Friday, 15 February 2019

Of tropo, soldering and unusual work

I have been off the air for a while - the dreaded house decoration I mentioned before finally came to happen. I tried to avoid it, but there was no stopping it. So the shack was completely dismantled, everything in the shack was cleaned, and then dumped back where it had been dumped before. Well, not quite, my shelving has been dismantled and strengthened to take the weight of two Linear Amp Gemini amplifiers, which previously caused the top two shelves to sag. A stout piece of dowel now supports each shelf. Expensive stuff, good dowel, so this takes the form of a brush shaft sourced from that well known speciality emporium, "Homebase". That place definitely gets my brush shaft recommendation.
Strengthened shelving unit with added brush shaft and corner plates
The decorating original plan involved moving the shack desk, which did happen, and also moving the amplifiers to near ground level. In the event the amplifiers have remained where they were, but they now seem to be more or less level on a non-sagging top shelf.

Of course, as soon as this work was complete, one of the amplifiers (the 2m one) developed a fault, or rather showed again a fault it has been developing for some months. Thus it returned to the manufacturer for repair leaving a big gap in my 2m armoury.

I have been accused sometimes of writing too much - but regular readers know this cannot be true. It cannot be true because I have said it isn't true at great length. Nevertheless I did write a very long piece about linear amplifiers, preamplifiers and sequencing which I have decided to save for another day. Never mind the theory for now, what about the results?

With Hepburn's tropo predictions showing hopeful signs for yesterday (14 February) - a link to Hepburn is on the sidebar - there were also more signs of a possible lift in conditions. When somebody you respect suggests you should be prepared you take note, and then when two others of the same standing do the same, then you are obliged to get ready. And indeed, Colin GM0HBK, Jeremy, M0XVF and Dirk PA3FMP all suggested I should standby for better conditions. But I had no Gemini, which meant no working pre-amp too. So I needed a Plan B.

Without my Gemini 2 amplifier my hastily assembled Plan B was to use the parts I recently said I was stockpiling for some other, undefined, project. Viz, a second Down East Microwave (DEMI) sequencer, a "Bias Tee" from SSB Electronics, and to add to those my old Microset SR200 200W 2m linear amplifier. This assemblage would get my masthead pre-amp going and get me running enough power to work some DX. The only snag was that, starting yesterday morning, I had precisely nothing working. Some corners will have to be cut.

I had already got the Microset fixed in theory, although it had never been tested. I had called on the assistance of John, G1VVU, to investigate it. John quickly found that one of the output devices (it uses 2 2SC2782s) had gone short circuit and seemed to have died. I was able to find a new one fairly easily, in fact two, as it seemed best to change both of them. Well, not once we found how tangled the inside of the Microset was, so we changed the faulty one and kept the other new one as a spare. So far so good.

Apart from the fact that the Microset doesn't have a PSU, fans nor even N-type sockets, it should replace the Gemini fairly easily. The PSU is not such a stretch, as it only draws about 20 amps on full power. Then come the fans, so I dug out two dusty 12cm computer fans and mated them to a temperature controlled (27 degrees C fixed, but good enough) switch. Luckily I had boxed the temperature controller up with suitable sockets and so the cooling side of things could be organised quite easily. It isn't right that a transistorised amplifier should be perched on top of its own power supply as the heat of the PSU will rise, but for now that will have to do.
This jumble is the restored Microset SR200, fans, PSU and (left) the homebrew fan controller
Getting a replacement system going that morning was "the art of the possible". That stack of gear is not tidy but it worked for now.

Next task get the sequencer working. No need to explain what a sequencer is, that is for the later long-winded posting. (Is this not a long-winded posting?). Anyway, you need one if you are going to use a linear and a masthead pre-amp and not blow either or both of those up. With the DEMI sequencer this involves wiring a D15 socket and working out a wiring loom. No time for niceties, I got a bit of surfaced wood the right size for the shelving, stuck the sequencer to the wood with Velcro, stuck a chocolate box connector strip to the board with double sided tape and got soldering.

Oh I hate soldering D15 plugs. Actually, I hate soldering any plugs. I tried to cut a VGA cable in two to save the soldering, but despite it being an "all wired" cable, one pin (pin 5) was not connected. So soldering it was. Mrs FVM, who recently had cataract surgery, donated me her temporary +2.00 reading spectacles for the close work. Working out the sequences and testing the operation is fiddly. Once again lack of time meant a temporary arrangement and here it is photographed while I tested it...
Down East sequencer and wiring tangle under test, with the Bias-Tee lurking in the background.
Once I got this up and tested I even found time to organise the wiring, give it some strain relief and put the covers back on the D15 socket. Not before I got the wiring mixed up - why do I always think a D15 socket is a D18 socket with 6 pins on each row, and then get the rows upside down too?

