Invicta QRP Club WON the G-QRP Club's G4DQP Trophy for the 2008/9 Winter Sports

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Beach

Monday is usually a good day. I tend to arise early, check the bands and then the emails then after breakfast I head off to the 'Outlet' shopping centre in the middle of Chatham for lunch with the other retired local radio amateurs. Lately the bus pass has made this a cheaper episode with a tour of the North Kent villages thrown in.

It's usually a nice break at the 'Boomer' Australian café with plenty of conversation over coffee and a Marmite baguette talking about, well anything really. Charles G4VSZ tells us about his latest signalling problem on his 'G' gauge garden railway, John G6SXC relates to us his latest VLF receiver progress for tracking thunder storms, Brian G0LJD discusses his latest PSK31 exploits whilst Geoff G3YVF and I talk about CW and our long term interest in portable operating and..TRF receivers.

Ever since I was at school and built my first TRF receivers, 'bloopers' to the US readers, I've been fascinated at how you can get something for nothing in a simple receiver. There is plenty of gain, they are very sensitive, and although selectivity can be a bit of a washout - what fun to use. Having played with both direct conversion and regenerative receivers I would take the TRF any day.

One day Geoff came into the café, sat down and announced, 'I have a new project'. Our eyes swivelled towards him in unison. 'Another one?' we responded in chorus. Geoff is a prolific constructor and 'new projects' are a monthly occurrence. 'Yes' he replied, 'I've designed a single valve transceiver'. I shrank back in horror. I mean I've used a single 6V6 crystal oscillator in a simple TX many years ago and I once remember calling W3LPL in the 80m ARRL DX contest with a 6L6 crystal oscillator even more years ago, (I got 599!), but a receiver with the same valve? Geoff confirmed it would work and, in typical YVF style, he had the first version completed by Wednesday with a flight test on Saturday with his sights set for the forthcoming Minimal Art QRP Contest due in the following week.

To cut a long story short - it worked. He used a six pole switch to change the grid, plate, screen, cathode, antenna and receiver tuning connections on the 6V6 and the finished box had a black metal 6V6 sticking out of the front. The whole thing was powered by an inverter from a 12 volt supply and gave a thundering three watts output. 'You can operate this next week in the QRP contest' he said. 'I'm no operator, you're in FOC - you should be able to use it'. So using three FT243 80m crystals clustered around 3560 I worked for three hours faster than a one armed wall paper hanger, netting with an external oscillator, calling CQ, answering CQ's, fumbling for the right crystal, sending with a straight key and generally having fun. Who said I don't work contests?

As I recall we came about halfway down the pack but to work all around Germany with 3 watts from my location near London with our best DX as Munich with one valve on blow and suck was stunning. I mean all that way? Munich? The receiver proved better than I had dared hoped and had gain although luckily the British Army headphones I was wearing were resonated with a capacitor to give some degree of audio selectivity.

This got me interested in another project. Geoff and Charles had made transceivers based on the 'Paraset' espionage radio of WW2. If you look at Pierre Lorraine's excellent book on Clandestine Operations he gives the circuit of the Paraset and it has been copied all around Europe to this day. It's a simple 6V6 crystal oscillator and two 6SK7's as a receiver. Sure it's TRF but as it was intended to work with a strong control station, running anything from 250 watts to 10Kw according to Pierre's book, it was sufficient in terms of sensitivity, gain and selectivity and it was small.

Geoff's Paraset used valves but the internals had been removed and transistors inserted inside the beautiful metal screens, (remember those lovely black RCA metal tubes?), but from outside the case it looked like the real thing even down to the WW2 style control knobs. Chas had a modified Paraset using valves with a multitude of extra controls and an RF stage - I decided I wanted one too following the original circuit but after enjoying the outstanding Ten Tec QSK system for years I decided against a manual changeover switch choosing a TR switch and in the event I had to arrange a volume control as I had far too much audio gain. I have quite a few crystals by the way many of which are supplied by Rutland Crystals (G3MCK).

