IMPORTANT WARRANTY INFORMATION! PLEASE READ
Return Policy on Kits When Not Purchased Directly From Vectronics: Before continuing
any further with your VEC kit check with your Dealer about their return policy. If your Dealer
allows returns, your kit must be returned before you begin construction.
Return Policy on Kits When Purchased Directly From Vectronics: Your VEC kit may be
returned to the factory in its pre-assembled condition only. The reason for this stipulation is,
once you begin i nsta lli ng a nd sol deri ng pa rt s, you essenti al ly tak e over the rol e of the devic e's
manufacturer . From this point on, neither Vect ronics nor its dea lers can reas onably be held
accountab le for the qua lity or the outcome of your work. Because of this, Vectronics cannot
accept return of any kit-in-progress or completed work as a warranty item for any reason
whatsoever. If you are a new or inexperienced kit b uilder, we urge you to read the manual
carefully a nd determine whether or not you're r eady to tak e on the job. If you wish to c hange
your mind and return your ki t, you may--b ut you must do i t before you begin c ons tr uc ti on, a nd
within ten (10) working days of the time it arrives.
Vectronics Warrants: Your kit contains each item specified in the parts list.
Missing Parts: If you determine, during your pre-construction inventory, that any part is
missing, please contact Vectronics and we'll send the missing item to you free of charge.
However, before you contact Vect ronic s, please look carefully to c onf ir m you haven't misr ea d
the marking on one of the other items provided with the kit. Also, make certain an alternative
part hasn't been substituted for the item you're missing. If a specific part is no longer
available, or if Engineering has determined that an alternative component is more suitable,
Vectronics reserves the right to make substitutions at any time. In most cases, these changes
will be clearly noted in an addendum to the manual.
Defective Parts: Today's electronic parts are physically and electrically resilient, and
defective components a re r a re. However, if you disc over a n it em duri ng your pr e- c onst r uct i on
inventory that's obviously broken or unserviceable, we'll replace it. Just return the part to
Vectronics at the address below accompanied with an explanation. Upon receipt, we'll test it.
If it's defec tive and appear s unused, we'll ship you a new one right away at no charge.
Missing or Defective Parts After You Begin Assembly: Parts and materials lost or
damaged after construction begins are not covered under the terms of this warranty. However,
most parts supplied with VEC kits are relatively inexpensive and Vectronics can replace them
for a reasonable charge. Simply contact the factory with a complete description. We'll
process your order quickly and get you back on trac k.
Factory Repair After You Begin Assembly: Kits-in progress and completed kits are
specifically excluded from coverage by the Vectronics warranty. However, as a service to
customers, tec hnicia ns ar e availa ble t o evaluate a nd repai r malf unctioni ng kits for a minimum
service fee of $18.00 (½ hour rate) plus $7.00 shipping and handling (prices subject to
change). To qualify for repair service, your kit must be fully completed, unmodified, and the
printed circuit board assembled using rosin-core solder. In the event your repair will require
more than an hour to fi x (or $36.00, subject to change), our technicians will contact you in
advance by telephone b efore p erforming t he work. Def ective unit s should b e shipp ed prep aid
to:
Vectronics
1007 HWY 25 South
Starkville, MS 39759
When shipping, pack your kit well and include the minimum payment plus shipping and
handling charges ($25.00 total). No work can be performed without pre-payment. Also,
provide a valid UPS return address a nd a day time phone number where you may be reac hed.
