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Safe Operation of Clansman PRC344 (Tx disable mod)


G7MRV

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The Clansman PRC344 is a 2W UHF AM transceiver intended for FAC use. As such, there is nowhere within its range that it is legal to transmit. In fact, of all the Clansman equipment, this is the one where transmitting can at best get you into legal trouble, at worst endanger aircraft and lives.

But you say, I would NEVER transmit! Well, maybe not deliberately, but who hasnt turned a switch the wrong way accidentally? How easy is it to catch the pressel on a handset? And what about inquisitive fingers from the public at a display when your backs turned? There are no 'power on' lights on this to show your not just playing with a switched off set!

It is very easy to ensure you stay legal with the 344, regardless of whether you have a handset, headset, remote radio attached, or select BEACON mode, you simply need to disable the transmitter.
 

So, how do we do this? Surely it needs a technician? Well, no. The PRC344 is a modular system, and provided you take care, this is a very easy fix. We just need to remove a pair of numbered plug-in modules!

First, remove the battery! On the larger side cover (not the switch side), remove the 14 hex bolts and lift off the cover. On the plate with the switches underneath, you will see a U shaped section of thick stainless steel wire, clipped over a screw in the middle and with its ends going into two holes. Lift this up with a screwdriver near the screw, and it will come off - this is the module removal tool!

Now, locate module 3 (all modules are numbered on their tops), you will see it has holes in the corners. Insert the ends of the tool in these holes, and gently pull. The module will come out. Check it says Amplifier Direct Current on the side (to make sure you havent pulled out the wrong one!), and put it away somewhere safe (so you can put it back if you sell the set).

Then, locate module 8, and extract that. Check its says Regulator Audio Level on it to ensure its the right one. Put that in the same safe place as module 3.

Replace the extractor tool, making sure it is securely clipped down (if it comes loose inside it will cause big problems!), and refit the lid, making sure to put it back on the way around you removed it, as there are foam pads attached that hold the modules down. This should be easy, as there is a long dessicant canister attached in one corner, and a diagonal cut in another, that matches the diagonal on the body. Tighten up the bolts.

Your set will now work just as before, only it will not transmit.

Module 3 is the Direct Current Amplifier. It is responsible for providing the control voltages that activate the transmit amplifiers, and switch the antenna relay. It also provides the sidetone on transmit (audio feedback to the headgear). Inside it, there is a logic control gate, which will only activate if it gets a Phase Lock signal from the synthesiser, indicating that the frequency is stable. By removing module 3, there is no logic control, so no control signals to the rest of the transmitter.

With only module 3 removed, switching to beacon mode will still activate the Tx RF Oscillator and Driver circuits (these are hard wired into the set). As a result, there will be a slight leakage of RF energy. This is very low level, but may be detectable ( I can detect the emission from my set on a commercial scanner many tens of meters away!) so in order to be absolutely safe, removing module 8 disables the beacon oscillator and Tx microphone audio stages.

 

And after this, you still have an original condition radio, that will still receive properly. It will still look just as good at a display or show, but now you dont have to worry about accidentally calling in an air strike!

Martin G7MRV

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  • 1 year later...

Hello

As I understand the rules, persons and businesses can obtain licences from Ofcom to operate or repair radio transmitting equipment under Testing and Development (Radiating) conditions. Also testing under Suppressed Radiation conditions is exempt from licensing between certain frequency limits and levels of radiation. 

The PRC344 operates between 245-399.99MHz which lies outside the nearest band where suppressed radiation is permitted (244-400MHz).and where the limit for radiated power is 30dB uV/m measured at 30 metres.

This would indicate that testing this equipment even on receive without a valid licence may not be permitted.

The frequencies and limits allowed for testing radio equipment under suppressed radiation conditions is defined in The Wireless Telegraphy (Testing and Development Under Suppressed Radiation Conditions) (Exemption) Regulations  1989. Statutory Instrument No.1842 

.696348031_CaptureTDLimits.PNG.cdc4e5366913eb964bffca689162b9d4.PNG

The PRC344 operates on an Military Aeronautical band on which even the reception of signals, without proper authority, could be considered an illegal act. Potential owners of this equipment should be aware of the possible implications for anything other than non-working display.

I hope this helps clarify the situation. 

Barry G8DXU

 

 

 

 

 

Capture T&D Limits.PNG

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With clansman I would  remove one off the wires from the battery stud terminal , so there is no risk of powering up accidentally. For working sets like 320 321 351 and other, I have receive only hand and head sets on them with a TX hand set in a safe place for demo working Keep safe Graham G1DNZ 

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