Guide

including Chart of Significant Test Voltages

Checking for Solder Bridges

1254 - Getting Started – 2

1 2

3-5

6-14

15-23

24-28 25-35 36-39

Page 4

Table of Illustrations, Charts and Diagrams

ic details

Fig. 7.2: Functions of the chassis brackets

Fig. 1R: Frequency Display exam ple

Building one's own receiver from a kit has launched countless thousands of people into communications careers or the hobbies of amateur radio and shortwave listening ("SWLing"). The Model 1254 combines the satisfaction of the kit-building experience with the performance features expected in a modern shortwave receiver. You will build a true dual- conversion superhet with precise microprocessor-controlled frequency synthesizer. Alignment is surprisingly easy and does not require complicated test equipment. Building this receiver yourself also gives you the assurance that you can maintain it in perfect working order for years to come.

General Features:

You will build the Model 1254 in seven sections or phases, testing your work after completing each phase. We encourage you to study this entire manual before beginning const ruction.

A. Introduction to Model 1254

Receiver Features and Design

1 . Getting Started Section

Selected Component Illust rations

16-18

2. Assembly Section

Phase 1.0 schemat Phase 1.0 circuit board illustration Fig. 1.1 : LED alignment Fig. 1.2: Installation of J1 , J2 Fig. 1.3: Encoder wiring Phase 2.0 schematic details Phase 2.0 circuit board illustration Fig. 2.1: Installation of P1, P2 Fig. 2.2: DC Power Input section Phase 3.0 schematic details Phase 3.0 circuit board illustration Fig. 3.1: VCO-1 assembly Fig. 3.2: VCO 2 assembly Phase 4.0 schematic details Phase 4.0 circuit board illustration Fig. 4.1 : Headphone jack wiring Phase 5.0 schematic details Phase 5.0 circuit board illustration Fig. 5.1: balun transformer details Fig. 5.2: Installation of Q4, C63, Q7 Phase 6.0 schematic details Fig. 6.1: RF Input Bandpass Filter Assembly Fig. 6.2: First Mixer Assembly Fig. 6.2b: Alignment Preview Phase 6.0 Full circuit board illustration Fig.7.1: Chassis and panel assembly overview Table 7. 1: Small hardware preview

14 15 17 20 26 27 30 31 36 37 41 48 49 51 53 56 58 60 61 62 62 66 67

4 5 7 8 9

3. Reference Section

Fig. 2R: Spectrum plot examples Fig. 3R: Block Diagram of Circuit Stages Fig. 4R: PLL Block Diagram Fig. 5R: A simple outdoor SWL antenna Fig. 6R: DC power connector polarity Fig 7R: Headphone jack wiring

Foldout Pages (after "Getting Started" section): Mechanical Assembly Details X-Ray View of Circuit Boards (color-coded)

1254 - Getting Started – 3

16 19 21

4 7 8 9

Page 5

Building one's own receiver from a kit has launched countless thousands

A. Introduction to Model 1254

Receiver Features and Design

of people into communications careers or the hobbies of amateur radio and shortwave listening ("SWLing"). The Model 1254 combines the satisfaction of the kit-building experience with the performance features expected in a modern shortwave receiver. You will build a true dualconversion superhet with precise microprocessor-controlled frequency synthesizer. Alignment is surprisingly easy and does not require complicated test equipment. Building this receiver yourself also gives you the assurance that you can maintain it in perfect working order for years to come.

General Features:

Frequency coverage: 100 kHz to 30 MHz Choice of normal or fast tuning (2.5 kHz SSB, 5 kHz AM

or 100 kHz in either mode)

Fifteen programmable m emories Convenient default or "empty" memory: 15 MHz (WWV) Synthesized 45-75 MHz local oscillator 45 MHz firs t IF 455 kHz second IF 4 kHz filter bandwidth combines good AM audio response

with excellent SSB-CW selectivity

Semiconductors: 10 IC 's, 26 transistors, 16 diodes Antenna connector can supply DC voltage for active antenna 1.5W audio output, built-in speaker, headphone jack Includes a wall-type 15VDC power supply but will operates from

any 1 2-16 VDC 500 mA power source

You will build the Model 1254 in seven sections or phases, testing your work after completing each phase. We encourage you to study this entire manual before beginning const ruction.

A detailed circuit description and block diagrams are provided

in the Reference Section, Part 3 of this manual.

If you have never built an electronics kit before,

please see pages 18-19.

See page 14 for tools and supplies required

to build the kit and use the r eceiver.

1254 - Getting Started – 4

Page 6

This T-KIT Manual has THREE sections:

Electronic kit-building has changed dramatically during the 50 years since TEN-TEC's founder (Al Kahn, K4FW) gave a boxcar loaded with war surplus parts to some friends who started a company which became known as Heathkit™, so, the s everal generations of "the hams at TEN- TEC" are very aware of the standards remembered by all of us who enjoyed building major kit projects in decades gone by. Be assured that we refer to a large library of the most respected manuals of yesteryear as well as T-KIT customer comments in continuing to provide you with today's best in electronic kit projects.

Today's electronic parts are much smaller and more delicate than they were a few decades ago. This fact challenges today's kit-builders to become much more careful than in the past when identifying and installing circuit board components.

Those nice double-sided boards with the plated-through holes should be a further mot ivation for close attention to directions and parts identification. while soldering is fairly easy, the "desoldering" process is extremely tedious, often requiring the purchase of replacement parts.

On the other hand, we know you will appreciate the clas sic precision and sturdiness of your kit's metal enclosure hardware custom designed and manufactured here at TEN-TEC.

B. About This Manual and T

KIT

We understan

d you may be anxious to get going!

Before trying ANY soldering to the circuit boards!

This book is the key to your success with the

And we now count on

you to follow it.

C. Working with the Kit Parts

BEFORE beginning Assembly

1. Getting Started

(This one, which includes the KIT PARTS information prior to any soldering.)

2. Kit Assembly

(Presented in seven step-by-step illustrated "Phases".)

3. Reference Information

(Such as operating instructions, circuit description, troubleshooting

guide and much more.)

When you are ready to do something instead of read,

Go straight to the KIT PARTS LIST,

Starting on Page 8. Use the check boxes

To make SURE you have every single part listed.

But, PLEASE READ

At least this very short “Getting Started” chapter

ALL of us "build kits" of many kinds. We do it every time we bring home a new box marked "some assembly required"! And most of us love to use our own Common Sense first to see how quickly we can put together that new bike, computer desk or some gadget before we ever look at the instruction sheets! This approach is fine for mechanical assembly projects, but it is disas trous for modern electronic kit projects.

Model 1254 Receiver Kit project you are starting.

It's a TWO-WAY D E A L.

You count on the information in this manual

You just invested serious dollars in a box containing electronic and sheet metal parts plus this book. The same money could have gotten you a comparable receiver, maybe pre-owned, very nice and ready to use. But you still chose to build this kit. The main reason to build equipment such as the Model 1254 is usually the building experience itself . Plus some new electronics know-how and understanding which can come with such experience. The purposes of this manual are to help you have a kitbuilding experience which is both successful and enjoyable!

1254 - Getting Started - 5

Page 7

Electronic kit-building has changed dramatically during the 50 years since

C. Working with the Kit Parts

BEFORE beginning Assembly

TEN-TEC's founder (Al Kahn, K4FW) gave a boxcar loaded with war surplus parts to some friends who started a company which became known as Heathkit™, so, the s everal generations of "the hams at TENTEC" are very aware of the standards remembered by all of us who enjoyed building major kit projects in decades gone by. Be assured that we refer to a large library of the most respected manuals of yesteryear as well as T-KIT customer comments in continuing to provide you with today's best in electronic kit projects.

On the other hand, we know you will appreciate the clas sic precision and sturdiness of your kit's metal enclosure hardware custom designed and manufactured here at TEN-TEC.

1. Read the terms of the T-Kit Limited warranty Now! It explains both our responsibilities and yours.

2. The success of your project depends on your willingness to study this manual. Check your kit package Now for any update sheet(s) to supplement this manual.

3. The bag containing the Display Board includes ALL parts used for the Display Board, Assembly phase 1.0. After checking the

contents of the Display Board bag, keep those parts together and separate from all other kit parts.

1254 - Getting Started – 6

Page 8

4. Check and organize ALL Main Board parts per the Kit parts

A. Model 1254 Front Display Board Kit

(These are packed together in one bag. Keep them together, separate from the other kit parts.)

Quantity

8 1 4 3 6 4 4 2 1 1 1 1 1 1

There are a few VERY Small Parts . . .

● setscrew for main Tuning Knob

HARDWARE ITEMS

D. T-KIT Model 1254 Receiver

KIT PARTS LIST

List before you start soldering. Electronics hobbyists have many

different ways of sorting and organizing small parts: standing them on a block of styrofoam or in the holes along the edge of corrugated cardboard, arranging them in an egg carton or muffin tin, or making logical piles in a small tray.

5. This kit manual offers you the further opportunity to "PREORGANIZE" the parts exactly needed for each of the five Main Board Assembly Phases 2.0 through 6.0. After the sectional board drawings and schematics introducing each Assembly Phase, see the Quick Reference List of parts (with circuit functions) used for that phase.

The main goal, of course is to locate these and not to lose them!

● ferrite beads for C63 and Q7 (2)

● plastic crystal base insulators for Y1, Y3 (2)

Please refer as needed to the "Model 1254 Mechanical Details" foldout page at the end of this section to see how all major parts and sections of your receiver go together. Sizes and descriptions of smaller hardware items such as screws are specified clearly in instruction steps.

6. If you believe any parts are missing from your kit package, the warranty explains how to contact us for replacement parts.

7. We encourage you just to take your time with this project. Build it for the sake of the building experience. You'll use the receiver for years, but you'll only build it once. It really is worth your time to learn about it as you build it!

1254 - Getting Started - 7

Page 9

D. T-KIT Model 1254 Receiver

KIT PARTS LIST

1. Check and or ganize all parts before starting construction.

2. See T-KIT Warranty if you believe any parts are missing. The Warranty explai ns how to contact us.

3. If “***” appears in the "Schematic" column for a common part value, please refer to the Component Reference Index (in "Reference" section) to see all uses of that value.

A. Model 1254 Front Display Board Kit

(These are packed together in one bag. Keep them together, separate from the other kit parts.)

Quantity

8 1 4

3 6 4 4 2 1 1 1 1 1 1

Description and Value

Resistor: 33 ohm (orange-orange-black) 1/4watt...........

Resistor: 1K (brown-black-red) 1/8 watt.........................

1N4148 silicon diode …....................................................

Green LED …..................................................................

LED Display …......................................................

Mini pushbutton switches, momentary ….........................

Switch button keycap ….....................................

8 position pin header socket …........................................

Rotary Encoder …............................................................

3-wire plug assembly ( for encoder ) …...........................

SPDT toggle switch …......................................................

2-wire (red) plug assembly (power switch) …................

Insulating sleeve (for power switch, phone jack) 5”Piece Display circuit board, 2-sided, plated-through h

..............

oles …....

Schematic

R1-R8 R9 D1-D4

D5-D6

D5-D7 U1-U6 SW1-4 for SW1-4 J1, J2 EN1

DC power

….............

.................

Part No.

30120 30138 28001 28082 28201 32113 38235 35277 32122

86085-02

32121

86085-01

......44035

78092D

1254 - Getting Started – 8

Page 10

B. Main Receiver Circuit Board Parts

Quantity

1 14 8 26

Quantity

2 1 2 1 1

Quantity

1 2 4 8 4

Quantity

1 1 2 2 3 1 1 1 1 4 1 2 1 2 1 3 2 3 2

See page 16 for help in identifying molded inductors!

SORTING THE SHIELDED COILS

See Page 17 for VCO

coil details (L2, L3)

Fixed Res istors

The 3 color bands denote resistance value. The 4th band (gold) denotes 5% tolerance. All resistors are l/4-watt unless specified otherwise.

Quantity

4 2 3 12 2 6 5 5 2 4 5 18 1 5 12 1 1 1 1

Description and Value

“zero ohm” jumper (single black band) …....................

4.7 ohm (yellow-violet-gold) …....................................

47 ohm (yellow-violet-black) …....................................

100 ohm (brown-black-brown) ….................................

150 ohm (brown-green-brown)….................................

220 ohm (red-red-brown)…..........................................

470 ohm (yellow-violet-brown) …................................

1K (brown-black-red) …..................................

.............

1.5K (brown-green-red) …............................................

2.2K (red-red-red)….....................................................

4.7K (yellow-violet-orange) ….....................................

10K (brown-black-orange)…........................................

15K (brown-green-orange) ….......................................

22K (red-red-orange)…................................................

47K (yellow-violet-orange) …......................................

150K (brown-green-yellow) ….....................................

220K (red-red-yellow) …............

..................................

1 megohm (brown-black-green)…................................

10 megohm (brown-black-blue)…................................

Schematic

JMP1-3, R66 R1, R45 R28, 34, 40 *** R20, R21 *** *** *** R16, R17 R47, 61, 85, 87 *** *** R15 *** *** R44 R49 R48 R2

Disc Ceramic Capacitors

Quantity

1 1 1 1 3 1 1 2 1 4 1 4 1 2 2 1 4

Description and Value

1 pF 2 pF 3 pF 8 pF 10 pF 15 pF 18 pF 20 pF 27 pF 33 pF (wider lead spacing) 33 pF (narrow lead spacing) 47 pF 56 pF 75 pF 100 pF (marked 101) 150 pF (marked 151) 180 pF (marked 181)

Schematic

C55 C30 C23 C57 C24, 27, 28 C52 C31 C94, C95 C19 C21, 22, 77, 78 C5 C54, 56, 70, 73 C83 C39, C84 C91, C92 C37 C37, 40, 71 72

Part No.

30353

30 111 30122 30126 30128 30130 30134 30138 30140 30142 30146 30150 30076 30154 30157 30163 30077 30173 30185

Part No.

23247 23301 23248 23250 23251 23253 23302 23254 23375 23376 23246 23378 23379 23382 23385 23388 23389

1254 - Getting Started – 9

Page 11

Disc capacitors cont.

See page 16 for help in identifying molded inductors!

SORTING THE SHIELDED COILS

See Page 17 for VCO

coil details (L2, L3)

Quantity

1 14 8 26

Description and Value

220 pF (marked 221) …................................................

.001 μF (marked 102) …................................................

.01 μF (marked 103) ….................................................

0.1 μF (marked 104) ….................................................

 Film Capacitors (5% tolerance)

Quantity

2 1 2 1 1

Description and Value

.0022 μF (marked 221) ….............................................

.0068 μF (marked 68

.047 μF (marked 473) …...............................................

.01 μF (marked 103) ….................................................

0.47 μF (marked 474) …...............................................

2) ….............................................

 Other Capacitors

Quantity

1 2 4 8 4

Description and Value

Trimmer capacitor, 5-40 pF …......................................

1 μF electrolytic …........................................................

10 μF elec

33 μF electrolytic …......................................................

470 μF electrolytic …....................................................

trolytic …......................................................

 Inductors

Quantity

1 1 2 2 3 1 1 1 1 4 1 2 1 2 1 3 2 3 2

Description and Value

0.12 μH unshielded adjustable coil…..........................

Shield can for L11 ….....................................................

0.25 μH unshield

Shield cans for L9, L10 ….............................................

Shielded 455 kHz adjustable coil….............................

0.1 μH coil shielded (5 pins, no marking) …...............

VCO coil, 48-58 MHz (white, 3 wires, more turns) … VCO coil, 58-75 MHz (white, 3 wires, fewer turns) …

0.27 μH molded inductor (red-violet-silver-gold) …...

0.39 μH molded inductor (orange-white-silver-gold)...

0.47 μH

molded inductor (yellow-violet-silver-gold) ..

0.56 μH molded inductor (green-blue-silver-gold) …...

1.0 μH molded inductor (brown-black-gold-gold) …....

4.7 μH molded inductor (yellow-violet-gold-gold) …..

6.8 μH molded inductor (blue-gray-gold-gold) …........

100 μH molded choke (brown-black-brown-gold) …...

Balun transformer, bifilar …..........................................

Balun transformer, trifilar ….........................................

Ferrite bead (.120X.060X.085) ….................................

ed adjustable coil…..........................

Schematic

C36 *** *** ***

Schematic

C89, C90 C74 C10, 12 C11 C9

Schematic

C2 C8, C93 C18, 32, 45, 98 *** C1, 43, 51, 106

Schematic

L11 (L11) L9, L10 (L9, L10) T2, T3, T7 T6 L3 L2 L4 L5, 13, 14, 17 L8 L7, L15 L18 L6, L19 L16 L1, L12, L20 T1, T8 T4, T5, T9 at Q4, Q7

Part No.

23396 23245 23260 23261

Part No.

23286 23338 23291 23340 23330

Part No.

23413 23264 23266 23308 23228

Part No.

21180 38131 21059 38226 21093

21194

85421-01 85421-02

21105

21107

21108

21109

2111 2 21120 21122 21164 21152 21153

21090

1. T2, T3, T7: 455 kHz transformers (3) are factory-shielded

2. T6 is the pre-shielded coil larger than T2, T3, T7.

3. L9 and L10 are identical; add shield “cans” during assembly.

4. L11 is the small adjustable coil, shield added during assembly.

1254 - Getting Started – 10

Page 12

 Integrated Circuits

Quantity

1 1 2

1 1 1 1 1 1 2 2 1 1 2 2 4 2 1 1

About IC Sockets: T

KIT s include DIP sockets for ICs only if we consider a

See page 17 for help in identifying diodes!

LOOK AHEAD . . .

To the “Component Reference Index”!

Quantity

1 1 2 1 1 1 1 1 1

Description and Value

PIC16C57-XT/P microcontroller IC (pre-programmed) ….............

MC7805CT (or LM340T-5) 5-volt regulator IC ….........................

MC1350P IF Amp IC ….................................................................

MC145170P1 PLL synthesizer IC ….............................................

NE612AN (orSA612AN) mixer-oscillator ..................................

SN74LS47N BCD decoder IC …...................................................

BA618 LED display driver IC .....................................................

NJM7810FA voltage regulator IC ..............................................

NTE 1852 audio amplifier IC …...........................................

Mounting hardware for U10 (packed with IC's):

Quantity

1 1 1

Description and Value

#4-40 3/8” screw, phillips (zinc) …...............................................

#4 lock washer, internal tooth …..................................................

#4-40 hex nut …............................................................................

........

Schematic

U2 U1 U8, U9 U3 U7 U4 U5 U10 U6

Part No.

98394-1.0

Part No.

socket essential for that kit design, such as the U2 microprocessor in this receiver. Out technicians find that sockets can cause more problems than permanently installed IC's.