TABLE OF CONTENTS
Introduction.....................................................................................................2
Tools and Supplies..........................................................................................2
Before You Start Building...............................................................................3
Soldering Tips:.......................................................................................3
Desoldering Tips:...................................................................................3
Work Habits:..........................................................................................4
Sorting and Reading Resistors:...............................................................4
Reading Capacitors:................................................................................5
Diodes: ...................................................................................................5
Transistors:.............................................................................................6
Integrated Circuits:.................................................................................6
Parts List..........................................................................................................7
Parts Placement Diagram ................................................................................7
Step-By-Step Assembly...................................................................................8
PC Board Inspection:.............................................................................. 11
Testing and Alignment ....................................................................................12
Generator Method: .................................................................................12
Off-air Method: ......................................................................................13
Operating Instructions.....................................................................................13
In Case of Difficulty........................................................................................15
Preamp Stops Amplifying:......................................................................15
Cannot Align or Test Preamp:................................................................15
Voltmeter Checks:..................................................................................15
Theory of Operation and Specifications..........................................................16
Operation:...............................................................................................16
Specifications:........................................................................................16
Schematic........................................................................................................17
VEC-1402K Instruction Manual 2 Meter Pre-Amp Kit
INTRODUCTION
Now you can soup-up your 2-meter receiver or scanner with a 16-dB boost. The
VEC-1402K breathes new life into "deaf" receivers and marginal antenna
systems. Unlike low-cost GaAsFET preamps, this kit uses a high-quality
microwave-type bipolar transistor that features exceptional low-noise
performance and good immunity from damaging electrostatic discharge. A
high-Q LC-tuned input filter fights overload from out-of-band signals, and
careful output matching ensures efficient energy transfer into your 50-ohm
feedline. In addition to covering 2-meters, the VEC-1402K can boost other
frequencies in the 135-165 MHz commercial 2-way FM and WeFAX radio
spectrum with only minor r etuning. Although big in pe rformance, the pre amps
are small in size (1" x 1-1/2"), and you can power them locally or remotely at the
antenna with 9-14 volts dc.
TOOLS AND SUPPLIES
Construction Area:
area where you can easily organize and handle small parts without losing them.
An inexpensive sheet of white poster board makes an excellent construction
surface, while providing protection for the underlying table or desk. Welldiffused overhead lighting is a plus, and a supplemental high-intensity desk lamp
will prove especially helpful for close-up work. Safety is an important
consideration. Be sure to use a suitable high-temperature stand for your
soldering iron, and keep the work area free of combustible clutter.
Universal Kit-building Tools:
additional items to complete, virtually all construction projects require a work
area outfitted with the following tools and supplies:
!
30 to 60 Watt Soldering Iron
!
High-temperature Iron Holder with Moist Cleaning Sponge
!
Rosin-core Solder (thin wire-size preferred)
!
Needle Nose Pliers or Surgical Hemostats
!
Diagonal Cutters or "Nippy Cutters"
!
Solder Sucker, Vacuum Pump, or Desoldering Braid
!
Bright Desk Lamp
!
Magnifying Glass
Special tool for this kit:
Kit construction requires a clean, smooth, and well-lighted
Although your particular kit may require
Hex-head insulated tuning tool.
BEFORE YOU START BUILDING
2
VEC-1402K Instruction Manual 2 Meter Pre-Amp Kit
Experience shows there are four common mistakes builders make. Avoid these,
and your kit will probably work on the first try! Here's what they are:
1. Installing the Wrong Part:
and a 10K resistor may look almost the same, but they may act very
differently in an electronic circuit! Same for capacitors--a device marked
102 (or .001 uF) may have very different operating characteristics from one
marked 103 (or .01uF).
2. Installing Parts Backwards:
capacitors to make sure the positive (+) lead goes in the (+) hole on the
circuit board. Transistors have a flat side or emitter tab to help you identify
the correct mounting position. ICs have a notch or dot at one end indicating
the correct direction of insertion. Diodes have a banded end indicating
correct polarity. Always double-check--especially before applying power to
the circuit!
3. Faulty Solder Connections:
bridges. Cold solder joints happen when you don't fully heat the connection-or when metallic corrosion and oxide contaminate a component lead or pad.
Solder bridges form when a trail of excess solder shorts pads or tracks
together (see Soldering Tips below).
4. Omitting or Misreading a Part:
Always double-check to make sure you completed each step in an assembly
sequence.
Soldering Tips:
Cleanliness and good heat distribution are the two secrets of professional
soldering. Before you install and solder each part, inspect leads or pins for
oxidation. If the metal surface is dull, sand with fine emery paper until shiny.
