Racal Clansman Key

Now, I obtained this quite some time back, along with a nice McMurdo key similar. This is a miniature Morse key complete with webbing strap, to fasten it around the operators leg, and intended for use with Clansman radios.

My example came without a cable, so I needed to open it up and replace the cable and plug. To do this a rubber seal must be removed, along with the knob, which just unscrews. Once opened, a new cable can be easily fed in and connected, and the key can be adjusted.

Some toroid winding was also needed recently, this is the combined doubler/mixer transformer for the transmit stage of the WSPR beacon. It did prove a tad fiddly

More on that to follow, but for various reasons i've not got much done this week.

Ominous Whispers

This afternoons construction session started badly. In trying to remove the key component I desperately need from the old modem it was attached to, I broke it. So, no audio isolation yet. As if anyone but me cares. Occasionally, I wonder whether or not anyone is actually reading all this wittering I post on here, apart from the odd unfortunate soul directed here to look at a picture, from some other forum or group. Not that it matters even remotely, I write this stuff just to have a good moan and put down my thoughts on the projects im working on.

Ive managed to separate all the  transistors from all what I aquired yesterday, all that remains is to actually sort through them and put them away in the appropriate containers. At the moment they are cluttering up my antistatic mat somewhat

  

Despite that, I managed finally to get somewhere with the 10m WSPR beacon transceiver. Now having the right parts, including a few from yesterdays haul, ive managed to complete the build of the 14MHz Local Oscillator. Surprisingly, theres a lot going on on that little Colpitts circuit! With the two output capacitors in place, plus the bypass and decoupling capacitors, its rather a tight little circuit. Powered up, working first time, and showing 14.055MHz, a little tweek of the trimmer capacitor and its now dead on 14.0623Mhz as required for doubling to 10m.

 

The two coupling capacitors can be seen, the one crossing over the black line will feed the Polyakov mixer in the receive chain. The black line separates the transmit chain (upper board) from the receive chain (lower board). All I need to do now is decide whether to build the transmit or receive chains next!

Apart from a few more bench tests on the receive converter, measuring FM SINAD etc, ive done nothing further on the 4m transverter. I might tomorrow rig up an antenna and let it listen on the band for a while, see if I can find anything off-air, whilst I get on with some of the jobs Julie has left for me nearby in the garden.

Sweet Luck Haul

What happens when you pay £8 for the random contents of a big junk box, on the floor at a rally, all because an old medicine bottle in it has a label on that suggests theres a transistor in there, probably worth 50p, that you need?

You hit the bloody jackpot, thats what!

I havent even found the BF199 transistors yet, what I bought it all for, but the sheer quantity of unused, brand new electolytics, ceramics, polyester caps, 4mm plugs, mixed transistors and literally hundreds of bandoliered mixed resistors, means my parts tubs are stocked up on basics for a long, long time to come!

Theres also quite a few vintage resistors and capacitors, a few ICs, some high voltage ceramic disk caps, and a brand new old stock 470kHz IF transformer, including paperwork. Well worth the £8. And I might claw a bit of that back from the vintage bits and bobs. Really wish i'd offered a tenner for this and the box underneath now! A good proportion of the resistors are also the very tiny body ones I think from Philips, which are good for miniature QRP circuits. The big bandolier on the top right of the picture is a mixed run of resistors, links, axial inductors, obviously from an automated production run for something.

I should have given that other fella £2 for that box Sam was rummaging. The 15MHz glass package crystal was nice, but the large number of new, boxed record player styli might have earnt me a good wadge.

If you cant stand the heat, dont be a test set!

After a lot of work and measurements, my Marconi 2955B decided to actually work again today. This is after several peoples advice, lots of measurements, and a good deal of relearning how to properly use an oscilloscope on my part! I also discovered that the unmarked x1/x10 switch on the scope probe I was using is actually the other way, and all my supposed bad measurements had been done on x10.

It seems the problem was ambient temperature, the last few days incredible heat made the workshop almost unbearable to me, and it seems completely unbearable to at least one of the 2955Bs circuits. Today, being considerably cooler, its working perfectly.

