DEMI L50-28CK User guide

Power Out Maximum:

Nominal 25 W linear

Noise Figure and Gain:

>1.0 dB maximum @ 17 dB conversion gain minimum

DC Power Requirement:

11.5 - 15.5 VDC @ 6 Amp Max.

IF Drive Level Maximum:

Range Selectable between -20dBm and 25 watts

Keying Option with/ without Sequencer:

PTT-L ( to ground) or PTT – H ( Positive Voltage)

User Installed Options:

IF Drive Sense , Negative Voltage Gen., Cooling Fan,
and Sequencer

DEMI Part Number L50-28CK and K

Transverter Specifications

Configuration Overview: The DEMI VHF/UHF transverter line is designed to interface and

operate with most High Frequency transceivers that are available on the market today. Since you
choose to purchase a kit version, you may configure it to your specifications and interface it with
your desired transceiver. This configuration may be changed or altered at any time if you desire to
utilize a different transceiver or change you system’s configuration.

DEMI Part Number Verification: All DEMI VHF/UHF transverters contain the operating
frequency within the part number, i.e. L50-28CK or K is equated to 50 MHz being converted to 28
MHz. Understand that the conversion is simple math. If you desire to operate on 51.500 MHz. with
your L50-28, it will require you to adjust you transceiver to 29.500 MHz.

Power Out Maximum: The maximum linear output power indicated on this kit is 25W. This level
should not be exceeded if linear operation is expected. The transverter may be capable of
producing higher output power but is not recommended because of excessive heating that will
interfere with its frequency stability while producing excessive “on the air” distortion products

Noise Figure and Gain: The noise figure and gain listed are nominal minimum requirements
and all transverters will exceed these specifications if assembled and adjusted correctly. In utilizing
the latest PHEMPT technology, we have designed the complete receive section of the transverter
with extra filtering, diplexing, and gain management in mind complete with a RXIF gain control.

DC Power Requirement: The DC power requirement is listed and should be used as a guideline.
Please include some “Buffer” in your power supply to eliminate voltage drop delivered to the
transverter. Basically, do not utilize a 6-amp power supply for a 6-amp requirement transverter.

RF Option: The 50 Mhz. RF section may be configured with either a single port (Common RF) for
both TX and RX or two separate ports, (Split RF) one RX and one TX. There is a PC board relay
doing the Common RF switching. Once configured, the unit may be changed from Comm o n to Spli t
RF if the user desires. It will be covered in the manual.

/Kits/L50-28CK.doc 1 Rev. B 7/4/2012

IF Option: The IF (28 Mhz.) configuration options may be set up as Split IF (separate TXIF and
RXIF in/out lines) or can be configured as a Common IF. There is a relay that will switch the RX
and TX in the correct direction and is controlled by the PTT circuit.

IF Drive Level Maximum: After configuration, the transverter will operate at its maximum output
power with any drive level between -20dBm and 25 watts. The overall drive level range is
determined by different attenuators and/or gain stages if required. The TXIF gain control with 15-20
dB of dynamic range will allow the user to tailor a specific output power les s than maxi mu m.

Keying Option: The keying options are either PTT-L or PTT-H. PTT-L requires a connection
to Ground to transmit. This is the most common keying option. PTT-H requires a voltage between

1.7 and 17VDC to transmit. This option can also be placed on the IF coax if desired. If you desire
the sequencer to be utilized, the PTT connection will go directly to the sequencer to key it. In turn,
it will key the transverter on the last step of the sequence. Now doing so creates other caveats if
you choose to use a High IF drive level (above 1/2W). This is covered in the next section.

User installed Options: The IF Drive Sense option should be i ns t al l e d for any Common IF drive
level above 100 mW. This circuit is a protection circuit that will prevent excessive IF drive levels
from damaging the RXIF circuitry and the Mixer. When utilizing a high- level IF drive transceiver,
the IF drive from your transceiver may be applied to the trans v er ter at the same time as the PTT is
energized. If the transverters sequencer is utilized, the transverter will be keyed last in the
sequence. This would res ul t in the high level IF drive being applied to the transverter’s RXIF
section which would cause the damage. With the IF drive sense circuit installed, it detects the high­level drive and enables the TXIF attenuator. This protects the transverter’s RXIF section and Mixer.
It then holds and waits for the Transverter to “Catch up” in the sequence. This circuit will allow a
user to key the sequencer circuit with the standard PTT circuit of a transceiver without having an
issue or requiring external wiring and modifications to the transceivers PTT circuit. This circuit will
also protect the transverter in case the PTT circuit fails between the transverter and the
transceiver. If the transverter is keyed directly with the PTT (sequencer is disabled) it will function
normally. CAUTION: The IF drive sense circuit should not be used to key the sequencer because it
will produce long delays between transmit and receive or chop off the beginning of a transmission.
The transverter’s IF drive sense was desig ne d for pr otec tion only.
The Negative Voltage option may be utilized by transceivers without transverter ports
but with ALC inputs to adjust the output power of the transceiver. If the transceiver has an ALC
input, this connection can be made through the AUX connecter and will be indicated.

The Cooling Fan should be installed and used with the temperature sense circuit because it
is crucial for frequency stability in digital modes. As the temperature increases the fan speed will
increase to provide the additional cooling and frequency stability.

The Sequencer is a 4 step circuit that may be used to key any external devices and the
transverter itself. It may be configured in any fashion and set up to switch external voltages such

/Kits/L50-28CK.doc 2 Rev. B 7/4/2012

R1 1K

R23 470

R39 220

R53 470

R67 10K

R2 – R8 NR

R26 24

R40 220

R54 10K

R68 1M

R9 5.6K

R27 5.6

R41 10K

R55 10K

R69 10K

R10 10K

R28 51

R42 10K

R56 10K

R70 10K

R11 220

R29 51

R43 470

R57 10K

R71 10K

R12 330

R30 51

R44 10K

R58 1M

R72 1M

R13 330

R31 12

R45 220K

R59 10K

R73 10K

R14 330

R32 51

R46 1M

R60 220

R75 100

R15 120

R33 1K

R47 10K

R61 10K

R76 51

R16 - R18 NR

R34 330

R48 10K

R62 10K

R77 1K

R19 470

R35 220

R49 1K

R63 1M

R78 220

R20 330

R36 1K POT

R50 5.6K

R64 10K

R81 5.6K

R21 150 ½ LEAD

R37 220

R51 5.6K

R65 220

R82 5.6K

R22 51

R38 1K POT

R52 22K

R66 10K

R84 5.6K

as a 24 VDC relay. The voltage may be run into the transverter through the AUX connector and
switched through the sequencer.

The transverter has a provision for an External Local Oscillator connection. This will be
discussed in the text and explained how to either configure a future Synthesized LO or use an
external one of your own design.

The KIT Details: This assembly manual calls out a reference to one or two picture numbers for
most assembly procedures. The pictures can be found on our website in the “Product Manuals”
section. It is a full copy of this manual with all numbered pictures at the end of the document in
.PDF format. You may down load a complete copy of this document or just reference the pictures.
You will find that the details offered in the pictures will aid any assemble instruction.

The following component list contains both pre-assembled components and components to
be assembled by the kit builder in Bold Print. Verify that all components in Bold print are supplied
in the kit. The component containers will have extra components of some values. There may also
be component values included in the kit not found on the list. These will be used in the testing
section of the document. ALSO, because this is a board us ed for all transverters from 50 thru 432
MHz, there are some components installed on the circuit board that will need to be removed,
changed, or not required in the circuit (labeled NR) because they will have no function in your
frequency specific version. It is suggested to Highlight the components on the component
placement document that are to be installed as you inventory the values.