Also, clean the oxidation and excess solder from the soldering iron tip to ensure
maximum heat transfer. Allow the tip of your iron to contact both the lead and
pad for about one second (count "one-thousand-one") before feeding solder to
the connection. Surfaces must become hot enough for solder to flow smoothly.
Feed solder to the opposite side of the lead from your iron tip--solder will wick
around the lead toward the tip, wetting all exposed surfaces. Apply solder
sparingly, and do not touch solder directly to the hot iron tip to promote rapid
melting.
It always pays to double-check each step. A 1K
Always check the polarity of electrolytic
Inspect for cold-solder joints and solder
This is easier to do than you might think!
Desoldering Tips:
3
VEC-1402K Instruction Manual 2 Meter Pre-Amp Kit
If you make a mistake and need to remove a part, follow these instructions
carefully! First, grasp the component with a pair of hemostats or needle-nose
pliers. Heat the pad beneath the lead you intend to extract, and pull gently. The
lead should come out. Repeat for the other lead. Solder may fill in behind the
lead as you extract it--especially if you are working on a double-sided board with
plate-through ho les. Should this happen, try heating the p ad again and inserting
a common pin into the hole. Solder won't stick to the pin's chromium plating.
When the pad cools, remove the pin and insert the correct component. For ICs
or multi-pin parts, use desoldering braid to remove excess solder before
attempting to extract the part. Alternatively, a low-cost vacuum-bulb or springloaded solder sucker may be used. Parts damaged or severely overheated during
extraction should be replaced rather than reinstalled.
Work Habits:
Kit construction requires the ability to follow detailed instructions and, in many
cases, to perform new and unfamiliar tasks. To avoid making needless mistakes,
work for short periods when you're fresh and alert. Recreational construction
projects are more informative and more fun when you take your time. Enjoy!
Sorting and Reading Resistors:
The electrical value of resistors is indicated by a color code (shown below). You
don't have to memorize this code to work with resistors, but you do need to
understand how it works:
Resistor Color Code
Black = 0 (tens)
1st Digit
2nd Digit
Multiplier
Tolerence
(gold or silver)
When you look at a resistor, check its multiplier code first. Any resistor with a
black multiplier band falls between 10 and 99 ohms in value. Brown designates
a value between 100 and 999 ohms. Red indicates a value from 1000 to 9999
ohms, which is also expressed as 1.0K to 9.9K. An orange multiplier band
designates 10K to 99K, etc. To sort and inventory resistors, first separate them
into groups by multiplier band (make a pile of 10s, 100s, Ks, 10Ks, etc.). Next,
sort each group by specific value (1K, 2.2K, 4.7K, etc.). This procedure makes
the inventory easier, and also makes locating specific parts more convenient later
4
Brown = 1 (hundreds)
Red = 2 (K)
Orange = 3 (10K)
Yellow = 4 (100K)
Green = 5 (1Meg)
Blue = 6
Violet = 7
Gray = 8
White = 9
Silver = 10%
Gold = 5%
VEC-1402K Instruction Manual 2 Meter Pre-Amp Kit
on during construction. Some builders find it especially helpful to arrange
resistors in ascending order along a strip of double-sided tape.
Some VEC kits may contain molded chokes which appear, at first glance, similar
to resistors in both shape and band marking. However, a closer look will enable
you to differentiate between the two--chokes are generally larger in diameter and
fatter at the ends than resistors. When doing your inventory, separate out any
chokes and consult the parts list for specific color-code information.
Reading Capacitors:
Unlike resistors, capacitors no longer use a color code for value identification.
Instead, the value, or a 3-number code, is printed on the body.
Value Code
10 pF = 100
100 pF = 101
1000 pF = 102
.001 uF = 102*
.01 uF = 103
.1 uF = 104
As with resistors, it's helpful to sort capacitors by type, and then to arrange them
in ascending order of value. Small-value capacitors are characterized in pF (or
pico-Farads), while larger values are labeled in uF (or micro-Farads). The
transition from pF to uF occurs at 1000 pF (or .001 uF)*. Today, most
monolithic and disc-ceramic capacitors are marked with a three-number code.