 Transistors and Diodes

Quantity

15 3 6 1 1 8

2 1

Description and Value

2N4124 NPN transistor …........................................................

2N5087 PN

J310 JFET transistor …............................................................

BF988 dual-gate MOSFET transistor …................................

MPSA14 transistor …...............................................................

IN4148 silicon diode …............................................................

BA479 PIN diode ….................................................................

1N7

1N748A zener diode, 3.9 volt ................................................

P transistor …........................................................

53A zener diode, 6.2 volt …..............................................

Schematic

*** Q10, Q17, Q18 *** Q4 Q19 D1,4,5,10,11,12 ,15,16 D13, D14

D6, D7 D17

Part No.

25095 25062 25296 25319 25336 25341 25400 25356

60003 51002 54002

25258 25001 25115 25388 25253

28001 28062

28055 28021

1254 - Getting Started – 11

Page 13

 Other Components, Boa rd-Mounted Hardware:

LOOK AHEAD . . .

Quantity

1 1 2

1 1 1 1 1 1 2 2 1 1 2 2 4 2 1 1

Description and Value

Circuit Board for Model 1254 …................................................

28 pin IC socket for microprocessor U2 …................................

10K potentiometer (volume, clarifier controls) …......................

NOTE: (The mounting nuts and washers for the volume and clarifier controls may be pre-attached or included with other hardware.)

100 ohm trimmer potentiometer (1st mixer balance) …............

Crystal, 3.579545 MHz ….........................................................

Cryst

al, 44.545 MHz ….............................................................

455 kHz ceramic resonator {marked 4558K) …........................

45 MHz crystal filter (crystal case, 3 leads) …..........................

455 kHz lF filter (Murata CFR455I) ….......................................

2-pin PC-mount terminal (DC switch, speaker) …....................

3-pin PC-mount terminal (encoder, phone jack) …...................

RCA phono ja

Coaxial DC power jack ….........................................................

Right-angle 8 pin header ..........................................................

Crystal base insulator …...........................................................

RF shield main enclosure ….....................................................

RF shield top cover …...............................................................

9-volt battery snap (for memory backup battery) ….................

Insulator pad HC-45U

ck (antenna) …....................................................

To the “Component Reference Index”!

Schematic

(U2) R73, R82

R70 Y1 Y3 Y2 FL1 FL2 J2, J5 J4, J6 J3 J1 P1, P2 for YI, Y3

….....................

Part No.

78138 27021 30267

30856 48079 48235 48228 48339 48284 35065 35066 35238 35266 35276 38229 91744 91745 35174 38262

This Parts List shows the quality of each type of part supplied in your kit. The Component Reference Index in the Reference Section, Part 3 of this manual, keyed To the schematic diagram, identifies the assembly step for each part as well as Descriptive information about each part. This Index is your assurance (and ours!) That every component is accounted for in the Assembly Steps, cross-checked to the Full schematic and sectional schematic diagrams.

EXAMPLE:

C1 470/16v el. 2-30 23228 Filter Cap for display driver C2 5-40 pF var. 2-33 23413 Master clock (adjust to 3.5800 MHz) C3 0.11tF 2-23 23261 Bypass o n PLL chip C4 33/16v el. 2-31a 23308 Bypass on PLL chip

1254 – Getting Started - 12

Page 14

C. Chassis Parts and 0ther Hardware

REQUIRED, NOT SUPPIIED

RECOMMENDED, NOT SUPPLIED:

MINIMUM TOOLS FOR KIT ASSEMBLY:

MINIMUM TEST EOUIPMENT:

OPTIONAL TEST EOUIPMENT:

HELPFUL ADDITIONAL TOOLS

See Foldout titled "Mechanical Assembly Details" inserted at the end of this

section. This drawing will help you identify major mechanical parts.

Quantity

1 1 1 1 1 1 1 1 1

Description and Value

Front panel assembly for Model 1254 …..................................

Plastic insert for front panel headphone jack …........................

Rear panel …............................................................................

Left side chassis panel ….........................................................

Right side chassis panel ….......................................................

Speaker/

battery shelf …............................................................

Steel bottom shell cover ….......................................................

Steel top shell cover ….............................................................

3" round speaker …..................................................................

Hardware Parts Bag:

Quantity

1 1 4 4 8 4 8 4 1 2 1 1 1 1 1

Description and Value

1/8" panel-mount phone jack …....................

.050" hex allen wrench (for front panel knobs) ….....................

Rubber bumper feet (self-adhesive) ….....................................

#4 lock washer (split style) …....................................................

#4-40 1/4" screw, phillips (zinc) …............................................

#4-40 1/4" screw, phillip, (black) …...........................................

#4-40 3/16" undercut ("countersink") screw ..........................

#4 self-threading screw (to secure front panel) …..

#4-40 Setscrew (for Tuning knob - SEE NOTE BELOW) ….....

Control knob ….........................................................................

3-wire plug assembly (headphone jack) …...............................

2-wire plug assembly (speaker) …............................................

Tuning knob …..........................................................................

TEN-TEC logo …......................................................................

Tinted, screened display lens …................

D. Standard Accessories

Quantity

1 1 1 1

Description and Value

Model 1254 instruction manual ….............................................

del 1254 Quick Reference Guide and SWL Log …..............

Model 1254 full schematic/construction overview sheet ….......

15VDC @800mA wall-plug power supply ….............................

............................

..................

...............................

Schematic Part No.

93341-1A

93367

93342-CN1A

93116

93109

93110

93 111-CN

93112-CN

47011

Schematic

….....................

Schematic

…..................

Part No.

35298 38040 42001 51058 60001 60032 60080 65009 65015

81559 86085-3 86085-4

93029

98228

98393

Part No.

74477

74353

74354

21195

Suggestion: Use the allen wrench supplied to install the No. 65015 setscrew into the Tuning Knob NOW, so it will not be lost!

1254 – Getting Started - 13

Page 15

E. What YOU provide to build and operate this T-KIT M odel 1254 Receiver

REQUIRED, NOT SUPPIIED

9-volt battery (memory backup) Antenna(s) for bands of interest thin-diameter rosin core solder contact cement (to secure panel jack insert, speaker and logo)

RECOMMENDED, NOT SUPPLIED:

masking tape (to protect front panel during final assembly) headphones with 1/8" stereo plug

MINIMUM TOOLS FOR KIT ASSEMBLY:

25 to 35 watt soldering iron diagonal cutters or wire "nippers" needle-nose pliers utility (household) pliers adjustable wire stripping tool insulated alignment tools (may be home made from plastic stirrer, etc.) medium phillips and slotted screwdrivers

MINIMUM TEST EOUIPMENT:

VOM or DVM for DC voltage measurements

OPTIONAL TEST EOUIPMENT:

Frequency counter RF signal generator

HELPFUL ADDITIONAL TOOLS

miniature alligator clip jumper leads

desoldering tool

illuminated magnifier

1254 – Getting Started - 14

Page 16

Table 1-C

Diode Identification Guide The main board uses eight 1N 4 148 diodes easily recognized as identical to the four diodes installed on the Display Board. The Zener, and Varactor diodes must be identified exactly. Here's some help:

TYPE Body Type/Color Cathode Band 1N4148 (8) Glass, copper-color inside Black Zener (3) Silver-gray Grayish black

BA479 (2) Glass Black Grey

Table 1-D

F. Model 1254 Receiver

Parts ldentification Notes

We r ely on you to know already what a resistor, transistor, lC "chip" and other common electronic parts "look like." REMINDER: Both the back and inside front covers of this manual provide some light-hear ted help on basic parts identification.

Each assembly step provides useful help in identifying any part, whether by shape, color-code, manufacturer's markings, or other description.

Since correct parts installation is the key to this Receiver working perfectly, we encourage you to refer to the following Parts Identification Notes whenever you feel it necessary.

Table 1-A

RESISTORS:

The Main Board uses only 1/4-watt resistors, while the Display Board uses smaller 1/8-watt resistors packed in the bag with the Display Board itself. Each instruction step lists the first THREE color bands, assuming the fourth band to be gold (5% tolerance). Just be careful about that third "multiplier" band. For example, your kit uses 4.7, 47, 470, 4.7K and 47K resistors, each for very different purposes.

Table 1-B

MOLDED INDUCTORS

(also c al l ed "CH0KES"). These parts are readily recognized because:

1. They are packed with other coils, transformers, etc.

2. W hile similar to resistors, they have "bullet"-shaped ends.

3. The body consistently has a green-bluish color. While these parts follow the resistor color code chart for value identification, we will be the first to agree with you that these color bands really can be HARD to read. EXAMPLE: red, orange and brown can each look like some shade of mud. NO, your eyesight is NOT the problem!

We suggest:

1. Sort all the inductors by quantity required in the Parts List.

2. Set aside (and mark on paper) those which are completely clear to you.

3. Compare PAIRS of bands and pay close attention to the 3rd (multiplier) band

4. A "Process of Elimination" is the easiest way to resolve questions .

1254 – Getting Started – 15

Page 17

Table 1-C

TYPE Body Type/Color Cathode Band 1N4148 (8) Glass, copper-color inside Black Zener (3) Silver-gray Grayish black

6.2V marked “1N 75 3A- nnn” (D6, D7)

3.9V marked “1N 74 8A- nnn” (D17)

BA479 (2) Glass Black Grey

Cathode

Table 1-D

1254 Getting Started – 16

Page 18

Table 1-E

protocol is to identify those in picofarads up to 99 pF simply as 1 pF or 33 pF, etc.

characteristics (e.g. 33J = 33 pF.)

If you've never built an electronics kit before, you are a GOOD candidate for successful construction of this receiver - because we think you'll rely on this instruction manual very diligently. ("Experienced" builders tend to be more inclined to shortcuts which can lead to mistakes!)

Both this manual and the engineering discipline for this receiver were done with YOU very much in mind. We won't insult you by claiming that "anybody" can build this receiver: you'll certainly need the knowledge and skills you gained by working for your ham license or studying electronics theory, and you'll want to allow for a little more assembly tim e than may he needed by those with more building experience"

Aside from the willingness to follow the directions in this manual, the main skill you need is that of soldering. Here, it's a ver y good idea to get s ome practice before working on the receiver circuit boards. Building some simpler T-KlT projects is, of course, a great way to get into kit building. Another way is to take a circuit board from any discarded radio or other electronics device and then remove a number of parts by melting their solder connections. Re-install some or all of the parts, doing so until your solder connections look as clean and professional as the factory work. Don't hesitate to ask an electronics repair technician to critique your work or show you a few tips.

Kit-Building Tips . . .

1 . Please USE the bits of knowledge and wisdom capsulized on the back c over of your T-KIT Instruct ion Manual! You'll find resistor color-codes, soldering tips and more!

2. Unfamiliar Words: We try to use plain language throughout this manual, but electronics does have its special terms and abbreviations. A "glossary" useful to this receiver pr oject is printed in the REFERENCE SECTION (Part 3) of this manual.

G. Building Electronic Kit Projects:

THE ESSENTIALS

CERAMIC DISC CAPACITORS

The vast majority of capacitors in this circuit are the ceramic disc type. Our

There may be one letter to identify temperature

From 100 pF (marked 101) on up to capacitors in the μF range, we provide the

exact part marking (101, 102, 103, 151, 181, etc.) minus any letter. All disc capacitors are specified to fit the exact lead spacing on the board: if a capacitor seems too big or too little for the spacing, you have selected the wrong part!

Table 1-F

MYLAR FILM CAPACITORS

These capacitors have shiny, thick, rectangular bodies with value markings jus t like on the ceramic disc capacitors. In this kit design, the mylar film parts (used in the PLL filter and RF bandpass filter) have values different from any of the disc capacitors, with the sole exception of C11, .01 μF.

Table 1-G

ELECTROLYTIC CAPACITORS

These cylinder shaped parts are easy to recognize from their longer (+) leads and clearly marked wide negative band. In this kit, just be sure to identify an

install correctly those smallest 1μF and 10μF

capacitors as specified in the directions.

Table 1-H

“SPECIAL” PARTS

“Special” parts include crystals, filters, balun transformers which are identified

clearly by a manufacturer's number on the part itself OR by detailed description in a k i t assembly step. We give you plenty of help in the assembly ins tructions for identifying and installing these parts correctly.

The VCO coils (Phase 3.0) are wound on WHITE forms easily identified: L3 (VCO-1): BROWN paint dot L2 (VCO-2): RED paint dot

1254 – Getting Started – 17

Page 19

If you've never built an electronics kit before, you are a GOOD

G. Building Electronic Kit Projects:

THE ESSENTIALS

candidate for successful construction of this receiver - because we think you'll rely on this instruction manual very diligently. ("Experienced" builders tend to be more inclined to shortcuts which can lead to mistakes!)

Kit-Building Tips . . .

1 . Please USE the bits of knowledge and wisdom capsulized on the back c over of your T-KIT Instruct ion Manual! You'll find resistor color-codes, soldering tips and more!

1254 – Getting Started – 18

Page 20

3. SOLDERING: If you are inexperienced, ask any electronics

WORTH REPEATING

Let the heated connection itself melt the solder, NOT the iron tip!

H. Model 1254 SWL Receiver

Kit Assembly OVERVIEW

technician to show you how it's done, then do practice soldering/de-soldering on a junked circuit board before working on your kit. Here's what is important:

Keep the soldering iron tip CLEAN, using a damp sponge Let the heated connection itself melt the solder, not the iron tip Use a thin diameter of rosin-core solder Use VERY good lighting; NEVER be embarrassed to use a

magnifier!

4. DE-SOLDERING is the opposite of soldering and is a more tedious procedure. Again, a repair technician can show you the best technique. Take care not to damage circuit board pads or traces - save yourself f rom desoldering agony by installing the right part the right way the first time!

5. Except for P1 , P2 and J5 mounted on the bottom ("solder side") of the board, ALL Main Board parts are inserted into the top silkscreened side, with leads passing through the holes to t he bottom solder side. (This advice m ay seem insulting, but some folks DO carefully mount and solder all parts on the copper side of the board and wonder why the kit won't work!)

6. Insert all parts as close to the board surface as possi ble before soldering and trimming. Excess wire length above the board can cause unwanted oscillations.

7. Reminder about your Kit Manual: NEVER "Solder first and ask questions later" ! The Success of your project depends on your willingness to study our published directions attentively. Check your kit package for any update sheet(s) to supplement this manual. Use the double check blocks to review your work (ideally with someone else) before connecting voltage.

8. TOOLS: Page 14 lists the "minimum" tools needed f or this particular project. However, you'll appreciate owning a more varied collection of small tools for electronics work: the selection at Radio Shack'" is good, with the lower-priced versions being quite sufficient. If buying your first voltmeter ("multitester"), you may find the "analog" meter type easier to use at first than the digital type.

1254 – Getting Started - 19

Page 21

 You will build the Display Board first and then occasionally plug it into

H. Model 1254 SWL Receiver

Kit Assembly OVERVIEW

the Main Board for further testing. To get a good fit of the LED's and 3digit displays, you'll be handling the front panel and display lens - be VERY careful not to touch these with your soldering iron!

 After finishing PHASE 2.0 (Logic and DC Power Input sections), the

powered-up Display Board plugged to the Main Board (via P1, P2) can now simulate all receiver functions or features described in the Operating Instructions in the Reference section, though not executing them.

 Finishing PHASE 3.0 requires VCO coil adjustments done with a simple

voltmeter measurement at "VCO TP." Individual board drawings are provided as a help for correct assembly of the two shielded VCO sections.

 Completing Phase 4.0 lets you verify that the audio amplifier, product

detector and Second IF amplifier work properly. This Phase also includes the AGC and uses the largest number of parts of any of the assembly sections.

 Phase 5.0: Finishing this section results in a non-tuneable receiver with

full s ensitivity capable of receiving a 45 MHz test signal , with the Clarifier control operational. Mixing the 45 MHz 1st output with the 44.545 2nd LO produces the 455 kHz signal detected and amplified in the Phase 4.0 circuitry. The receiver is designed to generate its own 45 M Hz test signal.

 Phases 6.0 and 7:0: (RF Input and First Mixer sections, Final

Assembly): You're ALMOST ready to start using your receiver, so don't rush these building phases! This work brings in the antenna

signals through the shielded Bandpass Filter circuitry to the First Mixer (also s hi el ded), where received signals are mixed with the tuneable 45-75 MHz LO si gnal from the VCO's. This mixing results in a 45 MHz 1st IF signal fed to the input of the circuitry you built in Phase 5.0. Very simple alignment is done in Phase 7,0 with the receiver mostly assembled. The result is a frequency-synthesized dual-conversion receiver rivaling radio sets costing much more.

See following foldout page for details on the major

mechanical parts used to finish your receiver in Phase 7.0.

►

1254 – Getting Started – 20

Page 22

Before you do ANY soldering, we remind you again to do the following:

Installing Parts on the Circuit Boards:

When we say "INSTALL" a part, this is what we mean:

Model 1254 Receiver

USE ROSIN.CORE SOLDER ONLY.

Kit Assembly

Steps and Illustrations

Installing parts on the boards Preview of Display Board Assembly

Phase 1.0: Display Board Assembly

Sectional Schematic Parts Quic k-Reference and Display Board P ictorial Step -by-Step Assembly

Notes on Main Board Assembly

Phase 2.0: Logic Section and Display Drivers

Sectional Schematic and Ci rcuit Board Pictorial Quick-Reference Parts List Step -by-Step Assembly

Note on Circuit Function Demonstrations

Phase 2.O Progress Test

Phase 3.0: VCO's and PLL ("Phase-Locked Loop")

Sectional Schematic and Ci rcuit Board Pictorial Quick-Reference Parts List Step -by-Step Assembly Phase 3.0 Progress Test:

Phase 4.0: Receiver Audio, AM and Product Detectors, 455 kHz IF Amplifier, AGC circuit

Sectional Schematic and Ci rcuit Board Pictorial Quick-Reference Parts List Step -by-Step Assembly Progress Tests: Audio, p. 41, IF amplifier, p. 45-46

Phase 5.0: 2nd Mixer, 2nd LO, Clarifier control

Sectional Schematic and Ci rcuit Board Pictorial Quick-Reference Parts List Step -by-Step Assembly Progress Test:

Phase 6.0: RF Input, 1st Mi xer, 1st LO amplifier

Sectional Schematic Quick-Reference Parts List Bandpass filt er pictorial and assembly steps First mixer pictorial and assembly steps Installation of rem aining parts

6-10

11-12

14-15

16 17-20 21-22 23-24

26-27 28-29 30-33 34-35

36-37 38-39 40-45

48-49

50 51-53 54-55

57 58-59 60-61 62-63

2 3

4 5

Phase 7.0: Final Assembly and Alignment Model 1254 Receiver Alignment

64-72 68-69

1254 – Assembly - 1

Page 23

Before you do ANY soldering,

USE ROSIN.CORE SOLDER ONLY.

we remind you again to do the following:

Check and or ganize your kit parts in whatever way Is most convenient for you. A special IDENTIFICATION GUIDE is provided after the Parts List.

