Don't Try This At Home

No, seriously, I do mean it! Alright, so this is a project that I hope, sometime in the future, other radio hams may copy, and add modern amateur like VFO control to their vintage Clansman PRC-320 HF manpacks...

... but, until I can demonstrate a working system, please dont try to copy what ive done so far!

The reason I say this, is that part of the mod is to add nineteen (yes -19!) additional wires to the module 9 synthesizer pins. Even following the recommended method of accessing these pins as detailed in the EMERs, this is a seriously difficult task! Just simply dont attempt it, unless, like me, you can do it to a spare radio, and that you are prepared to knacker that radio up!

There are nine connections to be made to the lower bank of pins. Three of these are around the lower right corner, where the wiring loom is densest, and access is nearly impossible. Expect to scorch or melt insulation! There is also a clear plastic insulating film to deal with, and also ensuring that the pins dont bend and short out on the casing!

Ive used two lengths of ribbon cable to do this. In the photo above, ive got that awkward corner done, and about half the remaining lower bank. It is essential to match up the pin numbers with the diagrams and the cable loom wire numbers! Ive loosened the bolts on the 1kHz module to the left, just enough to be able to move it slightly.

In the 2nd photo, ribbon cable A is completed. Thats the hard one! I found that wherever possible, tinning the pin was very helpful. As was the use of surgical locking forceps to hold the wires in position, and an eldest son to hold a high power torch! The big problem is light - without help I found I could either see what I was doing, or attempt to solder, not both!

And in photo 3 half of ribbon cable B is now connected, this has ten connections to the upper bank of pins. On this one im cutting the individual wires to length to keep the body of the ribbon as close to the module as possible. Its also essential to make a written record of that pins connect to which wires on the ribbons!

Five wires remain to connect. With luck, ive managed to solder them all to the correct pins, and made a reliable connection to each. Time will tell!

'Final' RT-320 mod started!

When I say 'final', I of course mean the final mod to be made directly to the radio! This will be the addition of the ribbon cable(s) required to connect the microcontroller to the synthesizer. Ive decided to go ahead with this now, even though the radio is not operating quite right,as it will give me a set of 'break-out' connections to the synthesizer, which will allow me to safely and conveniently meter out the data coming from the decade switches. Hopefully this will allow me to identify which switch lines are not functioning quite right, and work out if its a voltage drop issue or a physical contact problem.

This will make the list of mods done to this rig as follows -

1. All decade switches output pins have BAT85 schottky diodes to prevent data contention
2. SSB and CW(N) modes have 2kHz offset removed
3. CW(W) mode changed to provide select line for LSB
4. S-meter added
5. One audio accessory port replaced with external connection for data control
6. 2-3.1MHz range widened to 1.8MHz to cover 160m band
7. Synthesizer programming lines available for external control

A pair of ribbon cables have been found out for this task, which should be easier to route inside the radio casing than one big flat one. They have been marked with a red band for the first series of connections, and two red bands for the second series. The ribbon carrying the external data connections is marked with a pair of red crosses!

Whoops! Slight Synthesizer input problem!

Well, I 'think' ive found one of the problems!

As expected, 5.450MHz is received 'reasonably well', with a -75dBm 70% AM signal from my Marconi 2955. The set is clearly 'deaf' though, as the signal is pretty much lost by -90dBm!

However, changing to test at 5.505MHz showed an interesting oddity! At first, as expected, it didnt receive. But then, I accidentally jogged the 10kHz switch between settings - and it started to receive!

Take a look ...

My suspicion is that the extra voltage drop caused by the anti data-contention diodes, is putting some of the synthesizer input lines on or below the threshold for the logic to detect it cleanly as either a 1 or 0. Now, this was always a risk of this modification and one that I had already addressed in the design phase. Solving this should just be a case of measuring the actual 3v supply line to see its true value, then adjusting module 5 to ensure its actually within spec. Then, if the issue still occurs, to take the supply of this line away from module 5s PSU and replace it with a custom 3v line derived from one of the higher voltage supplies, and adjusted to be just that bit higher, in order to compensate for the diodes.

Of course, its worth my checking that the pins on the switches prior to the diodes are giving the right voltages - just in case its actually a problem with mucky switch contacts!

Discovering this has also enabled me to discover that the AGC link does in fact come up to something a bit more like an AGC line voltage, and moving the S-meter connection to that point does in fact provide a meter indication! Its not right though, as the AGC line seems to ramp up very fast then dwindle away even with a steady input level, and anything above -60dBm and the AGC volts actually start going down again!

Testbed RT-320 Faulty - How to approach the faultfinding?

ok so its quite clear theres a fault(s) on this radio! The question now is, how to find it! (or them!)

