From: "Greg Fismer" <DF2IC@DARC.de>
To: <rsgb_lf_group@blacksheep.org>
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Date: Fri, 25 Jan 2019 17:49:55 +0100
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Subject: LF: AW: TXing WSPR/MF on an indoor loop
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Hi Stefan,

Solid copy in JN48jo over a distance of 20km at approx. -20db

73 de Greg DF2IC

-----Ursprüngliche Nachricht-----
Von: owner-rsgb_lf_group@blacksheep.org [mailto:owner-rsgb_lf_group@blacksheep.org] Im Auftrag von DK7FC
Gesendet: Freitag, 25. Januar 2019 15:23
An: rsgb_lf_group@blacksheep.org
Betreff: LF: TXing WSPR/MF on an indoor loop

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