27th December 2007 14:19
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
Alan, is this the circuit you built.
(Hey, great that you now have comments!)
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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