It seems quite clear that since the radio is not responding to received signals correctly in frequency terms, and that after probing the AGC lines its clear that the AGC is not reaching anything like its correct levels, that going immediately for the manuals recommended alignment process, which starts with the AGC, is likely to be futile.

I think first I should look into the odd frequency problem. I know that I can receive at 5.450MHz but not seemingly at 5.505MHz, so I will start here and see if I can work out what is actually happening. Its possible that the data-contention diodes, even being low forward voltage Schottkys, might be causing issues with low volts on the synthesizer pins, in which case I will need to add the extra 3v regulator to allow me to bump up the 3v line to compensate.

However, with the odd frequency issue I suspect its going to be something else. As it effects Tx as well as Rx, I think I can rule out the RF side between antenna and the VCO controlled frequency conversion.

This is a very complex radio, but when alls said and done, its still just a superhet!

S-Meter mod...and faults!

Almost all the mods are done now on the Testbed RT-320. The final 'official' mod to do was the S-meter. To do this one, Assy 6 had to come up again, to access the meter switch

The pink wire going off the side of the radio in the lower right of the above picture is this connection. Next up was to make up the diode chain that would take the AGC voltage and create a drive for the meter

Ive hot melt glued this down to the PCB, with the ends exposed, that way I can easily unsolder the wire to the switch in order to remove the PCB. In the picture below I think I have it connected to the wrong place on the PCB! Im waiting for clarification on that. At present, this mod isnt working, see below!

With all these mods completed, I put the set to the test - not good! Now, I had a suspicion that this set wasnt performing very well, so I suspect this is all part of, but it seems that the set cant receive my test set signal, and on Tx its also off frequency. A very very strong input signal from the test set it can just receive, but again off frequency, yet the synthesizer is locked and functioning! Also odd, there is no AGC voltage (so the above S-meter mod doesnt work!). But perhaps the strangest issue - If I put it to antenna, I can receive RAF Volmet on 5.450MHz ok but distorted, yet if I tune to Shannon Volmet at 5.505MHz, it doesnt hear anything! This despite Shannon being much stronger than the RAF! Also, I can tune in an AM broadcast using the SSB mode, again ok but distorted, yet hardly hear anything of it in AM mode!?

So, something is definately amiss in this radio. And I suspect its going to be a pig to solve. I will complete the mods necessary for the Remote Control Project before trying to fix the fault(s), as the one remaining mod is to add the ribbon cable to the synthesizer inputs, and that will be useful for fault finding!

On another note, I have a PRC-350 on order from LRseries near York, likely to be a project job in itself, plus an EKGSA kit to allow me to use the GSA antenna on one of my 5.4m masts. Ive also taken a punt on a pair of PRC-349s - no use for amateur bands but they are full CES kits so might prove fun, but at any rate will complete the collection.

RT-320 RF oscillator alignment

Phew! Never have I worked on a radio before that way so physically tiring to do!

I realised that this Testbed radio was a bit out of alignment, so this morning before any further mod work, ive at least brought all the RF oscillator sections in the module 3 turret tuner into correct alignment.

I decided probing the synthesizer VCO pin was a bit risky, so followed the service manual and used TPq in module 3a. This required removing the ATU module 4!

The main reason I took the above photo is as a record of where that pink wire goes! Ive unsoldered it to allow me to put the ATU module somewhere safe.

Inside the tuner turret, there are various trimmer capacitors and variable inductors to adjust. The caps proved to be a little sticky but moved ok using a proper trimming tool.

The inductors though are awkward. These have a very odd little adjuster, which required the fabrication of a special tool. For this I adapted an old brass tipped trimmer by soldering on a couple of PCB header pins, and adjusting the spacing between them

All the RF oscillators are now aligned within spec. The only one that is not within the manual specifications is range 1: 2.0 - 3.1MHz, as I have adjusted this to give full coverage of the 160m band, so this is now 1.8 - 3.1MHz! I couldnt get the VCO volts exactly as the mod suggested, going to about 95v instead of 90v at the top of the range, but the set locks at both extremes.

I'll deal with receiver alignment later. For now, I think the final mod, the S-meter, is in order. With that done the only thing left will be to again remove the mother board, physically remove the synthesizer, and add a ribbon cable to its pins to allow connection of the microcontroller in due course.

Can anyone spare a couple of Clansman 7-pin audio plugs?

Ok so I know this is a long shot, but if any other Clansman enthusiasts actually do read my blog, I wonder if anyone can spare one or two of the 7-pin audio plugs? Ideally with a bit of cable, but doesnt have to be the full lead.