The first two digits indicate a numerical value, while the last digit indicates a
multiplier (same as resistors).
Electrolytic capacitors are always marked in uF. Electrolytics are polarized
devices and must be oriented correctly during installation. If you become
confused by markings on the case, remember the uncut negative lead is slightly
shorter than the positive lead.
Diodes:
Diodes are also polarized devices that must be installed correctly. Always look
for the banded or cathode end when installing, and follow instructions carefully.
Multilayer
(270 pF)
271
Ceramic Discs
(.001 uF) (.1 uF)
102
104
Electrolytic
1 uF
1uF
|
35V
|
+
-
Diode
Cathode
(shorter Lead)
LED
5
VEC-1402K Instruction Manual 2 Meter Pre-Amp Kit
Transistors:
If transistors are installed incorrectly, damage may result when power is applied.
Transistors in metal cases have a small tab near the emitter lead to identify
correct positioning. Semiconductors housed in small plastic cases (TO-92) have
an easily-identified flat side to identify mounting orientation. Many specialized
diodes and low-current voltage regulators also use this type packaging. Larger
plastic transistors and voltage regulators use a case backed with a prominent
metal tab to dissipate heat (T-220). Here orientation is indicated by the
positioning of the cooling tab.
Metal Can Device Plastic Device Tab-cooled Device
Emitter
Flat Side
Integrated Circuits:
Proper IC positioning is indicated by a dot or square marking located on one end
of the device. A corresponding mark will be silk-screened on the PC board and
printed on the kit's parts-placement diagram. To identify specific IC pin
numbers for testing purposes, see the diagram below. Pin numbers always start
at the keyed end of the case and progress counter-clockwise around the device,
as shown:
8 7 6 5
Installation
Key
Installation
Key
1 2 3 4
Pin Numbers
Metal Tab
6
VEC-1402K Instruction Manual 2 Meter Pre-Amp Kit
STEP-BY-STEP ASSEMBLY
Before assembling your kit, please take time to read and understand the VEC kit
warranty printed on the inside cover of this manual. Also, read through the
assembly instructions to make sure the kit does not exceed your skill level. Once
you begin construction, your kit will be non-returnable. Finally, if you haven't
already done so, please verify that all parts listed in the inventory are included.
If anything is missing or broken, refer to the warranty instructions for replacing
missing or damaged parts.
Note that part designators, such as R1, C3, etc., appear on a silk-screened legend
on the component-mounting side of the printed circuit board. This corresponds
with the parts placement page in the manual. All parts will be inserted on the
silk-screen side of the board.
Except for Q1, none of the parts used in this preamp are polarized, so it makes
no difference which way the part is inserted into the board. If you orient
capacitors so their values face the board edges, you'll be able to read them easily
when the kit is finished.
If you have last-minute questions about tools and materials needed to build your
kit, please refer back to the section tilted "Before You Begin". If you're ready to
begin now, let's get started! The directions use two sets of check boxes. Check
one when a step is complete and use the other for double-checking your work
before operation.
! !
1. Locate capacitor C1 (56pF). This part may be marked with the 3-digit
numerical code "560"--or "56", its actual value in pF.
Important Note:
except that it has a lead spot-welded onto each end of the capacitor body.
Multilayers have superior operating characteristics, but the lead welds may fail if
the device is over-stressed. For this reason, never use force to seat a multilayer
cap into the PC board. If the spacing isn't right, pre-form the leads to the correct
spacing before installation!
A multilayer cap is similar to a surface-mount "chip" capacitor,
Incorrect
Ooops!
Correct
8
VEC-1402K Instruction Manual 2 Meter Pre-Amp Kit
! !
2. Install and solder C1, making sure the capacitor remains firmly seated
during installation. Cut off excess leads with a pair of side-cutting
electronic pliers.
! !
3. Locate capacitor C2 (22 pF). This is also a multilayer capacitor,
marked with the 3-digit code "220"--or "22", the actual value in pF.
