R: LF: TXing WSPR/MF on an indoor loop

["marcocadeddu@tin.it" <marcocadeddu@tin.it>]

Hi Stefan,

I just checked on WSPRnet and red you got plenty of reports from your QRP activity so my 3 spots are a drop in the sea.. but

3 spots:

Timestamp	Call	MHz	SNR	Drift	Grid	Pwr	Reporter	RGrid	km	az
2019-01-26 03:34	DK7FC	0.475683	-27	0	JN49ik	0.01	IK1HSS	JN35tb	493	190
2019-01-26 03:28	DK7FC	0.475683	-25	0	JN49ik	0.01	IK1HSS	JN35tb	493	190
2019-01-25 16:10	DK7FC	0.475683	-27	0	JN49ik	0.01	IK1HSS	JN35tb	493	190

the rx is a direct conversion rx with a simple bandpass input filter.. it is sensitive but lacks of course of image rejection and other features that make a real receiver another thing :-)
The strange point is how the 3 spots are spreaded in the period: 16:10 03:28 03:34..

Some years ago I made some trials on 137 kHz using an (outside) 2 turns loop (5x5m) and it was funny

73, Marco IK1HSS


----Messaggio originale----
Da: selberdenken@posteo.de
Data: 25-gen-2019 15.23
A: <rsgb_lf_group@blacksheep.org>
Ogg: 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