HAMTRONICS R302 Series Owner's manual

©20
10
Hamtronics, Inc.; Hilton NY; USA. All rights reserved. Hamtronics is a registered trademark. evised:
12/20/10
-
Page
1
-
GENERAL INFORMATION.
The R302 is the latest in a series of popu-
lar receivers for demanding applications
which require exceptional sensitivity and se-
lectivity. It is especially suited for repeaters
audio and data links and remote control. The
R302 was designed to provide instant setup
without lengthy waits to obtain channel crys-
tals. It is a single-channel vhf fm receiver
available in several models for reception in
the 144 MHz ham band the 148-174 MHz
commercial band or 216-226 MHz.
The R302 is our 8th generation vhf fm re-
ceiver and it packs in features you've told us
are important to you during our 40 years of
designing receivers. It's up to the difficult jobs
you've told us you have.
The R302 retains all of the popular fea-
tures Hamtronics
®
receivers have been noted
for. It uses triple-tuned circuits in the front
end and excellent crystal and ceramic filters in
the i-f with steep skirts for close channel spac-
ing or repeater operation. The i-f selectivity
for instance is down over 100dB at ±12 kHz
away from the carrier which is 40-50 dB bet-
ter than most transceivers. Low noise fet's in
the front end provide good overload resis-
tance and excellent sensitivity.
The R302 is designed for narrow-band fm
with ±5 kHz deviation. The audio output will
drive any load as low as 8Ω with up to 1 Watt
continuous output. The receiver may be used
with either voice or fsk data up to 9600 baud
using an external data interface unit. An ac-
cessory TD-5 CTCSS Decoder unit is available
for subaudible tone control.
The R302 features a positive-acting wide-
range squelch circuit and additional output
terminals for low-level squelched audio and
discriminator audio as well as COS.
There are several models which have mi-
nor variations in parts and microcontroller
programming to provide coverage as shown
in table 1. Channel frequency is controlled by
a synthesizer with DIP switch channel setting.
The TCXO (temperature controlled xtal os-
cillator) provides a temperature stability of
±2ppm over a temperature range of -30°C to
+60°C.
INSTALLATION.
Mounting.
Some form of support should be provided
under the pc board generally mounting the
board with spacers to a chassis. 3/8-inch
holes should be provided in a front panel for
the bushings of the SQUELCH and VOLUME
controls. After sliding bushings through panel
washers and nuts can be installed on the out-
side of the panel. Be sure to provide support
for the board; do not rely on the controls to
support the board since that could cause a
break in the pcb solder connections.
The receiver board relies on the mounting
hardware to provide the dc and speaker
ground connections to the ground plane on
the board; so metal standoffs and screws
should be used for mounting.
Electrical Connections.
Power and input audio or data signals
should be connected to the solder pads on the
pc board with #22 solid hookup wire which
can be attached to a connector or
feedthrough capacitors used on the cabinet in
which it is installed. Be very careful not to
route the wiring near the components on the
left hand side of the board which contains
sensitive loop filter and vco circuits which
could pick up noise from the wiring.
Power Connections.
The receiver operates on +13.6 Vdc at
about 200 mA peak with full audio. Current
drain with no audio is only about 45 mA. A
well regulated power supply should be used.
Be sure that the power source does not
carry high voltage or reverse polarity tran-
sients on the line since semiconductors in the
receiver can be damaged. The positive power
supply lead should be connected to the re-
ceiver at terminal E3 and the negative power
lead should be connected to the ground plane
of the board through the mounting hardware
or the shield of the coaxial cable. Be sure to
observe polarity!
Speaker.
An 8-ohm loudspeaker should be con-
nected to E2 with ground return through the
mounting hardware. Use of lower impedance
speaker or shorting of speaker terminal can
result in ic damage. The receiver can also
drive higher impedances such as the 1K to
20K input impedances of repeater controller
boards. There is no need to load down the
output to 8 ohms.
Note that the audio output ic is de-
signed to be heatsunk to the pc board through
the many ground pins on the ic. When run-
ning moderately low audio levels as most ap-
plications require it is no problem to use an ic
socket; so we have provided one for your con-
venience. If you will be running high audio
levels check to see if the ic is getting hot. If
so you should remove the ic socket and sol-
der the LM-386 ic directly to the board for
better heatsinking.
Antenna Connections.
The antenna connection should be made
to the pc board with an RCA plug of the low-
loss type made for rf. We sell good RCA plugs
with cable clamp. See A5 plug on website.
If you want to extend the antenna con-
nection to a panel connector we recommend
using a short length of RG-174/u coax with the
plug and keep the pigtails very short.
We do not recommend trying to use di-
rect coax soldered to board or another type of
connector. The method designed into the
board results in lowest loss practical. When
soldering the cable keep the stripped ends as
short as possible.