Go through this ent ire manual: familiarize yourself with its organization and illustrations.

Prepare a clean, well-lighted work space.

Study the ASSEMBLY OVERVIEW (Getting Started Section, Page 20)

Build the Display Board FIRST. All its parts are packed with the board itself, and it is a good orientation project.

Installing Parts on the Circuit Boards:

When we say "INSTALL" a part, this is what we mean:

Choose correct part value Insert in correct PC Board location Insert correctly, if there is a r ight way and wrong way such as f or diodes, IC's, electrolytic capacitors, transistors etc. Insert the part as far as it can go into the board. Solder all wires or pins Trim or "nip" excess wire lengths

of a type intended for el ectronic PC-board assembly.

(Available at electronics distributors or Radio Shack" stores.)

DO NOT use hardware store solder, paste or flux,

Solder contains LEAD: wash hands before eating!

1254 – Assembly - 2

Page 24

Model 1254 SWL Receiver

PREVIEW of

Phase 1.0 Display Board Assembly

The Display Board is a useful "warmup" project before getting

started on the more complex Main Board. It will be plugged in temporarily for Progress Tests in Phases 2.0 through 5.0 and installed permanently at the end of Phase 6.0.

To help you make a good beginning, this Preview and Phase 1.0

assembly directions provide a bit more detail than will be needed for most Main Board assembly steps. This board appears simple, using only a handful of parts. However, correct construction is vital to the success of this kit project and the reliability of your Model 1254 Receiver.

All parts used for the Display Board are packed together with the

board itself . Except for the common 1N4148 diode, all parts in the Display Board kit are unique to this assembly phase, even the resistors! (The display board uses 1/8 watt resistors, while all other resistors are 1/4 watt.)

KIT PARTS REOUIRED for Phase 1.0:

Display Board Parts Kit Model 1254 Front Panel Model 1254 Front Panel Display Lens

PROCEDURES REOUIRED:

Installing all Display Board parts, with special attention to

directions for Display LED's U1-U6, LED's (D5-D7) and J1 , J2

Wiring and mounting of the ENCODER Wiring and mounting of the D C Power Switch

(D5-D6)

1254 – Assembly - 3

Page 25

1254 – Assembly – 4

Page 26

PHASE 1.0: Display Board

All parts used for the Display Board are packed together with the board itself . Except for the common 1N4148 diode, all parts in the Display Board kit bag are unique to this assembly phase, even the resistors! (The display board uses 1/8 watt resistors, while all other resistors are 1/4 watt.)

All parts except J1 and J2 are mounted on what we will refer to as the FRONT or silkscreened side of the display board, with soldering done on the back side. J1 and J2 are mounted on the back, soldered on the front.

INSTALLING U1-U6 DISPLAY LED MODULES:

one possible orientation on the board. Insert U1 in its board position, making very sure all four support legs are squarely seated on the board. Solder ONE pin in each row. Before further soldering, CHECK carefully to make sure the display is squarely against the board. If necessary, reheat and adjust the two connections. Because of the length of the pins, you will probably find it easiest to nip excess length after soldering each pin, to provide clearance to s older the next connection. Solder and nip all pins of U1.

Lay the receiver's molded front panel fac e down on a clean, non- abrasive surface. (A dry wash cloth works nicely, or use the packing foam from your kit.)

QUICK REFERENCE SUMMARY

PHASE 1.0

Display Board Assembly

CAUTION: To install the LED indicators, you will be working

with the receiver's front panel to get a good fit. Be VERY careful with your soldering iron tip during these processes so as not to scar (melt) the front panel!

EN1 D1 D2 D3 D4 D5 D6 D7 U1-U6

R1 R2 R3 R4 R5 R6 R7 R8 R9 SW1 SW2 SW3 SW4 S1 J1 J2

Encoder 1N4148 1N4148 1N4148 1N4148 Green LED Green LED Green LED Display LED

33 ohm, 1/4watt 33 ohm, 1/4 watt 33 ohm, 1/4 watt 33 ohm, 1/4 watt 33 ohm, 1/4 watt 33 ohm, 1/4 watt 33 ohm, 1/4 watt 33 ohm, 1/4 watt 1K, 1/4 watt momentary

“ “ “

SPDT Toggle 8-pin socket 8-pin socket

Phase 1.0: Display Board

Freq/Memory TUNE pushbutton switch multiplexing diode

“ “ “

AM mode indicator SSB mode indicator FAST tuning mode indicator frequency dis play

LED display current limiting

“ “ “ “ “ “ “

multiplexing resistor MODE MW V/M Tuning SPEED DC power mates P1 on main board mates P2 on main board

1254 – Assembly – 5

Page 27

PHASE 1.0

Display Board Assembly

CAUTION: To install the LED indicators, you will be working

INSTALLING U1-U6 DISPLAY LED MODULES:

1-1. The pin arrangements of U1-U6 permit only one possible orientation on the board. Insert U1 in its board position, making very sure all four support legs are squarely seated on the board. Solder ONE pin in each row. Before further soldering, CHECK carefully to make sure the display is squarely against the board. If necessary, reheat and adjust the two connections. Because of the length of the pins, you will probably find it easiest to nip excess length after soldering each pin, to provide clearance to s older the next connection. Solder and nip all pins of U1.

1-2. Install U2-U6 exactly as explained in 1-1 for U1.

with the receiver's front panel to get a good fit. Be VERY careful with your soldering iron tip during these processes so as not to scar (melt) the front panel!

1-3a. Preparation to install LED's: Lay the receiver's molded front panel fac e down on a clean, nonabrasive surface. (A dry wash cloth works nicely, or use the packing foam from your kit.)

1254 – Assembly – 6

Page 28

1-3b. Examine one of the small LEDs and the LED outlines

IMPORTANT: Examine these sockets and notice the row of openings and tiny metal tabs on one side. These tabs will protrude when the sockets are mated to plugs. Ther efore install the sockets with the tab rows facing UP, so there is no chance that extended spring tabs can short against the main board.

for squareness and resolder if necessary. Then solder the remaining 6 pins; no trimming is required.

Install the following 1/8 watt resistors:

Install the following diodes, type 1N4148, making sure to position the banded ends (cathodes) as outlined on the board:

but insert them carefully so as not to crumple any of the mount- ing legs. Each switch must rest flush against t he surface of the board. Solder all four pins for each switch.

illustrated in Figure 1.1 Notice that the anode and cathode ends

of the LED's are clearly silkscreened on the board. The anode is the LONGER of the two LED leads.

Figure 1.1

1-4. LED Installation Procedure. First, insert all 3 LED's with correct anode orientation per Step 1-3 and Fig. 1.1. Don't push them in very far, because they need to extend into the front panel for a good fit.

Seat the plastic lens for the 6-digit display in its panel position and then lay the display board into the panel. (Remove the protective paper from the lens.) While holding the board and panel face down, slide all 3 LED's into their panel positions as far as they can go. Solder ONE side of each LED and check front panel for a good fit. Resolder any LED which needs adjusting and then solder all remaining wires. Before trimming, check to make s ure that all the longer anode leads are oriented in the same direction per Fig. 1.1.

1-5. Green LED D5 installed per Steps 1-3 and 1-4.

1-6. Green LED D6 installed per Steps 1-3 and 1-4.

1-7. Green LED D7 installed per Steps 1-3 and 1-4.

1-8. Set aside the front panel and display lens

carefully so they will not be scratched.

INSTALLING SOCKETS J1 and J2:

1-9. Read First: Sockets J1 and J2 ar e inserted on the back (non-screened) side of the display board and soldered on the front. It is important that the edges of J1 and J2 be squarely against the rear of the board to ensure a good fit to the rightangle pin plugs on the main board.

1254 – Assembly - 7

Page 29

Figure 1.2

IMPORTANT: Examine these sockets and notice the row of

openings and tiny metal tabs on one side. These tabs will protrude when the sockets are mated to plugs. Ther efore install the sockets with the tab rows facing UP, so there is no chance that extended spring tabs can short against the main board.

1-10. Insert socket J1 and solder the two end pins. Check for squareness and resolder if necessary. Then solder the remaining 6 pins; no trimming is required.

1-11. Install socket J2 exactly as explained in steps 1-9,10.

Install the following 1/8 watt resistors:

1-12. Resistor R1, 33 ohm (orange-orange-black).

1-13. Resistor R2, also 33 ohm.

1-14. Resistor R3, also 33 ohm.

1-15. Resistor R4, also 33 ohm.

1-16. Resistor R5, also 33 ohm.

1-17. Resistor R6, also 33 ohm.

1-18. Resistor R7, also 33 ohm.

1-19. Resistor R8, also 33 ohm.

1-20. Resistor R9, 1K (brown-black-red).

Install the following diodes, type 1N4148, making sure to position the banded ends (cathodes) as outlined on the board:

1-21. Diode D1, type 1N4148. 1-22. Diode D2, type 1N4148. 1-23. Diode D3, type 1N4148. 1-24. Diode D4, type 1N4148.

1-25. The four push-button switches snap into place neatly, but insert them carefully so as not to crumple any of the mounting legs. Each switch must rest flush against t he surface of the board. Solder all four pins for each switch.

1254 – Assembly - 8

Page 30

1-26. Install switch SW1 (MODE) per Step 1-25.

on each of the two switch wires.

The bottom lug is identified per mounting done in step 1 -34.

connections.

aside until it is needed for various tests. It will be mounted permanently after completion of the work in Phase 6.0. Do not attempt to mount the fr ont panel to the display board until instructed to do so in Phase 7.0.

1-27. Install switch SW2 (MW) per Step 1-25. 1-28. Install switch SW3 (V/M) per Step 1 -25. 1-29. Install switch SW4 (SPEED) per Step 1-25.

IMPORTANT SOLDERING TIP! Examine the Rotary Encoder: regardless of whether the 3 silver terminals appear to you to be tarnished, rub them anyway with a clean p encil eraser. This will make for much easier soldering.

Figure 1.3. Encoder cable connections

1-30. Strip 1/8" of

insulation from each of the 3 wires of the cable/plug assembly.

1-31. Study the

A-B markings on the encoder and compare to Figure 1.3.

1-32. The 3 wires

should be inserted from the back and soldered on the front side. Insert the red wire and the white A and gray B wires EXACTLY how Figure 1.3 depicts the front of the encoder and design of the plug.

1-33. Mount the rotary encoder to the display board with the

lock washer and nut provided. The washer goes on the front side of the board. (If you wish, the large tuning knob may be mounted temporarily to the encoder shaft for easy tuning dur ing progress tests).

1-34. Mount the SPDT power switch on the display board.

Both the tabbed "alignment" washer and the lock washer should be on the FRONT side of the display board. Be sure to get this switch mounting and wiring done c orrectly, because you will be instructed in Phase 5.0 to cut off the un-used switch lug.

1-35. Strip 1/8" insulation from the ends of both red wires of

the pre-assembled power switch cable.

1254 – Assembly - 9

Page 31

1-36. Cut two 1/2" lengths of insulating sleeve and slip one

on each of the two switch wires.

1-37. Solder one wire to the center lug of the SPDT switch.

1-38. Solder the other red wire to the bottom switch lug.

The bottom lug is identified per mounting done in step 1 -34.

1-39. Slide the insulating sleeves over t he completed switch

connections.

1-40. Double-check all your work and set the display board aside until it is needed for various tests. It will be mounted permanently after completion of the work in Phase 6.0. Do not attempt to mount the fr ont panel to the display board until instructed to do so in Phase 7.0.

1254 – Assembly – 10

Page 32

● About the Circuit Board Drawings:

The sectional circuit board drawings are adapted directly from the silk-screening on the board itself, but they have been modified in two important ways:

1. Component "designators" (C1, R1, Q1, etc.) are consistently within the outline of the part for maximum convenience in identifying a part's real location. On the board itself, many such designators are off to the side , tor two reasons. First, screening over plated holes is not good manufacturing practice. Second, it helps to see some clear designators AFTER parts-installation is finished.

2. USEFUL NOTES AND SKETCHES have been added to the sectional board drawings. As needed, we ref er to these in the Assembly Instructions.

● The Quick-Reference Summaries

A Quick Reference Summary of the parts used in each Assembly Phase is printed at the beginning of the instructions for that phase. It may be used first as a guide to gathering parts for this phase. It is pr ovided as an extra help in double-checking correctness of parts values with brief notes on the function of each part. These summaries are adapted from the complete Component Reference Index in the Reference Section of this manual.

● Main Board Soldering Hints

In addition to all our nagging about avoiding solder bridges, here's a tip about working with this double-sided board with plated-through holes. Many of the solder pads are elongated with two or more holes. W hen soldering a part to such a multi - connection pad or connected group of pads, just be careful to use the minimum solder needed for a good connec tion, because it is VERY easy for excess solder to flow into an empty hole. Such extra solder must be "de-soldered" before using that mounting hole.

We discourage those "l know best" marathons in which "board- stuffing" for t his whole receiver might be done in a long evening. BUT we do NOT expect you to insert, solder and trim just one part at a time. We suggest inserting 3-5 parts, bending the leads to hold them well, double-check, then solder and trim. In choosing the kit-building experience, we are not trying to outpace the robotic manufacturing processes used at TEN-TEC and worldwide!

Model 1254

Main Circuit Board Assembly

NEVER GUESS about the identification or orientation of a

part if it is not absol utely clear on the board silkscreen.

In discussing the Display Board, we referred to the "front" and "back" sides of the board. In the Main Board assembly steps, we will refer to the silkscreened side as the TOP and the solder side as the BOTTOM. However, when the display board is plugged in and facing you correctly, the component or top side of the main board actually faces downward!

VERY IMPORTANT: Ta ke the time to s tudy the board itself and all board drawings in this manual . Some silkscreened component outlines or identifications may be obscured by the space required for the plated-through pads. Therefore, you must consult the circuit board outline drawings printed in this manual.

Conventions used in this Instruction Manual

Our primary goal is accuracy of parts selection and correct installation, NOT the fastest possible "stuffing" of the board. That's why a numbered instruction is provided for each part, and why we follow a specific pattern for listing instruction sequences for similar groups of parts such as resistors or disc capacitors.

● Groups of similar parts:

Our assembly lists of similar parts begin with the lowest value of resistance or capacitance, etc., and go up in value, grouping identical values together, starting with the lowest designator number. For example:

Install the following 1/4-watt resistors:

2-1. Resistor R1, 4.7 ohm (yellow-violet-gold). 2-2. Resistor R10, 470 ohm (yellow-violet-brown). 2-3. Resistor R4, 10K, (brown-black-orange). 2-5. Resistor R9, also 10K.

2-8. Resistor R5, 47K (yellow-violet-orange). 2-9. Resistor R6, also 47K. 2-10. Resistor R2, 10 megohm (brown-black-blue).

1254 – Assembly - 11

Page 33

● About the Circuit Board Drawings:

The sectional circuit board drawings are adapted directly from the silk-screening on the board itself, but they have been modified in two important ways:

2. USEFUL NOTES AND SKETCHES have been added to the sectional board drawings. As needed, we ref er to these in the Assembly Instructions.

● The Quick-Reference Summaries

● Main Board Soldering Hints

In addition to all our nagging about avoiding solder bridges, here's a tip about working with this double-sided board with plated-through holes. Many of the solder pads are elongated with two or more holes. W hen soldering a part to such a multi connection pad or connected group of pads, just be careful to use the minimum solder needed for a good connec tion, because it is VERY easy for excess solder to flow into an empty hole. Such extra solder must be "de-soldered" before using that mounting hole.

We discourage those "l know best" marathons in which "boardstuffing" for t his whole receiver might be done in a long evening. BUT we do NOT expect you to insert, solder and trim just one part at a time. We suggest inserting 3-5 parts, bending the leads to hold them well, double-check, then solder and trim. In choosing the kit-building experience, we are not trying to outpace the robotic manufacturing processes used at TEN-TEC and worldwide!

1254 – Assembly - 12

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● This space is for your notes

Phase 2.0 Schematic Diagram Details

1254 – Assembly - 13

Phase 2.0 Assembly

begins on page 14 ►

Page 35

Phase 2.0 Schematic Diagram Details

1254 – Assembly - 14

Page 36

Phase 2.0: Frequency Synthesizer and DC Input

Phase

2.0

and DC Power Input Circuits

QUICK REFERENCE SUMMARY

Display Driver, Microprocessor

PLL synthesizer IC U3 and some of its supporting parts are included, in this phase because its 3.580 MHz reference oscillator also supplies the microprocessor clock signal.

1254 – Assembly - 15

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QUICK REFERENCE SUMMARY

Phase 2.0: Frequency Synthesizer and DC Input

470/16v el.

5-40 pF var.

0.1μF

33/16v el.

33pF

1/50v el.

33/16v el.

C15

.001μF

C20

.01μF

C87

10/25v el.

C98

33/16v el.

C104

33/16v el.

C105

470μf/16v el.

C106

1N4148

6.2V zener

DC jack

2-pin

3-pin

100 μH

8-pin header

2N4124

Q12

2N4124

Q13

2N4124

Q14

4.7 ohms

10 megohm

10K

47K

10K

470

R10

10K

R12

10K

R13

10K

R14

MC7805CT

(U1 also may be LM340T-5) PIC16C57

28-pin DIP socket for U2

(U2)

Microprocessor MC145170P

SN74LS47N

BA618

NJM7810A

U10

3.579546 MHz

“zero ohm resistor“ (black band)

JMP1

“zero ohm resistor” (black band)

JMP2

Filter Cap for display driver Trimcap for master clock (adjust to 3.58 MHz) Bypass on PLL chip Bypass on PLL chip Shunt cap on clock crystal Reset coupling cap Vdd supply bypass for μP Couples PLL to VCO circuits Supply bypass for U2 Supply bypass on U4 Bypass on output of U10 Bypass on input of U10 Main DC input bypass Supply summing diode for U2 Supply turn-off detector Backup battery summing diode Coaxial DC power connection DC power switch connection Encoder cable connection RFC for U3 DC supply Mates Display Board J1 (install on solder side!) Mates Display Board J2 (install on solder side!) Decimal point current sink Power-on reset transistor Power-down detector Supply lead to U5 Clock oscillator for U3 Display decimal point Pull-down for pushbuttons Pull-down for encoder

“ “

Pull-up for reset pin Pull-down for Q13 Power-off detector Power-off detector Pull-up on RTCC pin 5V regulator for synthesizer circuitry

8-bit microprocessor (P/N 98384)

PLL synthesizer LED segment driver Digit driver 10V voltage regulator Synthesizer clock set to 3.58 MHz (use base insulator)

1254 – Assembly – 16

Page 38

microprocessor, with the notched end aligned per the notch outlined on the board. Insert carefully, making sure all pins mate their holes with no pin bent back under the socket. Use good lighting and a clean solder tip to avoid making solder bridges.