! !
4. Carefully install C2 and solder in place.
! !
5. In similar fashion, locate capacitor C3, a 4.7-pF ceramic disc marked
"4.7". Install and solder.
! !
6. Locate and install multilayer capacitor C4 (100 pF). This will be
marked with the digit code "101". Solder.
! !
7. Locate disc ceramic capacitor C5 (.1 uF). Its body will be marked
with the 3-digit code "104". Install and solder.
! !
8. There should be one remaining capacitor. Locate C6, a 470 pF disc
ceramic marked "471". Install and solder.
Although a silk-screene d l ege nd for C7 ap p ea rs o n the PC bo ar d , this co mpone nt
is not used on the 2-meter version of the preamp. Do not install a part at this
location.
! !
9. Locate R1, a 100K resistor (brown-black-yellow-gold). Carefully
bend the leads to form right-angles, install flush with the surface of the
PC board, and solder.
.4"
! !
10. Locate R2, the one remaining resistor in your kit. R2 is 470-ohms
(yellow-violet-brown-gold). Install and solder.
! !
11. Carefully recheck all your work to present. It will be easier to spot
and correct errors now, before L1 and Q1 are installed.
! !
12. Locate L1, a slug-tuned coil shielded in a metal can (.074 uH, red coil
form). Note the two small solder tabs and wire coil leads. These must
be straight before you attempt to install the coil.
! !
13. Install L1, making sure it is straight and seated flush to the PC board
(some coils may have shouldered tabs that limit insertion depth.) On
9
VEC-1402K Instruction Manual 2 Meter Pre-Amp Kit
the bottom of the board, fold both tabs over onto the foil, securing the
shield can in place. Solder the tabs and leads.
Important Note:
discharge. However, if you are working in a carpeted area, it's always a good
idea to touch a metal ground before handling semiconductors.
Q1 is a rugged bipolar device that has good immunity to static
! !
14. Find Q1, a 2SC2498 transistor with a black plastic case.
! !
15. Note that Q1 has a round and a flat side. Carefully insert the three
leads of Q1 into the three mounting holes provided. Make sure that
the transistor body is properly keyed to the silk-screened outline--if
you insert the transistor incorrectly, it may be damaged when power is
applied. To ensure stable preamp operation and best gain, the body of
Q1 should sit as close to the PC board as possible. If needed, gently
pre-form the leads so the bottom of the transistor is positioned
approximately .15" (or 1/8") above the surface of the board. Longer
leads may impair performance.
2SC2498
(C2498)
! !
16. Once you're satisfied each lead is properly oriented and the transistor
is mounted correctly, solder Q1 in place.
At this point, your kit is finished and it's time to take a well-earned break! When
you come back, be prepared to give your work a close "quality control"
inspection before moving on to the testing and alignment section.
10
VEC-1402K Instruction Manual 2 Meter Pre-Amp Kit
PC Board Inspection:
Before applying power to your kit, give it a thorough QC (quality control)
inspection. This will help you find inadvertent assembly errors that might
prevent the preamp from working or cause damage to sensitive parts. Follow
this procedure:
!
Compare parts locations against the parts-placement diagram. Was each
part installed where it is supposed to be? Was the correct value used? Start
at one side of the board and work your way across in an organized pattern.
!
Is transistor Q1 installed correctly?
!
Inspect the solder side of the board for cold-solder joints and solder bridges
between tracks or pads. Use a magnifying glass to obtain a clear view of the
track area. If you suspect a solder bridge, hold the board in front of a bright
light for a better view. All joints should be smooth and shiny, indicating
good solder wetting and flow. Resolder any beaded or dull-appearing
connections.
Important Note:
two, it will be easier if you have the right tools. One very convenient item for
freeing soldered-in parts is a "solder sucker". This consists of a suction bulb or
a spring loaded vacuum pump that draws molten solder away from the pad and
lead. Alternatively, you may use "solder wick". If you suspect you've damaged a
component during removal, it's better to replace the part than risk reusing it!
