Monday 21 October 2013

Disabling the 150Hz tone from the Clansman PCR-351/2 by Andrew EI3FEB.


The Clansman PRC-351 is a military VHF Man pack set that was manufactured for the British Army in the late 1970s. It is fully synthesized and covers 30 - 76MHz in 25KHz steps, making it suitable for the Amateur 6 and 4 meter bands. Power output is 4 watts of FM, however an optional 20W clip on module is also available.

With the British Army's move to the newer Bowman series of radios, many older Clansman Series are becoming available on the surplus market at reasonable prices. The basic unit is available for less than 50 Euro although a further expenditure of 20 Euro for a 24v/1AH battery and 15 Euro on a Clansman headset would be required.As this radio has a BNC socket in addition to its 1.2m whip antenna, it was possible to connect it to an external 4m half wave antenna enabling contacts with Michael EI3GYB and Arthur EI7GMB covering distances of 40 Km and 15 Km respectively. Due to the set's 25KHz channel spacing the 4m it does not cover the calling frequency of 70.2625. Contacts were scheduled via another 4 meter set before QSYing to a channel available on the PRC-351.

There was a notable presence of a 150Hz  tone superimposed on the transmitted audio. This is due to the military tone squelch used by US and UK military radios. A Google search led to the PRC-351 Yahoo Group which had instructions on how to disable the tone squelch.

Disconnect the antenna, accessories, and battery. 
The battery is held by the spring clips seen on the bottom of the set.

Open the 4 Allen Bolts on the side of the set containing the audio sockets.

Carefully remove the end panel of the radio.
It is connected to the main radio body by a fragile ribbon.

Remove the connector joining the end panel to the radio.

Remove the 4 Allen Bolts on the control panel and slide the radio out of its housing.
   
     Locate R9 on Module 13 - this is the preset resistor that adjusts the level of the 150Hz tone.

Rotate R9 fully anti-clockwise

Re-assemble the set taking care not to tear the sachets containing desiccant which prevents condensation inside the set.



Subsequent QSOs confirmed that this modification had disabled the 150Hz tone. On air tests revealed that this set had a sensitive receiver and the FM audio quality was comparable if not equal to other PMR sets tested.

A back pack frame is available to carry all of the components of the set whilst it is fully operational. It is possible to acquire a canvass ruck-sack which performs a similar function. The canvass ruck-sack along with a trailing wire antenna was designed to disguise the radio thereby making the operator less of a target in the field.



Special thanks to Andrew EI3FEB for his work on this transceiver.

Thursday 17 October 2013

Why have one when you can have two??

A second Clansman PCR 351 arrived this morning, this time the radio and the SURF unit, no amplifier.
This one is for my son Stephen MI6CQS who wants to do some /P with it on 4m and 6m. My clansman is the one on the left with 20 watt amplifier and antenna mod, Stephen's is on the right.
Both are in the same back pack and have batteries attached....


Sunday 13 October 2013

Clansman, Antenna Improvement.

My Clansman has been working very well since I replaced the lead for the handset and as I mentioned before I am very impressed with the research and development that has gone into the design of the radio.
The Clansman that I have has the 20 watt amplifier added to it which is very handy when attached to an outside antenna. I get 4 hours or so running the radio on the 20 watts, this got me thinking of the only downside of the Clansman for me, the fact that the antennas are not tuned for 4m or 6m and need to run through the SURF (Selector Unit Radio Frequency) on the top of the radio, also the SURF will only handle the 4 watts from the radio so when I go portable with the radio I will not be able to use the 20 watt amplifier without connecting it to an external antenna.
I would like to be walking with the Clansman on my back and able to run the 20 watts at the same time. I decided to make an antenna base which I could leave on the Clansman and would connect directly to the amplifier which has BNC input and outputs.
I had a look at the radio for a place to attach the new socket and decided that the best thing to do would be to have a metal plate “sandwiched” between the top of the radio and the bottom of the SURF, the reason for this is that I did not want to modify the radio itself and this would be easier to fit. I also wanted to use my existing 4m stainless whip antenna off my car and wanted the antenna to be behind the radio sloping away instead of out to the side as the existing antenna is, I found this to be annoying as it would catch in branches etc. while walking, if it is to the back and sloped behind it would not get caught so easy……
Firstly I removed the SURF from the top of the radio and placed it on a piece of cardboard to make a template, then after sourcing a piece of stainless steel I set about shaping and drilling the holes, 3 for the screws and one for the antenna connector, making sure that the antenna base would not hinder the opening of the SURF window. When the holes were done then I put a 5 degree bend on the plate so that the antenna would lean away from the radio.



