AR3500 Modification and Alignment
Information
By: W8CWE
Overview
The AR3500 is a multi-function,
microprocessor-controlled HF transceiver. It combines reliable performance and
ease of use with advanced features such as automatic scanning and split
frequency operation.
This transceiver operates in all modes and is designed to be operated as a
base or mobile unit.
I have used this radio as my primary base for about 6 months now and I have
never used a more powerful, more reliable radio. The AR3500 is capable of 120
Watts PEP on sideband, as well as over 100 Watts AM carrier. Once adjusted, the
modulation on this radio is so hot, you’ll have to tie it down to the table to
keep it from jumping off!
Specifications
Transmitter:
Frequency Range: 26.000 – 29.999 MHz
Tuning Steps: 100 Hz, 1 kHz, 10 kHz, 100 kHz, 1 MHz
Emission Types: LSB, USB, CW, AM, FM
Carrier Suppression: Better than 40 dB below peak
Unwanted Sideband Suppression: Better than 50 dB below peak
Spurious Radiation: Better than 50 dB below peak
Audio Response: Better than 30 dB below peak
Frequency Accuracy: Better than +10 PPM
Modulation Type: A3J Balanced Modulator
A3 Voltage Modulator
F3 Frequency Modulator
Maximum FM Deviation: +1.5 kHz
Microphone Impedance: low (500 to 600 ohms
Power Consumption: 25 Amps Max.
Power Output: CW 150 Watts
SSB 120 Watts
AM/FM 100 Watts
Receiver:
Circuit Type: Superheterodyne, dual conversion
Clarifier Range: +/- 500 Hz
Sensitivity: SSB/CW/AM 0.25uV
FM better than 0.3uV for 12 dB SINAD
Intermediate Frequencies: IF 1 10.695
IF 2 455 kHz
SSB, CW 10.695
Image Rejection: Better than 70 dB
IF Rejection: 80 dB
Selectivity: -6dB -60dB
SSB, CW 2.6KHz 4.7KHz
AM, FM 6.0 kHz 18 kHz
Noise Blanker: Switchable six stage high gain type
Dynamic Range: Better than 100 dB
Audio Output Power: 2-Watts minimum with less than 10% THD
Audio Output Impedance: 8-16 Ohms
Power Consumption: 500 Milliamps
Frequency Expansion:
- Remove the bottom cover.
- Locate the three pins near
the front of the radio
- Solder a jumper between
these three pins. Radio now has from 26.000 MHz to 29.999 MHz.
Peak and
Tune
- Turn VR-17 (AM MOD) fully
counterclockwise.
- Turn VR-15 (ALC) fully
clockwise
- Turn VR-16 (AM POWER) for
maximum carrier level.
- Modulate the radio. Tune
VR-16 (AM POWER) to achieve maximum carrier and still retain forward
movement on the RMS wattmeter. VR-16 can be removed and replaced with
three wire leads routing to an external 5K potentiometer for variable
power.
- As carrier is decreased,
modulation is increased. At 10-Watts dead key using a D-104 Silver Eagle,
I get 25-30 Watts peak swing with tremendous modulation.
Talkback
Cut one leg of D-73 to provide talkback in AM mode.
Variable Power Modification
This modification adds variable power to the AR3500. You will need a 5K
chassis-mount potentiometer, an appropriate knob for the pot, and enough hook-up
wire for three lengths to route from the main board to the outside of the radio
chassis. The potentiometer is mounted to the side of the radio chassis, on the
left side of the radio as you are facing it (with the speaker down). A
through-hole for the potentiometer shaft must be drilled through the radio
chassis as well as through the radio covers. This modification will provide
variable RF out for AM/FM/CW modes only. The instructions below assume the
potentiometer has been installed in the radio chassis.
- Unsolder VR-16 (AM POWER)
from the main board.
- Solder a length of hook-up
wire to each of the three holes vacated by VR-16.
- Install the three loose ends
of the hook-up wire to the potentiometer terminals.
- Solder the center wire to the
center terminal of the new pot. Solder the other two wires to the
remaining terminals on the new pot.
