Monday, 18 April 2016

RT-320 Refurbishment Started

The new, testbed RT-320, whilst having its faults, also had a couple of advantages over my 'good' radio. First, it has all the front fins. Second, it has its original tuning chart. It also had some of the knobs better than my good set.

And so began the refurbishment of the good set. The key element of this is the transfer of the front panel from the testbed radio. Since this is a major undertaking, I decided a total paint job was in order at the same time.


The first task, bearing in mind both radios were open, was to remove all the knobs. This in itself was a big learning curve! Some levered off easily, a few others were quite stuck and needed careful manipulation. Then, the nuts had to be undone. The photos here show the 'good' radio, the 'testbed' set had already been dismantled at this point and the front panel removed.


With all the nuts and washers removed, the delicate tasks of removing the internals could begin. I decided it was safest to start with the ATU. The main body of which came out easily once its four screws were removed. This remained attached to the LOAD switch. 


The thin coax to the LOAD switch was then unsoldered, note being made that the center goes to the tag with the Blue wire, and the screen to the solder tag screwed to the pot core coil.


With that done, the whole ATU assembly was carefully lifted out, along with the drive coupler for the TUNE knob. Finally, the two wires to the meter were unsoldered. I have left the meter in place as I have no suitable tool to remove it with.


Placing the ATU assembly aside, the photo below shows just what I was up against next! It was clear that the safest technique now would be to remove the screws holding the turret tuner and the main board assembly, and gently ease the front panel away, to gain access to the cable clips.


No photos can show just how tricky this proved to be! Gently easing the boards and modules away, pushing the controls through, undoing and removing the screws without losing any or dropping a washer into the works!


There was also the need to collect up the seals from each control shaft. One important thing to note is that the tuning shaft is not part of the turret unit, but instead used a loose pressure fit bushing, very easy to drop and lose! But eventually I had the front panel away from the radio, attached by a few remaining wires


These remaining wires connect to the battery terminals. Unfastening the screw holding the +ve terminals to the front panel, its essential to take care not to lose the insulating washers and bushes.


The -ve terminal required the removal of its securing nut, in very tight confines, in order to disconnect the wires, which also needed bringing out form under the smoothing capacitor.


But, eventually it all came away. The 'good' front panel from the other radio, liberally covered as needed in masking tape and sprayed with primer, will eventually fit on this radio. The front panel removed above, has already been re-assembled onto the 'testbed' radio. One small mistake was made when I put that back together, in that I forgot to replace the seals! So the testbed radio is not waterproof! Refitting is pretty much the careful reverse of dismantling, with a few added continuity tests to check for any mistakes! However the testbed radio, with its new 'old' front panel, is back together on the bench and working exactly as it was before.

Another aspect of this job was to give the 'good' radio the better main housing. But, the whip adapter on this one was not as good as the 'good' radios unit, so that had to be changed over as well. This is a surprisingly complex bit of kit, and to get to the main fasteners requires the removal of a screening plate inside the housing, lots of tiny screws in a very confined space


The various part of the antenna adapter are shown below. This doesnt show the odd shaped internal plastic housing, nor the thick PTFE insulated silver plated wires connecting it all up.


But now, I have the best front panel, the best main housing, the best whip antenna adapter, and the best back panel, all ready to fit on the best radio. I have made a start on the repaint of the front panel, but have run out of brush cleaner, so cant proceed with that until I can clean my brushes.

In the meantime, ive completed the balance charger cable for the LiPo battery.


Ive also started the paintwork refurb of the PRC-352, starting with the amplifier, which needs quite a bit of 'touch up' but not a complete repaint, and the SURF, which just needs a little touching up in places. The main radio needs quite a bit of paintwork, so will get a proper dismantle and prime job

Im also looking at how to program this little beauty - a Yaesu VX-2000V VHF 25W FM mobile. 40ch PMR set but very small. It should go on 2m nicely, and make a nice compact little VHF manpack!

 But as expected other jobs are getting in the way. Ive had to repair my watch, which needed a new strap and, as I found out this morning when I was late for work, a new battery. Luckily the strap and pins was awaiting my arrival home, and the back press for refitting the back of the watch arrived at work today. So I have a nice working repaired watch now.

The VX-2000V programs using a very similar serial to TTL converter as the old Kenwoods, just with a different plug. So, ive made a plug up, and will wire that to sockets to fit the Kenwood KPG-22D programming lead, and with any luck that will work.