We recommend you always use anten-
nas with a matching network which provides a
dc ground on the driven element to avoid
static buildup damaging the input stage of the
receiver.
OPTIONS.
Repeater Use.
E5 provides a COS (carrier operated
switch) output which may be connected to a
COR module to turn a transmitter on and off.
The output level is about 8V unsquelched and
0V squelched. There is a resistor in series
with the output to limit current. Therefore
the voltage that appears at the COR board will
depend on the load resistance at the input of
that board. For best results be sure that the
input resistance of the COR board is at least
47K. If the input resistance is too low no
damage to the receiver will occur; but the
squelch circuit hysteresis will be affected.
If your repeater controller uses discrimi-
nator audio rather than the speaker output
filtered discriminator audio is available at E4.
The level is about 2V p-p. Note that discrimi-
nator audio is not de-emphasized or
squelched. If you need audio which is
squelched take it from Repeater Audio termi-
nal E1.
If your controller uses low level audio and
HAMTRONICS
®
R302 VHF FM RECEIVE
R:
INSTALLATION, OPERATION, & MAINTENANCE
Table 1. Quick Specification Reference
Model R302-1 138.000 - 148.235 MHz
Model R302-2 144.000 - 154.235 MHz
Model R302-3 154.200 - 164.435 MHz
Model R302-4 164.400 - 174.635 MHz
Model R302-5 216.000 - 226.235 MHz
Model R302-6 220.000 - 230.235 MHz
Sensitivity (12dB SINAD): 0.15 to 0.2µV
Squelch Sensitivity: 0.2µV
Adjacent Channel Selectivity:
±12 kHz at -100dB!
mage Rejection: 60-70dB
Modulation Acceptance: ±7.5 kHz
Frequency Stability: ±2ppm -30°C to +60°C
Audio Output: up to 1 Watt (8 ohms).
Operating Power: +13.6Vdc (+10 to +15Vdc)
at 45-200 mA depending on audio level.
Size: 4 in. W x 2-7/8 in. D (plus pot. shafts)

©20
10
Hamtronics, Inc.; Hilton NY; USA. All rights reserved. Hamtronics is a registered trademark. evised:
12/20/10
-
Page
2
-
has a high input impedance (20K or higher)
squelched audio can be obtained from E1 in-
dependent of the VOLUME control.
Discriminator Meter.
If you wish to use a discriminator meter
and you are handy in designing with op-amps
you can run a sample of the dc voltage at DIS-
CRIMINATOR output terminal E4 to one input
of an op-amp and tie the other input to a volt-
age divider pot set to provide a reference volt-
age of about +3.3Vdc.
S-Meter.
There is no s-meter function as such
available in i-f amplifier ic's made for profes-
sional receivers; however a signal strength
indication is available at test point TP-4. This
voltage is a function of the noise level de-
tected in the squelch circuit. It also varies
with SQUELCH control setting. With the
SQUELCH set to where the squelch just closes
the dc voltage at TP-4 is about -0.5V with no
signal and +1V with full quieting signal. You
can tap off this test point with a high-
impedance circuit such as an op-amp to drive
a meter or a computerized repeater control-
ler.
Subaudible Tone Decoder.
To use our TD-5 Subaudible Tone Decoder
or a similar module connect its audio input to
DISCRIMINATOR terminal E4. If you want to
use it to mute the audio (instead of inhibiting
a repeater transmitter as is normally done)
connect the mute output of the TD-5 to E1 on
the receiver.
ADJUSTMENTS.
Frequency Netting.
All crystals age a little over a long period
of time; so it is customary to tweak any re-
ceiver back onto the precise channel fre-
quency once a year during routine
maintenance. Because modern solid state
equipment doesn’t require much routine
maintenance many receivers don’t get their
oscillators tweaked as a matter of routine any
more but they should.
The adjustment should be done using an
accurate service monitor or frequency
counter. Of course make sure the test
equipment is exactly on frequency first by
checking it against WWV or another fre-
quency standard.
The channel frequency is trimmed pre-
cisely on frequency with a small variable ca-
pacitor which is accessible through a hole in
the top of the shield can on the TCXO. The
proper tool is a plastic wand with a small
metal bit in the end.
To perform this adjustment it is first nec-
essary to verify that the discriminator is prop-
erly adjusted. Do this by connecting a dc
voltmeter to E4. Connect a signal generator
set for 10.700 MHz to TP3 and set the level
for a relatively strong signal so there is very
little white noise. Adjust discriminator coil T2
for 3.3Vdc. Then reconnect the signal gen-
erator to antenna connector J1 and set it for
the precise channel frequency. You can also
use a strong signal on the air if you are sure it
is right on frequency. Adjust the TCXO capaci-
tor for 3.3Vdc (to match the voltage obtained
with the 10.700 MHz signal).