DEM 50-28 COM PONE NT LIST

Resistors (R) values are in Ohms and are chips unless otherwise specified. Some values are NR

All inductors (L) are in ηH and are 1008 chip unless otherwise specified. “HW”=hand-wound and
utilize enamel wire. Some values are NR

/Kits/L50-28CK.doc 3 Rev. B 7/4/2012

L1-L4 NR

L13 9Turns #24 T37-12 Green/white HW

L22 330

L5 1.0 µH

L14 10Turns #24 T37-12 Green/white HW

L23 150

L6 1.0 µH

L15 10Turns #24 T37-12 Green/white HW

L24 220

L7 330

L16 9 Turns #24 T37-12 Green/white HW

L25 150

L8 680

L17 14Turns #28 T25-10 Black/gray HW

L26 330

L9 680

L18 330

L27 330

L10 330

L19 330

L29 220

L11 – L12 NR

L20 68

L30 1.0 µH

L21 1.0 µH

1.0 µH molded choke

C1 1000

C43 1000

C66 0.1 µF 1210

C91 10 or 1000

C2 –C12 NR

C44 1000

C67 0.1 µF 1210

C92 1000

C13 27

C45 1000

C68 1000

C93 1000

C14 Test Option

C46 1000

C69 0.1 µF 1210

C94 10

C15 56

C47 0.1 µF

C70 100

C95 –C97 1000

C16 Test Option

C48 0.1 µF

C71 33

C98 0.1 µF

C17 0.1 µF

C49 1000

C72 1000

C99 10 µF T (1210)

C18 2-6ρF Trimmer

C50 1000

C75 1.0 µF T

C100 1000

C19 1000

C51 0.1 µF

C76 0.1 µF

C102 1000

C20 56

C52 100

C77 0.1 µF

C103 22 µF T (2312)

C21 0.1 µF

C53 100 µF E

C78 1000

C104 10 µF T (1210)

C22 1000

C54 120

C79 1000

C105 10 µF T (opt)

C23 1000

C55 120

C80 1000

C106 10 µF T (opt)

C24 Remove

C56 120

C81 56

C107 10 µF T (opt)

C25 220

C57 1000

C82 150

C108 1000

C26 270

C58 100

C83 150

C110 220

C27 220

C59 0.1 µF

C85 150

C111 3

C28 1000

C60 1.0 µF T

C86 56

C112 100 µF E

C29 - C38 NR

C61 0.1 µF

C87 1000

C113 68

C39 1.0 µF T

C62 1000

C88 1000

C114 68

C40 0.1 µF

C63 2-10ρF Trimmer

C89 0.1 µF

C115 10 µF T (2312)

C41,C42 NR

C64 2-6ρF Trimmer

C90 1000

C158 100

All capacitors (C) are in ρF and are chip unless otherwise specified. “E” = Leaded Electrolytic,
“T” = chip Tantalum, Band is positive. Some values are NR

/Kits/L50-28CK.doc 4 Rev. B 7/4/2012

Solid State, Relays and Filter Components. NR= Not required

CR1 1N4000 type

IC1 ,IC2 NR

Q7 PMBT3904

CR2 NR

IC3 MAR3

Q8 MJD31

CR3 MPN3404

IC4 MAV11

Q9 PMBT3904

CR4 MPN3404

IC5 RA30H0608M

Q10 MJD32

CR5 1N914 or 4148

IC6 PHA-1

Q11 PMBT3904

CR6 1N914 or 4148

IC7 MAR6 (option)

Q12 PMBT3904

CR7 HP2800 SMD

IC8 LM393

Q13 PMBT3904

CR8 HP2800 SMD

IC9 LM324

Q14 MJD31

CR9 MMBD914

IC10 7660 (option)

Q15 PMBT3904

CR10 1N4000 type

K1 G5V or D2N

Q24 PMBT3904

CR11 HP2800 SMD

K2 G6Y

Q26 PMBT3904

CR12 MMBD914

K3 G6Y

VR3 78L05

CR13 MMBD914

M1 SYM18H

VR4 78M05

CR14 1N4000 type

Q1,Q2 NR

VR5 78S09

CR21 MMBD914

Q3 PMBT3904

Y1 NR

F2 50M-3 pole

Q4 PMBT3904

Y2 22.000 Standard

F3 50M-2 pole

Q5 PMBT3904

PTC-50 Thermistor

F4 50M-2 pole

Q6 FPD750

Xtal Shield

(1) Heatsink

(1) #6 flat washer

(1) Back Panel of enclosure

(1) #6 ground lug

(1) U-channel enclosure

(1) #4 Ground lug

(1) Bottom panel

(1) 50 Ohm load

(7) Black 4-40 screws

(1) Switch

(16 ) 4-40 x ¼” screws

(1) Green LED

(12) Aluminum Shoulder Bushings

(1) Red LED

(10) 4-40 x 7/16” screws

(2) BNC connectors and Hardware

(3) 4-40 x ¼” threaded standoffs

(2) Type “N” connectors and hardware

(3) 4-40 nuts

(1) RCA connector

(1) 4-40 x3/8” screw

(1) 8 pin connector set

(1) Brass shield for Power module

(1) NL2 connector

(2) 6-32 x 5/16” screws

(1) NL2FC connector

(2) 3/8” hole plug

(2) Spade Terminal

(1) ¾” hole plug

(1) 1000pf disc cap

#16 wire, 2” black, 3” color

Coax, 20”

Power meter kit

#24 gauge wire, 6 feet (Green)

(1) Fan

(1) NTC Thermistor

(1) Fan guard

(4) 6-32 x 1-3/4” screws

Sleeving, 5”

(4) Tie Wraps

Tube of thermal compound

(4) Rubber feet

Bundle of precut #26 colored wire

5’ of Zip cord

Verify all of the listed hardware is in the Hardware Kit.

HARDWARE

/Kits/L50-28CK.doc 5 Rev. B 7/4/2012

Circuit Board Assembly:

Refer to the component placement diagram and install all topside components that require
soldering on the bottom side of the board. Install VR3, F2, F3, F4, K1, K2, K3, R36, R38, CR1,
CR3- CR6, CR10 and CR14. Even though K2 (RF relay) and K3 (IF relay) are to make the
common RF and IF connections, (combined TX and RX), separate TX and RX connections to both
RF and IF ports can still be made after relay installation. BUT—you may leave both relays un­installed if you only desire separate RX and TX ports for the IF and RF connections. Be sure to
heat the ground connections well before flowing solder on the filters and relays. Cut the excess
from all leads flush with the board. See Picture 1 and 2

Now examine the Bottom Side Board Assembly picture on the next page. It is suggested t o
complete all of the wiring on the bottom side. Some wires are for features that you may never
utilize in your configuration but will provide ease of a configuration change at a later date if you
decide to change trans cei vers. If you do not see the need for certain features, some of the wiring
may be omitted. The signals are marked on the picture. The negative voltage generator, (+9
connection) the IF drive sense (three wires), and the wiring for the RF TR relay may be left out if
those circuits will not be utilized. They could be added to the top side if required in the future. All
other wire connections are required for full transverter function. Each marked wire shows its
approximate length.

Find the 6 foot wind of #26 Green hook up wire, then cut, trim, tin, and install. It is best to
cut the wire a bit long (1/4”) and trail fit after soldering one end in place. If you are close with the
measurements, the wires will fall into place as shown. If the wire is too long they may get pinched
during the assembly of the board. One wire, the 9” 13.8V, is only attached at one end for now.
Save the extra wire out of the 6’ bundle for topside wiring. See picture 3 for correct technique of
wire soldering.

After all wires that you wish to install are installed, (10 max) be sure none of the wires cross
any of the bottom side solder connections of the filters, pots, and RF relays. This is to prevent any
RF signals from coupling to the DC connections. The exception is the 2-1/2” TXON wire for the TR
switch. It crosses under K1 which is a non-RF circuit relay. Also be sure that the wires do not cross
any mounting holes. Then with a small piece of tape, (any type) attach the wires as shown in the
next picture being sure that the wires are laying flat on the circuit board. If you desire to attach
other wires or configure the transverter differently, or desire to use any type of adhesive to hold
wire in place, please do so. Just be sure to clear all mounting holes and exposed RF circuits and
do not allow and excessive amount of adhesive to prevent the circuit board from attaching flat to
the mounting hardware on the heatsink. A 1/8” clearance is required between the board and
heatsink.

/Kits/L50-28CK.doc 6 Rev. B 7/4/2012

Bottom Side Board Wiring

Surface mounting assembly of components:

The rest of this document assumes that you have the complete kit version. If you have the

basic PC board kit, follow along in the instruction manual but skip the instructions that do n ot
pertain to your final assembly.

First, examine the board. It is a basic rectangle with two small notches and one large notch
on one corner. If you hold the board so you can read the majority of the screened text left to right,
you will find the large notch on the lower left hand side of the board. This is the orientation that the
top side component placement document will refer to. In brief, the TX chain and power amplifier is
in the lower left, the RX LNA in the upper left, the Local oscillator on the lower and center right. The
IF Drive sense and Negative voltage generator are on the upper right. The upper center of the
board is the IF section and the lower center is the sequencer as shown in Picture 4.

/Kits/L50-28CK.doc 7 Rev. B 7/4/2012

What is convenient for assembly is that the circuit board may be mounted to the heatsink
before any surface mount work is done. But, if you have a PC board vice that you utilize for board
projects, you may want to use it. It is your choice. Since there is no further work to be done on the
bottom side of the board, we recommend attaching the board to the heatsink to save a step.

