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15th June 2014 08:21

Alan Yates wrote...


The article links off to websites with quite similar circuits containing a circuit diagram. It also states the inductor was picked to resonate just below 80 metres at maximum capacitance with the capacitor I had. It is unlikely anyone building their own will have exactly the same bits, so they will have to do a few calculations to design theirs as I did. The core is a T68-2 and I needed about 11-12 uH or about 45 turns.



15th June 2014 04:00

Steven Walker wrote...

Doh! If you put the thing on the web number of turns would be a minimum, preferably a circuit.

20th August 2011 07:10

Randall wrote...

Hello, how are you doing? I would like to know how to make the bridge of swr, if possible

27th December 2007 14:19

Alan Yates wrote...

Peter, yeah that is pretty close. The SWR bridge in mine has a transformer instead of direct connection of the rectifier and LED. The turns ratio is 5:25 on an FT50-43, but that isn't too critical. The secondary has the larger turn count, feeding a 1N5711 rectifier, 100 nF capacitor and a 1 kΩ current limiting resistor through the ultra-bright green LED. A lower forward voltage ultra-LED like a red is probably a better idea.

I used a T68-2 (red) core for the actual matching circuit, not a ferrite one. Both gangs of the polyvaricon in parallel are needed to resonate the secondary on 80 metres.

I had to experiment with the primary a little to get a good match, as I had selected the secondary turns count to resonate at 3.2 MHz with the available capacitance (about 210 pF) and that needed quite a few turns. I think I ended up with 3 turns to get a good match into 4.7 kΩ, but I can pull it apart and check.

27th December 2007 10:40

marxy wrote...

Alan, is this the circuit you built.

(Hey, great that you now have comments!)