Thursday, 4 September 2008

Downsizing and other nonsense

Beyond amateur radio, I have other things to do. Oh, well...

Since the last post, I've discarded a lot of radio stuff. Old, unfinished and abandoned projects, items which 'might be useful one day', most of my surface-mount stock, and a pile of magazine cuttings. It had got thoroughly out-of-hand, and the carnage may yet continue. I have several A4 ring binders full of datasheets, all of which exist as PDFs or other electronic documents. Why keep all that paper?

An adventure at a local carnival convinced me that a lean and portable radio station was all I require, and anything I couldn't carry around in a shoulder-bag was a liability.

I'm a Petty Officer in the Sea Cadet Corps, and I instruct in communications at our local Unit (Worthing). As part of a recruitment exercise, I took an FT101-B, a field antenna, a tuner and a large (24Ah) gel-cell battery to Broadwater Carnival. I cannot use our Sea Cadet frequencies away from the Unit, as the transmitter permit won't allow that, so I operated as G1INF/P. All this should have been easy, and provide an interesting display.

The antenna, a 33-foot copper screw-together pole, was a success (it supported our Ensign). The tuner wouldn't load the thing on 20m, and there was no activity on 40m. The Yaesu's tuning knob seized (thirty years of zero-maintenance finally too its toll), so the Cadets were reduced to running 'errands' with PMR446 hand-helds, and helping to locate lost children in the crowds.

The whole affair was grossly overweight, and unmaintainable. The tuning gear on the radio needed a strip-down, clean and lube (gun-oil is excellent), something I couldn't hope to do with my 'field tool-kit'.

Regen receivers, again - I find the idea of regenerative so seductive, I had to try again. The thing works, but I have reservations. It's unstable below 8MHz, squarking loudly if oscillation is approached. It needs more gain, and a lower-Z output, as it currently uses a crystal earpiece. But it works; I've recovered SSB and cw from both 20m and 40m, and a host of commercial stations in between.

I'm going to try another, based closely on G0KJK's HF9 design, as published in Sprat 82. I'll take my time over it, and follow the design closely, using lessons learned in previous regens. Microphony, feedback and hand-capacitance all need careful attention. Stiffness, layout, and screening!

The 'simple' regen is pictured here; it's a variant on the G4KJJ 'Smid-Gen', itself a subset of the HF9. The top-left is the main tuning, under this is the bandspread. Top right is AF gain, with reaction below. Left switch adds 100pF to the tuning, an the right switch adds 9V to the radio. A random wire is seen attached as an antenna.

Onward, I hope to make a better regen receiver. I also want to make the add-on box for my Racal Minical (see previous posts), and that radio was designed for a shoulder-bag!