Find the 11 shoulder bushings in the hardware kit and install them in the holes in the
heatsink. These act as spacers for the board. Some may fit snug and it is alright to gently “tap”
them in. Be sure that they are completely seated. Next locate the position for the NTC as shown on
the component placement. It is the largest recessed hole in the heatsink. It requires to be filled
about ¾ of the way with thermal compound before the NTC is installed and is easier to do before
the board is attached to the heatsink. Find the tube of thermal compound, use, than save the rest
for the Power module mounting later in the kit instructions. See picture 5.

Now find VR5, the 9 VDC regulator. Its leads are mounted through the bottom side of the
board. Insert VR5’s leads through the board from the bottom side as far as it will go. Then bend it
over in the direc ti on as shown in the placement diagram. Do not solder! Align and place the circuit
board on the bushings along with VR5 in place. Be sure the one end of the 9” +13 8V wire is out
from under the board on the lower right hand side. This wire is connected to the switch during final
wiring. Then verify that the board sits flat on the bushings (no wires being pinched) and att ach the
board with eleven 4-40 x 7/16”, 4-40 x ¼” screw for VR5. Start all screws first, then tighten. Some
screws will be removed to ease assembly later during the process and will be specified, but for
now, you have a solid mounted circuit board ready for assembly. Solder VR5’s leads in place after
all screws are seated. See Pictures 6 and 7

Next step in the board assembly is to remove the components that will inhibit the operation
of your transverter. For the L50-28CK, there is only one component, C24. Wick all connections
clean if you can. All other components that are marked NR in the components list are not
connected if the board is assembled correctly and will not affect the performance of the
transverters. See Picture 8 for the location of C24.

It is now recommended to follow the assembly steps listed below but if you are an
experienced builder, you may start on the board anywhere you want placing all of the components
listed on the component lists. The assembly steps will cover some options and place importance
on some order of assembly but again, nothing is critical and does not need to be assembled in any
particular order. If you decide to go about this on your own path, the only precaution is if you desire
to test the local oscillator for the correct output level, do not install the Mixer, M1. Leaving the mixer
un-installed allows testing of the RF, LO and IF stages independently.

1. Comparing your boar d to Picture 9 and 10, you will see that only a couple of components
need to be assembled in the LO. Install C13, C20, L5, L6 and C18. C18 is now a smaller
surface mount trimmer and will not match the picture. There are open positions at C16 and
C14. These are to be left op en and will be discussed in the test procedure.

2. Prep the leads of the Y2 Crystal as shown in the next group of pictorials. Solder it to the
circuit board with the leads pointed at C17 and R10. Prep the PTC Thermistor and Xtal
shield as shown. With a solder iron, remove one lead from the Thermistor then solder the

/Kits/L50-28CK.doc 8 Rev. B 7/4/2012

PCB

To GND

Thermistor to the shield. When cooled, bend to shape and place the PTC and shield
assembly over the Xtal. Attach the previously removed wire to the side of the shield and
connect to ground in a via hole that is in the ground plane between C13 and Y2 with the
shortest connection possible. Cut and fit a piece of the sleeving to fit the “Hot” lead then
connect the “Hot” PTC wire to the via-hole near the LO6M designator on the board. See
picture 10.

To LO6M via

3. Install C39 near VR5 then install L7- L10, C23 and C25 - C27. This is the local oscillator
low pass filter and completes the oscillator. See Picture 11 and be sure C24 is remove not
like the picture shows! If you wish to test the oscillator level and hav e an mW power meter,
skip assembly Step 4. Leaving the mixer un-installed allows you to test the individual
sections of the transver ter if you desir e. BUT— if you do not have gain measuring capability
and accuracy to at least a dB, Complete Step 4 next.

4. If you do not wish to test the Oscillator level, install the mixer M1.Line it up on the pads and
solder. It is best to tin one pad and hold the mixer in place while heating the tinned pad.
Solder the other two by flowing solder and then do the ground pads (3) .It will require some
heat to flow the ground connections! See Picture 12.

5. Next assemble the IF section of the transverter. Install L22- L27,L29 and C110. Picture 13

6. All of the following components listed in Step 6 except for IC7 can now be installed but their
utilization is dependent on the IF configuration you require. An explanation of what certain
components do follows along with advice if you chose not to install. For further explanatio n

/Kits/L50-28CK.doc 9 Rev. B 7/4/2012

of the IF section, Refer to the “TXIF Drive Level Range” section found in the “Options
Setup” section on page 25.

a. CR5 and CR6 are only required for drive levels higher than 1/2W but not required at

all if you use separate TX and RX ports. BUT-Having them installed does not inhibit
any configuration.

b. CR7, CR8, C94 and C99 (near IC8) are part of the RF sense protection circuit. The

circuit is only required for a common IF greater than 1/2W drive configurations but will
not inhibit any configuration. Check polarity of C99

c. The 50 Ohm load is required with any drive level above 200 mw regardless of any IF

configuration. It will provide attenuation at all drive levels so do not install for lower
drive levels. Attach one lead to a #4 ground lug mounted to the load with a 4-40 x3/8”
See Picture 14

d. C91should be a 1000pf if the drive level is below 1/2W and 10 pF for all drive levels

above ½ watt.

e. IC7 is the TXIF gain stage and is only installed if the IF drive level is 1 mw (0dBm) or

less. If your drive level is close to 1mw, install it after the TXRF testing is complete.
Depending on test results, it may or may not be required to compensate for lower or
higher TX gains in the transverter.

7. If you require the negative voltage generator circuit, Install IC10, C105- C107. These
components need to be ordered separately. This circuit provides a negative voltage that is
supplied to transceivers that do not have a transverter port or a way of limiting the ou tput
power, and of course, have an ALC input. When voltage is supplied to ALC input of a
transceiver, it will limit the power delivered to a transverter. After assembly, it’s operation will
be discussed further in the set up and operation section of this manual. See Picture 15 and
the component placement document for correct assembly. C106 is marked backwards on
the circuit board screen printing.

8. Complete the assembly of the sequencer by installing Q8, Q10, C103 and C104. Do not mix
up Q8 and Q10 and check polarity of C103 and 104! See pict ur e 16.

9. Install TXRF gain stage components IC3, IC4, R21, and C60. Surface one lead of R21 (the
connection to IC4). Form the lead of IC3 and IC4 before soldering if required. Then install
C53 and C112 by surface mounting the leads. Picture 17 and 22.

10. Install the TX low pass filter. Place and solder C54-C56, C113, C111 and C114 first. Then
wind the T37-12 torroids using the #24 enamel wire described in the components parts list
as shown in Pictur e 1 8. Be sure to solder tin the ends before installation. Then install as
shown in Picture 19.

11. Install CR11 (lower left hand corner) the power detector diode. Then install Q14 and C115,
the fan speed control circuit. Picture 19.

12. Begin to install the RX section by installing Q6. Then install C63, C64, L17, C67, R27,
C158, C66, C69, L18 and L30. Be sure that C63 and 64 adjust after soldering. See picture

20. C63 and C64 are smaller surface mount versions not shown in the picture.

13. Complete the diplexer circuit by installing L19, L20, C70 and C71. See Picture 21.

14. Finish the RX section by installing IC6, L21, VR4 and C75. See picture 21.

/Kits/L50-28CK.doc 10 Rev. B 7/4/2012

Power Module Installation:

P in Out

1 RF I n
2 Bi as ( T XON)
3 Vcc (+13.8VDC)
4 RF Ou t
5 RF & DC ground (Flange)

1 2

3 4

55

Place the power module (IC5) on the heatsink in
its mounting location. Trim the leads so they do not
extend past the solder pads. They should be
approximately 3/8"-1/2” long once trimmed. Remove
the Module and wipe the mounting surfaces of the
heatsink and flange of IC5, verify the surfaces are free
of any foreign matter. Apply a thin even coating of the
supplied thermal compound to the mounting flange and the heatsink and the bottom of the power
module. Place IC5 on the heatsink and “Lap” the thermal compound by moving the module side to
side while exerting slight down ward pressure. You will
feel the resistance build up when lapped. Line up the
leads with the traces of the circuit board. Find the brass
shield and form to fit as shown. Using one 6-32 screw
and flat washer, install it through t he shi el d an d the
mounting flange, into the heatsink hole nearest the
Q11, 3 and PH3 marking on the PC board. Then install the other 6-32 screw with a #6 Lug in the
other hole. Tighten evenly into the heat sink. NOTE: Make sure IC5 is mechanically sound to the
heat sink because improper seating of the hybrid could result in poor grounding and heat transfer
causing damage to the power module. Also be sure that the shield does not shift of contact any of
the module leads. The shiel d fro nt sh ould fit between the module and the par t of PC boar d with the
bare metal and two board mounting screws. Form the module leads flat to the traces, and then
solder all leads of IC5 to the circuit board. Now observe where the shield contacts the bare metal
of the PCB. Tack solder along that edge. It will require a lot of heat so take your time. It helps if you
loosen the board mounting screws or remove completely. Just don’t fill the holes with solder. Re­tighten when complete. See picture 22.
Finally, install the NTC in the hole through the board and in the thermal compound in the
heatsink. Attach the leads as shown on the components placement after installing sleeving on the
leads. The PCB is complete. See picture 17.

