Wednesday, 30 March 2016

'Test Bed' PRC-320

Well, after some previous disappointments, I finally managed to get a second Clansman PRC-320 radio, for use as the development 'Test Bed' for the external VFO controller. Ended up paying a bit more than I really wanted though, but heyho,

In many ways im quite pleased with this one, all its front fins are good! and it has its original tuning chart. The battery clamps are a bit loose, as is the antenna socket, but other than that its only defects are the rear fin protecting the coax link broken off and a fair bit of scuffed paint...

... or so I thought!

Sold as 'tested and working' a few minutes of testing soon showed that this may be the case NOW, but it wont be for much longer, unless I step in very quickly with some repair work. It soon became apparent that the synthesiser was not locking correctly, and after about ten minutes would lose lock completely! Of course, I know what this unready tone means - the high voltage capacitors!

These capacitors provide the 110v line for the VFOs, and are metal cased tantalum electrolytics, well known for their poor end of life performance. Two of them are in the Synthesiser module 9, which is the oblong can on the right of the picture below (the one with all the circles on it), and two are in the PSU module 5, the big grey can front center.

Module 5 was found also to have a dent in the can lid! Luckily this just popped out with a bit of applied pressure. I have modern 160v radial electrolytics on order to replace these tantalum units, which should be with me by the end of the week.

At the top left of the radio and along the top of the cans, can be seen the pink wiring of the frequency decade switches. I will need to electrically disconnect these from all the synthesiser input pins, and the 3v supply to the switches, to prevent data contention. This is not going to be an easy task! And somewhere I also have to fit the microcontroller! The only space available is pretty much down the center line, between the IF filters and module 5, and the tuner turret!

So, Im now a bit miffed as to how to provide feedback to the seller.  On the one hand, although working, as described, the unit has a clear fault condition starting to cause an issue, something that the seller should have noticed if the unit was indeed tested shortly prior to sale, which by the last years date on the tested sticker seems unlikely. But then, on the other hand, its a fault I can nip in the bud now, and the rest of the radio, and indeed the case, is better than I expected. I dont think it really deserves positive feedback, but then I dont think it really deserves neutral either!

Another aspect of the controller development for this radio will be obtaining serial comms to the external unit without compromising the seal integrity of the radio. For this, it is proposed to sacrifice one of the two audio ports. To see just what a squeeze that will be, take a look below

Thats the audio accessory board, in its nice tight little space in the rear panel beside the PA. Theres an aluminium panel goes over the top of this as well.

The final picture is just a view of the underside of the radio. There really is very little space inside these for any additional circuitry, so fitting in a microcontroller capable of reliably taking over the synthesiser control, is almost certain to require some clever SMD work!

Thursday, 17 March 2016

Back on 2m FM

A few days ago, I stepped out into the sun in the garden, with the intention of filling the bird feeders and clearing away the ivy from my main HF feeder.

... a few minutes later I was up the ladder installing a 2m monopole!

I hadnt intended doing it, but the nice weather and it just suddenly felt right to do some antenna works. To get the monopole up on the small mast, I first had to lower the 6m Yagi by a few inches, so took the opportunity to adjust the azimuth a bit as well. With this done and the monopole installed, I went off to decide what feeder to use.

Ideally it would have been cut to length, but I really couldnt be bothered with fitting N-types that day, so I used the pre-cut length of TFC-T10 that I used with this antenna on special events. This is far, far too long, so most of it is coiled up just outside the shack. I will get around to measuring and cutting it at some point, but being 75 ohm it needs a bit more care to get an exact electrical half-wave multiple, plus its aluminium braid and copper plated steel core, not the easiest to work with!

But, it seems to be working ok.

Wednesday, 9 March 2016

Radio Magazine Archives

Everything looks good in hindsight, so they say. Back in the '60s, people said 'cor, wern't the 40s great!' - oh yes, doodlebugs, death, ricketts, wonderful! And now, people pine for the 'classic tunes' of yesteryear - the Ibiza tat 'duvva duvva' music of the '90s!

But one thing from the past that really was good - were the Practical Wireless magazines of the 1980s! Real articles, real projects.

Which brings me to the link below -

A collection of whole scans of many radio and electronics magazines, back over the years. A massive collection, including PW, Wireless World (back as far as 1913!!!) and many others. Hours of nostalgic reading, and were everyone looks smart and wears a tie (and in an amazing number of the earlier magazines - smokes a pipe!),

So have a read. Browse the many interesting projects that you can still build. Yearn back for the old days of Bi-Pak and Home Radio, when Maplin still sold actual components at sensible prices with staff who knew what they were selling, when a Pye Westminster would set you back 50p, and when every town had a radio shop and a components shop, and the only place to buy silly cheap toy electronic tat was Tandys, when Radio Rentals actually rented out radios, and handheld radios needed both hands to hold!

Saturday, 5 March 2016

Manpack fun with a big antenna

After repairing the Clansman antenna drop coax yesterday, and finding time today to finally connect my 2-way coax switch in line between the Alinco DX-70TH and the MFJ manual ATU, I decided to have a little play with the PRC-320 on a proper, big antenna for the first time,

The repaired coax connecting the -320 to the spare port on the antenna switch, meant that I could trawl the bands with the Alinco, a damn sight easier on the fingers! And then switch across to the Clansman once i'd decided where to operate.

The Clansman certainly holds its own in terms of receive! Ive not had a QSO on this setup yet, as ive just been tuning about, listening and seeing whats happening, plus, theres a big HF contest on at present, so im really not bothered about jumping into that melee!

 Ive spent quite a bit of time today though helping Sam create his first 'sketch' on Arduino. We decided to start at the simple flashing LED, but then moved on steadily until we had recreated a set of Level Crossing lights! This caused us a bit of trouble, as we couldnt at first work out how to code for a transition from the steady amber to the alternating red LEDs! But after a bit of a think and some trial and error, I worked it out, and from there we went on to include a push button to simulate a train!

I'd intended today wiring my Clansman morse key to the plug from the second handset, but ive found that I cannot remember how to disassemble these plugs! After a lot of thinking back to my early days with ntl ive managed to open the plug up, but still cannot remember how to either undo the cable clamp, or remove the pins!

I could just use the whole cable I suppose...

Friday, 4 March 2016

Making Good

After a small bit of discussion with my seller, an amicable arrangement was reached with regard to the Clansman coaxial cable found to be faulty on receipt. Without going into detail, lets say that an agreement was reached whereby neither of us are significantly out of pocket.
As such, it meant that I could no crack on with effecting repair of the cable. Now, I have to say it wasnt quite as straightforward as expected, as the connectors internal layout, insulator spacing etc, was a little unfamiliar. But, a repair had been made

Now, with the analyser on one end, and the test load on the other, the VSWR is 1.1:1 or better across the MF, HF and VHF spectrum from 2 - 175MHz. As it should be!

Ive also, since the iron was on, got a bit further with the balanced charging cable for the Clansman LiPo battery. I need now to make note of the colour code used, and sleeve the cable, before soldering on the D type connector for the battery.

I also received another Racal Clansman handset this week, in generally much better condition than the one I have, but with a small problem - the PTT sticking! After a fair bit of examination, I concluded that the pressel bar is probably slightly bent, not an easy thing to determine exactly. So, I swapped it with the one from my other handset! So now I have a good working handset with a webbing hook on it, and the older handset that now 'may' have a sticky PTT, something to fix later if need be.

Im still waiting on a few of the parts to complete the Theremin, so apart from adding some more Velcro to the tape measure antennas to make them stow away a bit easier, ive not done a great deal more radio or electronics wise.