Tuesday, 12 April 2016

Arrrgh! Getting fed up of this bloody PSU!

After studying the circuit diagram of module 5 for a long time, I began to think that the only remaining tantalum capacitor likely to have any influence on the timing of the HV soft start was the 330uF smoothing cap on the pulse transformer.

So, I changed it. In removing it I also removed the PCB trace between the through hole and the via to the groundplane, as the damn -ve leg was bent over and soldered. I ended up having to cut it off. Not having any 330uF caps, I opted after much pondering to use a modern 470uF radial electrolytic. This required some clever leg bending to solder the -ve to the top groundplane and route the +ve to the through hole.

I then reinstalled it and tested it. Still faulty! Arrrgh!

It was then I had a brainwave. Testing the 110v rail showed the same steady creep up to full volts, and I had always assumed that the 121v test point did the same. But now, on a hunch, I put the meter probe to the 121v TP and switched on - almost instant 121v! So - whatever is causing the issue must exist after the 121v section.

Looking again at the circuit diagram, and this time ignoring everything to the left of TR6, I turned my attention to the 110v adjustable regulator, the HV electrolytic in which I have already changed out. It was then I noticed that TR7's emitter connects not only to ML2's precision zener, but also to C7 to ground, and to R9 to the 110v rail - a bloody RC timing circuit!

I have the module dismantled and opened out on the bench. Tomorrow, I will pull R9 and C7 and test them. If my hunch is right (and theres absolutely NO reason that it should be!) one or the other will be out of spec.

On a slightly different note, I decided that im happy with the red paint job on the LiPo battery for the Clansman equipment, so have taken the masking tape off. A coat of clear lacquer might be needed to smooth down the paint edges.


Curly Handset and the non-moving RT-320 fault

Yesterday I swapped the PSU module 5 from my 'good' RT-320 into the 'test bed' RT-320, ready to work on this evening. This module was completely rebuilt by David G3RYP using modern DC-DC converter modules.


This left my good radio looking a little vulnerable! So, I placed some liberal 'Do Not Touch' notices about the place to ensure my good lady left well alone!


The picture above (apologies for the poor focus!) shows the uncanned module in situ on the test bed radio chassis. The modern modular construction can be seen.

Tonight, Ive powered the radio up and tested with this module - no fault! So, the issue is definitely in the original  PSU module 5. I just have to figure out what!

In the meantime, I finally got around to sorting out my spare handset with a curly cable! I could find no info on this cable, so after metering out all the wires and making a list of which pin goes to which colour wire, against the known use of each pin, I set about working out which terminals in the handset did what.

I managed to get all but one connection made using the press on terminals. Testing as I went, first the PTT pressel, then the loudspeaker audio. The audio output of the RT-320 goes in parallel to both 'channels' so I just chose to use the one with the most conveniently sized wire! The final wire, seen above being tested with a jumper lead, was one of the mic connections. As this was a spade terminal on the mic element, the round connector on the wire was no use. This had to be cut off (retaining enough of the crimp so I could solder to it without having to deal with Litz wire!) and another length of wire added to reach the mic, where it was swiftly soldered to the terminal.

Lots of testing followed, including dealing with the PTT being stuck on if the middle case back screws were tightened up first! But its now working, and will be much more convenient than the straight cable of the other handset for some jobs.

I now have the BAT53 Schottky diodes and the 3.3V regulator modules ordered. Once these arrive I can start modifying the test bed radio ready for trials of remote control. I'll also need to work on making one of the audio ports a data port.

Monday, 11 April 2016

Clansman Swap Shop

In readiness for testing tomorrow, tonight I opened up my 'good' PRC-320, and removed the PSU module 5. This is a completely rebuilt unit with modern switch mode DC-DC converters. I have fitted this into the 'test bed' radio, and will see if the fault still occurs with this module in circuit.

Im not testing it tonight, as after removing another two dozen hex bolts im knackered!

Baofeng BF-888S On Test - You must be joking!

The programming lead for the Baofeng BF-888S radios arrived today, so I was able finally to ditch the factory fill (full of un-usable frequencies) and put the radios on some channels I could test them on. For a cable that cost under a quid and a half, it works very well. Even the Baofeng software is relatively easy to use if youve experience of programming software for commercial radios. Its certainly no more awkward than anything Kenwood, Yaesu or Motorola provide!