Getting hold of one or two (which I cant afford to buy at the moment!) would allow me to make up a break-out box for the newly modified data control port on my Testbed RT-320, which in turn will make developing the Remote VFO controller system much easier!

If anyone can offer any help, drop me a comment with a contact email etc. I moderate comments so it wont be published!

CW(W) to LSB mod proven

I had my doubts about whether this mod had worked, as my newly added white 'LSB Select' wire, which at present has no where to go as ive no LSB module, was reading 0v all the time, and i'd sort of expected to see 3 or 6v on it when in any other mode but CW(W),

So after proving the 2kHz offset mod was working in both USB (SSB) and CW(N), I revisited the mod documentation from Martin G8JNJ, and the circuit diagrams...

...ah! When selecting CW(W), yes the line is pulled down to ground, as the switch grounds it. But - in any other mode... its floating! and since it doesnt connect to anything other than an unselected switch contact, theres clearly no voltage on it from anywhere! I'd for some reason thought that since the mod write up said that the line is pulled low, that it implied that in other modes it was pulled high!

It just hadnt occurred to me that my nice new wire didnt actually connect to anything when not in CW(W) mode!

A check with the multimeter with the radio off shows that it does indeed connect to ground when in CW(W) mode. So, it is in fact working as it should.

Nice to know, since these mods are pretty scary to do!

Modification Results - Good, and Bad

Having finally completed the mods (apart from the S-meter one) on the RT-320 Testbed radio, ive brought it in to the shack to test, and see how they have done.

Well, on a positive note, the diodes do not effect the operation of the synthesizer. Thats very good, as that means I dont need to provide an alternative, boosted 3v supply to the decade switches. I managed to track down which of the wires was the 3v supply from pin 19 of the synthesizer module, and reconnect that minus the diode.

On a much less positive note, it seems the 2kHz offset mod and/or the CW(W) to LSB mod have not gone quite right. It works perfectly on USB, ive got the set listening to RAF Volmet on 5.450MHz right now, with the dials set to 5.450! But I cant find a signal on the CW(N) setting to check against!

Now, if I select CW(W), which should now pull an added white wire to 0v to switch in whatever LSB module I add, I get RAF Volmet, but with a 2kHz offset!!! Now, im not sure if this is right or not?  I think that in this mode I should be getting an offset SSB signal, as the SSB filter is switched in, and the offset is still applied in this mode. When an LSB module is added, it has the job of muting the USB. But, my new white wire which is meant to go to 0v on CW(W) selection, seems to be at 0v anyway, regardless of switch setting!
I think I need to find a CW(N) signal to check that mode!

One thing I have discovered is that the radio needs a damn good re-alignment! much of 7MHz is out of lock, including the amateur band! And it has a weak unready tone, with lots of noise, which is odd.

I will see what happens if I use the white wire to apply an USB mute signal...

Update - after finally finding a steady carrier that I could resolve to a beat tone of suitable pitch, which turned out to be the 'white' carrier of Hamburg Meteo WEFAX on 7.880MHz, I have been able to switch between USB and CW(N), and find that the tone remains of the same pitch, so the offset mod has worked on CW(N).

2nd and 3rd mods complete (hopefully!) - taking a breather!

Phew! Now that proved to be a marathon soldering session!

After deciding that all the decade switch lines should have the anti-data-contention diodes, even the 10 and 1MHz switches, which will not be subject to remote control, there were twenty-six diodes to install, plus around five done early that I decided I wasnt happy with (no heatshrink) so redid.  It took several hours of careful work to install and insulate all these diodes.

The above photo was taken about half way through, and before I decided to redo those first unsleeved diodes (on the left), which are on the 10 and 1MHz switches.

Once all these were done, note was made of the two wires loom numbers (001 and 004) that connect to the 3v common line. Now, both of these have diodes fitted, but one will have to be removed, as it will be the 3v supply! At this time though I havent yet been able to work out which! Once ive found that out, which will take a bit of detective work, then the diode on that line will be removed - but the line will be diverted to the space for the microcontroller, as this line will need to be electrically cut by the controller in order to take remote control of the synthesiser.

Whilst I have the radio dismantled, all possible mods are being done, despite the risks! Modification 3 is the removal of the 2kHz offset. This is a simple wire link, but in a very awkward position on a difficult to access switch

You can just see the mod wire, the orange one, on the side of switch 1S1B. In the future, this might also be a control line taken over by the remote control system, but if it is, i'll do that at pin 2 of the synthesiser!

The next mod will be to replace the current wideband CW(W)  option with LSB. This is a much more complex set of tasks based around this switch, so will now wait until ive had something to eat, or maybe even until another day!