Final Wiring and Assembly

The final wiring and assembly starts with installing the connectors in the rear panel. You

may install all of them or only the connectors you will use. All connectors require all supplied
hardware. Install all connectors through the labeled side of the panel. All but the PTT and the DC
power connector are self aligning. The 8 pin AUX connector may have two flat sides so chose the
fit that allows Pins 1 and 7 to be closest to the top side of the panel. Install all with the lock rings on
the panel surface and then the ground lugs (if applicable) between the Nut and the Lock ring. The
DC power connector (flanged black plastic) is positioned so that 1+ Pin is closest to the top of the
panel in relationship to the labeling. See picture 23 for the correct placement of the solder lugs
before wire assembly.

/Kits/L50-28CK.doc 11 Rev. B 7/4/2012

Desired Length

1/4"

3/4"

Board end

Connector End

solder coax shield

to formed lug

Connector

Solder lug

Coax

PCB

DC POWER

TX

AUX

PTT

10 MHZ

TX IF

IF

ANT/RX

Rear Panel view

Depending on your requirements, Cut, strip, and tin both ends of the coaxes as shown in the
next pictorial. Different configurations are explained in the Options Setup section at the en d of the
manual. The lengths of coax are shown below and depend on you specific configuration.

RFIF (the IF BNC Connector) 5-1/2”
TXIF (the TXIF BNC connector) 6 ½”

Common IF (the IF BNC Connector) 5-1/2”

Common RF (the ANT/RX “N” connector) 3”
RXRF (the ANT/RX “N” connector) 3”
TXRF (the TX “N” connector) 3”

Also see Picture 25.

Attach the longer stripped end of the coax to the connector as shown in the next pictorial.
Push the end through the hole in the ground lug, solder the center conductor to the center pin, then
solder the shield to the ground lug. See picture 24.

/Kits/L50-28CK.doc 12 Rev. B 7/4/2012

With the pre-cut bundle of colored wire, m ake wire connections to the AUX and PTT
connectors. Follow the wire chart. Strip and tin one end of the wires to 3/16”. Tin the connector
pins before soldering. All wires are required for sequencer operation and PTT control. Picture 24.

AUX Pin 1 11”Orange wire
AUX Pin 2 11” Yellow wire
AUX Pin 3 9” Blue wire
AUX Pin 6, 7, and 8 1-1/2” Bl ack wires (cut from 6” wire)
PTT connector 12” White wire--- Also install 1000pF disc to ground

The DC power connector should now be wired. Crimp a terminal to the 1 ½” #18 Black wire

and one to the 2 ½’ # 18 Orange wire. Then strip and tin each wire to 3/8” on the other. Connect
the terminals to the DC power connector. See Picture 26.

Place one Ty-Wrap on the bundle of wires less the black ground wires and including the
PTT wire as close to the AUX connector as possible. Then attach the rear connector panel to the
heat sink using two 4-40 x ¼” screws. Run the bundled AUX and P TT wi r es betw een the p anel and
the circuit board towards the DC power connector bending them around the corner and behind the
Power Module. Strip and tin one end of the 15” purple wire and connect it to the PWR via near
CR11 on the lower left corner of the board where the AUX wires wrap around the Power Module.
Install a second Ty-Wrap at that point. Now, connect the black wire from the Power connector to
the ground lug on IC5 flange. Attach the +DC wire form the power connector to the bare metal
marked 13.8V on pin 3 of the power Module. Then Ty-Wrap the bundle to the DC ground wire
connection on the side of the power module. See picture 27 and 28.

Finish the panel wiring by connecting the short Black wires from the AUX connector (Pins 6,
7, 8) to ground. Insert the three wires into any of the via-holes in the circuit board below the
connector. The via-holes are plated through so use a lot of heat to flow the solder. Then begin to
connect all of the coaxes to the circuit boards as you have planned for your configuration. If you
are unsure of their connections, you may refer to the “Common or Split IF Option” and the
“Common or Split RF connections” section found in the “Options Setup” section on page 24
of this manual. There should be a Minimum of two and a maximum of four coaxes. Be sure that the
shields are soldered to the board well. It is Teflon coax so do not be afraid to heat the connection!
See picture 29. T hen c onn ect the other AUX connector wires to the sequencer section. Pin 1 to
Via 1 on the board, then Pin 2 to 2, Pin 3 to 3. This will provide Pin 1 with voltage on RX, Pin 2 with
Voltage on TX and Pin 3 will be a connection to Ground on TX. Trim, strip and tin the wires before
connecting. If you desire anything other sequenced signal, consult the Sequencer schematic and
its matrix for alternative connections. See Picture 19.

The PTT wire may be connected to the PTT – H or L in the sequencer if you plan to use t he
sequencer or connected directly to the transverter’s PTT –H or L near the K1 relay. This will
depend on your configurati on pl ans . If you are using the sequencer, install the 6” White/Org wire

/Kits/L50-28CK.doc 13 Rev. B 7/4/2012

from the “4” via in the sequencer to the PTT-L via near CR9. With the left over green wire, strip and
tin two 1”green wires and connect them from the +DC to the DC1 and DC2 vias in the sequencer.
See Picture 16. Connect a 3” wire between the +9 (near VR5) and the +LO6M via. Strip and tin a
3” wire and install one end in the +13.8SW via near VR5. If you require the negative voltage option,
connect an 8” green wire from the ALC via and pin 4 on the AUX connector. See Picture 29

Begin to Pre-wire the U-channel front panel by assembling the enclosed RFPM kit. See
page 26 for the assembly document. This is the bar graph power meter. When completed, install a
2” black wire (GND Connection) and a 6” green wire (+V). Strip and Tin both ends of both wires.
You may test the RFPM separately before installing. It requires 12VDC (+ and -) on the two w ir es
and a variable voltage from 0 to 5 VDC on the DET connection. You should be able to vary the
voltage and move the Bar Graph display up and down. The Pot will adjust its sensitivity. When
complete, find two ¼” threaded hex stand-offs and two 4-40 nuts. Pass the threa de d end of the
stand-offs through the two mounting holes on the RFPM board so that the threads are on the
component side of the board not the display side. Then hand-tighten the nuts. Install the RFPM in
the front panel with two 4-40 Black screws. Center the display and tighten the nuts and the screws.
See picture 30. Then cut, strip and tin the wires on the two LEDs to 2”.Install the Green (ON) LED
and the Red (XMIT). Install the switch in the front panel then install the front panel to the heatsink
with four 4-40 X ¼” screws and four 4-40 black screws to the rear panel. Start all screws first, and
then tighten. It may be necessary to loosen the rear panel a bit to get all screws started. Be sure
not to trap any wires under the panel.

The fron t panel wiring starts by connecting the black wire of the power meter to the ground
via hole in the circuit board below. See Picture 30. The +DC wire connects to the 13.8SW via near
VR5. The 15” purple wire from the PWR via on the board connects to the DET via on the RFPM.
Strip, tin and connect. The LED’s are connected next. The Red connects to the TX via and the
Green to the ON LED via. There is associated ground vias near each connection. Strip, tin, and
solder. Now, attach the wire coming out from under the board to the center pole of the switch.
Strip, tin and solder. Then conn ec t the w i re from the +1 3.8SW connection to the top lug on the
switch. See picture 29.

Installation of the Fan Option is recommended for the best possible frequency stability for
digital operation. Turn the transverter over so the Heat sink is up. Notice that all of the holes are
not filled. There are four 6-32 tapped holes and a large thru- hole. The thru-hole is for the wire of
the fan. Feed the wire through the hole and place the fan on the heatsink, label down so that it
blow air into the fins. Be sure that the wire is not trapped bet ween the fan and a rib of the heat sink,
You may need to cut a notch in the fan’s wire channel so the wires pass through. Place the fan grill
on it and bolt down the assembly with four 6-32 x 1-3/4” bolts. Make them snug but do not over
tighten. See picture 31. Turn the asse mbly back over and dress the wires by Ty-Wrapping them
to the sequencer wires near the step “3” connection. Then follow the PTT and DC power wire
across the Module. Cut, trim and tin the Red fan wire and attach it to the +13.8V pad with the DC
power wire. Continue to route the Black fan wire to the –F pad. Cut, trim and solder. Install a Fifth
Ty-wrap to bundle the PTT, +DC and fan wires if desired. See picture 17.

