Tuesday, 31 January 2012

Theremin and CW

Yesterday, I decided enough was enough, and that the power supply for Daz's theremin just had to be completed. So, with a mug of tea, and the fan heater running flat out, i ventured into the garage and cracked on. A bit of customising was required on the case, but the power supply is now finished. +/- 12v dual rail, independently fused, to a standard 5pin 180deg DIN plug. I can now, when i have the time, start working on the main Theremin circuit again.

I also built an incredibly simple circuit - a meter tester. This is nothing more than a 1M linear pot and a AA battery, housed in an old shaving stick. Yet, oddly, it doesnt seem to work properly! Everything seems to measure ok, but when on a meter, its all or nothing. Odd.

Since ive decided to make the concerted effort to master morse, I though as well that getting the practice oscillator running properly was in order. Up until now, the headphone output had a strange 'drop-off' tail on key up. The output transistor, a BFY51, was feeding the speaker via a 100uF electrolytic and a 100 ohm emitter load as a common emitter circuit. I suspect the cap was responsible for the problem with phones at low levels. I tested it today with the load resistor replaced by an audio transformer, and the speaker and phone socket on the secondary, and it seems to work just fine. Only problem, it no longer fits the box its in. So rebuilding it will have to await the Wakefield rally in a couple of weeks to aquire a suitable box.

The next little project is just that, little! I have a stash of ZN414 equivalents, and Sam has shown an interest in a matchbox receiver. Its a long time since i built a little AM receiver, so i think we'll have a go at this. Just need the matchbox!

Friday, 27 January 2012


Well, the weather has been dire today, far too cold and damp to put either mast up, or to run the coax. So, it has been indoor tasks only.

The VHF vertical doesnt fit on the top of the Clansman mast. I need a spare mast section to cut down to form an adaptor to allow mounting of antennas like this, but short of buying a whole spare mast, it might be hard to come by. Ive put the feelers out.

As for the telescopic mast, the big task was meant to be fathoming out suitable guying. I think a stay point at the 4m and 7m levels is needed, the bottom can still be held by the 1m level bungees, and the antenna wires will attach at the 8m level. Except for verticals, the top two sections are too thin to be of use. Ive a couple of sheets of PVC gluing together to make a thick rigid sheet from which to fabricate guying rings. As the mast tapers, each ring will be unique to its level, and so they will only fit in a set order. The other problem is tensioning the guys. The Dacron line i have, whilst incredibly strong, is very thin, some 2mm if that. £3 in Yeomans, i found a pack of ten 'bent-runners', ie guy line tensioners for tents. These have got big holes in them so i didnt think they would work, but the homemade one i fabricated earlier today the holes were too small, and passing the line through would be awkward. A quick trial with one of these and a length of the Dacron however and the seem to hold fast. I might have cracked that problem!

I have played some radio today, tried for HK0NA but the level of idiocy and QRM was astounding! Did work a SOS radio week station in Torquay though.

Thursday, 26 January 2012

Antenna Work & VP8s

Up the side of the house today, removing the remains of the wind shattered 2m slim jim, and salvaging its coax. Luckily, the rain hasnt got into the coax, so that can be rerouted up the rear of the house and into the loft, where i can then use it as a test bed for smaller, short term antennas, with a dipole orientation N-S (so a chance to work the African continent on the higher HF bands!)

Anyone who knows me will know i have no fear of hights, but i hate ladders!

Ive already made an 80m inverted V for use with the 10m mast, plus a 10m J-pole. However, with the new year started and the offer of the SES for the Doncaster Show in september, somewhat more radical, practical and portable antennas are now needed! Apart from 2m FM (the mainstay of town SES'es) such a 2 day event calls for HF, and a selection of bands to cover eventuallities. Ideally of course, i'd be able to use any band, but that would call for a compromise of the G5RV type, and two masts, at least. This may be possible using mine AND G7PZLs 5.4m clansman masts, but it wouldnt be very high. So, a fan dipole/maypole design based on the 10m telescopic mast is needed. The question is - which bands?

In the past, ive found 80m to be a prerequestite for SES. So which others? 40 and 20? What about 15, 12, and 10m? Topband is out on the practicallity side, and 30m isnt needed as this will be a phone op.

Im going to test a few ideas out tomorrow based on the clansman 5.4m mast, at the very least to verify that it will take the 2m vertical without any issues!

On the operating side recently, not much! However, yesterday i was very pleased with my little tune around on 17m whilst taking a break from gardening. Heard VP8LP Bob, calling CQ, no replies, so thinks i, grab him if i can before the EU zoo arrives! So, i called him, little realising i was set to 10w. Anyway, to my immense amazement, he replies! I quickly hit the button to go to 100w, as 10 just wasnt going to be reliable, and instead hit the AM/FM button. A good few seconds later i was back in control, and Bobs phone is ringing! I QRX, he returns and we have a pleasent natter for a few minutes. I give my 73 as i need to crack on with the veg plots, but Bob asks if i'd like to work another VP8 before i go? (Having been after the Falklands ever since i got HF, then its a moot question!), turns out Zorro VP8DNT is visiting Bob, they quickly change over, and ive got two VP8s logged in 10mins!