Hardware Hacking

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, youÕll 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 OÕscope to TP-2. Adjust T-12 for maximum in AM mode.
* Connect OÕscope 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 Ocilloscope 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 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.

This entry was posted on Thursday, March 24th, 2005 at 1:04 pm and is filed under CB Radio Mods, Citizen Band Radio, Ranger. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.