If you find a construction error and need to remove a part or
Your preamp may be installed inside a receiver, or mounted in a small external
"project" enclosure with RF-type connectors mounted on each end. The length
of bare-wire leads attaching connectors should be 1" or less. For longer
connections (up to a couple of feet), use small flexible 50-ohm coaxial cable
such as RG-174.
Finally, rosin flux can absorb moisture, which may cause a problem for VHF
preamplifiers --especially when they are mast-mounted in a damp environment.
To remove flux, use isopropyl alcohol (or 95% grain alcohol) and an old
toothbrush. Apply a generous amount of alcohol with the toothbrush and scrub
gently. Once the flux has fully dissolved, blot the bottom of the board dry with
an untreated t i ssue. Give it a final alcohol wash, and al low to dry thoroughly.
Caution: alcohol is highly flammable and must be used
with adequate ventilation! Use safety
goggles, and avoid prolonged skin contact.
It's also best to do this outdoors.
11
VEC-1402K Instruction Manual 2 Meter Pre-Amp Kit
Now that your inspection is completed, you're ready to begin the testing and
alignment phase of construction.
TESTING AND ALIGNMENT
The best way to align a preamp
is with a calibrated signal
generator. However, it is also possible to align the VEC-1402K using off-air
signals. Alignment is easiest using a receiver that features a built-in signalstrength meter (an analog meter is generally better than a digital one for
observing small changes in signal strength). If your receiver has no meter, you
may still conduct the test by listening to signals in the speaker—or by viewing
the audio waveform using an oscilloscope. The preamp must be powered from a
9-15 volt DC source during ali gnment.
Generator Method:
Begin by connecting the output side of your preamp to a FM receiver equipped
with a bar-graph or analog type S-meter. Connect the input side to your signal
generator's output jack. Adjust the generator as follows:
•
Frequency..........................146 MHz (mid-band)
•
Output Level.....................Start at -90 to -100 dBm (weak signal)
•
Modulation........................FM, 1 KHz tone at 3-5 KHz deviation
Power up the preamp, and adjust as follows:
!
1 . T une in the gene rator signa l and adj ust the gener ator out put level fo r a ½
scale reading on the receiver S-meter. Do not exceed -20 dBm or overload
will result.
!
2. Using a hex alignment tool, adjust the slug in coil L1 until it is even with
the top of the coil form.
!
3. While observing the signal strength indicator, slowly turn the slug into the
coil until the point where the signal becomes strongest. This is typically 5
to 6 turns clockwise for 146 MHz.
Important Note:
noise meter, you may use this in place of the receiver's S-meter to find the
optimal alignment point. Alternatively, if your receiver has no S-meter, you may
view the receiver's audio output signal on an oscilloscope and adjust the preamp
for minimum noise-ripple on the 1-khz sine wave.
If you have access to a SinadderTM, or SINAD type signal-to-
12
VEC-1402K Instruction Manual 2 Meter Pre-Amp Kit
Off-air Method:
Set your preamp and receiver up, as described above, using an antenna in place
of the signal generator.
!
1. Tune in a steady-but-weak signal. Distant repeaters are especially good
because they transmit from a fixed location and remain "keyed up" during
both sides of the conversation. I f you have no S-meter, the signal must
have audible background hiss for you to tell when it is getting stronger or
weaker. Stronger signals have less background noise (or better
"quieting"). Make sure the signal isn't fluctuating due to atmospheric
conditions or passing aircraft.
!
2. Carefully adjust coil L1 for maximum signal strength.
!
3. T o achieve broad-band scanner coverage, peak the preamp at the center
of the range of frequencies to be covered. For example, if you monitor
activity between 146 and 162 MHz, peaking the preamp at 154 MHz will
give optimum performance.
This completes alignment of your preamp.
OPERATING INSTRUCTIONS
You may use the VEC-1402K with VHF receivers, scanners, or ham-radio
transceivers operating in the 140 to 162 MHz range. It may be mounted
internally in most receivers. Short runs of RG-174 cable should be used for the
RF connections. The preamp requires a 9-15 volt DC power source. This
voltage is easily “borrowed” from your receiver.