/Kits/L50-28CK.doc 14 Rev. B 7/4/2012

Last step before testing is to assemble the DC power cable. They are a little complex but

just a great locking connector when complete. First find the NL2FC mate to the flange connector
mounted on the transverter. Notice it is 4 parts. The main body, with the Gray lock ring, (2 parts)
“semi-installed.” Do not push the gray ring down covering the contact screws or you will spend
some time figuring out how to unlock the cover!! Prep the Red/Black -#14 zip cable by striping and
tinning ¼’ on one end. Tin solder both end. Be sure to control the heat (it’s not Teflon!) Now, the
positive voltage connection is clearly marked on the black body and the gray ring as “1+” the
negative or ground connection of the connector is not so clear. Look on the lock tab of the black
body. It says “1-“. Insert the tined end of the wires in to the clamping holes and tighten the screws.
Then it is best to review Picture 32 for the correct alignment of the rest of the connector parts
because words just can’t do it! The tricky part is aligning the three sided wire clamp. It only fits one
way and requires some manipulation. After its inserted, screw down the blue lock nut and then
slide down the Gray sleeve. Check out how it mates a nd dis connects.

NOW—consider an inline fuse or limit ed power supply for testing. The Basic assembly is

complete and the transverter is now ready for test.
Transverter Testing: Before applying DC power to the complete transverter, verify main DC

wiring and have a proper fuse installed in the DC power cable or supply. Install some sort of 50
Ohm load on the ANT, TXRF, or RXRF ports. Verify that the PTT port is not shorted. If all looks
good, apply DC power and switch on. The Green LED should light and the TX LED (RED) will
remain off.

Start by verifying voltages on the board. All voltages should coincide with the DC input
voltage from the power supply unless it is on the output of a regulator. There is a voltage matrix at
the end of the test section that may be used for checking and troubleshooting. You could verify
every point or in general, check VR4 (5 VDC) and VR5 (9 VDC). Verify the +13.8SW voltages and
the +DC in the sequencer. Check Pin one in the sequencer for +12VDC or greater. The drain of Q6
(junction of L18 and C69) shoul d be ar oun d 3.8 VDC. Verify –F to be somewhere between 6 and
13 VDC depending if the fan is running or not. If voltages do not fall in line, check wiring or
assembly. When complete, shut power switch off.

Oscillator testing without mixer installed: If you encounter a problem with the Oscillator, refer
to the voltage matrix and verify Q3 and Q4’s function. Start by connecting a test coax to the LO
input pad of the mixer M1 and ground. This will allow the measure m ent o f the level injected into the
mixer. You may also measure the frequency of the oscillator with this connection. Connect the
coax to a power meter set to measure 100 mW. Switch the DC power on. The osci l l ator should just
start up but an adjustment of C18 may be required. Verify its level on the power meter. It should be
between +15 and +19 dBm. If low, check for missing or unsoldered components in the LO Low
Pass Filter. Also refer to the voltage check sheet at the end of the test document if needed. If the
level is OK and you have a spectrum analyzer, you may verify the 2nd harmonic content. It should
be a minimum of -40 dBC (40 dB below the fundamental. If not verify the Low pass filter (the
components between C 23 and C28). Now, if all tests are ok, you may install the mixer or not and

/Kits/L50-28CK.doc 15 Rev. B 7/4/2012

proceed to the General Oscillator testing section. Leaving the mixer un-installed will allow complete
testing of the transverter if you have the test equipment. Proceed to the General Oscillator testing.

Oscillator testing with mixer installed: If you encounter a problem with the Oscillator, refer to
the voltage matrix and verify Q3 and Q4’s function. With the mixer instal led, you can only test and
adjust the frequency of the oscillator by probing the input of the mixer. Proceed to the General
Oscillator testing section for this.

General Oscillator testing: The frequency may be checked now but the circuit should be allowed
to warm up about 15 minutes for its first time. Verify that the Xtal heater is warm and allow it to
soak. The frequency may be probed at the LO input to the mixer or on the coax if the mixer is not
installed. You should be able to adjust to the frequency of the oscillator with C18. See Picture 9
and 10. It will be a small amount of adjustment but if you can achieve anything within 50 Hz of the
final frequency, skip the Frequency Net modification step. If you do not have enoug h adjustment to
achieve this, it will require one or two additional chip capacitors to be added to the circuit.

Frequency Net Modification: The goal here is to get the frequency within 50 Hz of 22 MHz. and
allow a 24 hr burn in before the final “Netting” of the frequency occurs. If the frequency is low (less
than 22.000 MHz) start by replacing C20 with one of the spare 27ρF chips. If the frequency then
goes to high, place another 27ρF on the C20A position to bring it back down.

If the frequency is high, (most common) it will matter how high. Verify the amount. If it is more than
3 kHz, place a 27ρF in the C16 position. If it is less than 3 kHz, place a 27ρF in the C14 position.
Just get it close and allow it to burn in for a minimum of 24 hrs. You can complete the rest of the
transverter testing and then do the burn in. ALSO—the mixer should be ins t al l ed now after a final
level check. After the burn in, net the frequency. If it becomes out of adjustment, review the steps
and the procedure of what you did. There are some smaller value (10 ρF) chip caps that can be
use to replace the 27ρF or added to the 27’s you have placed. Makes no difference how you get it
to net.

Receiver Testing: Depending on your configuration, the RXRF input port and RXIF output ports
will vary. It is assumed that the voltage checks were made and determined to be in spec before the
Receive RF test is made. Use whatever means to generate a signal into the RF port (on air signal,
signal generator -30dBm or less, or a Noise figure meter) and use whatever 28 MHz receiving
device you desire to peak C63 and C64 for maximum gain. See picture 20. If you use a noise
figure meter, you may find that the best noise figure is not the maximum gain but if you only have
gain measurement capabilities, the noise figure will close enough if optimized for gain. Also, with a
Noise figure meter, depending on the LO leakage level, (22 MHz), it may interfere with the meters
measurement. There is a 22 MHz trap built into the transverter (C110 and L29) that should allow
the measurement to be made but if not, check its construction. You may also use and external
high pass or band pass filter for the Meter if required. The level of leakage is not an issue because
the 28 MHz. band pass filtering in any transceiver will eliminate the problem if it does exist. Be
sure to rotate R39 (RXIF Gain adjustment) to verify function. There should not be a need for
adjusting the filters. If 17dB of conversion gain (15 minimum) cannot be achieved, start by verifying

/Kits/L50-28CK.doc 16 Rev. B 7/4/2012

voltages on Q6 and IC6 then check kit installed components. Use whatever means to signal trace
from input to output to find the problem. Be sure of the RXRF and RXIF configuration and check for
shorts on the coaxes and solder shorts on the boards. If all is OK, proceed with testing.

Now, as mentioned or that you may have surmised, F4 is shared by both RX and TX. The
filters are factory adjusted but not exactly optimized for our expected performance. The Issue with
F4 is that it is wide enough to allow the 2nd harmonic of the 22 MHz LO (44 MHz.) to pass with very
little attenuation. Depending on the tolerance of the mixer and the level of the LO, it may or may
not be a problem. BUT- as a precaution, a solution is to adjust the performance of F4 to eliminate
reduce the 44 MHz level. What we found out and is quite simple is to remove two tuning slugs from
F4. This narrows the performance of the filter and since the “50 ohm matching” of the RF side of
the filter is compromised by IC6 and IC3, it’s a non issue. It is important to do this during the RX
test to be sure it does not reduce the RX performance. Remove the two slugs that are closest to
IC3 and IC6. See picture 33. Retest the RX and if none or slight degradation occurs, (1-2 dB) it’s
good. See Picture 34 and place the Aluminum foil tape on the filter to keep the holes covered.

Transmit Testing: If you plan on using the Negative voltage generator to reduce the output power
of your transceiver for transverter configuration, proceed to the “Negative Voltage Option” test
section first (page 20). Then come back to this section for the complete Transmit testing.

Depending on your configuration, be sure to have some sort of 50 Ohm load and or RF
power meter connected to the designated TX port of the transverter. Preliminary TX testing is done
without IF drive being applied. Start by manually enabling the PTT signal (High or Low depending
on your configuration). This in turn will enable the TX section and disable the RX section of the
transverter through the sequencer or directly depending on your configuration. All relays installed
will actuate and the Hybrid power module will draw quiescent current of up to 4-5 amps. The other
TX driver stages and the TXIF amp if utilized will also be biased. When the transverter is first
keyed, (without IF Drive) verify that there is no relay chatter and the total transverter current drain
is less than 6 amps. In this state, verify the TX voltages on the matrix. You may notice the fan
speed increasing as the transverters TX time is extended. When finished checking all of the TX
voltages, un-key the transverter. If there is a problem, find it by checking the wiring first then the kit
assembled components. Also verify that there is “Zero” RF output power on the RF met er .

