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Date: Wed, 27 Mar 2019 18:14:33 +0100
From: DK7FC <selberdenken@posteo.de>
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To: "rsgb_lf_group@blacksheep.org" <rsgb_lf_group@blacksheep.org>
Subject: VLF: Staircase, also by amateurs?
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Hi VLF,

Yesterday there was a sudden transmission at 14.5 kHz, coming from the 
west. Today, there was a VLF staircase beginning at 12 kHz upwards, 
coming from the east... ;-)

After the recent successful experiment at 5170 Hz, with very high SNR 
levels in a short time received at DL0AO and Paul, i already discussed a 
bit with Markus about a VLF staircase that could be transmitted from 8.3 
kHz downwards. It seems we are able to characterise propagation of a 
ground loop antenna. It would be interesting to find 'the best' 
frequency for a QSO attempt over the path between TX and RX stations. 
This will of course differ with daytime and locations.

For frequencies between 8.3 and 5 kHz it looks like a short carrier of 
<= 5 minutes will be sufficient to produce a strong enough signal peak 
(SNR >= 14 dB). Thus i could transmit for e.g. 5 minutes in frequency 
steps of 200 Hz beginning at 8.3 kHz. The experiment could be repeated 
at night, to see the difference. And another one could be done at lower 
frequencies, e.g. starting at 5 kHz downwards, using longer carrier 
intervals.

Especially the range below 4 kHz could be interesting. Thinking back to 
the experiment between me and Paul, at 2.97 kHz, we have always been 
uncertain if propagation could be 6 dB better when moving by 100 ...200 
Hz. Now we may be able to analyse that.
The experiment could be done in a reasonable short time, so that 
propagation doesn't change to much during the experiment. Also, i can 
tune the antenna within less than 5 seconds to a new frequency. Using 
SpectrumLab, a pre-arranged frequency list schedule could be worked out, 
so QSY happens precisely timed.

Markus and i were thinking about a kite / ground-loop VLF QSO with 15 
character messages in 15 minute intervals. In the past it turned out 
that 5170 Hz is a very useful frequency for a QSO over a distance of ~ 
200 km, even better than 8270 Hz, at least in daytime, because the QRN 
begins to drop in that frequency range in daytime and skywave-groundwave 
interfering effect seem to be constructive.

Are there ideas for a better way to characterise propagation?

Maybe a newcomer is interested to take part? Now it is the chance for a 
new project :-) Forget the summer hole.

73, Stefan