Do NOT insert U2 until instructed to do so.

or dotted end is oriented toward the right-side edge of the board as designated by the notch outlined on the board.

dotted end is oriented as outlined on the board.

notched or dotted end is oriented as outlined on the board. Solder U5 directly to the board; do not use a socket.

5), into its position as far as you can push it. Then bend it back so that its heatsink and hole line up with the groundplane area and m ounting hole in the board. Later, a screw will be secured through U1 to the aluminum side panel.

Install the following ceramic disc capacitors:

Review Table 1-C in “Getting Started” as needed before installing diodes D5, D6, and D7 in the following steps:

polarity as outlined on the board.

cathode polarity as outlined on the board.

Phase 2.0 Assembly Steps

Before You Start: A Quick Referen ce Summary of the parts used

in Phase 2.0 is printed on page 16. It may be used first as a guide to gathering parts for this phase. It is provided as an extra help in double-checking correctness of parts values with brief notes on the function of each part.

CAUTION!

Do NOT at tempt to install P1 and P2 until instructed to do so

and you understand the directions thoroughly.

Install the following ¼-watt resistors:

2-1. Resistor R1, 4.7 ohm (yellow-violet-gold) 2-2. Resistor R10, 470 ohm (yellow-violet-brown) 2-3. Resistor R3, 10K (brown-black-orange) 2-4. Resistor R4, also 10K. 2-5. Resistor R9, also 10K. 2-6. Resistor R12, also 10K. 2-7. Resistor R13, also 10K. 2-8. Resistor R14, also 10K. 2-9. Resistor R5, 47K (yellow-violet-orange). 2-10a. Resistor R6, also 47K. 2-10b. Resistor R2, 10 megohm (brown-black-blue).

2-11. Install electrolytic capacitor C98, 10 μF, being sure to

insert the longer ( + ) lead as shown on the board.

2-12. READ FIRST : When installing the right-angle headers (P1 and P2), it is important that they sit squarely against the board for a good fit to the display board. VERY IMPORTANT:

P1 and P2 are MOUNTED on the BOTTOM side of the board as illustrated below and should be soldered from the top side.

Installing P1 at this time presumes that R3 and C 9 8 are already installed, making the holes used for P1 perfectly clear w hen viewed from the bottom side of the board.

Fig. 2.1: Installation of P1 and P2 on solder side of board

1254 – Assembly – 17

Page 39

2-13. Ins tall right-angle header P1 per Step 2-12. 2-14. Ins tall right-angle header P2 per Step 2-12.

2-15. Ins tall the 28-pin DIP socket s uppl i ed for the U2 PIC microprocessor, with the notched end aligned per the notch outlined on the board. Insert carefully, making sure all pins mate their holes with no pin bent back under the socket. Use good lighting and a clean solder tip to avoid making solder bridges.

Do NOT insert U2 until instructed to do so.

2-16. Ins tall U4, type 74LS47N, making sure that its notched or dotted end is oriented toward the right-side edge of the board as designated by the notch outlined on the board.

2-17. Ins tall U5, type BA618, making sure that its notched or dotted end is oriented as outlined on the board.

2-18. Ins tall U3, type MC145170P1, making sure that its notched or dotted end is oriented as outlined on the board. Solder U5 directly to the board; do not use a socket.

2-19. Slide voltage regulator U1, type 7805CT (or LM340T-

2-20. Solder and trim the 3 leads of voltage regulator U1.

Install the following ceramic disc capacitors:

2-21. Capacitor C5, 33 pF.(narrow lead spacing,

NOT the 33 pF capacitors used tor C21 ,C22, etc.).

2-22. Capacitor C20, .001 μF (marked 102).

2-23. Capacitor C3, 0.1 μF (marked 104).

2-24. Capacitor C87, also 0.1 μF.

Review Table 1-C in “Getting Started” as needed before installing diodes D5, D6, and D7 in the following steps:

2-25. Ins tall diode D5, type 1N4148, with correct cathode polarity as outlined on the board.

2-26. Ins tall 6.2V zener diode D6, type 1N753A, with correct cathode polarity as outlined on the board.

2-27. Ins tall 6.2V zener diode D7, type 1N753A, with correct cathode polarity as outlined on the board.

1254 – Assembly – 18

Page 40

2-28. Ins tall JMP1 , a "zero ohm resistor" (one black band.)

28. DC Power Circuitry

The following parts are installed near the left rear of the board.

side toward the back end of the board as outlined and illustrated in Figure 2.2.

Figure 2.2

goes between the nut and bottom side of board. ) NOTE: the stiffness of the leads will make it almost impossible for the part to lay perfectly flat on the board. This is OK

Solder all three leads and trim away the excess lengths.

2-29. Ins tall JMP2 per step 2-28.

2-30. Ins tall electrolytic capacitor C1,470 μF, being sure to

insert the longer ( + ) lead as shown on the board.

2-31a. Ins tall electrolytic C4, 33 μF per Step 2-30. 2-31b. Ins tall electrolytic C15, also 33 μF.

2-32. Ins tall electrolytic C8, 1μF per Step 2-30. (Be careful

not to mix up the small 1 μF and 10 μF electrolytics.)

2-33. Ins tall trimmer capacitor C2; its flat side faces R2 as shown on the board. Insert the part gently so as not to bend its mounting terminals.

2-34. Slip a crystal base insulator over the leads of crystal Y1, 3.579545 MHz. This insulator is white or clear plastic in the shape of the crystal base.

2-35. Ins tall crystal Y1, making sure you select the 3.579 MHz crystal and not Y3 to be used in the 1st IF section.

2-36. Ins tall transistor Q12, type 2N4124, with the flat side toward R1 as outlined on the board.

2-37. Ins tall transistor Q13, type 2N4124, with the flat side toward U3 as outlined on the board.

2-38. Ins tall transistor Q14, type 2N4124, with the flat side oriented as outlined on the board.

2-39. Ins tall the three-pin terminal J4 with the vertical locking tab toward the socket for U2 as outlined on the board.

2-40. Ins tall L1 , 100 μH RF choke (brown-black-brown-gold).

2-41. Double-chec k all work you have done so far.

2-42. Remove the PIC microprocessor from its protective Foam, check al l 28 pins for straightness, and straighten any pin which appears to need it. Insert U2 into its socket with the notched end toward D7 as plainly outlined on all drawings and the board silksc reen.

1254 – Assembly – 19

Page 41

28. DC Power Circuitry

The following parts are installed near the left rear of the board.

2-43. Install the two-pin terminal J2 with the vertic al locking side toward the back end of the board as outlined and illustrated in Figure 2.2.

Figure 2.2

2-44. Install electrolytic capacitor C106, 470 μF, being sure to insert the l onger ( + ) lead as shown on the board.

2-45. Install electrolytic C104, 33 μF per Step 2-44.

2-46. Install electrolytic C105, 33 μF per Step 2-44.

2-47. Install coaxial DC connector J1: use sufficient soldering heat to ensure a solid, shiny mechanical bond from each lug to the plated circuit board holes.

2-48. Voltage regulator U10, typeNJM7810A,

resembles U1 in style, but the lead dimensions differ. Using needle-nose pliers as needed, shape the wide parts of the three leads so that U10's mounting hole lines up with the hole in the board. After shaping the leads, mount U10 to the board using the 3/8" #440 screw, lockwasher and #4-40 nut. (This is the longest screw used in the kit and the lock washer

goes between the nut and bottom side of board. ) NOTE: the stiffness of the leads will make it almost impossible for the part to lay perfectly flat on the board. This is OK

2-49. Install the 10 volt regulator U10 as explained in 2-48.

Solder all three leads and trim away the excess lengths.

1254 – Assembly - 20

Page 42

OPTIONAL: For Educators and Experimenters

Phase 4.0: 455 kHz 2nd IF

An RF signal generator tuned to 455 kHz can be coupled to the input of U7 at C40 after completing Phase 4B.

A nearby general coverage HF receiver or transceiver can be tuned to 455 kHz to confirm oscillation of ceramic resonator Y2. NO adjustment on the 1254 b oard is required or provided for.

An RF signal generator tuned to 455 kHz can used as a short-range "transm itter" (1 to 3 feet) after completing Phase 4C. Connect a foot or two of wire to serve as its "transmitting antenna."

Find the CENTER pad for T7 (not yet installed) in the row of 3 pads nearest J5/J6. Here, you will simply touch a test probe from your meter to serve as a "receiving antenna." lt does not matter whether the test lead is connected to your meter.

With this set-up, the 1254 shoul d easily detect the nearby 455 kHz test signal. (Coincidentally, the T-KIT Model 1050 "Universal BFO', with its tuneable 452-457 kHz output, works very nicely for such demonstrations.)

Phase 5.0: 45 MHz 1st IF

At this point the receiver can easily detect the output of an RF signal generator tuned to 45 MHz.

REMINDER: This is the ONLY discussion in this manual of what we consider to be optional circuit section demonstrations for those builders or educators who wish them. They are not needed in the Progress Tests.

Circuit Stage Demonstrations

Each Phase of the receiver construction process adds several related circuit stages. In most cases, these circuit sections are capable of "doing something" of possible interest to you if connected to external test equipment of some kind. For example, you can hear an oscillator signal using another receiver, 0r use a signal generator to hear that an IF section is working.

Each Assembly Phase for your recei ver kit includes "Progress Test" procedures. Our goal in such tests is to verify that the completed circuit section simply "works" as engineered. We specify the simplest possible testing to do this, such as a meter reading. From experience, we find it best not to include nonessential circuit performance demonstrations as part of kit building Progress Tests.

Setting up a useful circuit demonstration may require more external equipment than you have on hand or is really needed. The following testing suggestions are provided for those builders who enjoy observing or dem onstrating what various sections of the receiver can "do." These possible demonstrations ar e NOT mentioned in the Progress Tests: it is up to YOU to return to this section of the manual after each Progress Test and determine whether you want to try out these suggestions.

Phase 2.0: Frequency Synthesi zer

The 3.58 MHz clock oscillator may be heard using another receiver tuned to that frequency. C2 may be adjusted to exactly 3.5800 MHz using this method. The real adjustment of C2 is done with the receiver completed and tuned to WWV.

Phase 3.0: 45-75 MHz local Oscillator and PLL

The synthesized LO tunes 45 MHz above the frequency indicated on the display, i.e. 45-75 MHz. In addition to the option of checking the LO output with a frequency counter, the LO signal may be heard with any receiver capable of tuning in the 45-75 MHz range. Even an ordinary TV set can be used. simply run a jumper wire fro m the "FREQ TIP" to the VHF antenna input and tune the 1254 per the following table:

Display

0.000.0

0.100.0

5.000.0

10.250.0

14.750.0

16.250.0

21.750.0

22.250.0

26.750.0

LO Output (MHz)

45.000

45.100

50.000

55.250

59.750

61.250

65.750

67.250

71.750

NOTES

Test signal: 1

IF (Phase 5.0)

6 m eter ham band (50-54 MHz) TV channel 2 video TV channel 2 audio TV channel 3 video TV channel 3 audio TV channel 4 video TV channel 4 audio

1254 – Assembly - 21

Page 43

Phase 4.0: 455 kHz 2nd IF

An RF signal generator tuned to 455 kHz can be coupled to the input of U7 at C40 after completing Phase 4B.

A nearby general coverage HF receiver or transceiver can be tuned to 455 kHz to confirm oscillation of ceramic resonator Y2. NO adjustment on the 1254 b oard is required or provided for.

An RF signal generator tuned to 455 kHz can used as a short-range "transm itter" (1 to 3 feet) after completing Phase 4C. Connect a foot or two of wire to serve as its "transmitting antenna."

Phase 5.0: 45 MHz 1st IF

At this point the receiver can easily detect the output of an RF signal generator tuned to 45 MHz.

1254 – Assembly - 22

Page 44

Phase 2.0 Progress Test

At this point, further testing of this circuitry consists simply of just playing with it as much as You care to! For example, you can turn to the Operating Instructions in the Reference Section and try out the [MW] and [V/M] f unctions.

You can use the [MW] (Memory Write) function to store frequencies in memory, but keep in mind that the stored information will be lost when power is turned off, because the memory backup battery is not yet in use.

DO NOT install the 9-volt memory battery snap until instructed to do so in Phase 7.0. Its wires will not withstand all the boar d handling yet to be done.

beginning Phase 3.0.

2-50. Carefully plug the Display board into the sockets on the solder side of the board. With the display facing you correctly, the solder side of the main board faces up.

2-51. Plug the encoder cable into J4.

2-52. Plug the power switch cable into J2.

2-53. Connect the 1 SVDC power supply module to J1.

2-54. Turn on DC power: the display should read 15.000.0 (MHz), and only the [AM] or [SSB] LED should be lit. If the

display reads differently, perform the Microprocessor Reset (also explained in the Operating Instructions) as follows:

Turn off DC power

Press and hold both the [Mode] and [MW] switch buttons

Turn on DC power

Release the switch buttons

2-55. Press the [MODE] button to select SSB mode and turn the encoder shaft or knob slightly clockwise: the display should advance to 15.002.5, 15.005.0, 15.007.5 and so forth in 2.5 kHz steps. lf the displayed frequency went DOWN (i.e. to

14.997.5, etc.), this means that the A and B wires to the encoder are reversed. lf this is so, t urn off DC power and fix that problem before proceeding.

2-56. Press the IMODE] button to s elect AM mode; turning the encoder shaft should advance the display in 5 kHz steps, such as 15.010.0, 15.015.0, 15.020.0, etc.

2-57. Press the [SPEED] switch button. The "FAST" LED below it should light up, and you should observe tuning in 100 kHz steps such as 15.100.0, 15.200.0, etc. You will notice that only a few gentle turns of the tuning control shaft easily moves you several MHz in either direction.

2-58. Set your VOM or DVM to read DC voltage. Locate the "10V TP" test point and measure the voltage between that pad and ground. Any of the four mounting holes on the boar d is a convenient ground. The reading should be about 10 volts DC.

1254 – Assembly - 23

Page 45

DO NOT install the 9-volt memory battery snap until instructed to do so in Phase 7.0. Its wires will not withstand all the boar d handling yet to be done.

2-60. Unplug and set aside the front display board before

beginning Phase 3.0.

1254 – Assembly - 24

Page 46

This space is for your notes

Phase 3.0 Schematic Details

1254 – Assembly - 25

Phase 3.0 Assembly

begins on page 26 ►

Page 47

Phase 3.0 Schematic Details

1254 – Assembly - 26

Page 48

QUICK REFERENCE SUMMARY

Phase 3.0: VCO's and PLL Circuit

Phase

3.0

VCO's and PLL Circuit

The VCO's (Voltage Controlled Oscillators) will be permanently enclosed in metal shields only after their operation is thoroughly verified in Phase 7.0. Four different transistor types are used in Phase 3.0: be sure to identify them correctly and to orient them as outlined on the board. Consult Figures 3.1 and 3.2 carefully as you work on the VCO's, which we'll do first.

1254 – Assembly - 27

Page 49

QUICK REFERENCE SUMMARY

Phase 3.0: VCO's and PLL Circuit

C6 C7 C9 C10 C11 C12 C13 C14 C16 C17 C18 C19 C20 C21 C22 C23 C24 C32 C91 C92 C102 C103 D1 D2 D4 D8 JMP3 L2 L3 L4 L5 Q15 Q16 Q17 Q18 Q19 Q20 Q21 Q22 Q23 Q24 Q25 Q26 R7 R8 R11 R15 R16 R17 R18 R19 R20

.001μF .001μF

0.47μF film .047μF film .01μF film .047μF film .01μF .01μF .001μF .01μF

10/25v el. 27 pF

.001μF

33 pF 33 pF 3 pF 10 pF

10 μF el.

100 pF 100 pF 33/16v el.

.001μF

1N4148 Factory Installed 1N4148 Factory Installed

“0 ohm”

VCO coil VCO coil

0.27μH

0.39μH

2N4124 2N4124 2N5087 2N5087 MPSA14 J310 J310 2N4124 2N4124 2N4124 2N4124 2N4124 100 100 47K 15K

1.5K

4.7K

4.7K 150

DC block on VCO

“ “

PLL loop filter

“ “ “

PLL active filer

“ “ “

VCO bypass cap

“ “ “

Supply bypass for Q25 Base bypass for Q25 Supply bypass for Q25 VCO bypass filter VCO coupli ng cap to PLL VCO lowpass filter VCO lowpass filter VCO lowpass filter Coupling cap into Q26 Base bypass on charge pump VCO varactor coupling cap

“ “ “ “

Collector bypass on Q19 RF bypass on VCO tuning line VCO switching diode

VCO switching diode

circuit board jumper VCO-2 coil VCO-1 coil PLL feedback lowpass filter

“ “ “ “

PLL charge pump

“ “

“ “ “ “ “ “ “

PLL active loop filter VCO-2 VCO-1 VCO enable transistor

“ “ “ “

First LO amplifier VCO buffer for PLL PLL Charge pump PLL Charge pump Pull-up for VCO PLL damping resistor Charge pump input Charge pump input Active loop filter input Active loop filter VCO source resistor

1254 – Assembly - 28

Page 50

Phase 3.0 QUICK REFERENCE SUMMARY, cont.

This receiver uses two voltage-controlled oscillator (VCO) circuits to cover the total tuning range. We'll begin with VCO-1 which uses adjustable coil L3 to tune the 45-58 MHz 1st LO range.

3A. VCO-1 Com ponents

is the VCO c oil with the gr eater number of windings. The "B" corner has two wire leads, as indicated in Figure 3.1.

3.1. Before soldering, make sure the coil base is seated FIR MLY against the board. A solid mechanical fit is needed for these VCO coils to minimize vibration.

Refer to PARTS IDENTIFICATION GUIDE for help in identifying diode D1

R21 R22 R23 R24 R25 R26 R27 R28 R29 R30 R31 R32 R37 R38 R39 R87 T1

150 10K 22K 47K 47K 47K 47K 47 10K 10K 470 10K 47K 10K 47K

2.2K bifilar bal un

VCO source resistor VCO select Active loop filter emitter VCO pull-up resistor Varactor bias resistor VCO switching VCO switching Supply resistor for Q25 Base bias for Q25 Bias for Q26 Emitter resistor for Q26 Bias resistor for Q26 Varactor bias resistor Charge pump bias Charge pump bias Collector feed for Q19 LO output

1254 – Assembly – 29

Page 51

Phase 3.0 Assembly

This receiver uses two voltage-controlled oscillator (VCO) circuits to cover the total tuning range. We'll begin with VCO-1 which uses adjustable coil L3 to t une the 45-58 MHz 1st LO ran ge.