Warning: The preamp must never be installed in-line
with a transmitter or it will be severely
damaged! When used in a transceiver, the
VEC-1402K must be installed between the
antenna switch (pin-diode or mechanical
relay) and the radio's receiver circuitry.
When peaked for 146 MHz, the preamp delivers optimum performance across
the entire amateur band. In receive-only applications, you can remotely locate
the 1402K at your antenna site using a simple “bias tee”. The "bias-T” will
provide DC power over the coax line to run the preamp without attenuating VHF
13
VEC-1402K Instruction Manual 2 Meter Pre-Amp Kit
signals. Many scanner listeners use 100 feet or more of poor-grade RG-58 or
TV-type coax between the scanner and antenna, not realizing this cable has
considerable loss. Police and radio amateurs may run only a few watts,
transmitting weak signals that may become lost to feedline attenuation before
ever reaching your scanner. By mounting the preamp at your antenna, you boost
weak signals before they enter the cable. This allows previously noisy or
unreadable signals to come in loud and clear at the far end of the line!
You can make a simple bias-T using a couple inexpensive molded chokes and
capacitors (see below), or you can buy one at most CATV supply houses. The
"T" keeps RF energy isolated from your power supply, and keeps DC voltage
from being fed into your receiver where it might do some damage.
Antenna
2.2 uH Molded Choke
+
In
Out
VEC-1402K
Preamp
100 pF Capacitor
Coaxial Cable
Bias-T
2.2 uH Molded Choke
-
+ 9 - 15 VDC
To Receiver
100 pF Capacitor
Warning: Never reverse-install a bias-T so DC voltage
is fed into your receiver's antenna
terminals. Also, never reverse-polarize the
supply voltage to your preamp (swap + and leads). In both instances, damage may
result!
14
VEC-1402K Instruction Manual 2 Meter Pre-Amp Kit
IN CASE OF DIFFICULTY
Preamp Stops Amplifying:
A working preamp that fails "in-service" generally indicates a failure of
transistor Q1. Other things that should be checked are the supply voltage and RF
cable connections. If the preamp failed after being installed in a transceiver, it
might be due to excessive transmitter RF “leaking” back into the preamplifier
and damaging Q1.
Cannot Align or Test Preamp:
A newly constructed preamp that fails to work requires a careful recheck of all
work. Low gain, or inability to properly tune the preamp may indicate damaged
capacitors, an improperly wound coil, or parts in the wrong positions on the pc
board. A preamp that operates intermittently may have poor solder connections,
a problem with coax connections, or an intermittent connection to the power
source. Instability, or self-oscillation, may be caused by RF-cable problems, or
by excessive component lead lengths on the pc board.
Voltmeter Checks:
With 13.8 Vdc applied to the preamp, the collector voltage on Q1 should read
approximately 9 V, and the base voltage at .76 V. These voltages are easily
measured at the opposite ends of 100-k bias-resistor R1.
If technical assistance or factory repair is desired, please refer to the warranty
instructions on the inside front cover.
15
VEC-1402K Instruction Manual 2 Meter Pre-Amp Kit
THEORY OF OPERATION AND SPECIFICATIONS
Operation:
Coil L1 and capacitors C1 and C2 combine to form a tuned LC input filter, and
C3 matches the filter to Q1. Q1 is a high-gain "microwave" type transistor
operated as a common-emitter amplifier. It is self-biased for minimum noise
figure at 146 MHz, and normally exhibits a stage-gain of 16 dB. The output
impedance of Q1 approximates that of 50 or 70-ohm line.
Specifications:
Tuning range:..................................140 to 155 MHz
-3dB bandwidth:..............................>6 MHz
Gain at 13.8 Vdc: ............................16 dB typical
Power requirement:.........................9 - 15 Vdc, 8 mA typical
Input/Output Impedance:.................50 - 75 ohms, Unbalanced coaxial
PC Board.........................................1.500" x 1.000"
16
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