Sam came with me yesterday to the Red Rose QRP rally. I'd won Amtools charity auction for the entrance and lunch, but even with Sams round of toast, I think the charity gets the best deal! Still, I had some decent pie and peas and a brew which took most of the time we were there to cool! Picked up a set of telescopic fish poles to use as spreaders for the show cobwebb, IF i manage to get it built in time. I havent finished the Larkspur mast yet, nor tested the 40m antenna. At this rate we'll be falling back on the big fishpole and the link dipole.

Of the list of items I actually wanted, I think I got two. One, the isolation audio transformer, was found on a defunct 56k modem card for 20p. The other, a BF199 transistor, is somewhere in the dozens of transistors and hundreds of resistors I picked up in a £8 deal for the entire contents of a junk box! A bit steep for the transistor, but the box contained two brand new unopened Velleman component packs of electrolytics and ceramic caps, several unopened Tandy ICs of which two at least look to be quite rare, and a nice NOS ATP-4 valve. Thats just what ive dug out so far. The bits that are no use to me I should be able to sell to make a few bob to cover the cost of the box, and perhaps if im lucky make enough to go someway to offset the cost of the cobwebb spreaders.

Two things I do have to sell, are these Pye telecom extender boards -

Ive got no idea what they extend, they look like maybe Pye Olympic or Europa PMR radios. I'll offer them first on the Vintage forum for a couple of quid, someone might have a use for them. Theres a load of unused old Hunts capacitors in the box as well, not sure if anyone will want those!

So, I'll have a sort of the bag see what there is further to keep, and what else there may be to offer for sale. Ive still to shift those Marconi fill-guns, looks like the last person isnt interested anymore. Plus a Philips repeater and some met grade thermometers! The more I can sell the less Julie will complain at all my junk, and the less the show will cost me in antenna systems!

Well, ive the HF antenna mount on the car to test now. Im sure the bands are not as dead as that radio makes out, but the radio tests out fine. Dinner first I think though - frankfurters, onions, shrooms and scrambled egg, oh and a bit of red sauce.

Marconi Cheesed

Bollocks! Thats the only word I can think to describe this. I went into the workshop this afternoon to show Sam the transverters receive chain working, switched on the Marconi 2955B and was greeted by a screen full of random ASCII characters. So, thats my one and only signal generator U/S. Ive found only one reference to a fault on these that causes the display to mess up, and that suggests the crystal oven 10MHz frequency standard has failed. Thats almost certainly an obsolete part. Its also mounted on the same board as the EHT circuits for the CRT, so im really not looking forward to trying to find a way of getting the scope on it.

But, until thats fixed, or I get another signal generator, im rather stumped on quite a few projects. 4m especially is not an easy band to try and work with off-air signals either.

Red Rose QRP festival tomorrow. I put a bit on the charity entrance fee auction, and ended up winning it! So ive already got my entrance fee and dinner paid for, albeit at a bit more than it would have cost on the door! Just need to take something tomorrow to prove it was me who won! Ive a small list of things to get, but generally just looking for a few bargains. Wonder if there will be a scrap 2955B...

Time out

Since the last posting on here, Ive been a bit off, plus had to work, so not got anything further done on any of the projects. So why the heck am I writing a post?

Red Rose QRP festival is on sunday. Now that Sam is back off his residential visit to Hadrians Wall, he says he'll come with me. I have a small list of things to look out for. Top of the list is a small audio isolation transformer to isolate the scanner audio output from the Marconi 2955's audio input. This should sort out the problems using it on the transverter test bed. A couple of nice ali boxes for the transverter and the WSPR transceiver are also on the list, as is a discone antenna for use as a test off-air source.

All the trimmer capacitors I ordered have arrived, so ive a good basic stock now. Some even came from the Netherlands. Hopefully I can pick up some older PMR kit to strip down soon. I also need to try and off-load the Philips repeater I have, no use to me at all and taking up a load of space. Wonder if there will be a free ebay listing weekend?