Setting Channel Frequency.
The channel frequency is determined by
frequency synthesizer circuits which use a dip
switch in conjunction with programming in a
microcontroller to set the channel. The mi-
crocontroller reads the dip switch information
and does mathematics applying serial data to
the synthesizer ic whenever power is applied.
Following is a discussion of how to set the dip
switch to the desired channel frequency.
☞
☞☞
☞ NOTE: If the frequency is changed
more than about 1 MHz a complete align-
ment of the receiver should be performed as
described in later text. Optimum operation
only occurs if the synthesizer is adjusted to
match the frequency switch setting and all the
tuned amplifier circuits are peaked for the de-
sired frequency.
To determine what channel frequency to
use the microcontroller adds the frequency
information from the dip switch to a “base”
frequency stored in eprom used for microcon-
troller programming. Each model of the R302
Receiver has a particular base frequency. For
example the R302-2 has a base frequency of
144.000 MHz as shown in Table 1.
Dip switch settings are binary which
means each switch section has a different
weighting twice as great as the next lower
section. Sections have weights such as 5 kHz
10 kHz etc. all the way up to 2.56 MHz. (See
Table 2 or the schematic diagram for switch
values.)
The system sounds cumbersome but it
really is fairly simple and you don’t need to
do this frequently. A piece of paper or a small
calculator is handy to aid in determining
which sections of the switch to turn on. When
done you might want to record the switch
settings in table 3 for future reference.
Begin by subtracting the base frequency
e.g. 144.000 from the desired frequency to
determine the total value of all the switch sec-
tions required to be turned on.
If the difference is more than 5.120MHz
solder a jumper to pads to the left of the
switch and subtract 5.120 from the starting
frequency.
Note: The board was designed to use an
11 position dip switch which is no longer
available. For the few times it is needed a
jumper can be installed in place of that switch
position.
Likewise look at the remainder frequency
and see if you can subtract 2.560 from it. If
so turn on dip switch section 1 and subtract
2.560 from to get a new remainder. Other-
wise turn off section 1.
Do the same for each of the other sec-
tions from highest to lowest weighting in se-
quence. Each time you consider the
remainder turn on the switch section with
the highest weighting which will fit within the
remainder without exceeding it. Each time it
is found necessary to turn on a switch section
subtract the value of that section from the
remainder to get the new remainder.
As an example let us consider how to set
the Receiver for 146.94 MHz. The following
discussion is broken down into steps so you
can visualize the process easier.
a. 146.940 - 144.000 base freq. = 2.940
MHz remainder. Turn on switch #1 which
represents the largest increment to fit re-
mainder.
b. 2.940 - 2.560 value of switch #2 =
0.380 MHz. Turn on #4 which is 0.320 MHz
the largest increment to fit the remainder.
c. 0.380 - 0.320 = .060 MHz remainder.
Turn on switch #7 and switch #8 which have
values of .040 and .020 respectively which
adds up to the remainder of .060 MHz. Note
that when the remainder gets down into the
double digit range it is very easy to visualize
turning on multiple switch sections to satisfy
the entire remainder such as we just did.
d. When we finished we had turned on
switch sections 1 4 7 and 8.
Note: Dip switch information is read by
the synthesizer only when power is first ap-
plied. If switch settings are changed turn the
power off and on again.
Shortcut ---
If you have access to the internet our
website has a long table of numbers which
gives the equivalent binary number settings
for every possible frequency. We couldn’t
print it here because it takes many printed
pages of space. Surf to our website at
www.hamtronics.com and look for Dip Switch
Freq Programming for newer R302 Receivers
under Reference Info. Look up the frequency
and it will give you all the binary switch set-
tings.
ALIGNMENT.
General Procedure.
A complete alignment is needed when-
ever the frequency is changed by more than
about 1 MHz. Alignment ensures that the fre-
quency synthesizer is optimized at the center
Table 3. My Switch Settings
Frequency: MHz
Switch Sections Turned On: (circle)
1 2 3 4 5 6 7 8 9 10

©20
10
Hamtronics, Inc.; Hilton NY; USA. All rights reserved. Hamtronics is a registered trademark. evised:
12/20/10
-
Page
3
-
of the vco range and that all stages are tuned
to resonance.
Equipment needed for alignment is a sen-
sitive dc voltmeter a stable and accurate sig-
nal generator for the channel frequency and
a regulated 13.6Vdc power supply with a 0-
200 mA meter internally or externally con-
nected in the supply line.
