Amateur Radio with a Clansman PRC351 / PRC352

Amateur Radio with a Clansman PRC351 / PRC352

This particular radio consists of a transceiver, a 24 volt battery, an antenna tuning unit, a 20 watt amplifier, a telephone style handset and a combat whip antenna.

Why does this Clansman have the number 351 and 352? Well it all depends on whether the amplifier is attached. The 20 watt amplifier on the right of the picture above, the one with the heat dissipation fins, is what turns the PRC351 into a PRC352. Note that when connecting the amplifier the whip antenna can no longer be used, it requires a ground spike, and a resonant antenna such as a dipole or the Land Rover FFR Antenna Tuning Module and Whip. Also remember that the output with amplifier is 20 watts so it exceeds the maximum permitted power limit of a UK Foundation Licence.

The transceiver unit of the PRC351 provides an RF output of 4 watts on transmit, with a frequency range of 30 MHz up to 75.975 MHz NFM. So for Amateur Radio I plan to use the PRC351 on the 4m and 6m bands NFM segments of the UK band plan.

But before I start I need to assemble the separate components that make up the radio and make sure it works. Having completed the PRC351 assembly I planned to confirm the operating frequencies of the PRC351 on 4m and 6m with a SDR receiver. I tuned the SDR to 52.000mhz (6m) and tuned the PRC351 using the frequency control knobs. I then set the “ON” knob to the “*” position to remove any squelch, and selected the “L” setting for local. The next step is to match the antenna with the radio’s ATU, the ATU is designed to provide tuning to the whip when fitted. On completion I pressed the PTT button on the telephone handset. Unfortunately I noticed that there was a noticeable buzzing sound and no transmitted audio.

On close inspection of the telephone handset the probable cause was clear to see, the microphone mouth piece slots were full of mud. I stripped the handset and cleaned away any debris and gave the speaker and microphone a check over using the multi meter. Now that the handset was reassembled, another test, and I had audio, however there was still an annoying buzz. I did a bit of research on the Internet and it turns out that the PRC351 radio has tone squelch of 150khz. I haven’t found any information so far on how to disable the feature, so I plan to use the PRC351 with the squelch OFF as the background noise isn’t too offensive through the handset, and inhibit the tone as much as possible during transmit.

 To do this the unit needs to be opened which is simply undoing 8 Allen bolts, being very careful not to damage the internal brown ribbon cable while removing the end panel and unplugging it. Once apart disabling the 150khz tone is quite simple, locate the module “13” and gently turn pot “R9” fully ant-clockwise. Now that the PRC351 is re-assembled I conducted another transmission test, The SDR demonstrated it was on frequency and with clear modulation, and no annoying 150khz tone.

    

If you’re like me now’s the opportunity to tidy up the radio with a quick clean and paint job, gently removing the labels to be re-applied later.

Power to the PRC351 is from a Nickel Cadmium rechargeable battery pack which includes a “state of charge” indicator. The label on the battery provides some relevant battery information and a date of manufacture of 2005, so I’ll probably replace the cells in the pack with new lithium equivalents and include a charging circuit.

  

Hope to hear you on the 4m or 6m bands using my refurbished PRC351…

Ray M6OZA

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