Worked a couple of special events on 20m on way home from work this morning, and got compliments on my audio. You can stick your Heil prosets - my mobile headset is a converted old Plantronics office telephone headset!

Tranfixed by Transverter

Last night, after one of my quite regular bouts of total inability to sleep, hatred of the covers, and before the Nytol had chance to kick in, I decided to think back over the receive sensitivity problem. So, I sat and thunked. Suddenly, the folly of my argument hit me. If I have to have the capacitor fully meshed, then my resonant frequency is too high, and no amount of widening the inductor turns spacing will make it lower! What I need is more turns, or more capacitance.

Tonight then, once the boys were in bed, I slunked my way back out to the workbench. Having already put the new coil on, and having during the day found a few moments to build the LO Buffer and put the SBL-1 DBM in place, I decided to properly connect the IF and Antenna connectors, and to run the tests again with a view to seeing what needed to be done.

Well, tonight I had to put a stonking -67dBm signal on in order to even hear the received signal, let alone measure the SINAD. Very odd. Both AM and FM were the same, and couldnt hear a thing in SSB. So, in frustration i disconnected the audio out from the scanner - and bang, stonking loud received audio tone!. It seems the funny issue I had with the scanner must be some sort of ground problem due to it being on battery and all the rest of the kit being off the mains. Test set up works fine until I connect the audio lead from the scanner to the 2955, which kills the received audio.

So, doing an FM SINAD test by ear, I found a perfectly acceptable -117dBm for 12dB SINAD. With the test set in AM mode and the modulation off, the slight frequency reading error of the scanner allowed me to hear the high pitched difference tone down to -127dBm just discernable, thats a pretty decent 0.091uV!. The audio tone was perfectly obvious at -120dBm/0.27uV.

But, heres the real surprise! I adjusted the test set to zero beat the scanner, and then backed it off a little to give a strong to my ears 800Hz tone. This was at 70.401MHz on the test set, 28.400MHz on the scanner. I then peaked the input tuned circuit by squeezing the coil turns together a bit, and adjusting the trimmer. It peaked best signal with the cap just short of fully meshed. So, I started turning down the signal, and down, and down, until the test set wouldnt go any lower! At -135dBm the tone was still very readable, had it been CW it would have been reasonable if not easy copy. Thats 0.039uV! I even swapped to the BNC output on the test set, but all that happened is it got better! (which shows that my N to BNC adaptor needs cleaning). It was even obvious back in the house listening from the open kitchen door!

I have to say I am amazed. Such a simple circuit, just a tuned circuit and an NE602 IC, and its sensitivity is awesome, even when used with lets face it a pretty poor IF receiver. The video above shows the set-up and the circuit under test. The warble is the signal from the Marconi 2955 test set.

It does of course mean that I owe Roger an apology, as I suggested that perhaps there was a typo in his schematic, as the diagram says a 35pF trimmer in this circuit, but his photo shows that his transverter has a 65pF one. Mine has the 35pF. I will stand by however my ascertion that 35pF is too small. Mine is very close to fully meshed, I think with a 65pF it would be more like half meshed, which I think is preferable in this case, I dont like things to be at the limit. I probably wont change the trimmer though, but instead add a 27pF or so fixed cap in parallel. So Roger, if you happen to read this, my apology on record, but also my gratitude and admiration for an amazing circuit!

Strangely, when I tried to check the LO Buffer, I couldnt get a frequency reading on my counter, neither could I from the oscillator (which was quite clearly running properly!). This is probably an issue with the counter rather than anything else, something to look at another day now.

CaPs LoCk

After the 12 or so hours of preparation yesterday at home and today at the village hall, the couple of hours of Toms birthday party were brilliant. On arriving home afterwards, there was a small packet awaiting my return, marked Saffron Electronics, residing within which were 10 65pF trimmers.

Eventually, I managed to slip out to the workbench for a short while. Much of my time was spent putting a small cable entry chassis mount BNC socket on the end of a bit of RG-174, and sticking F-connectors onto a length of RG-59. Those two jobs done, I added one of the new trimmers to the crystal already mounted on the 10m WSPR transceiver board. I can at least now start building the LO proper, and hopefully have it running on the 14MHz fundamental soon.