3A. VCO-1 Com ponents

Adjustable coil L3 is marked with a brown paint dot and is the VCO c oil with the gr eater number of windings. The "B" corner has two wire leads, as indicated in Figure 3.1.

3-2. Identify and install VCO coil L3 per step 3-1 and Fig.

3.1. Before soldering, make sure the coil base is seated FIR MLY against the board. A solid mechanical fit is needed for these VCO coils to minimize vibration.

3-3. Identify and install JFET transistor Q21, type J310.

3-4. Identify and install NPN transistor Q22, type 2N4124.

Refer to PARTS IDENTIFICATION GUIDE for help in identifying diode D1

3-5. Diode D2 is factory installed.

3-6. Identify and install PIN diode D1, type 1N4148.

1254 – Assembly – 30

Page 52

Install the following resistors:

Install the following disc capacitors:

parts within the shield enclosures . Recheck component selection and the quality of solder connections before proceeding. Do NOT install the shielding until instructed to do so.

3C. PLL Circuit Completion

and its silkscreen outline on the board. The oblong ferrite core of T1 must be or iented as outlined on the board and noted in the drawing on page 27.

Install the following 1/4 watt resistors:

1/4-watt resistors, cont.

3-7. Resistor R21, 150Ω (brown-green-brown). 3-8. Resistor R22, 10K (brown-black-orange). 3-9. Install R11, 47K (yellow-violet-orange). 3-10. Install R25, also 47K. 3-11. Install R27, also 47K.

Install the following disc capacitors:

3-12. Capacitor C91,100 pF.(marked 101). 3-13. Capacitor C6, .001 μF (marked 102). 3-14. Capacitor C14, .01 μF (marked 103). 3-15, 16. reserved

38. VCO-2 Components

3-17. Adjustable coil L2 is the VCO coil with the fewer

number of windings and marked with a RED paint dot. The "B"

corner has two wire leads, as indicated in Fig ure 3.2.

Figure 3.2

3-18. Identify and install VCO coil L2 per step 3-17 and Fig.

3.2. Make sure the coil base is seated FIRMLY against th e board.

3-19. Identify and install JFET transistor Q20, type J310. 3-20. Identify and install NPN transistor Q24, type 2N4124. 3-21. Identify and install NPN transistor Q23, type 2N4124.

1254 – Assembly – 31

Page 53

3-22. Diode D8, is factory installed.

3-23. Identify and install PIN diode D4, type 1N4148.

Install the following resistors:

3-24. Resistor R20, 150Ω (brown-green-brown).

3-25. Resistor R24, 47K (yellow-violet-orange).

3-26. Resistor R26, also 47K.

3-27. Resistor R37, also 47K.

Install the following disc capacitors:

3-28. Capacitor C92, 100 pF.(marked 101).

3-29. Capacitor C7, .001 μF (marked 102).

3-30. Capacitor C103, also .001 μF.

3-31. Capacitor C13, .01 μF (marked 103).

3-32. The preceding steps complete installation of all VCO parts within the shield enclosures . Recheck component selection and the quality of solder connections before proceeding. Do NOT install the shielding until instructed to do so.

3C. PLL Circuit Completion

3-33. Install PNP transistor Q17, type 2N5087.

3-34. Install PNP transistor Q18, also type 2N5087.

3-35. Install NPN transistor Q15, type 2N4124.

3-36. Install NPN transistor Q16, also type 2N4124.

3-37. Install transistor Q19, type MPSA14.

3-38a. Install NPN transistor Q25, type 2N4124.

3-38b. Install NPN transistor Q26, also type 2N4124.

3-39. Examine tr ansformer T1, the pre-ass embled bifilar balun and its silkscreen outline on the board. The oblong ferrite core of T1 must be or iented as outlined on the board and noted in the drawing on page 27.

3-40. Install bifilar transformer T1 per 3-39.

Install the following 1/4 watt resistors:

3-41. Resistor R28, 47 ohm (yellow-violet-black).

3-42. Resistor R7, 100 ohm (brown-black-brown).

3-43. Resistor R8, also 100 ohm.

3-44. Resistor R31, 470 ohm (yellow-violet-brown).

3-45. Resistor R16, 1.5K (brown-green-red).

3-46. Resistor R17, also 1.5K.

3-47. Resistor R87, 2.2K (red-red-red).

1254 – Assembly - 32

1/4-watt resistors, cont.

Page 54

3-48. Resistor R18, 4.7K (yellow-violet-red).

which you will connect your voltmeter to do the L2 and L3 VCO coil adjustments. lf more convenient for your test leads, you can also solder a length of insulated hookup wire instead, and tr im it shorter after c ompleting the adjustment.

already installed) to the pad marked "FREQ TP".

Adjustment of VCO c oils L2 and L3 r equires an alignment blade of the CORRECT SIZE to fit the slot in the slug. A blade that is too small can easily crack the slug. If you cannot find the right size tool, use sandpaper to shape carefully the tip of a plastic beverage stirrer or wooden kabob stick.

plug to J4 as in Phase 2.0 test ing.

switch plug to J2, and rec onnect the wall transformer power supply t o J1.

the VCO test point and ground. You will be observing voltages in the 2.5 to 8 volt range.

should read 15.000.0 MHz. If not, perform the Processor Reset explained in the Operating Instructions (Reference Section) and in the Phase 2.0 test.

L3 for a reading of 2.0 VDC at the VCO TP.

the VCO test point, there is a problem. Turn off DC power and thoroughly recheck your work.

upward in frequency. You should observe a gradual rise in voltage: about 4.5 volts at 7.000 MHz. The maximum will be about 8.5 volts ± .5 volt at 13 .235 MHz.

3-49. Resistor R19, also 4.7K. 3-50a. Resistor R29, 10K, (brown-black-orange). 3-50b. Resistor R30, also 10K. 3-51. Resistor R32, also 10K. 3-52. Resistor R38, also 10K. 3-53. Resistor R15, 15K, (brown-green-orange). 3-54. Resistor R23, 22K (red-red-orange). 3-55. Resistor R39, 47K (yellow-violet-orange).

3-56. Install inductor L4, 0.27 μH (red-violet-silver-gold).

3-57. Install inductor L5, 0.39 μH (orange-white-silver-gold).

3-58. Install C9, the large mylar film 0.47 μF capacitor

(marked 474).

3-59. Install C10, the mylar film .047 μF capacitor (marked

473).

3-60. Install capacitor C12, also mylar film .047 μF.

3-61. Install C11, .01 pF mylar film (marked 103). [Be sure

to use a f ilm type capacitor, not ceramic disc for C11.]

3-62. Install electrolytic capacitor C32, 10 μF, with correct

(+ ) polarization as outlined on the board.

3-63. Install electrolytic capacitor C18, 10μF, per step 3-62.

3-64. Install electrolytic capacitor C102, 33μF, per step 3-62.

Install the following disc ceramic capacitors:

3-65. Capacitor C 23 , 3 pF. 3-66. Capacitor C24, 10 pF. 3-67. Capacitor C19, 27 pF. 3-68. Capacitor C21, 33 pF. 3-69. Capacitor C22, 33 pF. 3-70. reserved 3-71. Capacitor C16, .001 μF {marked 102). 3-72. Capacitor C17, .01 μF (marked 103).

3-73. Install "0 ohm" jumper JMP3.

3-74. Read entire text before soldering: Solder a 1/2" length of bare wire (trimmed from a part already installed) to the pad marked "VCO TP" near 019. This is the VCO Test Point to

1254 - Assembly - 33

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3-75. Solder a 1/2" length of bare wire (trimmed from a part

already installed) to the pad marked "FREQ TP".

VCO Test and Alignment

3-76. Re-attach the Display Board and reconnect the encoder

plug to J4 as in Phase 2.0 test ing.

3-77. With power switch turned off, reconnect the red wire switch plug to J2, and rec onnect the wall transformer power supply t o J1.

3-78. Connect your meter's red + lead (DC volts range) to the VCO test point and ground. You will be observing voltages in the 2.5 to 8 volt range.

3-79. Turn on DC power. Again, the frequency display should read 15.000.0 MHz. If not, perform the Processor Reset explained in the Operating Instructions (Reference Section) and in the Phase 2.0 test.

3-80. Tune down to 100 kHz. (Use FAST tuning mode!)

3-81. Using the proper size of alignment tool, adjust VCO coil L3 for a reading of 2.0 VDC at the VCO TP.

3-82. If you do NOT observe at least 2 volts DC present at the VCO test point, there is a problem. Turn off DC power and thoroughly recheck your work.

3-83. With 2.0 VDC at the VCO TP for 100 kHz, start tuning upward in frequency. You should observe a gradual rise in voltage: about 4.5 volts at 7.000 MHz. The maximum will be about 8.5 volts ± .5 volt at 13 .235 MHz.

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3-84. Tune from 13.235 MHz to 13.240 MHz. You will likely

Phase 4.0 Schematic Details

observe a sharp downward shift in DC voltage at the VCO Test Point, indicating that VCO-2 has been switched in.

3-85. Adjust VCO-2 coil L2 as needed for a DC voltmeter reading of 2.5 volts at 13.240 MH z. As you tune higher, you should observe a gradual rise in voltage: about 5.5 volts at

19.000 MHz. The maximum will be about 8.0 volts ± .5 volt at

30.000 MHz.

3-86. If you have a frequency counter, connect it to "FREQ TP. " Tune to several of the sample frequencies shown in Table

3.1 to confirm that the selected display frequency res ults in the corresponding LO output frequency.

Table 3.1

Displayed Frequency vs. Local Oscillator Output

Display LO Output (MHz) NOTES

0.000.0 45.000 Test signal: 1st IF (Phase 5.0)

0.100.0 45.100

1.000.0 46.000

2.000.0 47.000

5.000.0 50.000 6 meter ham band (50-54 MHz)

10.000.0 55.000

15.000.0 60.000

20.000.0 65.000

30.000.0 75.000

The preceding is all that is needed to do basic VCO alignment. A slight touchup will be done after installing the VCO shield assembly, done in Phase 7.0, as part of final alignment.

3-87. Turn off DC power; unplug and set aside the display board.

Phase 4.0 Assembly

begins on page 36 ►

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Phase 4.0 Schematic Details

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Phase 4.0 QUICK-REFERENCE SUMMARY

Before You Start: The f ollowing Quick Reference Summary of the parts used in Phase 4.0 may be used first as a guid e to gathering parts for this phase. lt is provided as an extra help in double-checking correctness of parts values with brief notes on the function of each part.

Phase 4.0

Audio Section, AGC, 455 kHz 2nd IF

After part 4A this phase is completed, we can test for audio output and proper operat ion of the volume control. When this phase is completed, the receiver also can detect a 455 kHz signal such as from its 2nd mixer (Phase 5.0) in either AM or SSB mode.

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Phase 4.0 QUICK-REFERENCE SUMMARY

C33 C34 C35 C36 C37 C38 C40 C41 C42 C43 C44 C45 C46 C47 C48 C49 C50 C51 C64 C65 C66 C67 C68 C75 C98 D12 T2 T3 U6 U7 U8 U9 Q8 Q9 Q10 Q11 R40 R41 R42 R43 R44 R45

0.1μF

33/16v el. 220 pF 180 pF

0.1μF

180 pF

0.1μF

470/16v el.

0.1μF

10/25v el.

0.1μF

470/16v el. 33/16v el.

0.1μF

0.1μF .01μF

0.1μF

33/16v el. 1N4148 455 kHz coil 455 kHz coil NTE1852 NE612N MC1350P MC1350P 2N4124 2N4124 2N5087 2N4124 47 10K 100 100 150K

4.7

Input bypass on U7 Bypass on output of T3 Supply bypass on U7 Oscillator cap on U7

“ “ “

Bypass on input of U8 Coupling cap into U7 Input bypass on U9 High frequency shunt on U8 Audio output coupling cap RF bypass on Q8 base AGC time cons tant cap RF bypass on Q9 Supply bypass on U8 Supply bypass on U9 RF bypass on U8 RF bypass on U9 Supply bypass on U6 audio lC Collector bypass on Q8 Output coupling from Q8 AM detector Output coupling from product detector Turn-on cap for U6 Bypass on input to U6 Interstage coupling on U6 Filter cap on volume control Forward bias for AM detector 455 kHz lF amplifier

“ “

Audio amplifier Product detector IF amplifier IF amplifier AM detector AGC rectifier AGC integrator AGC voltage follower Input resistor to U7 product detector Input resistor to AM detector Supply to U8 Supply to U9 Power-on bias to U6 High frequency shunt on U6

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Phase 4.0 Quick Reference, cont.

Phase 4.0 Assembly Steps

Section 4A. Audio Amplifier Circuit

U6 is a self-contained audio amplifier SIP (single inline pin) IC, using only a volume control and a very few resistors and capacitors to complete a 1.5 wat t audio amplifier. We will assemble this circuitry plus the speaker/headphone connections now, then test their functioning, to confirm audio amplifier performance before adding further stages to the receiver.

notched/ banded end is similar to other IC's used in the circuit. Insert this end per the notched end on the silkscreen (nearest t he space for C79) . Sol der carefully to avoid bridges, because shorts

can permanently damage U6!

jack cable. Align the locking end as outlined on the board, just as you did when installing the jack for the enc oder cable.

the board, insert J5, the 2-pin header (just like the power switch connector) for connecting the built-in speaker. Soldering is done on the top (component) side. Align the locking end of J5 as outlined on the top side. This header must be on the solder-side for proper connection to the speaker when installed permanently.

Install the following electrolytic capacitors with correct polarity:

Install these supporting parts for U6:

making sure that all three solder tabs are squarely into the board as far as they can go, to ensure a proper fit to the display board.

R46 R47 R48 R49 R50 R51 R52 R53 R59 R61 R62 R63 R64 R65 R66 R67 R73 R74 R88 R89 FL2 J5 J6 Y2

1.0K

2.2K

1.0 M 220K 10K 10K

4.7K

1.0K 10K

2.2K

1.0K 22K 10K

4.7K 0 ohm

1.0K 10K var

4.7K 100 100 CFR455I 2-pin header 3-pin header 455 kHz

AM detector emitter resistor AGC discharging resistor AGC time cons tant AGC charging resistor AGC rectifier pull-down AGC input resistor IF amp input load AM detector emitter resistor Forward bias for AM detector IF amp output load, U8 IF amp output load, U9 AGC input resistor, U8 AGC input resistor, U9 AGC pull-down resistor Front end AGC voltage divider Front end AGC pull-down Front panel volume Volume control pull-up Power feed for product detector Power feed for AM detector 455 kHz filter Internal speaker cable connector Headphone jack cable connector 0scillator for product detector

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Phase 4.0 Assembly Steps

Section 4A. Audio Amplifier Circuit

4-1a. Examine amplifier IC U6, type TDA1013B and not ice its notched/ banded end is similar to other IC's used in the circuit. Insert this end per the notched end on the silkscreen (nearest t he space for C79) . Sol der carefully to avoid bridges, because shorts

can permanently damage U6!

4-1b. Install audio IC U6, type NTE1852 per 4-1a.

4-2. Install J6, the three-pin connector for the headphone jack cable. Align the locking end as outlined on the board, just as you did when installing the jack for the enc oder cable.

4-3. READ before soldering: on the BOTTOM solder-side of the board, insert J5, the 2-pin header (just like the power switch connector) for connecting the built-in speaker. Soldering is done on the top (component) side. Align the locking end of J5 as outlined on the top side. This header must be on the solder-side for proper connection to the speaker when installed permanently.

Install the following electrolytic capacitors with correct polarity:

4-4. Capacitor C96, 33 μF.

4-5a. Capacitor C43, 470 μF.

4-5b. Capacitor C51, also 470 μF.

Install these supporting parts for U6:

4-6. Resistor R45, 4.7 ohms (yellow-violet-gold).

4-7. Resistor R74, 4.7K (yellow-violet-red).

4-8. Resistor R44, 150K (brown-green-yellow)

4-9. Ceramic disc capacitor C42, 0.1 μF (marked 104).

4-10. Capacitor C67 , also 0.1 μF.

4-11. Capacitor C75, also 0.1 μF.

4-12. Install 10K potentiometer R73, the volume control, making sure that all three solder tabs are squarely into the board as far as they can go, to ensure a proper fit to the display board.

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4-13. Strip 1/8" insulation from the ends of the black and

3.0 VCO tests. For this test, re-attaching the Display Board is optional, but DO connect the power switch plug to J2. If you do attach the display board, handle the volume control gently.

You should hear only a faint hiss which grows stronger with the turning of the volume control. Hold a small screwdriver by its shaft and touch the pad for C66 (not yet installed) which is nearest audio IC U6. Your body contact with this input to U8 should produce a fairly loud hum (60 Hz AC house wiring).

correct your work before proceeding. The intentional AC hum and the soft background hiss are the only sounds you should hear. i.e., there must be no squeals or "putt-putt" motorboating sounds.

During further assembly, handle the hoard carefully so that the Volume Control leads are not bent hack and forth. The Clarifier control will be mounted in Phase 5.0 and will require similar carefulness.

Section 4B. Product Detector and AM Detector Section

aligning the notched or dotted end as outlined on the board.

resonator, rectangular plastic case, 2 pins, marked 455BK).

Install the following 1/4-watt resistors:

white wires of the 2-conductor speaker cable. Solder the stripped ends to the two terminals of t he 3" speaker supplied in the kit. (White is "+", black is "-", but speaker polarity is not critical in this application.)

4-14. Strip F 1/8" insulation from all three ends of the wires of the 3-wire headphone jack cable. Solder the stripped ends to the 1/8" jack as illustrated in Figure 4.1.

Decide NOW if this jack should be wired for stereo (normal) or mono 1/8" plugs. (A mono plug will short out the jack if wired for stereo.)

igure 4.1: Headphone Jack Wiring Options

Progress Test 4A: Audio Amplifier

4-15. Connect the headphone jack cable assembly to J6. This connection MUST be made regardless of whether you have headphones or plan to tr y them out later. This is because the stereo jack 's internal switching routes the amplifier output to the J6 speaker connection with no plug inserted in the stereo jack.

4-16. Connect the r eceiver speaker to J5 on the solder-side on the board and turn the volume control fully counter-clockwise.

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4-17. Reconnect the 15 volt DC supply to J1 as for the phase

3.0 VCO tests. For this test, re-attaching the Display Board is optional, but DO connect the power switch plug to J2. If you do attach the display board, handle the volume control gently.

4-18. Turn on DC power, then advance the volume control. You should hear only a faint hiss which grows stronger with the turning of the volume control. Hold a small screwdriver by its shaft and touch the pad for C66 (not yet installed) which is nearest audio IC U6. Your body contact with this input to U8 should produce a fairly loud hum (60 Hz AC house wiring).