NOTE: If the direction of increased power is opposite from what you
want, reverse the
two outside wire.
Programming
Add a Frequency to one of the Five
Presets
- Manually enter the frequency
to be programmed. Press ENTER.
- Press the button
corresponding to the desired preset location (1-5). Press ENTER.
- Repeat for the remaining four
memory locations.
You can scan your five presets by setting the squelch (to
silence). Press the MEM button to begin scanning. To cancel a memory location,
scan to that location and open the squelch to maintain the frequency. Press
CANCEL to delete the memory.
Soft Frequency Expansion (24.850 MHz
to 29.999 MHz)
Aside from the hard frequency expansion (26.000.0 MHz to 29.000.0 MHz), the
AR3500 (3300) can be further expanded using the microprocessor. This is called
soft expansion since it involves programming the radio's microprocessor. The
radio will not lock for transmit much past 24.850 MHz, but it does have receive
capabilities down as low as .102.4 MHz. I have obtained best results when
programming the radio for 2.9 MHz to 30 MHz. This first programming sequence
will soft expand the radio for 24.850 MHz to 29.999 MHz.
- Program any frequency into
one of the memory locations and press ENTER. Make sure that when you are
done, you still have one memory location open.
- Press MANUAL.
- Press ENTER.
- Press the 10K Down button
once.
- Press ENTER.
- Press MEMORY. The frequency
display will now show 2.933.0.
- Press the 1K Up button once.
- Press the 1 MHz Up button
slowly until the display reads 24.450.0 MHz.
- Press ENTER.
- Press MEMORY.
- Press MANUAL.
- Press SCAN PROG. Once.
- Press 10K Up once.
- Press ENTER twice.
- Press 1 MHz Up twice. The
display will now read 26.450.0.
- Press ENTER.
To scan through the frequencies, you must use only the SCAN
UP or SCAN DOWN buttons. You can also autoscan if you turn the squelch up to
silence the radio. The radio should transmit between 24.850 and 30 MHz.
Soft Frequency Expansion (2.933.0 MHz
to 29.933.0 MHz)
Program any frequency into one of the memory locations and press ENTER. Make
sure that when you are done, you still have one memory location open.
- Press MANUAL.
- Press ENTER.
- Press the 10K Down button
once.
- Press ENTER.
- Press MEMORY. The frequency
display will now show 2.933.0.
- Press MANUAL.
- Press SCAN PROG. Once.
- Press 1K Up once.
- Press ENTER twice.
- Press 1 MHz Up until the
display reads 29.933.0.
- Press ENTER. You can now scan
from 2.933.0 MHz to 29.933.0 MHz.
To scan through the frequencies, you must use only the SCAN
UP or SCAN DOWN buttons. You can also autoscan if you turn the squelch up to
silence the radio. The radio will only transmit between 24.850 and 29.933.0
MHz.
Alignment Procedure
Receive
PLL – VCO
- Let the radio warm up for ½
hour with the covers installed before beginning.
- Set the radio to 29.90000MHz
FM mode.
- Connect DVM to TP-1 and
adjust T-13 for 3.8 VDC.
- Set the radio to 28.0000MHz,
clarifier at center point.
- Connect O’scope to TP-2.
Adjust T-12 for maximum in AM mode.
- Connect O’scope to cathode
of D-77. Adjust T-11 for maximum in AM mode.
- Connect frequency counter to
TP-3.
NOTE: Radios with the optional 2.6KHz SSB
filter use different offset frequency adjustments. The filter is identified by
the markings on the top (10M2.6D is the 2.6KHz filter).
4.2KHz
2.6KHz
- Adjust T-16 for 10.6925MHz
or 10.6935MHz in USB mode.
- Adjust T-17 for 10.6975MHz
or 10.6965MHz in LSB mode.
- Adjust T-15 for 10.6943MHz
or 10.6943MHz in CW mode.
- Adjust T-14 for 10.9650MHz
or 10.9650MHz in AM mode.
- Connect frequency
counter to TP-2
4.2KHz
2.6KHz
- Adjust VR-3 for 17.3050MHz
or 17.3050MHz in FM mode.