If RF output power is measured, it can only be two causes. Oscillations cause by mistakes

in construction or LO leakage. Oscillations can be cause by bad grounding of the hybrid and
shield, poor construction/missing components and incorrect wiring or damaged components.
Check all work! LO leakage caused by the second harmonic of 22 MHz, 44 MHz, could be an
issue if the M1 mixer is not soldered correctly on ground or is defective. It can be detected with a
frequency counter anywhere in the TX chain. If the 2nd harmonic is found to be the problem after
verification of assembly, please consult DEMI by phone or via the Technical e-mail address foun d
on the website. If all is good, proceed with the testing.

IMPORTANT NOTE: In the following step, do not assume that if the output power of the
transverter is low, it is because you do not have enough IF drive. Please consult DEMI if you have

/Kits/L50-28CK.doc 17 Rev. B 7/4/2012

problems obtaining full output power with your specified drive level during the test procedure after
you have exhausted all possibilities discussed in the procedure.

Rotate R36 fully counter-clockwise (maximum attenuation) and then connect the TXIF drive

source. Manually enable the PTT and apply the minimum amount of drive that your transceiver can
produce. Verify any output on the power meter. Then, slowly increase the drive level of the
transceiver to your maximum desired drive level (maximum of 10 watts) you have configured the
transverter for while observing the power meter. Then adjust the TXIF gain control (R36) to obtain
20-25 watts of output pow er .

If you cannot achieve any output power, verify opens or shorts starting with the TX output

connector then back through the TX section. Look for opens in the Low pass filter L13-L16.
Picture 19. If the TR relay is in your configuration, verify its function. You may disable the bias to
the RF power module by removing R22. The relay and Low pas filter can then be checked with an
Ohm meter. Recheck the TX voltag es in the TX chain. Then proceed through the IF section looking
for opens or shorts and the function of the TX IF relay if in use. Retest with low drive power first
after finding problem.

If the correct amount of power cann ot be ac hieved, (low power) the problem can only be a

few things. First check the output low pass filter, L13-L16, C54-56, C113 and C114. Verify the
windings (re-count the turns) and you may try to spread or compress the turns for an additional
output power. The filter is there to eliminate the 2nd harmonic so—no matter how you adjust the
“L’s” it will not affect the 2nd harmonic but may increase or decrease the insertion loss at the
operating frequency. Also verify that the filter components are not he ati ng . Touch them with RF off.
The cores should not heat at 25 watts output. If so, something is installed incorrectly.

Next suspect the TXIF components. Verify that the Pin diodes CR3 and CR4 are

functioning. If the RX gain is OK, the filter diplexer should be OK but you can verify with an ohm
meter anyway. Next understand that even if you have configured the transverter correctly, the
operating range may be on the edge. Your drive level from your transceiver may not be what was
specified. If you have measured and verified it, and depending on your configuration, you may vary
the value of C91 if you are using the load. If you are using a low drive level (around 0 dBm) you
may need to install the TXIF gain stage. Do not install it if you use more than 5 mW of drive.

If all is OK, the transverter should very easily exceed the rated output with your desired

drive level in any mode. Finish the test by setting the TXIF to produce 25 watts of output power.
Bar Graph RF Power Meter: While the power meter is connected, the RF bar graph meter

calibration can be done. During key down with a 25 watt output level, adjust VR1 on the bar graph
to show 9 bars lit. Then vary the power or use SSB to generate RF and follow your speech pattern
on the bar graph. Remember that the Bar Graph display is relative and its function may be affected
by high VSWR. If maximum deflection cannot be obtained, verify that C111 is installed and that the
RFPM is assembled and wired correctly. You may also check CR11 with a ohm meter in the diode
function. Keep a load of some sort on the transverter’s out for the following tests

/Kits/L50-28CK.doc 18 Rev. B 7/4/2012

IF Drive Sense Circuit: The IF drive sense circuit is a protection circuit only. It needs to be
utilized with IF drive powers above 200 mW and is only used with a common IF configuration. It will
operate at drive levels down to 10 mW. To preliminary test it, you can apply a low level voltage to e
any RFS via (1-2 volts) and the TIF signal near Q26 should go high. This voltage energizes the K3
relay. The purpose of C94, CR7 and CR8 is to sample and convert the 28 MHz RF energy to DC
voltage. To test, lower your IF drive down to the lowest level possible. Then key your transceiver
and apply drive. The TIF signal should go high. If not verify the CR7 and CR8 diodes and the RFS
signal with an ohm meter. When the PTT is enabled on transmit either through the sequencer or
directly by your transceivers PTT, the K3 relay and the rest of the TXIF circuit will be energized by
the transverters TXON voltage and over ride the protection through the CR21 isolation diode.

Fan Speed Controller: The fan speed controller should operate on its own speeding the fan up
as the transverter heats. You can check the voltage at –F as the transverter is heating. This is the
negative lead to the fan and as the transverter increases in temp er ature, this voltage will move
closer to Zero or ground as the heat sink warms. If you find that the fan is running too early, you
can lower the value of R77 from 1K to 910 ohms or even 820 ohms. This also means it will start
later in the temp cycle which may affect the frequency stability but its adjustment may increase or
decrease the delta in frequency change over temperature.

Sequencer: Testing of the sequencer is simple. Just verify the steps are what it is connected to in
both TX and RX modes. If wired as recommended, 1 is positive voltage in RX, open in TX. 2 is
open in RX, positive voltage in TX. 3 is open in RX and Ground in TX. 4 is what enables the
transverter and is ground in TX. It is open in RX and Gr ou nd in TX . This is reflected on the matrix
on the sequencer schematic. If you wire it differently, use that matrix to note your changes.

For mast mount LNA operation with the basic transverter or with an external high power

amplifier, all switching tests should be done without RF applied. Verify that the switching is
completed in your desired sequence and gradually add in your external components and verify
their operation. All testing can be done without coaxial cables connected. Connect the transverters
IF or TXIF cable last.

Step 1 +12VDC on RX for a preamp @ 500 mA maximum
Step 2 +12VDC on TX for a TR relay (around the preamp) @ 500 mA maximum
Step 3 Ground on TX to key a power amplifier. Sinks 100 mA maximum
Step 4 Ground on TX to key Transverter. Sinks 100 mA maximum

Optional Sequencer Connections:

Step 1 and 2. They can be connected to switch higher DC voltages. The DC voltage is applied to
the DC1 and DC2 connections on the board (30VDC maximum).

/Kits/L50-28CK.doc 19 Rev. B 7/4/2012

Step 2 TL2 is a secondary connection to the second step. It is a “LOW” on transmit. It can be
used to drive a relay or key an amplifier but an external isolation device should be utilized. It will
sink 100 mA maximum

Step 3 and Step 4. They have secondary outputs that are both “High” on transmit. They are
labeled PH3 and PH4. These should be isolated from devices that require high currents and are
intended to drive low current devices or Pass transistors or FETs. They will source 5mA.

The transverter’s sequencer may be by-passed to eliminate switching time delays. The
external PTT input of the transverter may be connected directly to the transverter’s PTT inputs (see
component placement doc u me nt) PTT-H is near C100 and PTT-L is near C102.

Negative Voltage Option: If you have installed the negative voltage generator option, an
approximate -9VDC will be available on the AUX connector pin 4. To set this up with your
transceiver, connect pin 4 and one of the ground pins to your transceiver’s ALC input. Connect
your transceivers output to a power meter and load. With both the transverter and Transceiver
powered on, measure the output power of the transceiver on somewhere in the 28 MHz band to
verify that the ALC circuit within your transceiver is operating correctly. With the negative voltage
applied, there should be minimum power output (less than 1 watt or as low as a few mW’s
depending on what type of transceiver it is) With the power meter still connected, if the transverter
is powered off, the transceivers output power should come back to normal. Be careful if you are
using an mW power meter!! If it all checks out, continue with the transverter testing and installation
Connect the RF drive to the transverter and with the transverter switch on, you may then adjust the
TXIF drive level in the transverter for your desired output power level.

IMPORTANT NOTE: If you are using the ALC (negative voltage generator) circuit and you desire
to use your transceiver for other than transverter use, operating it with the RF/IF cable connected
without the ALC voltage running will damage the transverter. What is suggested is to place a
coaxial relay (SPDT) between the transverter’s IF port and the Transceiver’s RF port. Wire the
relay so that it directs the RF path to the Transverter when energized. Connect the +13.8SW buss
and ground to the relay through the AUX connector.