The slug tuned coils in the Receiver should
be adjusted with the proper tuning tool to
avoid cracking the powdered iron slugs. Vari-
able capacitors should be adjusted with a
plastic tool having a small metal bit. (See A1
A28 and A2 tools on website.) All variable
capacitors should be set to the center of their
range. Turn them 90° if they have not previ-
ously been aligned (except on the optional
TCXO).
☞
☞☞
☞Note: Meter indications used as refer-
ences are typical but may vary widely due to
many factors not related to performance
such as type of meter and circuit tolerances.
Typical test point indications are for the 144
MHz band unit and may differ for other
bands.
a. Set the SQUELCH pot fully counter-
clockwise and the VOLUME pot just a little
clockwise.
b. Connect speaker and +13.6 Vdc. You
should hear white noise.
c. Set dip switches for desired fre-
quency.
d. Connect voltmeter to TP1. Adjust vco
coil L1 for +2.0Vdc. (Although the vco will op-
erate over a wide range of tuning voltages
from about 0.5V to 4.5V operation is opti-
mum if the vco is adjusted to 2.0V.)
e. Connect voltmeter to TP2. Adjust
buffer coil L3 for a peak typically about
+0.35V.
f. Connect stable signal generator to
TP-3. Set generator to exactly 10.7000 MHz.
Use a frequency counter or synthesized signal
generator. Set level just high enough for full
quieting. At 1 uV you should notice some
quieting but you need something near full
quieting for the test (about 20µV).
g. Connect dc voltmeter to Discrimina-
tor terminal E4. Adjust discriminator trans-
former T2 for +3.3Vdc.
 Be careful not to turn the slug tight
against either the top or bottom because the
winding of the transformer can be broken.
The tuning response is an S-curve; so if you
turn the slug several turns you may think you
are going in the proper direction even though
you are tuning further away from center fre-
quency.
h. Connect signal generator to J1 using a
coax cable with RCA plug. Adjust signal gen-
erator to exact channel frequency and turn
output level up fairly high (about 1000µV). Ad-
just frequency trimmer in TCXO to net the
crystal to channel frequency indicated by
+3.3Vdc at E4.
Note: There are two methods of adjusting
the mixer and front end. One is to use a volt-
meter with test point TP-4. The voltage at this
point is proportional to the amount of noise
detected in the squelch circuit; so it gives an
indication of the quieting of the receiver. With
SQUELCH control fully ccw the dc voltage at
TP-4 varies from -0.5 Vdc with no signal (full
noise) to +1 Vdc with full quieting signal.
The other method is to use a regular pro-
fessional SINAD meter and a tone modulated
signal.
In either case a weak to moderate signal
is required to observe any change in noise. If
the signal is too strong there will be no
change in the reading as tuning progresses; so
keep the signal generator turned down as re-
ceiver sensitivity increases during tuning.
If you use TP-4 with a voltmeter the sig-
nal can be modulated or unmodulated. If you
use a SINAD meter the standard method is a
1000 Hz tone with 3 kHz deviation.
i. Connect fet dc voltmeter to TP4. Set
signal generator for relatively weak signal one
which shows some change in the dc voltage
indication at TP4. Alternately peak RF ampli-
fier and mixer coils L4-L8 until no further im-
provement can be made.
When properly tuned sensitivity should
be about 0.15 to 0.2µV for 12 dB SINAD.
 Crystal filter trimmer coil T1 normally
should not be adjusted. It is set at the factory.
The purpose of the adjustment is to provide
proper loading for the crystal filter and if mis-
adjusted ripple in the filter response will re-
sult in a little distortion of the detected audio.
If it becomes necessary to adjust T1 tune the
signal generator accurately on frequency with
about 4.5kHz fm deviation using a 1000 Hz
tone. In order of preference use either a
SINAD meter an oscilloscope or just your
ears and fine tune T1 for minimum distortion
of the detected audio.
THEORY OF OPERATION.
The R302 is a frequency synthesized vhf
fm Receiver. Refer to the schematic diagram
for the following discussion.
Low noise dual-gate mos fet’s are used for
the RF amplifier and mixer stages. The output
of mixer Q5 passes through an 8-pole crystal
filter to get exceptional adjacent channel se-
lectivity.
U4 provides IF amplification a 2
nd
mixer
to convert to 455 kHz a discriminator noise
amplifier and squelch. Ceramic filter FL5 pro-
vides additional selectivity at 455 kHz. The
noise amplifier is an op amp active filter
peaked at 10 kHz. It detects noise at frequen-
cies normally far above the voice band. Its
output at pin 11 is rectified and combined
with a dc voltage from the SQUELCH control
to turn a squelch transistor on and off inside
the ic which grounds the audio path when
only noise is present. Inverter Q6 provides a
dc output for use as a COS signal to repeater
controllers.