I set a few 'clear' channels, a few with CTCSS, some with DCS, some high some low power, and a couble with 'scrambler', and then headed out to give them the once over on the Marconi 2955B.

First test up, receive. I expected these to fall a bit flat, and just hoped that they would at least approach -118dBm for 12dB SINAD...

..what the? Fully quieting at -122? still going down? You MUST be joking!

According to the venerable old 2955, the radio I was testing, with its squelch set to level 3, broke the squelch at -127dBm, with little noise!

After realising that the audio output (speaker) connection was 2.5mm, and finding an adapter, I measured the SINAD. I then measured it again and again! -126dBm for 12dB SINAD!!! Ive never even got a Kenwood TK-359 to do that!

Transmit next. Modulation in Narrow mode is for my liking a bit low, but the CTCSS and DCS worked fine. Power output seems to be 1.8W in High, and in Low, er, 1.8W! I'll look into that, not sure why that wouldnt change as programmed, or with the side button set to select power level. Frequency accuracy, well on the test frequency it was 20Hz out! That will vary with temperature im sure, but thats pretty good!

As a final check, I moved one 12.5kHz channel away, and started to crank up the signal level, to see how it handles adjacent channel interference. I fully expected the radio to respond once I got to -75dBm or better. I kept going - and hit the limit of the 75W port on the test set! It hadnt even noticed a -15dBm signal 12.5kHz away! I went to the 1W port and cranked it right up to +5dBm - nothing! Not a peep!

Of course, I cant vouch for the level of desense this may have caused to the working channel, but it certainly didnt disturb monitoring.

Finally, me and Sam tested them on air out in the garden. Testing a clear channel, a CTCSS, a DCS, a High, a Low, and a 'scrambled' channel. All were good and clear over our 100ft path. The audio is a little tinny, and the mic could do with some foam sound baffle around it. But not too bad.

As for the 'scrambler' what tosh! What these radios have, and what it plainly says in the documentation, is Beat Shift. This is used to move the VCO a fraction if birdies from the CPU clock cause interference. It is NOT a scrambler, but when used with a radio that doesnt have the feature enabled could put the signal off frequency enough to make the audio unintelligible. I checked on the 2955's 'scope, and there was most definately NO speech inversion going on!


PRC-352 Battle Antenna Connector Swap

Well, I'd allowed myself most of my lunch break for this task, but on popping out at tea break, and after picking up a mint tea, thought i'd at least take the hex bolts out of the RT-351.


With the new but not tremendously sturdy connector removed from the RT-351, and my tea still hot enough to smelt iron, I moved around to the passenger side of the car and removed the connector from the SURF, which involved also removing the attached 1.2m whip antenna.


With the connector removed, I refitted the connector from the RT-351 onto the SURF, and then moved back to the drivers seat (tea still too hot to drink without major oral damage) and installed the strong and rigid connector from the SURF onto the RT-351, using the nice hex bolts and crinkle washers from the SURF unit.

 
 
And finally, I refitted the 1.2m whip, onto the RT-351, and checked the operation of the connector. It now requires more force than needed to bend the antenna at its sprung ball joint to turn the connector. Hopefully now, when in use, the antenna will stay upright! And all completed during my tea break!

Sunday, 10 April 2016

Clansman PRC-352 - First Blood

With Bob M1BBV out on the Yorkshire 3 Peaks today, I decided to give the PRC-352 its first on-air trial. After humping it up to the top of Emley Moor, I set up the GSA for 50MHz, and dropped Bob a text that I was in position. I knew Bob at this stage was close to the summit of Ingleborough with his little Yaesu handheld.


Although not strong enough to break the squelch, so I had to operate in '*' mode, contact was made with Bob. I was using the amp so putting out around 20W, Bob a rubber ducky and perhaps 3W. Although in the noise, Bob was mostly readable, i'd give him a 43 to 56 report. Bob reported me as 59. This was a path of around 48 miles!

Afterwards, I walked back with the whip up to test that out. Sadly at one point I caught a telegraph pole with it and it fell over. So, the new antenna socket is, as I thought, not quite as secure as it should be. I might swap it with the one on the SURF which I know is very solid.

So the PRC-352 is now very nearly complete. All that remains is to clean up the cabinets and the GS carrier (I bashed the bend in the adapter plate out yesterday) and redo the paintwork. And ive just ordered the paint for that!