When the Transverter is switch on, the relay will direct the RF path of the transceiver to the

transverter and the transverter will apply the negative voltage to the transceivers ALC port. Power
the transverter off will simply switch the transceiver back to normal.

With all circuitry now checked close up the transver ter . The TXIF and RXIF adjustments are

accessible through the bottom cover. The frequency adjustment is not and it is best not to drill an
extra hole for it. This will be explained in the General Operation, Oscillator section.

/Kits/L50-28CK.doc 20 Rev. B 7/4/2012

Test Point Matrix

Device/mode

Input

Output

Emitter/Source

Base/Gate

Collector/Drain

Q3 RX

NA

NA

2.0-3.0VDC

2.5-3.5VDC

8.4-9.1VDC

Q4 RX

NA

NA

0.00 VDC

-0.70 to0.7VDC

8.4-9.1VDC

IC6 RX

0.95-1.7VDC

4.5-5.5VDC

NA

NA

NA

Q6 RX

NA

NA

0.35-0.65VDC

0VDC

3.4-3.9VDC

SEQ Pin1 RX

NA

13-14VDC

NA

NA

NA

IC3 TX

2.2-2.8VDC

4.5-5.0VDC

NA

NA

NA

IC4 TX

1.5-2.0VDC

5.0-6.0VDC

NA

NA

NA

IC7 TX

2.2-2.8VDC

4.5-5.0VDC

NA

NA

NA

TIF TX

NA

12-14VDC

NA

NA

NA

CR3-CR4 TX

NA

0.65-0.95

NA

NA

NA

IC5 Pin2 TX 4.2-4.8VDC NA NA NA NA

SEQ Pin2 TX NA 13-14VDC NA NA NA

Installation and Oper a t ion

Theory of Operation: The basic principle of a VHF/UHF transverter is to convert a chosen
band of operation to the 28 MHz. band of a HF transceiver. Following the recommendations of the
HF transceiver’s operation manual for transverter use is the most important aspect of correct
transverter operation. If configured correctly, the transverter will convert both transmit and receive
signals to a new band of operation and seam “invisible” to your HF transceivers operation. In
simple terms, the transverter will not improve the performance of your HF transceiver but will not
cause any degradation of performance in any way.

Interfacing and Operation:

MOST IMPORTANT: When interfacing your transverter, it is recommended that all usable

features of the transverter are tested and proven before integrating the transverter into your
system. This means verify the transverter functions correctly with the transceiver before interfacing
to High Power amplifiers, mast-mount LN A’ s, and ex t er nal TR rel ays. During the initial setup of the
transverter, test all switching functions before applying RF. Implement one accessory at a time
confirming the switching function, then RF function. Start with low RF drive levels and gradually
increase to the final desired level.

It is assumed that since you have assembled this transverter to your specifications,

interfacing will be easy. But—we will offer some tips that may have been over looked. Start the
interfacing with good quality 50 ohm cables for the IF (28 MHz.) connections. These connections
may be low level or at the 25 watt level depending on your configuration and good quality BNC
type connectors with adapters to your transceiver are fine! The shielding quality is important to
prevent other 28 MHz signals from “Creeping” into your transceiver.

/Kits/L50-28CK.doc 21 Rev. B 7/4/2012

All transverters will require a PTT (to ground or positive voltage on TX) to enable the

transmit mode of the transverter. The PTT input to the transverter is a RCA connector. This cable
does not need to be shielded, but extra protection in a QRO station is a good idea! Most
transceivers have RCA connectors for PTT outputs but others have various connections. Be sure
to have whatever cable that is required ready to go.

The DC power cable should be connected to the des ir ed power supply. If you require a

longer DC power lead, consider moving up one gauge to eliminate a voltage drop problem. Plan on
6 amp current drain and please fuse the line.

The AUX connector will contain all sequencer connections and any other special

requirements such as the negative voltage or any other inputs or outputs you desire. The matching
connector to the AUX connecter is supplied and should be wired before final interfacing.

If using a mast mount LNA, the IP3 performance of the transverter will be limited by the LNA

and total system IP3 performance will be degraded. The amount of degradation will depend on the
performance characteristics of the LNA. Yes, the total system gain can be controlled by the RXIF
gain control but the dynamic range of the transverter will be reduced by the amount of gain of the
LNA at the minimum. Such a system should have the capability of switching the mast mount LNA
out of the system. Use of an “In the Shack” LNA in front of the transverter is total nonsense! If you
believe your system is lacking gain and the transverter is in spec, find the problem in your
transceiver or—if you must, install an IF amplifier on 28 MHz so not to degrade the transverters
“RF” performance.

Another suggestion is if you are to use a mast mount preamplifier, you may consider

bypassing the transverters LNA. It requires removing R31 and R26 from the circuit. Then move the
RXRF connector cable to the C68 pad. A ground pad is cleared for a coax shield nearby. This will
utilize the diplexer and first filter in the receive chain and disable all DC power to the Q6 FET.

Unless you have ordered a special order Crystal, the national calling frequencies will be on

50.100 or 28.100 MHz on you IF transceiver. Use of the transverter outside of the Weak Signal
portion of the band (above 52MHz) is possible but slightly degraded performance may be
expected. The transverter is designed specifically for the weak signal portion of the band.

Setting your final output power of the transverter is recommended to be done in the CW

mode. BUT—verify that if you change modes of your transceiver, the drive levels do not change or
overdrive may occur in the SSB mode causing undesirable effects on the band!

The bar graph display is a relative power meter and is driven by the directional coupler and
RF detector circuit found in the Low pass filter section of the board (CR11, R76, R75, C108, C111)
RF is detected and converted to DC voltage and conducted to the Bar graph display on the front
panel. If you find that you operate the transverter at any other level than what it is calibrated to,
you may change it by adjusting VR1 on the display board. Also remember being that is a reference
meter, if your VSWR should increase, it may or may not show an increase or decrease on the bar
graph display.

General Operation: General operation of the transverter, if everything is adjusted correctly,
should be transparent to the transceiver and the user. Except for the frequency read out, (if your
transceiver doesn’t allow its display to be adjusted for transverter operation) it will be like operating

/Kits/L50-28CK.doc 22 Rev. B 7/4/2012

on 10 Meters. All of the functions of the transceiver (filtering, DSP, split band operation, dual VFO)
will be transposed to the frequency band of the transverter.

Some cautions should be taken when operating CW or VOX. Operating the transverter in a

“Full Break-in” mode is not recommended. Because of the mechanical relays in the transverter,
there will be too much delay to operate “Full Break-in” effectively. AND—the relays would be
abused if “Full break-in “is enabled. It is best to operate in “semi break-in” and adjust the delay of
the PTT on your transceiver to match your comfortable CW operating speed in a way that the delay
will hold the PTT until your transmission is complete. If you have implemented the sequencer, its
delay will need to be longer to allow all components within the system (Power amplifier, LNA,
relays,) to complete their transition if utilized. If just the transverter is to be used alone, the
transceiver PTT signal may be connected directly to the transverter’s PTT input bypassing the
sequencer. This will shorten up the delay but will still not allow “full break-in” without relay chatter.

General Operation, Oscillator: The transverter will experience frequency drift through aging.
Even if you took time to “Net” the frequency of the transverter’s local oscillator at its normal
operating temperature after a long bur n-in, frequency shift from ageing may still cause a need to be
re-adjusted after prolonged operation. This is because of the physical nature of crystal ageing
through temperature cycling. As the hours of operation time increase, this “Zero Offset” frequency
will be less and less and eventually will not require adjustment.

As for frequency drift during operation, great care has been taken to minimize it in the

design. The oscillator section of the transverter board is “Ovenized” and the speed of the cooling
fan on the heat sink is controlled by the actual heat sink temperature. The pr obl e m stil l ari ses from
the internal air temperature of the transverter and the heat conduction of the heat sink to the
oscillator section of the transverter board. The frequency drift the transverter exhibits may not be
noticed on SSB and CW operati on. But, a carful understanding of how much “drift” the transverter
exhibits and in what direction is moves is important for dig i tal mod e operat ion.