The injection frequency for the first mixer
is generated by vco (voltage controlled oscilla-
tor) Q1. The injection frequency is 10.700
MHz below the receive channel frequency.
The output of the vco is buffered by Q2 to
minimize effects of loading and voltage varia-
tions of following stages from modulating the
carrier frequency. The buffer output is ap-
plied through a double tuned circuit to gate 2
of mixer Q5.
The frequency of the vco stage is con-
trolled by phase locked loop synthesizer U2. A
sample of the vco output is applied through
the buffer stage and R1 to a prescaler in U2.
The prescaler and other dividers in the syn-
thesizer divide the sample down to 5kHz.
A reference frequency of 10.240 MHz is
generated by a TCXO (temperature compen-
sated crystal oscillator). The reference is di-
vided down to 5 kHz.
The two 5kHz signals are compared to de-
termine what error exists between them. The
result is a varying dc tuning voltage used to
phase lock the vco precisely onto the desired
channel frequency.
The tuning voltage is applied to carrier
tune varactor diode D1 which varies its ca-
pacitance to tune the tank circuit formed by
L1/C20/C21. C16 limits the tuning range of
D1. The tuning voltage is applied to D1
through a third order low pass loop filter
which removes the 5kHz reference frequency
from the tuning voltage to avoid whine.
In order for the synthesizer to lock the
vco must be tuned to allow it to generate the
proper frequency within the range of voltages
the phase detector in the synthesizer can gen-
erate roughly 0.5Vdc to 4.5Vdc.
Serial data to indicate the desired channel
frequency and other operational characteris-
tics of the synthesizer are applied to synthe-
sizer U2 by microcontroller U1. Everything
Table 2. Frequency Settings
Device Frequency Weight
Jumper 5.120 MHz
Switch #1 2.560 MHz
Switch #2 1.280 MHz
Switch #3 640 kHz
Switch #4 320 kHz
Switch #5 160 kHz
Switch #6 80 kHz
Switch #7 40 kHz
Switch #8 20 kHz
Switch #9 10 kHz
Switch #10 5 kHz
+3.3Vdc
Figure 1. Discriminator tuning curve.

©20
10
Hamtronics, Inc.; Hilton NY; USA. All rights reserved. Hamtronics is a registered trademark. evised:
12/20/10
-
Page
4
-
the synthesizer needs to know about the
band division schemes reference frequency
and oscillator options is generated by the con-
troller. Information about the base frequency
of the band the receiver is to operate on and
the channel within that band is calculated in
the controller based on information pro-
grammed in the eprom on the controller and
on channel settings done on dip switch S1.
Whenever the microcontroller boots at power
up the microcontroller sends several bytes of
serial data to the synthesizer using the data
clock and /enable lines running between the
two ic’s.
+13.6Vdc power for the Receiver is ap-
plied at E1. Audio output amplifier U5 is
powered directly by the +13.6Vdc. All the
other stages are powered through voltage
regulators for stability and to eliminate noise.
U6 is an 8Vdc regulator to power detector U4
RF amplifier Q4 mixer Q5 and the vco and
buffer. Additional filtering for the vco and
buffer stages is provided by capacitance am-
plifier Q3 which uses the characteristics of an
emitter follower to provide a very stiff supply
eliminating any possible noise on the power
supply line. Regulator U7 provides a +5Vdc
supply for the frequency synthesizer and mi-
crocontroller which are both low current
CMOS devices.
TROUBLESHOOTING.
General.
The usual troubleshooting techniques of
checking dc voltages and signal tracing with
an RF voltmeter probe and oscilloscope will
work well in troubleshooting the R302. DC
voltage charts and a list of typical audio levels
are given to act as a guide to troubleshooting.
Although voltages may vary widely from set to
set and under various operating and measure-
ment conditions the indications may be help-
ful when used in a logical troubleshooting
procedure.
Current Drain.
Power line current drain normally is about
45 mA with volume turned down or squelched
and up to 200 mA with full audio output.
If the current drain is approximately 100
mA with no audio output check to see if volt-
age regulator U6 or U7 is hot. If so and the
voltage on the 8V or 5V line is low there is a
short circuit on that bus somewhere and U6
or U7 is limiting the short circuit current to
100mA to protect the receiver from damage.
If you clear the short circuit the voltage
should rise again. U6 or U7 should not be
damaged by short circuits on its output line;
however it may be damaged by reverse volt-
age or high transient voltages.
Audio Output Stage.
Note that audio output ic U5 is designed
to be heatsunk to the pc board through the
many ground pins on the ic.
If audio is present at the volume control
but not at the speaker the audio ic may have
been damaged by reverse polarity or a tran-
sient on the B+ line. This is fairly common
with lightning damage.