Despite calling for some time from the top of the reservoir at full power, not a single contact was to be had on 4m! I seriously think the current licensing scheme with direct access to HF is going to be the death knell of VHF and UHF. No one is using them, even on 2m from the top of the hill only a single QSO could be heard. We need to go back to a VHF and up only licensing system like the old A and B class, to keep the VHF and UHF bands active. Im not saying that Foundation and Intermediate licenses should have no HF, but license class should not just confer a power increase as it does at the moment, but also access to more spectrum. There would be nothing wrong with Foundation being able to access VHF and Up, Plus say a portion of 80m and 10m, then Intermediate perhaps adding the WARC bands, and finally full access with Full license, with the powers also increasing likewise.

Not the 4u7 caps!

Well im buggered! Changed both the 4.7uF electrolytics in the Clansman PSU module - and the damn thing still takes ages to come to 110v!

Im starting to get a bit miffed by this! I think my next step will be to swap it over with the rebuilt one from my 'good' set, and see if the fault moves with it!

I really need to crack on with the VFO external controller, so even if I cant fathom this fault out, I will look at adding and testing the data contention control diodes into the lines from the decade switches to the synthesiser. This will allow me to test to see how well the logic copes with only 2.3v or so on it. I suspect I will have to modify the 3v supply to the switches to have a bit more poke. This will be an add-on 3.6v regulator feeding just that line, as I cant simply adjust the main 3v line without risking the other logic components.

This actually makes sense though, as it will simplify the control switching needed to isolate the decade switches when in remote control mode.

Saturday, 9 April 2016

Inside the Baofeng BF-888S Radio itself

Yesterday I took a look inside the desk charger that came with these radios. Today, lets see whats inside the handhelds themselves!

The first thing I will say is - Dont Try This At Home!

(unless you are, like me, a time served RF engineer with 25 years experience of servicing handhelds!)

Getting into these is pretty simple, although the manufacturers have opted for a pair of hex screws to keep out the idle curious.  Removing the hex screws from the bottom, and the three nuts holding the antenna sockets and controls, the radio body eases out. Care is needed as the loudspeaker is hard wired rather than having a connector.


With the case removed you can see that there is very little on this side of the PCB. There is however the one and only adjustable device, a single surface mount potentiometer. It will be interesting to discover what this controls, it could be the VCO reference, the Tx deviation, the low battery threshold. Is it too much to hope its the Tx output power?

I opted to desolder the wires at the loudspeaker, as this was less risky than at the PCB. To remove the PCB required removing five cross head screws, and unsoldering the +ve power terminal and the antenna socket pin.

On the other side of the PCB is where its all happening. You can easily see why these are known as 'radios on a chip'. There does at least seem to be some proper filtering at the antenna connector. Build quality wise, the board was soldered ok, I found a small solder splash which I brushed off.


Putting it back together is simply the reverse of taking it apart, with a bit of care to ensure the antenna pin and the power terminal solder back properly.

You will notice that there is no seal between the case and the chassis! Dont get these wet! But, for around £8 each, they are ok for what they are - cheap UHF walkie-talkies.

Friday, 8 April 2016

Inside the Baofeng BF-888S battery charger

The two Baofeng handhelds ive bought have come, as expected, with chargers for their 5v Li-ion batteries. The first thing I noticed about which, is the thinness of the AC power cable!


The next thing I noticed was the weight - or lack of! Clearly, there was no isolating transformer in these! So, I decided to open one up and take a skeg -


Opening these was really easy, but of course I know how. A single screw to be removed, followed by careful use of a blunt knife blade to tease the case clips apart. This revealed inside what looks to be a reasonably well made switch mode charger circuit.


What it clearly is not is any kind of 'intelligent' charger! Probably adequate for this purpose, but I would still be wary of the thin mains cable. It would be sensible to feed these via a 1:1 isolation transformer. Or, better yet, bypass the AC switch mode section and give it a decent DC feed from a good regulated PSU.

What would be easy though, and probably quite neat, due to the light and thin construction of the case, would be to mount several charger units on a board, say six or eight or whatever is needed, add a suitable DC PSU, a safety timer, and maybe a selector for the number of 'pods' active, and you'd have a quick and simple multi-charger for a fleet of these radios!

If I get time tomorrow, i'll run one of the radios over the Marconi 2955, and post a report on the performance of these cheap little radios.