Our testing of this design was done with 30 second transmit and receive times at the

transverter’s full rated outp ut power. After a 10-15 min warm up time, we have found that the most
extreme drift will occur during the first few transmissions while the transverter reaches its stable
internal operating temperature. If the room temperature is less than 75 degrees F (approximately
25 degrees C) the cooling fan may be running slow or not at all. The first or second transmission
will cause the Fan to cycle and if the heat sink temp rises enough, it will remain running. The first
cycle will cause the largest frequency shift. The next 3-4 transmissions will stabilize the frequency
drift. At the 5th or 6th transmissions, the frequency drift will settle down to be 1-2 Hz or less if all
conditions remain the same during 30-second cycles. Of course this may better or worse
depending on the transmit power and duty cycle. An operation recommendation would be to start
your digital Sked a few minutes early and you will achieve frequency stability at the actual start
time of the Sked. Realistically expect 50 Hz total drift. Some factory production units have achieved
less than 30 Hz

What is expected to keep the frequency drift to a minimum is to be sure all un-used

connector holes in the rear panel either have connectors or holeplugs in them. The IF adjustment

/Kits/L50-28CK.doc 23 Rev. B 7/4/2012

holes on the bottom cover plate may remain open but the addition of extra holes or enlarging the
existing ones will affect the cooling.

Removal of the fan from the transverter will allow the transverter to drift as much as 500 Hz

over a ½ hr. 30 second cycle schedule. This may be acceptable for SSB and CW operation but
we have found the ambient fan noise of the transverter to be un-noticeable so if you desire to
operate with a digital mode, install the fan. AND—the opposite goes for adding an extra fan. It will
not help the “Balance” of heat and air and most like cause excessive drift. But, feel free to
experiment if you desire.

Examine the fan control circuit schematic. Voltage from the NTC Thermistor drives the NPN

transistor which in turn drives the Pass transistor on the negative lead of the Fan. R77 controls at
what temperature the fan starts. The larger the resistance, the lower temp the fan starts at. BUT—if
you find that in the TX mode, the heat generated causes excessive drift, the –F connection may be
connected to the open contact s on K1 so that the f an op er ates at ful l spee d duri ng TX . Simply,
make the relay’s common connection to ground and run a wire between the NO contact and the –F
connection. The fan will now run at full speed during TX and its thermal speed on RX. Understand
that there is a delay in heat transfer and that the heatsink still heats up after the transverter is in the
RX mode.

You may find that if the frequency drift is excessive or just want to keep it to the very

minimum, a thermal “Blanket” may be applied to the crystal and oven, The custom fitting of a piece
of Styrofoam will insulate it all from the internal heat of the transverter.

Options Setup:

Common or Split IF Option: The IF configuration may be change at any time according to the

type of transceiver you are utilizing. Refer to the Component placement or schematic for
clarification. The component designators are also screened on the circuit board.

K3 is the common IF relay. To split the IF lines into separate RXIF and TXIF, remove the IF
coax from its position on the board (junction of C93 and C94) and re-attach the center conductor
between C95 and K3. The shield may be soldered where it was on the ground pad marked COM.
The TXIF cable can be prepped and soldered to the pad between K3 and C92. The shield can be
soldered to the ground pad labeled TXIF. Install a BNC connector in the rear panel (TXIF) and
attach the TXIF coax. Reverse the procedure if you want to change to or back to Common IF.

Please note that if you have a separate IF configuration, the IF drive sense option will no
longer function. It is not necessary with the split IF. It is to protect the RX circuit and Mixer from
being damaged with the TXIF drive power.

TXIF Drive Level Range: The TXIF drive level range can be changed at anytime to conform to
your transceiver type. Basically, there are three configurations. For high IF drive levels, (200 mW­25 watts) the 50 Ohm load will be installed with a low value capacitor in the C91 position (10 pF or
less for 25 watts). Mid level drives between 1mW and 250 mW will not have the load installed and
will have a 1000 ρF capacitor installed for C91. For the low drive levels (-20dBm to 0dBm or 1mW)
IC7 will be installed. If you desire to change the drive level for whatever reason, just duplicate the
info above. To install IC7, cut the ribs in the trace before installing. -10 to -6dBm inputs, use a

/Kits/L50-28CK.doc 24 Rev. B 7/4/2012

MAR-3 for IC7. For -20dBm, use a MAR-6. Other MMIC’s may be used but the bias resistor R34

BAR1 BAR GRAPH DISPLAY

IC1 LM3914

C2 100µF ELECTROLYTIC CAP

VR1 10K POTENTIOMETER

C3 0.1µF DISC CAP

X

X

X

1

+DC

GND

may need to be changed. Adjust R36 to obtain desired level in all cases. The important thing to
understand is the IF drive range is wide and can accommodate different drive levels between the
specified ranges.

Common or Split RF connections: The transverter utilizes K2 as the common RF relay. It is
mounted on the circuit board. The common port is marked ANT on the board. The split RF
connections are labeled TX and RX on the board at each e nd o f the rel ay. There is no need to
remove the relay for the split connections. Simply remove C62 and solder RX coax directly to the
C63 pad. The TX coax solders between C57 and K2 So--, depending on which way you are going,
install/uninstall ca bles and c onnectors as required. Remember, if you have separate ports, they
may be combined with an external coaxial relay to provide versatility.

PTT on IF Coax: A PTT-H signal on the IF coax from a transceiver may be used in the following
way. A 1.0uH molded choke has been included in the kit. Connect it from the COM IF pad to the
isolated pad with two via holes near the C94 indicator on the PCB. This isolated pad will then need
a 1000ρF chip cap soldered to ground. Then, a wire from the remaining via hole to the PTT-H
connection in either the Sequencer circuit (near R82) or directly to the transverters PTT-H input
near C100.

Power Meter

C1 1000 DISC CAP R1 2.7K 1/4W RESISTOR

/Kits/L50-28CK.doc 25 Rev. B 7/4/2012

50MHz

Transverter Schematic

01/2012

OPT

OPT

OPT

A

/Kits/L50-28CK.doc 26 Rev. B 7/4/2012

VHF-UHF Transv erter

6/30/2010

/Kits/L50-28CK.doc 27 Rev. B 7/4/2012

L50- 28 TRA NSVERT ER AS SEMB LY

02/2 012

50 Ohm Load OPTION

OPTION

X

X

XXX

X

X

X

X

X

X

X

X

XXX

X

X

X

NTC

X

X

XX

X

X

X

X

X

X

X

X

X

X

X

X

X

X

XX

X

X

X

X

X

X

X

XX XXXX

X

X

A

XX

X

X

/Kits/L50-28CK.doc 28 Rev. B 7/4/2012

1. Proper Filter soldering on bottom side.

2. Some bottom side soldered, topside components.

/Kits/L50-28CK.doc 29 Rev. B 7/4/2012

3. Correct soldering of wire on bottom side.

4. Topside board layout and label ed sections.

/Kits/L50-28CK.doc 30 Rev. B 7/4/2012

5. Shoulder bushings and NT C hole with thermal compound.

6. VR5 and PCB mount.

/Kits/L50-28CK.doc 31 Rev. B 7/4/2012

7. PCB correctly mounted.

8. Circuit modifications in the LO6M circuit.

/Kits/L50-28CK.doc 32 Rev. B 7/4/2012

9. LO Assembly

10. LO Assembly

/Kits/L50-28CK.doc 33 Rev. B 7/4/2012

11. Low pass filter for the L50-28CK LO (C24 not removed)

12. The correct mixer install ation.

/Kits/L50-28CK.doc 34 Rev. B 7/4/2012

13. IF filter and Diodes

14. TX load installation.

/Kits/L50-28CK.doc 35 Rev. B 7/4/2012

15. Negative Voltage generator installation on proto board.

16. Sequencer and wiring.

/Kits/L50-28CK.doc 36 Rev. B 7/4/2012

17. R21,C60,C112,C53 and NTC install with general wiring.

18. Low Pass Torroids

/Kits/L50-28CK.doc 37 Rev. B 7/4/2012

19. TX low pass filter, fan speed and power detect circuit.

20. LNA Assembly

/Kits/L50-28CK.doc 38 Rev. B 7/4/2012

21. RX diplexer, gain stage and fil ter.

22. Power module shield ins tall.

/Kits/L50-28CK.doc 39 Rev. B 7/4/2012

23. Connector panel and correct placement of lugs.

24. AUX, PTT and ANT connector wi ring

/Kits/L50-28CK.doc 40 Rev. B 7/4/2012

25. Correct coax preparation

26. DC power connector

/Kits/L50-28CK.doc 41 Rev. B 7/4/2012

27. Connector panel instal lation and wiring of Gener ic T ransverter.

28. Coax and AUX Ground wire install.

/Kits/L50-28CK.doc 42 Rev. B 7/4/2012

29. LO wiring and LED’s and switch.

30. Power meter install, front panel wiring

/Kits/L50-28CK.doc 43 Rev. B 7/4/2012

31. Rear view of transverter and fan i nstall.

32. DC power connector assembly.

/Kits/L50-28CK.doc 44 Rev. B 7/4/2012

33. Filter slugs removed for 44 MHz.

34. Aluminum tape on filter

/Kits/L50-28CK.doc 45 Rev. B 7/4/2012