The result is a total lash-up, and it looks awful. Stuff piled all over the place. The sequencer is on a desk at the other side of the shack. There is an SWR meter perched drunkenly on top of some books. But it was more or less ready when it was needed.

OK, everything working now, but will there be any lift conditions to justify all this work?

Due to the shack reconstruction I had not had a QSO since 25 January. I got basic operations going again in the "new" shack on 11 February with the Gemini but it was showing a fault. The Gemini went back to the manufacturer on the afternoon of 13 February. Thus it was only on the morning of 14 February that I started Plan B. Was there any point? Wouldn't the Gemini be back soon, and would all that work be justified by any DX before then at all?

First contact with the Plan B set-up was on 2 metres at 15:54 on 14 February to Dan OZ1BEF. I can work Dan in most conditions, but still that was positive sign. It proved that the Microset and my lash up were working.
2m FT8 stations worked at GM4FVM, 14 Jan to 12:00 15 Jan 2019
As usual, click the image to enlarge if you need to.

I have to say that I was rather pleased with that result. Could I have worked the same stations without all the work to get the temporary linear amplifier working? Well maybe, but the extra power does help get you noticed. Once they turn their beams it becomes easier and that extra clout means they find you while they are beaming at more obvious targets to the south of me. The linear was secondary, I needed the sequencer for the masthead pre-amp, so I had to do it all anyway.

Before anybody asks, yes both the Microset and the pre-amp have RF VOX and should, in theory, work without sequencing. That is very risky but more to the point, the IC-7100 objects to powering up into either RF VOX and so it cuts the output power. I did try briefly without the pre-amp it it was terrible.

70cms brought a new station worked plus one I had contacted last year. Both are much appreciated
70cms FT8 stations worked at GM4FVM, 14 January 2019
Both these 70cms contacts were the result of the stations suggesting we move band after a successful contact on 2m. This just goes to show that there are plenty of 70cms contacts to be had if we could only find them. DK0HAT even suggested going up to 23cms for a try, but sadly that is something I cannot do ... yet ... but even on 70cms he was new square.

During the opening there were long, strong, ducts forming. For example, Charly, DF5VAE was heard here on 2m for over an hour, and at stages registering +10dB on the WSJT software. That is a good 30dB over the minimum level I can reliably work anyone. I could hear Charly's signal loudly on the loudspeaker. Likewise, DK0HAT was heard calling CQ on 70cms for a long time. There was nobody around in GM to work them, which was a pity.

At the same time, at the other end of the tropo spectrum, there were short openings into various areas which came as a complete surprise. Unlike the ducts they were gone as soon as the contact was complete. SP6MJ calling me was a bit of a shock. Conditions held up just long enough for him to wait patiently while "Auto Seq" on WSJT-X answered and worked another station before reaching him. Then, contact complete, he vanished. SP6MJ, in JO81, was a new square on 2m and the best DX so far in this opening at 1370km. Several other 2m contacts contacts were near 1000km.

Is it over as I write? Well I have just worked OZ1CCM on 2m and he is clearly not beaming my way as I can hear him off the side of his beam working Polish stations. I also just worked OZ9PZ on 70cms after he came back to a random CQ call. He also asked me to go to 23cms - is there a pattern emerging here?

Was it worth all that effort to set up a ramshackle pile of gear to work one 18 hour period? I think so. 19 QSOs, 8 DXCCs, two new squares, and a test of my shaky constructional abilities. This hobby has to test us and I think it should never be easy. Certainly, I could have just sat back and watched a re-run of "Rising Damp" on the ITV hub, but that can wait. Radio happens when it happens.

I enjoyed jumping in and getting something sorted out, even if I have to take it all apart this afternoon. Eh? Well, the Gemini was only away for 36 hours - it arrived back at 11:00 this morning. Of course I did not know that in advance.

Thanks to Colin, Jeremy and Dirk for alerting me. The moral of the story, as the great Otis Redding almost sang on  "(Sittin' on) The Dock of the Bay" ... "I can't stop doin' what three people tell me to do, so I guess I'll never remain the same".

Now, I must unpack the Gemini and pull Plan B apart.

73

Jim
GM4FVM