Re: LF: AW: 8.97kHz - Near field and radiated signals?

[Roger Lapthorn <rogerlapthorn@gmail.com>]

Stefan, Rik (et al dreamers),

All noted regarding QRSS modes and likely impact on the near field range expected sub-9kHz - thanks all. Yes, I shall have to try it and see what happens in reality.

Update on the near-field test work today:

• Tried several things to improve the earth-mode transmitter, but none resulted in an improvement. The matching to the electrodes is optimised and I am putting about 4-5W into the ground with a measured current of around 0.3A. I've yet to try elevating the feed wire to the far electrode to increase the effective loop area. This will also give some indication of the size of the effective loop area within the ground and confirm the main transmission mode is induction. This will have to wait until later in June now as I cannot do tests next week (grandson here and using the shack as a bedroom). Also worth trying later will be replacing the 2 electrodes with a single continuous loop at the TX end to compare signal levels (loop area will be smaller but current higher).
  
• Tried a different "loop-amp-HPF-amp" RX arrangement but range was the same at 0.42kms before no further copy by ear.
• Tried my "back-to-front SBL1" up-converter (that works fine with SAQ) TXing at 5kHz with the loop and a small preamp, but sensitivity was poor. I need to work out why.
  

Tomorrow, if time permits, I may try to do a full 360 degree coverage map with the current best TX/RX set-up i.e. doing a more thorough walk-about test in all directions around the QTH rather than just in the fields to the south. Also, I may try taking the PC too and doing a screen grab of the signal at the limit of audible reception (or further) in the best direction.

After tomorrow I shall be on 2.5yr old grandson duty for a week taking him to drive toy tractors, going to the park, painting, cooking and playing cars :-)  Grampy will have to resume playing with his toys after he goes home.

73s
Roger G3XBM



2010/5/26 Stefan Schäfer <schaefer@hst.tu-darmstadt.de>

Hi Roger, Rik, VLF,

That's what i meant, try it in QRSS/DFCW 600 (or 400). Doing it practically is more fun and gives a secure answer if it works or not. Better for health than reading papers in front of the PC. All in all, the best you can do ;-)
I wish i would have the next receiving station in 3 km! Maybe i should visit the Heidelbergs radio club, maybe there are some interested OMs that can be motivated. In the Darmstadts club i do not really have any hope ;-)

73 es gl!

Horst: Any news about your ground electrodes?

Stefan/DK7FC

________________________________

Von: owner-rsgb_lf_group@blacksheep.org im Auftrag von Roger Lapthorn

Gesendet: Mi 26.05.2010 12:51
An: rsgb_lf_group@blacksheep.org
Betreff: Re: LF: AW: 8.97kHz - Near field and radiated signals?

Thanks to all for the explanations.
I'm glad others get confused too!!

73s
Roger G3XBM

-- 
http://g3xbm-qrp.blogspot.com/
http://www.g3xbm.co.uk
http://www.youtube.com/user/g3xbm
G3XBM    GQRP 1678      ISWL G11088