4-19. If you do NOT obtain these test results, recheck and correct your work before proceeding. The intentional AC hum and the soft background hiss are the only sounds you should hear. i.e., there must be no squeals or "putt-putt" motorboating sounds.

Section 4B. Product Detector and AM Detector Section

4-20. Install U7, the NE612AN or SA612AN 8-pin DIP IC, aligning the notched or dotted end as outlined on the board.

4-21 . Install transistor Q8, NPN type 2N4124.

4-22. Install Y2, the 455 kHz oscillator device (ceramic

resonator, rectangular plastic case, 2 pins, marked 455BK).

Install the following 1/4-watt resistors:

4-23. Resistor R40, 47 ohm (yellow-violet-black).

4-24. Resistor R88, 100 ohms (brown-black-brown).

4-25. Resistor R89, also 100 ohms.

4-26. Resistor R46, 1K ( brown-black-red).

4-27. Resistor R53, also 1K.

4-28. Resistor R41, 10K ( brown-black-orange).

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Install the following ceramic disc capacitors:

Section 4C: IF Amplifier and AGC

the notched or dotted end as outlined on the board.

band orientation as outlined on the board.

arrangement permits only one possible orientation. Simply ignore the group of small circuit board holes covered by the filter case.

arrangement permits only one possible orientation. (While the markings may vary, these transformers have 5 pins, 2 shield tabs and are the only parts in the kit which will fit here.)

information in t he preceding step.

Install the following 1/4-watt resistors:

4-29. Capacitor C37, 150 pF (marked 151). 4-30. Capacitor C36, 220 pF (marked 221). 4-31. Capacitor C40, 180 pF (marked 181). 4-32. Capacitor C33, 0.1μF (marked 104). 4-33. Capacitor C44, also 0.1 μF. 4-34. Capacitor C46, also 0.1 μF. 4-35. Capacitor C65, also 0.1 μF. 4-36. Capacitor C66, also 0.1 μF. 4-37. Capacitor C68, 0.01 μF.

Install the following electrolytic capacitors with correct p olarity:

4-38. Capacitor C35, 33 μF. 4-39. Capacitor C64, 33 μF.

Progress Test 4B

PROCEDURE:

4-40. Reconnect the speaker Headphone jack cable

power switch plug, and DC power supply

4-41. Reconnect the Display Board as in Phase 2.0 testing.

4-42. Find the pad f or R41 (not yet installed) nearest to C40, 180 pF, very close to the headphone jack connector. This pad is common to C40, the input coupling capacitor for U7.

4-43. Turn on DC power to the 1254 board. Adjust the volume control to maximum. Set [MODE] t o SSB.

4-44. Touc h one end of a test lead to the pad for R41 nearest C40. In SSB mode, you will hear a very slight increase in hiss level. Place the other end of the test wire next to the 6-digit LED display. You should hear low-level musical tones, which are harmonics of the LED multiplexing circuit.

4-46. If you get the above-described result, turn off DC power, disconnect all cables from the 1254 board, and proceed to part 4C of Phase 4.0. If not, the first thing to do is to review all parts installed in part 4B.

4-46-49. reserved

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Section 4C: IF Amplifier and AGC

4-50. Install U8, a MC1350P 8-pin DIP IC, being

the notched or dotted end as outlined on the board.

4-51. Install U9, a MC1350P 8-pin DIP IC, being

the notched or dotted end as outlined on the board.

4-52. Install transistor Q9, NPN type 2N4124. 4-53. Install transistor Q11, NPN type 2N4124.

4-54. Install transistor Q10, PNP t ype 2N5087.

4-55. Install diode D12, type 1N4148, with correct cathode

band orientation as outlined on the board.

4-56. Install the 455 kHz filter FL2 (labeled CFR455-I). Its pin arrangement permits only one possible orientation. Simply ignore the group of small circuit board holes covered by the filter case.

4-57. Install T2, a 455 kHz shielded transformer. Its pin arrangement permits only one possible orientation. (While the markings may vary, these transformers have 5 pins, 2 shield tabs and are the only parts in the kit which will fit here.)

4-58. Install T3, a 455 kHz shielded transformer, per the information in t he preceding step.

Install the following 1/4-watt resistors:

4-59. Resistor R66, "0 ohm" (one black band).

4-60. Resistor R42, 100 ohms (brown-black-brown).

4-61 . Resistor R43, also 100 ohms.

4-62. Resistor R62, 1K (brown-black-red).

4-63. Resistor R67, also 1K.

4-64. Resistor R47, 2.2K (red-red-red).

4-65. Resistor R61, also 2.2K.

4-66. Resistor R52, 4.7K (yellow-violet-red).

4-67. Resistor R65, also 4.7K.

4-68. Resistor R50, 10K ( brown-black-orange).

4-69. Resistor R51, also 10K.

4-70. Resistor R59, also 10K.

4-71 . Resistor R64, also 10K.

4-72. Resistor R63 , 22K (red-red-orange).

4-73. Resistor R49, 220K (red-red-yellow).

4-74. Resistor R48, 1 meg ohm (brown-black-green).

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Install these 0.1 μF disc capacitors (marked 104):

a problem in the circuitry associated with U7, the Product Detector.

power, disconnect all cables from the 1254 board, set aside the display board, and proceed to Phase 5.0! If not, please read on.

In this receiver project, it is impossible to say which is the most important or critical phase. That's because EVERY circuit section must perform correctly if this R e ceiver is to work as designed.

Hopefully, you found Phases 1.0 and 2.0 easy and fun: the microprocessor and front panel display do their thing, and we were off to a great start, thanks to digital technology.

The VCO/PLL circuitry in Phase 3.0 generates the RF tuning signal ("LO") essential for mixing and converting signal from your antenna, first to 45 MHz and then again to 455 kHz and then again to intelligible audio.

Phase 4.0 is very important simply because it is the meeting ground between your ear and all other "superheterodyne" activity converging on it f rom the other circuit phases. If you did not obtain the lest results explained for Phase 4.0, go over all parts installed in this phase, using the double-check blocks for the assembly steps, Then review the work using the Quick- Reference list of Phase 4.0 parts at the beginning of this section.

If you know for sure that Phases 2.0, 3.0, and 4.0 work exactly as explained in their Progress tests, then the upc oming work of building up two mixer sections and RF input should make clearer sense to you now.

4-75. Capacitor C34, 0.1 μF. 4-76. Capacitor C38, 0.1 μF. 4-77. Capacitor C41, 0.1 μF. 4-78. Capacitor C47, 0.1 μF. 4-79. Capacitor C48, 0.1 μF. 4-80. Capacitor C49, 0.1 μF. 4-81. Capacitor C50, 0.1 μF. 4-82. reserved

4-83. Install electrolytic capacitor C45, 10 μF with correct

( + ) polarity.

Final (4C) Phase 4.0 Progress Test

Some technicians may feel the only way to fully prove to all your senses that all the circuitry built in Phase 4.0 is worki ng properly is to see if a nearby 455 kHz signal can be detected. An RF signal generator is the usual source for such a signal.

HOWEVER, this circuit is eng ineered to permit an extremely SIMPLE test at this point!

If this section of the receiver has problems, no further amount of work on the mixers or 45 MHz 1st IF can f ix problems in THIS section.

PROCEDURE:

4-84. Reconnect: speaker headphone jack cable, power

switch plug DC power supply and the Display Board

4-85. Turn on DC power to the 1254 board. Adjust the volume control to its midway point. If you can recall what you heard in previous tests, you should notice a shar p increase in background noise level introduced by adding the IF amplifier section.

4-86. Touc h a meter test probe or even a screwdriver as you did for the audio amplifier to the lead of R52 nearest Q1O. You should note a sharp increase in background noise. This indicates that the IF amplifiers are working correctly.

4-87. Switch the [MODE] button back and forth between AM and SSB while still holding a probe at R52. In AM mode, you should hear mainly a loud hum. In SSB mode, the sound changes to a his s.

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4-88. If there is NO or very little sound in SSB mode, there is a problem in the circuitry associated with U7, the Product Detector.

4-89. If you get the above-described result, turn off DC power, disconnect all cables from the 1254 board, set aside the display board, and proceed to Phase 5.0! If not, please read on.

Building the T-KIT Model 1254 Receiver:

An “INTERMISSION”

In this receiver project, it is impossible to say which is the most important or critical phase. That's because EVERY circuit section must perform correctly if this R e ceiver is to work as designed.

Hopefully, you found Phases 1.0 and 2.0 easy and fun: the microprocessor and front panel display do their thing, and we were off to a great start, thanks to digital technology.

Phase 4.0 is very important simply because it is the meeting ground between your ear and all other "superheterodyne" activity converging on it f rom the other circuit phases. If you did not obtain the lest results explained for Phase 4.0, go over all parts installed in this phase, using the double-check blocks for the assembly steps, Then review the work using the QuickReference list of Phase 4.0 parts at the beginning of this section.

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Phase 5.0 Schematic Details

This space is for your notes

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Phase 5.0 Schematic Details

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Phase 5.0

Phase 5.0 QUICK-REFERENCE INFORMATION

Second Mixer and 45 MHz First IF

The result of successful completion of this assembly phase will be a receiver circuit capable of detect ing very strong nearby 45 MHz signals in either AM or SSB-CW mode. The Model 1254 has a built-in 45.000 MHz test signal capability.

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Phase 5.0 QUICK-REFERENCE INFORMATION

C39 C52 C53 C54 C55 C56 C63 C77 C78 C79 C80 C81 C82 C83 C84 C85 C88 C100 C101 D10 D11 D15 D16 D18 L9 L10 L11 L17 L18 L19 T4 T5 T7 T8 Q4 Q5 Q6 Q7 R54 R55 R58 R75 R76 R77 R78 R79 R80 R81 R82 R83 R84 R85 R86 FL1 Y3 FB1 FB2

75 pF 15 pF

.001μF

47 pF

1 μF

47 pF

.001μF

33 pF 33 pF

.01μF .001μF .01μF .01μF

56 pF 75 pF

.01μF

0.1μF .001μF

0.1μF

1N4148 1N4148 1N4148 1N4148 Factory Installed

0.25μH

0.12μH

0.39μH

1.0μH

4.7μH

trifilar balun trifilar balun 455 kHz coil bifilar bal un BF988 2N4124 2N4124 J310 100 10K 47K 220 22K

1.0K 47K 22K 22K 47K 10K variable 100 100

2.2K 100 45U1A

44.545 MHz ferrite bead ferrite bead

Second LO output filter Output coupling cap from Q4 Source bypass cap on Q4 Resonating cap on input of Q4 Input cap to FL1 Resonating cap on input to FL1 Gate-2 bypass on Q4 Second LO capacitor at Q6 base

" "" Coupling cap to clarifier varicap Base bypass on Q5 Second LO output coupling cap Supply bypass for Q4 Output resonating cap for Q4 Second LO output filter Supply bypass for Q5 Supply bypass for Q7 Bypass cap on clarifier control Coupling capintoQ7 Second mixer diode Second mixer diode Second mixer diode Second mixer diode

45 MHz filter 45 MHz filter Mixer circuit Mixer out Y3 crystal tuning network DC power RF choke 2nd mixer transformer 2nd mixer transformer 455 kHz output from mixer to 2nd IF 2nd LO output transformer First IF amplifier Second LO buffer Second LO oscillator 455 kHz IF preamplifier Source resistor for Q4 Gate load for Q4 Gate 2 bias for Q4 Second LO emitter resistor Second LO bias Crystal shunt resistor Clarifier varactor bias Second LO bias Second LO bias Gate 2 bias for Q4 Front panel Clarifier control Supply feed for Q4 Supply feed for Q7 Drain load for Q4 Source resistor for Q7 45 MHz crystal filter Second LO put on gate lead of Q7 put on lead closest to "FB2" on board

1254 – Assembly - 50

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Phase 5.0 Assembly Steps

Install the following 1/4-watt resistors:

Install these ceramic disc capacitors:

Install these molded inductors:

installed in Phase 4.0).

is seated squarely on the hoard before soldering. (L11 is similar to but smaller than coils L9 and L10).

Before You start: The preceding Quick Reference Summary of the parts used in Phase 5.0 may be used first as a guide to gathering parts for this phase. It is provided as an extr a help in double-checking correctness of parts values with brief notes on the function of each part.

Install mixer diodes D10-11, D1 5-16, type 1N4148, making sure to align the black cathode bands exactly as outlined on the board:

5-1. Diode D10, type 1N4148. 5-2. Diode D11, type 1N4148. 5-3. Diode D15, type 1N4148. 5-4. Diode D16, type 1N4148.

5-5. Select T4 and T5, the pre-

Figure 6.1

assembled trifilar (3 winding) balun transformers, noting that they have SIX pins. Notice carefully which end of the plastic base has the two yellow/gold primary wires coming from the ferrite core over the base to two pins. These two transformers must be installed with these primary ends furthest from the mixer diodes as indicated by the notches in the board silkscreen and Figure 5.1.

5-6. Install trifilar balun

transformer T4 per 5-5.

5-7. Install trifilar balun

transformer T5 per 5-5.

5-8a. Examine tr ansformer T8, the pre-assembled bifilar balun (4 pins) and its silkscreen outline on the board. The ferrite core of T8 must be or iented as outlined on the board and noted in Figure 5.1.

5-8b. Install transformer T8 per 5-8a.

5-9. Install transistor Q5, NPN type 2N4124. 5-10. Install transistor Q6, NPN type 2N4124.

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Install the following 1/4-watt resistors:

5-11. Resistor R54, 100 ohms (brown-black-brown). 5-12. Resistor R83, also 100 ohms. 5-13. Resistor R84, also 100 ohms. 5-14. Resistor R86, also 100 ohms. 5-15. Resistor R60, 220 ohms (red-red-brown). 5-16. Resistor R75, also 220 ohms. 5-17 Resistor R77, 1K (brown-black-red). 5-18. Resistor R85, 2.2K (red-red-red). 5-19. Resistor R55, 10K ( brown-black-orange). 5-20. Resistor R76, 22K (red-red-orange). 5-21. Resistor R79, also 22K. 5-22. Resistor R80, 22K. 5-23. Resistor R58, 47K (yellow-violet-orange). 5-24. Resistor R78, also 47K. 5-25. Resistor R81, also 47K.

Install these ceramic disc capacitors:

5-26. Capacitor C 55 , 1 pF. 5-27. Capacitor C52, 15 pF. 5-28. Capacitor C77,33 pF. 5-29. Capacitor C78, 33 pF. 5-30a. Capacitor C54, 47 pF. 5-30b. Capacitor C56, 47 pF. 5-31. Capacitor C83, 56 pF. 5-32. Capacitor C39, 75 pF. 5-33. Capacitor C84, 75 pF. 5-34. Capacitor C53, .001 μF (marked 102). 5-35. DO NOT install C63, .00l μF, until instructed. 5-36. Capacitor C80, also .001 μF. Capacitor C100, also .001 μF. Capacitor C79, .01 μF (marked 103). Capacitor C81, also .01 μF. Capacitor C82, also .01 μF. Capacitor C85, also .01 μF. Capacitor C88, 0.1 μF (marked 104). Capacitor C101, also 0.1 μF.

Install these molded inductors:

5-44. Coil L17, 0.39 μH (orange-white-silver-gold). 5-45. Coil L18, 1.0 μH {brown-black-gold-gold). 5-46. Coil L19, 4.7 μH (yellow-violet-

5-47. Install 455 kHz transformer T7 (identical to T2 and T3

installed in Phase 4.0).

5-48. Install the unshielded slug-tuned coil L11, being sure it is seated squarely on the hoard before soldering. (L11 is similar to but smaller than coils L9 and L10).

1254 - Assembly - 52

gold-gold).

Page 74

5-49. Install the unshielded slug-tuned coil L9, being sure it is

looks like a small crystal but with three leads.

44.545 MHz, then install Y3 in the normal manner.

Before soldering, make sure the control is mounted squarely against the board, to assure proper mating to the display board.

several times for previous Progress Tests, you should be satisfied that the DC on-off power switch is wired correctly. This means one red wire to the center terminal, and the other to the bottom when the display board faces you correctly.

REMOVE the unused (UPPER) lug of the power switch. Doing so will prevent the unneeded lug from pushing into the nearest parts on the main board when mounted permanently.

Phase 5.0 Progress Test

At this point in the project, we have a complete signal path from the input of the 45 MHz IF out to the speaker. We cannot tune the receiver because there is no mixer stage Yet. However, we can tune the synthesizer output down to 45.000 MHz to generate a built-in test signal.

Volume and Clar ifer controls and set them aside. Reconnect the display board, being gentle with the controls as the shafts are passed through their holes.

the power switch and adjust the volume control for moderate background noise. Set the Mode switch to SSB.

LEFT pad in the row of three pads within the outline for trans- former T6. This has t he effect of connecting a short "antenna" directly to the input of the 45 MHz 1st IF through C55.

seated squarely on the board before soldering.

5-50. Install the unshielded slug-tuned coil L10, being sure it

is seated squarely on the board before soldering.

5-51. Slip the smallest shield c an over L11 and the two larger shield cans over L9 and L10. These cans fit snugly over the inductors. Make sure all three are seated squarely on the board, then solder all six mounting tabs.

5-52. Diode D18, Is factory installed.

Correct installation of Q4, Q7 and C63

require careful attention to the following directions

while referring to Figure 5.2.

Figure 5.2: Q4, Q7, C63

type BF988, noting that the tab for the drain is longer than the other three. It must be aligned as illustrated in Figure 5.2. If you live in a dry climate, discharge static electricity from your hands and tools before handling Q4. The imprinted side of Q4 faces up. Bend all four tabs straight down from the transistor body, insert, then solder all four connections.

5-53. Examine Q 4,

5-54. Capacitor C63, .001 μF (marked 102), requires a ferrite bead on the lead nearest the "FB2" label on the board. Simply slip the bead on the lead, seat the capacitor as far as both leads can go down, and solder both leads in the normal way.

5-55. JFET transistor of, type J310, is installed in the normal manner but with a ferrite bead slipped over the gate (grounded) lead as illustrated in Figure 5.2.

1254 - Assembly – 53

Page 75

5-56. Install FL1, the 45 MHz crystal filter (45U1A), which

looks like a small crystal but with three leads.

5-57. Slip a base insulator over the leads of crystal Y3.

44.545 MHz, then install Y3 in the normal manner.

5-58. Install 10K potentiometer R82, the Clarifier control. Before soldering, make sure the control is mounted squarely against the board, to assure proper mating to the display board.

5-59a. Now that you have connected the Display Board several times for previous Progress Tests, you should be satisfied that the DC on-off power switch is wired correctly. This means one red wire to the center terminal, and the other to the bottom when the display board faces you correctly.