If no audio is present on the volume con-
trol the squelch circuit may not be operating
properly. Check the dc voltages and look for
noise in the 10 kHz region which should be
present at U1-pin 11 with no input signal.
(Between pins 10 and 11 of U1 is an op-amp
active filter tuned to 10 kHz.)
RF Signal Tracing.
If the receiver is completely dead try a
10.700 MHz signal applied to TP-3 using coax
test lead. Set level just high enough for full
quieting. At 1 µV you should notice some
quieting but you need something near full
quieting for the test.
You can also connect the 10.700 MHz test
lead through a blocking capacitor to various
sections of the crystal filter to see if there is a
large loss of signal across one of the filter sec-
tions. Also check the 10.245 MHz oscillator
with a scope or by listening with an hf receiver
or service monitor.
A signal generator on the channel fre-
quency can be injected at various points in the
front end. If the mixer is more sensitive than
the RF amplifier the RF stage is suspect.
Check the dc voltages looking for a damaged
fet which can occur due to transients or re-
verse polarity on the dc power line. Also it is
possible to have the input gate (gate 1) of the
RF amplifier fet damaged by high static
charges or high levels of RF on the antenna
line with no apparent change in dc voltages
since the input gate is normally at dc ground.
Synthesizer Circuits.
Following is a checklist of things to look
for if the synthesizer is suspected of not per-
forming properly.
a. Check the output frequency of the
vco buffer with a frequency counter.
c. Check tuning voltage at TP1. It
should be about +2.0Vdc. Actual range over
which the unit will operate is about +0.5Vdc
to about +4.5Vdc. However for optimum re-
sults the vco should be tuned to allow opera-
tion at about +2.0Vdc center voltage.
d. Check the operating voltage and bias
on the vco and buffer.
e. Check the TCXO at pin 1 of the syn-
thesizer ic. A scope should show strong signal
(several volts p-p) at 10.240 MHz.
f. Check the oscillator at pin 1 of micro-
controller ic U1 with a scope. There should be
a strong ac signal (several volts p-p) at the os-
cillator frequency.
g. The data clock and latch enable lines
between the microcontroller and synthesizer
ic’s should show very brief and very fast activ-
ity sending data to the synthesizer ic shortly
after the power is first applied or a dip switch
setting is changed. Because this happens very
fast it can be difficult to see on a scope. Use
100µSec/div 5Vdc/div and normal trigger.
h. Check the microcontroller to see that
its /reset line is held low momentarily when
the power is first applied. C1 works in con-
junction with an internal resistor and diode in
the ic to make C1 charge relatively slowly
when the power is applied. It should take
about a second to charge up.
i. Check the switch settings to be sure
you have the correct frequency information
going to the microcontroller.
Microphonics, Hum, and Noise.
The vco and loop filter are very sensitive
to hum and noise pickup from magnetic and
electrical sources. Some designs use a
shielded compartment for vco’s. We assume
the whole board will be installed in a shielded
enclosure; so we elected to keep the size
small by not using a separate shield on the
vco. However this means that you must use
care to keep wiring away from the vco circuit
at the right side of the board. Having the
board in a metal enclosure will shield these
sensitive circuits from florescent lights and
other strong sources of noise.
Because the frequency of a synthesizer
basically results from a free running L-C oscil-
lator the tank circuit especially L1 is very
sensitive to microphonics from mechanical
noise coupled to the coil. You should mini-
mize any sources of vibration which might be
coupled to the receiver such as motors. In
addition it helps greatly to prevent the
molded coil from vibrating with respect to the
shield can. Both the coil and can are soldered
to the board at the bottom but the top of the
coil can move relative to the can and there-
fore cause slight changes in inductance which
show up as frequency modulation. Therefore
the factory cements the top of the coil to the
can.
Excessive noise on the dc power supply
which operates the receiver can cause noise
to modulate the synthesizer output. Various
regulators and filters in the receiver are de-
signed to minimize sensitivity to wiring noise.
However in extreme cases such as in mobile
installations with alternator whine you may
need to add extra filtering in the power line to
prevent the noise from reaching the receiver.
Other usual practices for mobile installa-
tions are recommended such as connecting
the + power and ground return lines directly
to the battery instead of using cigarette
lighter sockets or dash board wiring.
To varying degrees whine from the 5kHz
reference frequency may be heard on the sig-
nal under various circumstances. If the tuning
voltage required to tune the vco on frequency
is very high or low near one extreme the
whine may be heard. This can also happen

©20
10
Hamtronics, Inc.; Hilton NY; USA. All rights reserved. Hamtronics is a registered trademark. evised:
12/20/10
-
Page
5
-
even when the tuning voltage is properly near
the 2.0Vdc center if there is dc loading on the
loop filter. Any current loading no matter
how small on the loop filter causes the phase
detector to pump harder to maintain the tun-
ing voltage. The result is whine on the signal.