Being rather knackered, I didnt wish to work on the LO buffer amp on the 4m transverter tonight. I have a particular aversion to dual gate MOSFETs as they are rather expensive four legged fuses, and with my antistatic wristband being 'somewhere' in a box under the bench, decided best leave that task for when im a little more awake. Instead, I decided to rebuild the input coil on the 70MHz receive side. This is a 7t 4mm dia air wound coil, tapped 1t from ground. I had built the original from 18swg wire, very sturdy, but found its associated trimmer capacitor had to be fully meshed for best results. Hmmm, I much prefer it when I can peak a tuned circuit and tune out either side. Being so sturdy, I couldnt open the turns up to reduce the inductance a fraction, and hence increase the resonant frequency. So, a new coil was would with 22swg wire, still sturdy enough, but now more manipulable. I suspect this inability to adjust both coil and cap, and hence not be able to tune the pair up to a high enough frequency, was responsible for the -87dBm receive measurement. I also this evening, took the liberty of running a 12dB SINAD test on the MVT-7100 at 28.4MHz, and it came in at better than -122dBm, so it does look like the loss is in the converter stage.

The photo above shows the transverter so far. The new coil can be seen on the right above the antenna changeover relay. On the left, roughly in place but not yet soldered on, is the SBL-1 double balanced mixer. Being a hot carrier diode ring, this can work at a higher level than the NE602 Gilbert Cell mixer used in the receive chain, and will form the heart of the transmit up-converter. However, before it can be fitted, the MOSFET buffer amp needs to go just above it.

Before going any further on the transmit side, I think I will connect the nice new coax connectors and retest the receive.The bulkhead BNC sockets mean I wont have the mismatch of a pair of crock clips during the test as was the case last time. But for now, im turning in for a good kip.

If its not one thing, Its yer mother

The Transverter is coming along, added the antenna changeover relay, ex- of an RC-690, and have started the 10m WSPR transceiver. When I say started, I mean ive soldered the crystal on, then come to a shuddering halt at the realisation ive no damn trimmer capacitors left in the right values. Not even anything I can bodge into the circuit.

So, ive had to order some. Bloody hell! Might as well be ordering a kilo of Columbian Gold! I really must find some junk with lots of trimmers in to strip, because the price of these things is getting extortionate.

So theres nothing more I can do on the WSPR side, until these arrive. I can do a bit more on the transverter though, although not much. Looks like i'll have to instead finish of some long overdue old projects.

4m Transverter - Receiver success

After a bit of lack-of-sleep brain addled cocking up, I have managed to get the coils for the receive side of the transverter wound properly. A quick, but not exactly accurate, test was set up, using the Marconi 2955 test set as signal generator on 70.4MHz, and the MVT-7100 scanner as the receiver, tuned 28.4MHz. With a source signal with 1kHz 45% AM, this little circuit worked nicely, giving a 12dB SINAD (roughly, by ear) of about -87dBm. With the modulation off, and the scanner in USB mode, a tone could be detected by ear with a signal of about -102dB. The set up was far from ideal, the input from the signal generator was connected with a croc-clip lead, and the scanner connected with an array of various adapters to connect to the TNC connector used to wire up the converter output. The scanner didnt even need tuning a couple of kHz away, as being a scanner its frequency resolution isnt great to start with. It was also a bit intermittent, did some odd changes when I touched the case. I suspect a proper test set up will be much better. I did notice that the trimmer capacitor in the receive circuit was best set at max, I may try a bigger value in here to see what effect it has, or maybe widen out the turns of the coil.

Onto the antenna and power switching arrangements now, which I want to have done before starting on the transmit side.

Before however, im going to pinch yet another of G3XBMs designs, and make a start on the 10m WSPR transceiver. I have the necessary toroids and crystals now, so first job is to make a rough draft layout, and then build and test the oscillator and doubler.