5-59b. If all is well per 5-59a, use your cutter or nipper to REMOVE the unused (UPPER) lug of the power switch. Doing so will prevent the unneeded lug from pushing into the nearest parts on the main board when mounted permanently.

Phase 5.0 Progress Test

5-60. Remove any m ounting nuts and washers from the Volume and Clar ifer controls and set them aside. Reconnect the display board, being gentle with the controls as the shafts are passed through their holes.

5-61. Reconnect these cables: Encoder Headphone jack

Internal Speaker DC power switch

5-62. Reconnect the 15VDC power supply to J1. Turn on the power switch and adjust the volume control for moderate background noise. Set the Mode switch to SSB.

5-63. Touc h the probe of one of your voltmeter leads to the LEFT pad in the row of three pads within the outline for transformer T6. This has t he effect of connecting a short "antenna" directly to the input of the 45 MHz 1st IF through C55.

1254 – Assembly - 54

Page 76

5-64. Touc hing the pr obe as explained above should cause a

Phase 6.0 Schematic Details

very dis tinct increase in background noise level. Adjust coils L9 and L10 for maximum noise level. If you can do this, you have confirmed that there is a functioning signal path from C55 through all the circuitry you installed in Phase 4.0 and 5.0 to the audio amplifier. (If there is any local noise or static which would cause interference in any other radio, you will hear that too! for example: lightning, noise from appliances, power lines, etc.)

5-65. Lay your test lead wire so that it is near the LED frequency display. With the probe touching the left T6 pad, you should hear a strong music-like blend of tones which are harmonics of the multiplexing signals which illuminate the display, as explained in the Circuit Description" Rotating the clarifier control should change the pitch of the tone(s) you are hearing. Rotating the tuning control will cause audible clicks.

5-66. Press the [SPEED] button for FAST (100 kHz) tuning steps as indicated by the LED below the switch button. Tune down until the display reads 0.000.0. The synthesizer is now programmed to a frequency of 45.000 MHz, and the output level is strong enough t o be picked up by the Q4 circuitry. (NOTE: the synthesizer cannot be tuned below the 100 kHz limit using 2.5 or 5 kHz steps.) The 45.000 MHz LO signal should be very strong, and you can adjust its pitch with the clar ifier control.

If you have observed the test results explained here, you can proceed with confidence to the RF input and First Mixer sections which will combine the signals from an antenna with the LO output of the 45- 75 MHz frequency synthesizer, feeding the 45 MHz IF, resulting in a completed receiver!

5-67. Disconnect the DC supply, disconnect all cables and set aside the display board.

Phase 6.0 Assembly

begins on page 56 ►

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Page 77

Phase 6.0 Schematic Details

1254 – Assembly - 56

Page 78

Phase 6.0 QUICK-REFERENCE INFORMATION

For your convenience, the complete hoard drawing for Phase 6.0 is presented on Page 62 after we finish the two shielded sections for which separat e drawings are provided.

Before You Start: The preceding Quick Reference Summary of the parts used in Phase 6.0 may be used first as a guide to gathering parts for this phase. It is provided as an extr a help in double-checking correctness of parts values with brief notes on the function of each part.

6A. Shielded RF Input Bandpass Filter

This circuitry will be enclosed within a shield just like the VCO's. Therefore, careful attention to correct parts selection is especially important. Figure 6.1 is provided for your convenience.

Figure 6.1

Phase

6.0

RF Input Circuit and First Mixer

C25 C26 C27 C28 C29 C30 C31 C57 C58 C60 C61 C62 C69 C70 C71 C72 C73 C74 C76 C86 C89 C90 C93 C94 C95 C97 C99 D13 D14 D17 L6 L7 L8 L12 L13 L14 L15 L16 L20 T6 T9 Q2 Q3 Q27 R33 R34 R35 R36 R56 R57 R60 R68 R69 R70 R71 R72 R90

.001μF .001μF

10 pF 10 pF

.001μF

2 pF 18 pF 8 pF

.001μF

0.1μF

47 pF 180 pF 180 pF 47 pF

.0068μF film

0.1μF

0.1μF .0022μF film .0022μF film

1/50v el. 20 pF 20 pF

0.1μF .001μF.

BA479G BA479G

3.9V zener

4.7μH

0.56μH

0.47μH 100 μH

0.39μH

0.56μH

6.8μH 100μH 1μH w/CT

trifilar balun J310 J310 J310 10K 47 100 220 100 220 220 470 470 100 trimmer 220 220 470

Coupling cap into Q27 Supply bypass for Q27 1st LO output filter " "" Source bypass on Q27 1st LO output filter

“ “ “

Resonating cap on mixer T6 Supply bypass on first mixer RF bypass on mixer transformer " " "" " " "" " " "" RF Input lowpass filter " "" " "" RF Input lowpass filter AM broadcast notch Antenna input coupling cap RF bypass on AGC diode Q14 AM broadcast input filter

“ “ “

Supply bypass for active antenna DC Antenna input lowpass filter

“ “ “ “

Supply bypass for antenna DC First LO output coupling cap Front end AGC series diode Front end AGC shunt diode Front end AGC bias LO amplifier DC supply choke LO output lowpass network

“ “

Front-end AGC RFC RF input bandpass filter "" " "" " AM broadcast notch with C74 RFC for active antenna DC supply First mixer input First mixer output First Mixer with Q3 First Mixer with Q2 First LO output amplifier Gate pull-down tor Q27 Supply resistor tor Q27 Source resistor tor Q27 Drain load tor Q27 Supply resistor for first mixer Front end AGC return Output load for first LO First mixer balance First mixer balance Mixer balance adjustment Front end AGC forward bias AM broadcast attenuator Source resistor fol antenna DC

“

Page 79

Phase

6.0

RF Input Circuit and First Mixer

For your convenience, the complete hoard drawing for Phase 6.0 is presented on Page 62 after we finish the two shielded sections for which separat e drawings are provided.

Phase 6.0 Assembly

Before You Start: The preceding Quick Reference Summary of

the parts used in Phase 6.0 may be used first as a guide to gathering parts for this phase. It is provided as an extr a help in double-checking correctness of parts values with brief notes on the function of each part.

6A. Shielded RF Input Bandpass Filter

This circuitry will be enclosed within a shield just like the VCO's. Therefore, careful attention to correct parts selection is especially important. Figure 6.1 is provided for your convenience.

Figure 6.1

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Page 80

Install these mylar film capacitors:

68. Shielded First Mixer Section

This circuitry will be enclosed within a shield just like the VCO's. Therefore, careful attention to correct parts selection is especially important. Figure 6.2 is provided for your convenience. The complete Phase 6.0 parts placement drawing is on page 58.

Figure 6.2

Be careful not to damage the mounting legs when inserting. Correctly installed, it is normal to have some space between the the board and the base of the trimmer.

but larger than the 455 kHz transformers installed in Phase 4.0.

with SIX pins, (identical to T4 and T5 installed in Phase 5.0). Notice carefully which end of the plastic base has the two copper-colored primary wires coming from the ferrite core over the base to two pins . This transformer must be installed with

this primary end nearest trimmer R70 as indicated by the notches in the board silkscreen and Figure 6.2.

6-1. Capacitor C89, .0022 μF (marked 222).

6-2. Capacitor C90, also .0022 μF.

6-3. Capacitor C74, .0068 μF (marked 682).

Install these ceramic disc capacitors:

6-4. Capacitor C94, 20 pF.

6-5. Capacitor C95, 20 pF.

6-6. Capacitor C70, 47 pF.

6-7 Capacitor C73, 47 pF.

6-8. Capacitor C71, 180 pF (marked 181).

6-9. Capacitor C72, also 180 pF.

6-10. Capacitor C69, 0.1 μF (marked 104).

6-11. Install resistor R72 220 ohms (red-red-brown).

6-12. Carefully identify PIN diode D13, type BA479G (Black body, red cathode band, middle green band) and install with correct cathode polarity.

6-13. Install diode D14, also type BA479G per 6-12.

Install the following molded inductors:

6-14. L13, 0.39 μH (orange-white-silver-gold).

6-15. L14, also 0.39 μH.

6-16. L15, 0.56 μH (green-blue-silver-gold)

6-17 L16, 6.8 μH (blue-gray-gold-gold).

6-18. L12, 100 μH (brown-black-brown-gold).

6-19. After carefully double-checking the parts just installed for correct values, install a shield enclosure, soldering all four mounting tabs. It is not necessary to bend these tabs before soldering. No top cover is used on this shield or on the 1st Mixer section to be built next.

REMINDER: Handle the board carefully to prevent damage to the mounting lugs of the Volume and Clarifier controls.

1254 - Assembly - 59

Page 81

68. Shielded First Mixer Section

Figure 6.2

6-20. Install the 100 ohm trimmer potentiometer R70. Be careful not to damage the mounting legs when inserting. Correctly installed, it is normal to have some space between the the board and the base of the trimmer.

6-21 . Install the shielded adjustable coil T6, similar in style but larger than the 455 kHz transformers installed in Phase 4.0.

6-22. Install T9, a pre-ass embled trifilar balun transformer, with SIX pins, (identical to T4 and T5 installed in Phase 5.0). Notice carefully which end of the plastic base has the two copper-colored primary wires coming from the ferrite core over the base to two pins . This transformer must be installed with

this primary end nearest trimmer R70 as indicated by the notches in the board silkscreen and Figure 6.2.

6-23. Install resistor R57, 220 ohms (red-red-brown).

1254 - Assembly - 60

Page 82

Install the following ceramic disc capacitors:

6C. Components Outside

Figure 6.3

Install these 1/4-watt resistors:

Install these ceramic disc capacitors:

6-24. Capacitor C57, 8pF. 6-25. Capacitor C60, 0.1 μF (marked 104). 6-26. Capacitor C61, also 0.1 μF. 6-27. Capacitor C62, also 0.1 μF.

NOTE: Ther e is an unlabeled outlined for a capacitor next to C57 which would serve as a shunt across trifilar balun T9. However, further engineering determined no capacitor is needed here, and this is the-only such "vacancy" on the entire 1254 circuit board.

6-28. Install transistor Q2, JFET type J310, being sure to

orient the flat side as outlined.

6-29. Install transistor Q3, JFET type J 310, being sure to

orient the flat side as outlined

6-30. After carefully double-checking the parts just installed for correct values, install a shield enclosure, soldering all four mounting tabs. No top cover is used here.

Figure 6.2b

Alignment Preview

After Phase 6.0 is finished and panel/chassis sections installed, the Model 1254 is aligned simply by adjusting these coils for peak signal strength.

T6 T9 L10 T7

R70 is adjusted for minimum background noise at 300 kHz

1254 - Assembly - 61

Page 83

6C. Components Outside

the Shielded Enclosures

Figure 6.3

Install these 1/4-watt resistors:

6-31. Resistor R34, 47 ohms (yellow-violet-black). 6-32. Resistor R35, 100 ohms (brown-black-brown). 6-33. Resistor R56, also 100 ohms. 6-34a. Resistor R36, 220 ohms (red-red-brown).

6-35. Resistor R71, also 220 ohms. 6-36. Resistor R68, 470 ohms (yellow-violet-brown). 6-37. Resistor R69, also 470 ohms. 6-38. Resistor R90, also 470 ohms. 6-39. Resistor R33, 10K (brown-black-orange).

Install these ceramic disc capacitors:

6-40. Capacitor C 30 , 2 pF. 6-41 . Capacitor C27, 10 pF. 6-42. Capacitor C28, 10 pF. 6-43. Capacitor C31, 18 pF. 6-44. Capacitor C25, .001 μF (marked 102). 6-45. Capacitor C26, also .001 μF. 6-46. Capacitor C29, also .001 μF. 6-47. Capacitor C58, also .001 μF.

1254 - Assembly - 62

Page 84

Ceramic disc capacitors, cont .

Final Assembly of Model 1254 Receiver

The completed Model 1254 Receiver can indeed be fully aligned and tested NOW while still in "board form" before adding the front panel and other hardware. Doing it this way seems advisable ONLY if you have nagging doubts about a previous circuit phase test and if you feel t he added har dware might interfere with testing and possible parts replacement in confined areas, especially near the front panel. However, if all previous "Progress Tests" have worked well for you, you'll probably prefer the satisfaction of doing the final checkout of a mostly- assembled receiver, nearly ready to use -- for real!

If you prefer the conservative approach, perform Step 7-1a, then perform all Final Alignment instructions in Part 7B. If all goes well, return to step 7-1b to continue Final Assembly.

both the Volume and Clarifier controls to the Display Board with the flat washers and mounting nuts supplied. Reconnect the Power Switch and Encoder Cables.

7A: Front Panel and Chassis Installation

Suggestion: Read over all the following panel assembly directions and see Figures 7.1 and 7.2 BEFORE starting. Also, you may wish to wrap the outer sides of the font panel with masking tape to prevent scuffing during further assembly.

and notice the 5 support posts for the mounting screws. Mounting the panel to the display board may be easier if you first "exercise" the 5 mounting holes in the posts simply by screwing in and removing a #4 self-tapping ("sheet metal") screw. Do this for each post .

board controls.

6-48. Capacitor C99, also .00l μF. 6-49. Capacitor C76, 0.1 μF (marked 104). 6-50. Capacitor C86, also 0.1 μF. 6-51. Capacitor C97, also 0.1 μF.

6-52. Install electrolytic capacitor C93, 1 μF with correct

polarity.

6-53. Install 3.9v zener diode D17 , type 1N748A. (Review

p. 62 if you have any question about identifying this diode.)

Install these molded inductors:

6-54. Coil L8, 0.47 μH (yellow-violet-silver-gold.) 6-55. Coil L7, 0.56 μH (green-blue-silver-gold.) 6-56. Coil L6, 4.7 μH (yellow-violet-gold-gold.) 6-57. Coil L20*, 100 μH (brown-black-brown-gold.)

*Note: L20 supplies DC voltage to the antenna jack to power a remote active antenna circuit. It is not essential to the receiver circuit and may be omitted.

6-58. Install transistor Q27, JFET type J310.

Please Read First

6-59. The RCA-type antenna jack J3 will be subjected to considerable stress over the life of the receiver as different connectors or adapters are used. Therefore, we recommend that its installation be as solid as possible, which means t hat it must be flush against the board with strong solder connections.

6-60. Install antenna jack J3 per 6-59. Make sure that solder

flows generously around the pins and solder pads.

6-61. Your 1254 Receiver is "built," now needing only the adjustment of a few coils and the addition of cabinet hardware to make it useful and attractive. This remaining work should be pure fun, so we encourage you to take your time and enjoy the results.

1254 - Assembly - 63

Page 85

Phase 7.0

Final Assembly of Model 1254 Receiver

ALIGNMENT SUGGESTION:

The completed Model 1254 Receiver can indeed be fully aligned and tested NOW while still in "board form" before adding the front panel and other hardware. Doing it this way seems advisable ONLY if you have nagging doubts about a previous circuit phase test and if you feel t he added har dware might interfere with testing and possible parts replacement in confined areas, especially near the front panel. However, if all previous "Progress Tests" have worked well for you, you'll probably prefer the satisfaction of doing the final checkout of a mostlyassembled receiver, nearly ready to use -- for real!

If you prefer the conservative approach, perform Step 7-1a, then perform all Final Alignment instructions in Part 7B. If all goes well, return to step 7-1b to continue Final Assembly.

7-1a. Plug the Display Board into the Main Board and secure both the Volume and Clarifier controls to the Display Board with the flat washers and mounting nuts supplied. Reconnect the Power Switch and Encoder Cables.

7A: Front Panel and Chassis Installation

7-1b. Lay the front panel face down on a protective cloth, and notice the 5 support posts for the mounting screws. Mounting the panel to the display board may be easier if you first "exercise" the 5 mounting holes in the posts simply by screwing in and removing a #4 self-tapping ("sheet metal") screw. Do this for each post .

7-2. Remove any knobs you may have attached to the display board controls.

7-3. Check all control and switch nuts for normal tightness.

1254 - Assembly - 64

Page 86

7-4. Make sur e none of the LED wires have been bent.

you are waiting, we again encourage you to read the remaining instructions and study the drawings. Glue is also used to secure the TEN-TEC logo and t o mount the speaker to its aluminum support shelf. You may wish to study those instructions and take care of those chores now.

panel hole created by the special insert. The body of the jack should be parallel to the top and bottom of the front panel. Tighten the jack's mounting nut very carefully to avoid scratching surrounding areas.

switches on the Dis play Board.

Table 7.1: SMALL HARDWABE PREVIEW

# Description P/N Function

8 #4-40 1/4” screw,

4 #4-40 1/4” screw,

8 #4-40 3/16”

4 #4 split

5 #4 self-threading

NOTE: a #4-40 screw, phillips, #4 i nternal tooth lock washer, and #4-40 hex nut were included in the Semiconductor package and should have been used already to mount Voltage Regulator U10.

handy, fit the panel to the display board, gently guiding the SPEED LED as needed. W hile holding everything together, ins tall the screw in the center mounting hole near t he Clarifier control.

four mounting holes in whatever order is most convenient.

7-5. Set the display lens in position, making sure that the "AM-SSB" lettering is facing correctly. The lens is locked into place by carefully melting with your soldering tip the 6 molded posts inside the panel along t he sides and bottom of the lens. (If you are reluctant to do it this Way, you have the option of securing the lens to the panel with very small drops of contact cement at the edges.) Wipe the inside of the lens clean of any fingerprints.

7-6a. Glue the front panel headphone jack insert in place. This is a custom-molded washer-like plastic part. (The large hole in the front panel is designed to accept connector s of various types using the proper insert.) Use just a drop or two of any fast-drying glue such as contact cement dried properly on both surfaces. Do not use "superglue" here -- there is too much risk

of damaging the front panel surface.

Figure 7.1

1254 – Assembly - 65

Page 87

7-6b. Let the glue for the jack insert dry as needed. While you are waiting, we again encourage you to read the remaining instructions and study the drawings. Glue is also used to secure the TEN-TEC logo and t o mount the speaker to its aluminum support shelf. You may wish to study those instructions and take care of those chores now.

7-7. Mount the 1/8" stereo jack (cable unplugged) to the panel hole created by the special insert. The body of the jack should be parallel to the top and bottom of the front panel. Tighten the jack's mounting nut very carefully to avoid scratching surrounding areas.

7-8. Press the four "key cap" buttons onto the button switches on the Dis play Board.

Table 7.1: SMALL HARDWABE PREVIEW

# Description P/N Function

8 #4-40 1/4” screw,

phillips [zinc]

4 #4-40 1/4” screw,

phillips, [black]

8 #4-40 3/16”

undercut (“counter-

sink”) screw

4 #4 split

lockwasher

5 #4 self-threading

(“sheet metal”)

screw

NOTE: a #4-40 screw, phillips, #4 i nternal tooth lock washer, and #4-40 hex nut were included in the Semiconductor package and should have been used already to mount Voltage Regulator U10.

