EMRFD Message Archive 7202
Message Date From Subject 7202 2012-01-28 07:04:58 Tim 160M QRP NAQCC sprint and 160M QRP homebrew I used my homebrew rig in the 160 QRP NAQCC sprint last Thursday. Rig was some bits and pieces I asked about here in the past year or two:
Receiver: R2Pro with a pretty tight bandpass filter as recommended by Wes last year to keep local BC stations out.
Transmitter: Single IRF510 approx 5W with 12V Vcc.
VFO: LC VFO with RIT, x3 then digital divide by 4 to get to 1.8 MHz quadrature.
Antenna coupler: L network with parameters a pretty good match to EZNEC's prediction for my doublet fed as a T against ground. Built out of old solenoidal coils I had laying around and some old variable C's.
I had never thought of 160M as a QRP band but the action Thursday night was surprisingly lively.
I still wonder (in EMRFD "measure it" sense) what sort of bridge I might cobble together from equipment already on the bench to measure complex feed impedance of my antenna on 160M and compare directly with EZNEC predictions. Maybe see how different radial systems (at least "none" and "poor"!) affect feedpoint impedance. I have a HP bench oscillator that goes up to 2MHz, a dual trace scope, a bunch of old variable capacitors and homewound solenoid inductors. There has to be some kind of antenna measurement bridge that would work at MW and below that I can cobble together :-)
One gotcha with daytime measurements on that antenna, is that the local BC station during the day (when they are at high power) induces 50-100V on my T. So I might need to boost up the HP bench oscillator to dominate over that in a bridge.