Such loading can be caused by connecting a
voltmeter to TP1 for testing and it can also be
caused by moisture on the loop filter compo-
nents.
Typical Dc Voltages.
Tables 4-6 give dc levels measured with a
sensitive dc voltmeter on a sample unit with
13.6 Vdc B+ applied. All voltages may vary
considerably without necessarily indicating
trouble. The charts should be used with a
logical troubleshooting plan. All voltages are
positive with respect to ground except as
indicated.
Use caution when measuring voltages on
the surface mount ic. The pins are close to-
gether and it is easy to short pins together
and damage the ic. We recommend trying to
connect meter to a nearby component con-
nected to the pin under question. Also some
pins are not used in this design and you can
generally not be concerned with making
measurements on them.
Typical Audio Levels.
Table 7 gives rough measurements of au-
dio levels. Measurements were taken using
an oscilloscope with no input signal just
white noise so conditions can be reproduced
easily.
REPAIRS.
If you need to unsolder and replace any
components be careful not to damage the
plated through holes on the pc board. Do not
drill out any holes. If you need to remove sol-
der use a solder sucker or solder wick. A
toothpick or dental probe can be used with
care to open up a hole.
If you need to replace a surface mount ic
first be very sure it is damaged. Then care-
fully cut each lead off the case with fine nose
cutters. Once the case is removed individual
leads can be unsoldered and the board can be
cleaned up. Carefully position the new ic and
tack solder the two opposite corner leads be-
fore any other leads are soldered. This allows
you to melt the solder and reposition the ic if
necessary. Once you are sure the remaining
leads can be soldered. If you get a solder
short between leads use a solder sucker or
solder wick to remove the excess solder.
Table 4. Typical Test Point Voltages
TP1 Tuning V. Normally set at 2V
TP2 Buffer approx. 0.35V
TP3 Test Input (No reading)
TP4 Sig. Level With SQUELCH control
fully ccw, varies from -0.5
Vdc with no to +1 Vdc full
quieting.
E4 Freq. Varies with frequency of
input signal. Voltage at
this point normally is ad-
justed for +3.3Vdc with a
signal exactly on fre-
quency. Can vary a little
without being a problem.
Table 5. Typical Xstr DC Voltages
Xstr Stage E(S) B(G1) C(D) G2
Q1 vco 1.3 2.0 6.5 -
Q2 buffer 0 0.7 4.5 -
Q3 dc filter 6.8 7.4 7.6 -
Q4 RF ampl 0 0 7.5 3.8
Q5 Mixer 0 0 7.6 0
Q6 sq. open 0 0 8 -
sq. closed 0 0.65 0.1 -
Table 6. Typical IC DC Voltages
U1-1 2.3
U1-2 2.3
U2-1 2.1
U2-2 1.9
U2-3&4
4.9
U2-5 0 – 5V
(~2V
tuned)
U2-7 4.8
U2-8 1.6
U2-9 0
U2-10
0
U2-11
0
U5-1 1.35
U5-3 0.05
U5-5 6.8
U5-6 13.6
U5-7 6.9
U5-8 1.35
U4-1 8
U4-2 7.5
U4-3 7.8
U4-4 8
U4-5 7.5
U4-6 7.5
U4-7 7.5
U4-8 8
U4-9 3.3
(aligned)
U4-10
0.75
U4-11
1.5
U4-12
0.6 (with
squelch just
closed)
U4-13
0 (sq open)
7.5 (sq
closed)
U4-14
0
U4-15
0
U4-16
1.8
Table 7. Typical Audio Voltages
Audio Test Point Normal Level
U4-9 (Discriminator) 3V p-p audio
E4 (Disc Output) 2V p-p audio
E1 (Repeater Output) 1V p-p audio
U4-11 (noise ampl) 2.5V p-p noise
Right lug of Vol cont. 500mV p-p audio
U5-2 (af ampl input) 0 to 300mV p-p
U5-6 or E2 (speaker 0 to 7V p-p audio
ampl output)

©20
10
Hamtronics, Inc.; Hilton NY; USA. All rights reserved. Hamtronics is a registered trademark. evised:
12/20/10
-
Page
6
-
PARTS LIST FOR R302
RECEIVER.
☞ Note: Values which vary with freq. band are
shown in a table at the end of the parts list. Resis-
tors and capacitors are 805 smt type unless noted
otherwise.
 Caution: IC’s are static sensitive. Use ap-
propriate handling precautions to avoid damage.