60001 Circuit board mounting (4)

Mount rear panel ends of chassis brackets (4)

60032 Mount top and bottom shells to chassis

brackets in final assembly

60080 Mount front panel to chassis ends (4)

Mount Speaker/Battery shelf to chassis (4)

51058 Use between #60001 screws and top of

board to mount circuit board.

65009 Mount Display Board to front panel

7-9. Keeping a #4 self-threading screw and small screwdriver handy, fit the panel to the display board, gently guiding the SPEED LED as needed. W hile holding everything together, ins tall the screw in the center mounting hole near t he Clarifier control.

7-10. Install additional #4 self-threading screws in the other four mounting holes in whatever order is most convenient.

1254 – Assembly - 66

Page 88

7-11. Tighten all 5 Display Board mounting screws.

1/4" #4-40 screws and two #4 lock washers.

#4-40 undercut screws.

panels, using four 1/4" #4-40 screws.

of the board.

mounting legs on the bottom side, leaving them straight (i.e., there is no need to bend them). Use a minimal amount of solder to get good connections to the groundplane.

of the board and solder the mounting legs as for VCO-1.

if the primary use of your receiver will be vehicle-mounted.

To assure maximum VCO stability, you can do exactly what we do in factory - built equipment. Use a hot-melt glue gun to flow glue liberally around the outside of each VCO coil. it's OK if glue also covers some of the nearby parts. The idea is to increase the body weight and mass of the coil itself , further securing i t to the board. Be sure not to get any glue inside the coil, which would interfere with any further adjustment. Again, this procedure is NOT NECESSARY for ordinary receiver operation.

accessible through the hole. Solder the cover to the main shield. Soldering each of the 4 corners is sufficient.

that the Power Switch and Encoder cables are plugged in.

your DC voltmeter to the VCO test point and ground as you did in Phase 2.0.

7-12. Install the the Volume and Clarifier control knobs. Before tightening the s etscrews, line up the index stripes correctly in reference to the silkscreened dot markings on the panel.

7-13. The large Tuning knob can be mounted to the encoder shaft in any way convenient to you. Allow enough clearance so the back of the knob does not scrape against the panel.

Figure 7.2

7-14. Attach the Left Side chassis panel bracket to the circuit board using two 1/4" #4- 40 screws and two #4 lock washers.

7-15. Secure the front panel to the left side panel us ing two #4-40 undercut screws.

1254 - Assembly - 67

Page 89

7-16. Mount the RIGHT side panel to the board using two

1/4" #4-40 screws and two #4 lock washers.

7-17. Secure the front panel to the right side panel using two

#4-40 undercut screws.

7-18. Mount the rear panel to the ends of the two side

panels, using four 1/4" #4-40 screws.

7-19. Set the VCO-1 shield enc losure in place on the top side

of the board.

7-20. While holding the shield in place, solder all four mounting legs on the bottom side, leaving them straight (i.e., there is no need to bend them). Use a minimal amount of solder to get good connections to the groundplane.

7-21 . Set the VCO-2 shield enclosure in place on the top side of the board and solder the mounting legs as for VCO-1.

7-22. The following procedure is OPTIONAL but is suggested

if the primary use of your receiver will be vehicle-mounted.

To assure maximum VCO stability, you can do exactly what we do in factory built equipment. Use a hot-melt glue gun to flow glue liberally around the outside of each VCO coil. it's OK if glue also covers some of the nearby parts. The idea is to increase the body weight and mass of the coil itself , further securing i t to the board. Be sure not to get any glue inside the coil, which would interfere with any further adjustment. Again, this procedure is NOT NECESSARY for ordinary receiver operation.

7-23a. Set the VCO-1 top cover in plac e so that L3 remains accessible through the hole. Solder the cover to the main shield. Soldering each of the 4 corners is sufficient.

7-23b. Install the VCO-2 top cover per 7-23.

7-24. Reconnect the headphone jack cable to J6 and be sure that the Power Switch and Encoder cables are plugged in.

7B: Model 1254 Receiver Alignment

7-25. Reconnect DC power and turn on the receiver. Connect your DC voltmeter to the VCO test point and ground as you did in Phase 2.0.

7-26. Turn on the receiver and tune to 100 kHz.

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7-27. If needed, re-adjust L3 f or a VCO voltage of 2.5 volts

the speaker in its mounting hole. If you wish, pencil a circle around the outer rim to indicate gluing area.

speaker to the shelf . ("Super glue" is NOT at all useful for this procedure") We suggest contact cement, coating both surfaces, because it is commonly available, very handy for other jobs and fast-drying. A bit of silicone caulk also can be used. While you are waiting for the glue to dry, there are other little things that can be done.

bottom cabinet shell.

the front panel in the corner above the microphone jack. Use a bit of contact cement on the back of the logos and between the two mounting holes. D O NOT USE SUPERGLUE: discoloration or other damage may result.

underside of the speaker shelf, using several turns of electrical tape through the slots.

(-black) polarity. These wires are installed on the solder trace side of the board and may be soldered on either side of the board.

shelf to the side panels using four #4-40 undercut screws.

encoder cables are plugged in securely.

front of the shell is the end with no folded seam.

DC at 100 kHz. As you observed in Phase 3.0, increasing the frequency will increase the VCO voltage to a maximum of about

8.0 volts at 13.2 MHz.

7-28. If needed, re-adjust L2 f or a VCO voltage of 2.5 volts DC at 13.240 MHz. As you observed in Phase 3.0, increasing the frequency will increase the VCO voltage to a maximum of about 8.0 volts at 30.000 MHz.

7-29. Connect an antenna to the receiver and tune anywhere between 5 and 15 MHz where your own experience would expect to find signals at this time of day or night. If shortwave is new to you, tune between 8 and 15 MH z during daylight and between 5 and 10 MHz at night.

7-30. Tune in any signal, any mode, which you would like to use as a test signal. Choose one you can hear well enough, but not too strong.

7-31. Adjust the following coils for maximum signal strength

T6 L9 L10 L11 T7

7-32. In AM Mode, tune in the strongest WWV signal for the time of day and your location, most typically at 5, 10, 15 or 20 MHz. Make sure the display indicates the WWV exactly, such as

15.000.0 MHz. Follow this procedure to set trimmer capacitor C2 correctly (3.58 MHz synthesizer clock):

TOOL: jeweler's screwdriver or alignm ent tool Select SSB Mode Set the Clarifier control to its midpoint or 12:00 position Slowly rotate trimmer C2 until t he carrier tone {whistle) of WWV is at lowest musical pitch ("null"). Rotating the Clarifier control in either direction should result in a higher pitch s ound of the WWV carrier.

7-33. Use FAST Tuning to go down to 300 kHz and select SSB mode. Adjust trimmer potentiometer R70 for lowest background noise level.

7-34. At this stage of receiver completion, no useful adjustment of 455 kHz transformers T2 and T3 makes any performance difference. If you noted any signal strength increase during Phase 4.0 tests, let those settings stand. Otherwise, just s et the T2 and T3 slugs about one turn below being flush with the t op of the coil form.

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7-35. Turn off and disconnect DC power.

7C: Final Assembly Procedure

7-36. With the bracket ends of the speaker facing down, set the speaker in its mounting hole. If you wish, pencil a circle around the outer rim to indicate gluing area.

7-37. Use any glue which you like working with to secure the speaker to the shelf . ("Super glue" is NOT at all useful for this procedure") We suggest contact cement, coating both surfaces, because it is commonly available, very handy for other jobs and fast-drying. A bit of silicone caulk also can be used. While you are waiting for the glue to dry, there are other little things that can be done.

7-38. Mount the four self-adhesive rubber bumper feet to the bottom cabinet shell.

7-39. Recheck all screws for reasonable tightness.

7-40. With considerable pride, attach the TEN-TEC logo t o the front panel in the corner above the microphone jack. Use a bit of contact cement on the back of the logos and between the two mounting holes. D O NOT USE SUPERGLUE: discoloration or other damage may result.

7-41. The 9-volt memory backup battery is secured to the underside of the speaker shelf, using several turns of electrical tape through the slots.

7-42. Solder the battery snap wires with correct (+ red) (-black) polarity. These wires are installed on the solder trace side of the board and may be soldered on either side of the board.

7-43. Plug in the speaker cable to J5 and mount the speaker shelf to the side panels using four #4-40 undercut screws.

7-44. Recheck that the power switch, headphone jack and encoder cables are plugged in securely.

7-45. Set the receiver into the bottom shell, noting that the front of the shell is the end with no folded seam.

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7-46. Place the top shell in position and complete the assembly with the four black #4-40 screws, Note that the screws go through both cabinet sections into the side chassis panels for excellent mechanical durability.

This completes construction

of the T-KIT Model 1254 SWL Receiver.

We thank you very much for

your trust in T-KIT products by TEN-TEC!

See REFERENCE SECTION,

Part III of this Manual,

For all Model 1254 Operating Instructions,

Discussion of features

And troubleshooting guide

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This space is for your notes

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Section 3:

Model 1254 Receiver Specifications and Features

Mode Select, Memory Write (MW), VFO/Memory tuning select (V/M), Tuning Rate Select (SPEED)

signal present; 15VDC @ 800 mA wall transformer supply included with kit.

phone jack for standard personal headphones or direct feed to 4-8 ohm external speaker, data inter face or both.

molded front panel.

REFERENCE INFORMATION

for T-KIT Model No. 1254

SSB-CW-AM

Microprocessor-Controlled

100 kHz - 30 MHz Receiver

Specifications: T-KlT Model 1254 Model 1254 Operating Instructions

1. Functions of Primary Controls

2. Tuning AM signals

3. Storing Frequencies in Memory

4. Recalling or Tuning Memory Frequencies

5. Tuning SSB signals

6. Tuning CW signals

7. Microprocessor RESET

8. Memory Battery Test

Circuit Description Block Diagram Practical Information for Receiver Use

Connecting Antennas "Active Antenna" Notes DC Power Supply Considerations "Mobile SWLing" External Audio Connections Receiving Digital/SSTV modes SWL basics and Communications Applications Beyond 30 MHz . . . and Below 100 kHz

Terms & Abbreviations Component Reference Index Troubleshooting Guide Chart of Significant Voltages Modification Notes Checking for Solder Bridges: (right-reading view of solder-trace side, main board)

6-14

15-18

17 19 20 21 21 22 23

24 28 28-35 36-38

38 39

3 3 4 4 5 5 5 5

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Model 1254 Receiver Specifications and Features

Frequency coverage: 100 kHz to 30 MHz Modes: AM, SSB/CW

Main Tuning: Normal or Fast tuning (2.5 kHz SSB, 5.0 kHz AM, or 100 k Hz steps for either mode) "Clarifier" Control: for ± 1.5 kHz SSB/CW fine tuning between 2.5 kHz steps.

Front panel controls: On/off switch, Tuning, Volume, Clarifier, Mode Select, Memory Write (MW), VFO/Memory tuning select (V/M), Tuning Rate Select (SPEED)

Memories: 15 programmable memories

Circuit: Synthesized 45-75 MHz local oscillator

45 MHz first I-F, 455 kHz second I-F

Sensitivity: AM mode: 2.5 μV for 10 dB SNR at 30% modulation

SSB/CW mode: 0.5 μV for 10 dB SNR

Selectivity: 4 kHz @ -6 dB

Frequency/Memory Display: 6-digit green LED with mode indicators

Power supply: 12-15 VDC, 250 mA current consumption with no

signal present; 15VDC @ 800 mA wall transformer supply included with kit.

Antenna connector: 50 ohm input, RCA-style phono jack

Audio: 1.5 watts audio output t o internal speaker, plus 1/8" stereo

phone jack for standard personal headphones or direct feed to 4-8 ohm external speaker, data inter face or both.

Semiconductors: 10 IC's, 26 transistors, 16 diodes

Compact Size: 2.25" x 6.5" x 6.5" ( HW D)

Construction: Steel clamshell case, aluminum chassis, custom-

molded front panel.

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Model 1254 Receiver

3. Storing Frequencies in Memory

To place the currently displayed frequency and reception mode in memory, do the following:

4. Recalling and Tuning Memory Frequencies

To scroll through or listen to the frequencies in memory:

Operating Instructions

1. Control Functions

The TUNE control performs two functions:

Direct frequency tuning Memory Tuning (Memories 01 through 15)

The VOLUME control sets the rec eiver audio gain.

The CLARIFIER control permits fine-tuning of SSB and CW signals within the 2.5 kHz tuning steps in SSB mode.

The POWER switch simply turns on the receiver on and off .

The [MODE] pushbutton selects between AM and CW-SSB reception modes. The current mode is always shown in the frequency display window.

The [MW] ("Memory write") button stores the current frequency and reception mode in any memory location you choose. See "storing Frequencies in Memory" for detailed instructions.

The [V/M] switch toggles between Frequency Tuning ("VFO") and Memory Tuning. See "Tuning Mode Indicator" below. When [V/M] is in Memory Tune mode, the Tuning Control is used to select the desired memory.

The Tuning Mode Indicator is the LED decimal point to the right of the last digit of the display. It is ON for direct frequency tuning and OFF for memory tuning.

The [SPEED] button toggles the [FAST] 100 kHz step tuning mode on and off as indicated by the FAST LED indicator.

2. Tuning AM Signals

Set the Clarifer control to its 12:00 position. Select AM with the [MODE] button. The receiver will tune in 5 kHz steps unless [FAST] 100 kHz tuning is selected. Adjusting the Clarifier control may have a slight effect on signal quality but this control is intended primarily for SSB-CW fine tuning.

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3. Storing Frequencies in Memory

To place the currently displayed frequency and reception mode in memory, do the following:

Press [MW ]: the most-recently addressed memory location will be displayed. Rotate the TUNE control to the memory you wish to use, either an empty location or to replace an unneeded frequency. Press [MW ] again to store the frequency and return the receiver to normal tuning mode.

4. Recalling and Tuning Memory Frequencies

To scroll through or listen to the frequencies in memory:

Press [V/M] to enter Memory Tune mode as indicated by the Tuning Mode Indicator being toggled OFF by. Rotate the tuning knob to selec t a memory location. The display will momentarily indicate the location, then display the stored frequency and reception mode. Press [V/M] again to exit the memory tune mode and return to the original VFO frequency

Figure 1R: Model 1254 Display and Mode Selection

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5. Tuning SSB Signals

Model 1254 Receiver Circuit Description

Before we begin a stage by stage description of the circuitry in this receiver, let's take a broader view of how shortwave receivers are designed in general. This should help show how signals actually make their way from the antenna to the speaker.

Depending on their intended function, radio receivers can be designed using several different electronic architectures. Very simple receivers can be built from kits or your own parts using classic autodyne, TRF, regenerative or direct-conversion designs. Such receiver projects continue to provide t he fun of discovering how radio originated and how simple it can be.

However, the most common approach used in short wave receivers is called the superheterodyne method, usually referred to as "superhet." In this approach, incoming signals from the antenna are translated in frequency by a s pecial stage of circuitry called a mixer. A radio frequency (RF) mixer is es sentially a high speed switching circuit that combines the incoming signals with a local oscillator ( LO) which is generated within the receiver.

This mixing process results in a frequency conversion to an Intermediate Frequency (IF). A superhet receiver typically may be single, double or triple conversion: the Model 1254 is a double-conversion receiver with a 45 MHz first IF and a 455 kHz second IF.

The simple receiver most closely related to the superhet is the direct conversion design in which a variable LO is mixed with incoming signals from the antenna. The resulting "IF" is in the audio spectrum range and is amplified directly for listening.

The local oscillator must be a very clean and stable sinewave because any undesirable characteristics on this signal would be transferred to the rec eived signal by the mixing process. Most modern receivers use a "synthesizer" to generate this signal. The synthesizer circuit is able to tune the local oscillator in very accurate steps and also hold the oscillator on frequency with very little drift.

Mathematically, the mixer multiplies the instantaneous values of the LO and the input together. The result is a pair of output bands that are the sum and difference, in f requency, of t he input and the LO. The LO frequency range is chosen so that one of these bands can be separated out for further amplification and

Set the Clarifier control to its 12:00 position. Select SSB Mode and tune to a signal of interest. Use the Clarifier control to adjust for intelligible voice audio. Tune up (clockwise) for USB s ignals and down for LSB signals. If you are tuning the Clarifier clockwise and the signal s till seems "out of reach," turn the Main Tuning one step higher and then re-tune the desired signal. Similarly, if you are tuning lower, then turn Main Tuning one step lower.

6. Tuning CW and RTTY/Data Signals

Set the Clarifier control to its 12:00 position. Select SSB Mode and tune to a signal of interest. Use the Clarifier control to adjust for desired audio pitch. If you are tuning the Clarifier clockwise and the signal still seems "out of reach," turn the Main Tuning one step higher and then re-tune the desired signal with the Clarifier. Similarly, if you are tuning lower, turn Main Tuning one step lower"

7. Microprocessor RESET

A "power-on reset" is a quick way to clear all the memories. This procedure can also be us ed to recover from fault conditions caused perhaps by power supply line noise. The symptom or evidence that somet hing is not right with the microprocessor can be an unusual or blank frequency display or locked-up tuning. To RESET the micr oprocessor, do the following:

Turn off the front panel DC power switch Press and hold down both [MODE] and [MW] Turn ON the power switch Release [MODE] and [MW ] pushbuttons Expect to see the 15.000 MHz default display Reprogram the memory channels as desired

8. Memory Battery Test

At intervals comfortable to you, at least once a year, check the condition of the memory backup battery with your VOM/DVM or a reliable battery tester. To pres erve stored memories, the battery removal, test and replacement should be done (carefully!) while the receiver is TURNED ON.

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Model 1254 Receiver Circuit Description

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processing. This is illustrated with some example spectrum plots

Figure 3R: Model 1254 Block Diagram

in Figure 2R.

Fig. 2R: Spectrum Plot examples

The stage of selectivity and gain that follows the mixer is called the intermediate frequency (IF) amplifier. Notice how the position of the loc al oscillator determines which part of the incoming spectrum falls within the bandwidth of the IF amplifier. As the LO is tuned, individual signals can be separated out for amplification and detection.

The typical receiver will use at least two mixers and two of these intermediate frequency stages to convert an incom ing signal down to audio. The desired tuning range of the receiver and the availability of certain standard filter frequencies is usually what determines the selection of the IF frequencies.

Let's now study the Block Diagram of the Model 1254 receiver shown in Figure 3R. We will follow the signal path from antenna to speaker, and explain the reasoning behind the design of each stage.

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