Hi MF,
A few days ago i took some RF litz wire and built a loop that is now
hanging on the wall inside my home, just 1m besides the bed :-) (no XYL
here spoiling the fun). The loop is beaming to about 150/330 deg.
After playing some days on 160m (an unusual high frequency, witch feels
very strange. And the band is full of unknown callsigns!!) i did now
move down to more or less low frequencies, the 630m band!
About 10 nF is needed to series resonate the loop. It has about 2m x 2m
of size. The antenna current is not stable because the WIMA FKP-1
capacitor becomes warm during the 2 minute WSPR sequence. But the
maximum current in the loop is 14 A. That explains why the cap becomes
warm. A small parallel variable capacitor tunes to resonance. It is
tuned so that the upheating capacitor runs into the resonance point in
the middle of the WSPR sequence, then it runs out of the resonance by
upheating further. It can cool down during the following quiet periods..
14A into a 4 square meter loop at 475.7 kHz, how much ERP is that? The
PA consumes about 3.5 A at 13.8V, i.e. about 50 W.
The system will run over the weekend, even during daylight. The signal
generator is a Raspi which will have no internet connectivity from now
on, so let's hope the time offset stays inside the accepted range for
this experiment.
What will the best distance be? So far the band is closed but i'm
optimistic to crack the 1000 km distance with this QRP setup.
73, Stefan
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