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Re: LF: Re: Two-Way QSO on Dreamer's Band

To: <[email protected]>
Subject: Re: LF: Re: Two-Way QSO on Dreamer's Band
From: "Markus Vester" <[email protected]>
Date: Sat, 5 Jun 2010 14:16:11 +0200
Importance: Normal
References: <657E7065AC4C454AB63F6C7C2FF043F6@Black> <85A6EDF74C464FF09E93E97F768BA81F@JimPC>
Reply-to: [email protected]
Sender: [email protected]
Dear Jim,
 
thank you for your comment.
 
It's certainly a good idea to get some more quantitative data on our VLF antennas, aiding optimisation, and ultimately getting a better idea on what long distance attenuation behaves like. On LF I have been using a roughly calibrated system based on DCF 39 receive measurements, but on 9 kHz it's all just guesswork with a lot of uncertainty.
 
Reviewing saved spectra from my narrowband grabber, the range of diurnal and day-to-day noise level variations currently seems to be on the order of 10 dB. This is after noise blanking at a 9 dB trigger threshold, and excluding times of regional thunderstorms. Yesterday night I had temporarily changed the antenna configuration (inserted the loaing coil and removed the preamp), so I can't give an accurate number here. Judging by the brightness on Stefan's and my grabbers, I would say it was average, about  5 dB above the bottom. I would however guess that during wintertime minima were perhaps another 5 dB lower.
 
The noise blanker often seems to improve SNR by some 6 to 10 dB, however there is a little uncertainty on how much it has cut out of the signal amplitude. During an absolute measurement, it may be worthwile to track gain by injecting an additional low-level test tone.
 
Kind regards,
Markus (DF6NM)

Sent: Saturday, June 05, 2010 12:54 AM
Subject: LF: Re: Two-Way QSO on Dreamer's Band

Dear Markus, Walter, LF Group,

Congratulations on the QSO - it is impressive to see that usable SNRs can be
achieved in the far-field at 9kHz with quite small antennas and limited TX
power. A long term objective at M0BMU for 9kHz is to do some field strength
measurements using TX antennas on a similar scale. The main practical
difficulty would seem to be the long time needed to integrate the signal at
the receiver in order to obtain an adequate SNR for useful measurements (and
to travel far enough to be out of the near field!) - I would be interested
to know what SNR you would expect under "quiet" conditions using the same TX
and RX parameters.

Cheers, Jim Moritz
73 de M0BMU

----- Original Message -----
From: "Markus Vester" <[email protected]>
To: <[email protected]>
Sent: Friday, June 04, 2010 9:59 PM
Subject: VLF: Two-Way QSO on Dreamer's Band


Dear LF,

this morning, June 4th between 6 and 8 UT, Walter (DJ2LF) and myself (DF6NM)
were able to successfully conduct a two-way contact (aka "QSO") on 8.97 kHz.


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