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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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