I then attached the plate to the radio simply by sitting it on top of the radio itself and by placing the SURF on top of that again, the three existing screws on the tuner fitted through the holes on my stainless steel plate and when tightened down holds the plate firmly in place, I am very glad that I put the bend on to the plate, if I left it flat it would have prevented the flap for the window to be opened….
A SURF (Selector Unit Radio Frequency) is used to prevent interference to operation of the radio sets. The SURF is an electrical filter, designed to reject unwanted interference from other radios when operating in close proximity to each other. The SURF is tuned using a manual control on the front of the unit, so that only the frequency in use, and those close to it, are accepted by the set. A Range of SURFs were provided for attachment to the VHF PRC350, PRC351/2 (SURF 4 Watt)



Setting up the rest is straight forward, I attached the antenna base, I looked around for an SO239 base, did not have one but I did find an N-Type socket with a short length of coax with a BNC plug on it. The antenna socket was attached to the plate; the short length of coax was a nice length and reached the OUTPUT of the amplifier easily. Then another length of coax was needed to reach from radio OUTPUT to amplifier INPUT, BNC’s both end, this was fed around the back of the radio between the radio and the backpack. Once this was done I connected up the antenna to the N-Type, the antenna itself terminates in a PL259 so an adaptor is used on the antenna/base.



I attached the antenna and checked the SWR, it reads around a 2.0-1 but shows a good RF output of over 20 watts. I played around with the antenna connected to an Antenna Analyzer and found that by adding more length to the whip I achieved a flat SWR, so my next purchase will be a longer whip for the radio….





I hope to do some on air testing soon while out portable and it will be interesting to see how the 4m whip will work on the radio, I also have a mobile Tri-Band (6m, 2m and 70cms) antenna and this tunes perfectly on 6m, so I will be now able to use pre-tuned antennas on the Clansman which will mean that on 4 watts the radio should have a better range and should be even better with 20 watts!!!!

For more info on the Clansman click on the following link:  Clansman Radio.

Saturday 12 October 2013

Replacing a faulty Clansman handset lead.

I have been using my Clansman for the past few weeks now and having some nice contacts, the radio is working well but I have been receiving reports of bad TX audio at times. There is intermittent “rustling” like a paper bag blowing in the background.
I had a look at the PTT of the handset and sure enough this had dust on it but was not the problem.
After a long and exhaustive search (about 5 minutes) I discovered that when I moved around the lead going from the handset to the radio the noise appeared and if I kept that lead perfectly still then the noise was gone and my audio was perfect.
So the noise was either being caused by fatigue in the curly lead or the pins on the plug going into the Clansman were worn.



I had a look on eBay and found a guy selling 3 brand new 1.5m long, never used straight handset leads with plugs attached for €15.00 including postage to Ireland.
So I done a “Buy It Now” and had them in a week.
When they arrived they were still in their sealed packs, as the seller said, brand new (old stock) never opened..
I opened one of the packs and seen that they were tagged for use with the handsets.




I also noticed that 5 of the wires have a round piece on the end and a green wire had a small spade connector, there was also a string which is used to tie off inside the handset so that the wires are not pulled from the connectors. Also on the lead is a piece to screw into the bottom of the handset which keeps the cable tightly in place.
I got my soldering iron ready, warming up on the desk, I then set about opening the back of the handset, there are eight flat head screws holding this down and on the bottom there are four screws, also the retaining piece that holds the cable tight needs to be unscrewed.
As the soldering iron was still heating up I did a sketch of the inside of the handset so that I would know where all the different wires would go, the coloured wires on new lead  matched what was already in the handset, this was going to be easy. As I was taking note of the colours I noticed that there was no solder on the pins that the wires were attached to, so with a small flat head screwdriver I tested one of the wires and sure enough it lifted off the pin, so I promptly lifted the other wires and unplugged the small spade connector from the microphone, the string was attached under a small retaining screw just above the wires.
No soldering needed, happy days!!!
The old wires and string were fed out through the bottom of the handset, I found this to be easier if there were taken out one by one due to the connecting rings on the top of each wire.



I then inserted the new lead through the bottom of the handset, in reverse order one wire at a time and pushed down the wires over the pins, these are a tight fit so the flat head screwdriver was called into service again, I then tied up the string and replaced the back and bottom of the handset, after which the retaining tensioner for the lead was tightened up.



After all this was done, which only took about ten minutes, I tested the handset with the new lead, monitoring myself on another radio, the audio was perfect, even while swinging the new 1.5m lead between the handset and the radio like a skipping rope.


I have to say that while doing this I have to admire the research and development people who put this radio together, there has been a lot of thought put into the making of this radio, after all if the handset lead gets damaged while the radio is being used on active duty there would not always be a means to repair it so easy, the idea of just opening the handset and “popping off” the old lead and being able to replace the whole lead in a few minutes  is great, wish it would be as easy for our ham Radio equipment……