- Adjust VR-1 for 17.3075MHz
or 17.3065MHz in USB mode.
- Adjust VR-2 for 17.3025MHz
or 17.3035MHz in LSB mode.
IF (10.695MHz)
- Set radio to AM mode. Apply
a 10.695MHz (AM modulated, 60%) signal through a 10-to-1 probe to the
emitter of Q2. Output of the signal generator should be just enough to
produce output at the speaker
- Adjust T-4, T-5, T-8, T-9
and T-10 for maximum AF output (speaker).
- Set the radio to CW mode,
signal generator at 0% modulation. Adjust T-6 and T-7 for maximum audio
output.
NOTE: Excessive output from the signal generator will activate the AGC and
result in false alignment.
Noise Blanker Circuit
- Connect a noise generator in
series with signal generator output. Connect O’scope to TP-4. Set signal
generator for 20 uV output. Adjust T-400 and T-401 for maximum peaks.
High Frequency
- Set the radio to 28.0000MHz
in AM mode.
- Apply a 28.0000MHz (Am
modulated at 60%) signal to the antenna terminal.
- Adjust T-1, T-2 and T-3 for
maximum AF output.
IF Noise
- Set the radio to LSB mode
and disconnect any input to the antenna terminal.
- Adjust R-39 (IF Gain) for
an AF output of 0.2 VRMS with the AF GAIN at maximum.
S-Meter
- Set the radio to 28.0000MHz
in FM Mode.
- Apply a 28.0000MHz signal to
the antenna terminal at 50uV.
- Adjust VR-7 so that four LED
bars are lit.
- Set the radio to USB Mode.
- Adjust VR-8 so that four LED
bars are lit.
FM Quadrature
- Set the radio to FM Mode.
Inject a 28.0000MHz FM signal at 5KHz deviation, 1KHz tone signal to the
antenna jack.
- Connect O'Scope to the
junction of R-123 and C-96.
- Adjust T-18 for maximum sine
wave with minimum distortion.
Transmit
SSB Mode
- Set the radio to 28.0000MHz
in USB Mode.
- Set the Mic Gain to minimum
and adjust VR-9 and VR-10 (Balanced Modulator) for minimum RF output.
NOTE: These controls must be balanced for even
output on LSB and USB. If adjustment is necessary, you must repeat step 7 of
the PLL-VCO alignment.
- Set the Mic Gain to minimum
and in LSB transmit mode. Connect DVM to ferrite bead side of R-198 and
ground. Adjust VR-14 for 0.68VDC.
- Move the DVM to the ferrite
bead side of R-194 and adjust VR-13 for 0.68VDC (final amplifier bias).
- For the AR3500 100 Watt bias
adjustment, remove the red power lead of the amplifier at the power jack.
Insert amp meter in series with the removed red wire and the positive pin
of the power jack. Adjust VR-101 for 150 milliamperes.
- Set the Mic Gain to maximum
and apply a 1,000Hz to the microphone. Adjust VR-15 for maximum RF output.
- Adjust T-22, T-21, T-20, and
T-19 for maximum RF output power.
- Balance RF output between
the lowest and highest frequency with L-6, L-7, and L-9.
- Re-adjust VR-15 (ALC) so
that the output power just starts to drop (about 2 Watts).
AM Mode
- Set the radio to 28.0000MHz
in the AM mode, Mic Gain to maximum.
- Adjust VR-16 (AM PWR) for 7
Watts output (30 Watts <or more> for AR3500).
- Apply a 1,000Hz tome to the
microphone. Adjust VR-17 (AMC) for 95% modulation.
FM Mode
- Set the radio to 28.0000MHz
in the FM Mode, Mic Gain to maximum.
- Apply a 1,000Hz tone to the
microphone and adjust VR-4 (FM DEV) for a maximum deviation of 5KHz.
RF Output Meter
- Set the radio to 28.0000MHz
in the FM Mode.
- Adjust RV-11 so that two
LED bars are lit with 7-Watts output power (AR3300). Decrease VR-16 to 7
Watts for AR3500. When RF meter is adjusted, Re-adjust RV-16 using the
steps under AM Mode above.