Ref Desig Value (marking)
C1 1 µf electrolytic
C2 100pf
C3 0.1µf
C4 not assigned
C5 0.1µf
C6 100µf electrolytic
C7 not assigned
C8* 0.1µf
C9 100µf electrolytic
C10 0.15µf mylar (red)
C11 .01µf
C12 .001uf
C13 2pf
C14 100µf electrolytic
C15 0.1µf
C17-C18 390pf
C19 100µf electrolytic
C22 4pf
C23 390pf
C26-C27 390pf
C30 not assigned
C36 4pf
C40 .01µf
C41 7pf
C42 4pf
C43 7pf
C44 0.47µf electrolytic
C45 0.1µf
C46-C47 .001uf
C48 0.1µf
C49-C50 .01µf
C51* 220µf electrolytic
C52* 4.7µf electrolytic
C53 1µf electrolytic
C54 100µf electrolytic
C55 not used
C56 220pf
C57 68pf
C58-C60 0.1µf
D1 BB132 varactor diode
D2 MSC3130 (used as diode)
D3-D4 MMBT3904 (used as diode)
FL1-FL4 10.7MHz crystal filter
(matched set of 4)
FL5 455kHz ceramic filter
J1 RCA Jack
L2 0.33µH RF choke
(red-sil-orn-orn)
L3-L8 2½ t. slug tuned (red)
L9 0.33µH RF choke
(red-sil-orn-orn)
Q1-Q2 MSC3130
Q3 MMBT3904
Q4-Q5 BF998 MOS FET
Q6 MMBT3904
R1 180Ω
R2 2.2K
R3 2 Meg
R4 27Ω
R5 10K
R6 47K
R7-R8 2.2K
R9 10K
R10 6.8K
R11 3.9K
R12 180Ω
R13 47Ω
R14 15K
R15 470Ω
R16 3.9meg
R17-R18 100K
R19 47K
R20 330K
R21 15K
R22 47K
R23 100K panel mount pot
R24 47K
R25 100K
R26 47K
R27 510K
R28 4.7K
R29 680Ω
R30 1K
R31 22K
R32* 100K panel mount pot.
R33-R34 not assigned
R35 47K
R36* 100K
R37 2Meg
R38 27Ω
R39* 10Ω
R40-R42 27Ω
S1 10 pos. DIP switch
T1 10.7 MHz IF xfmr (T1005)
T2 455kHz IF xfmr (T1003)
T3 10.7 MHz IF xfmr (T1005)
U1  MC68HC705J1A µP
U2  LMX1501A PLL
U3  10.240 MHz TCXO
U4 MC3361BP IF ampl
U5* LM386N-1 AF output
U6 78L08ACD regulator
U7 78L05ACD regulator
Y1 10.245 MHz crystal
*On R302-RE receivers omit volume con-
trol R32 U5 C8 C52 C51 and R36 and R39.
Values which vary with frequency band:
R302-RE 118.000 - 128.000 MHz
R302-1 is 138.000 - 144.000 MHz
R302-2 is 144.000 - 154.235 MHz
R302-3 is 154.200 - 164.435 MHz
R302-4 is 164.400 - 174.635 MHz
R302-B is 178.000 - 182.000 MHz
R302-5 is 216.000 - 226.235 MHz
R302-6 is 220.000 - 230.235 MHz
Ref -RE* -1 -2 -3 -4 -B -5, -6
C16 10 10 10 10 10 7 8
C20 18 18 15 12 10 6 10
C21 68 68 68 62 47 33 47
C24 39 39 33 27 22 15 10
C25 68 68 62 47 47 39 33
C28 39 33 27 22 20 15 8
C29 100 68 68 62 62 39 27
C31 30 22 20 18 15 12 6
C32 0.5 0.5 0.5 0.5 0.5 0.3 0.3
C33 30 22 20 18 15 12 8
C34 n/u 0.3 0.3 0.3 0.3 n/u n/u
C35 27 20 18 15 12 10 6
C37 39 39 27 22 20 18 10
C38 82 82 82 62 62 47 27
C39 1 1 1 1 0.5 0.5 0.3
L1 2½t
(red)
2½t
(red)
2½t
(red)
2½t
(red)
2½t
(red)
2½t
(red)
1½t
(dark
brown)

©20
10
Hamtronics, Inc.; Hilton NY; USA. All rights reserved. Hamtronics is a registered trademark. evised:
12/20/10
-
Page
7
-
View of top of board.
Note that board was designed originally for 11 position dip switch which is no longer available. 10 position switch is
installed in positions 2-11 on board. For those rare cases requiring first position to be on install jumper on left hand pair
of pads on board. See schematic for clarification.

©20
10
Hamtronics, Inc.; Hilton NY; USA. All rights reserved. Hamtronics is a registered trademark. evised:
12/20/10
-
Page
8
-