G3VTT's version of the Paraset

Working but not complete

The photograph shows my version. It's not quite completed as there are no markings on the controls and I have still to do some more development on the audio side with improvements to AF selectivity, but it works. The TR switch uses a 3pf capacitor from the hot side of the transmitter pi network to a tap low down on the receiver tuning coil. There's just the one coil in the receiver front end and RF on transmit, that thundering three watts, turns off the detector due to charging up of the input capacitor and high value grid resistor of the detector grid leak. In fact the values are similar to those used in the old valve TR switches of the 50's. I also found out that 6SJ7 valves give more gain particularly the one I have stamped 'US Navy'. Would you American readers like it back under reverse Lease/Lend?

A pair of diodes, modern but necessary 1N5408's, pulls down the AF pentode screen voltage to mute the audio and another pair back to back are wired across the headphones to limit audio crashes at TR changeover.

Over the winter break in January 2009 I took part in the GQRP club Winter Sports event where a number of our FOC crew mingled and operated with the QRP operators some of whom have quite slow fists and need encouragement.

I decided with Geoff G3YVF and Brian G0LJD to operate from our local portable site at Coombe Beach North Kent about 35 miles east of London on Tuesday 30th of December 2008 and to see what could be done.

Yes I know we need psychiatric help. Hilary, my wife, took one look at us loaded with equipment and food on our sack barrow and said 'the pair of you are bonkers' (which is a quaint colloquial term English readers will recognise regarding madness). It was cold, very cold, and as we have done this before in 2005 for the Winter Sports we were aware that you can easily die in the English winter without correct food, drink, clothing and a warming fire. After 1500z in December with a sea breeze coming in it can be quite dangerous on the beach. You could easily die of hypothermia in the low temperatures in an hour or two.

The single valve transceiver

Battery, inverter, transceiver and key

As you can see from the photograph I'm wearing a waxed 'Barbour' jacket and trousers over three layers of clothing and jeans, thermalite gloves, a genuine Angora Peruvian scarf courtesy of my son Bob who brought it back as a gift after his last trip, a genuine Russian fur hat and… a pair of clogs. Cold? - you bet. It was initially calm then we had freezing winds from beyond the Urals haranguing the island kingdom. Geoff, due to his metabolism, is always racing about and is always hot hence limiting his clothing to a few layers and his Canadian fur hat. Either that or he was born on Mars. Sitting still, despite pounding my US Navy key, I soon got very cold and my skin stuck to the steel base of the key at one point.

Using an 80m doublet at 25 feet and a 2:1 balun fed through an Electraft T1 auto atu, (I must have some modern technology somewhere), we put all three valve transceivers on the air in sequence. The best DX was Ray GI3PDN with G4BUE as a second QSO. A variety of other stations were worked including an excellent QRQ contact with David G4HMC. In total we only worked seven stations on the VTT Paraset including OP5R (ON6WJ) who was also using his Paraset from near Antwerp. Whilst the band spread of the Paraset was much smaller than the original, with the tuning covering 3500 to 3580 KHz and not 3 to 9 MHz, tuning was fairly easy although you had to ride the regeneration controls and the audio control if fitted. Luckily the single valver also had a limited tuning range.

Hard at work - yes the BBQ is being used to warm my seat! Brian G0LJD's legs at rear.

On the culinary front we did manage to consume a large number of sausage and onion baguettes cooked on an open fire, a canister of Hilary's patented hot spicy soup, some banana baguettes and plenty of coffee. That is real coffee by the way. As English gentleman we have opted to take a cafetiere on our beach trips having decided to drop the prerequisite of tea. One should never consume instant coffee of course.

Was it worth it? Of course, Coombe Beach is always fun. Ask G3XAQ, G3MCK and W4CK all of whom have visited this lovely spot opposite Canvey Island. Why do we do it? It's the love of fresh air and a chance to experience radio as it was with simple homemade equipment. This is the first complete transceiver I've made in over 44 years of Amateur radio and although contacts were few and far between it was fun.

As we pushed our barrow back to the car Geoff turned to me and said 'that was a full days work'. 'Quite' I replied. 'Next one in February then?' He shuddered.

Transistorised Paraset on ground, single valve set above with G3VTT's Paraset on the table.

A freezing G3VTT on left and G3YVF to the right.

Subsequently on behalf of the Invicta QRP Club, the G - QRP Club G4DQP Trophy for the 2008/9 Winter Sports was won by these three frozen individuals!

Article printed by permission of FOC Magazine 'Focus' Spring 2009.