As a next result from today's experiment, here is a spectrum peak of the
2970.005 Hz transmission. I reached 20 dB SNR in 180 uHz! This far more
than expected, in July anyway.
It is the first ULF transmission (by amateurs) from an earth electrode
TX antenna, detected in the far field.
Spectrograms will be produced soon...
73, Stefan
Am 29.07.2018 16:01, schrieb DK7FC:
Hello Roman, VLF,
I transmitted pure carriers each time. It was just a first test.
Today i've done a second experiment, this time using a 900m long wire!
So the wire should have about 125 Ohm DC resistance. I measured 220 mA
DC at 38.4 V, so the overall loss is 175 Ohm. Very interesting; the
ground loss resistance stays at 50 Ohm although the distance between
the electrodes has doubled!
If i would use the 0.75 mm loudspeaker cable then i can reduce the
losses by 100 Ohm which is more than 50 %, so i will gain 3 dB at the
same output power! Then with a switch mode PA having nearly 100%
efficiency i may gain 2 dB more (mmy lonear mode PA was not well
matched today and quite warm). So maybe i can reach 1 A antenna
current with just 75 watts??!!!
Today i tuned to 550 mA antenna current again, at 8270 Hz. With the
scope, i measured the phas, it was more inductive than yesterday. I
actually found a 1 uF MKP-10 cap in my car and switched it in series
to the antenna. This improved the phase slightly. Then i also found a
low pass filter for 137 kHz, the pypical pi configuration, i.e. it
acts as 4*22 nF in parallel here on this frequency. Switching this in
series leads to a low current, so the C is to small. So for the next
experiment i'm preraring a switchable C network (47n, 100n, 220n,
470n, 1u, 2.2u, 4.7u). It will be even more necessary when i lower the
wire resistance (higher Q).
Well, today the QRN was much lower, especially for the 2970.005 Hz
transmission period. Yesterday this was totally buried in the noise on
my RX on the tree. But today! I transmitted another 90 minutes with
much lower QRN background. I already have a clear spectrum peak but i
like to try to improve it a bit more before presenting it here.
Todays carrier transmissions:
8270.000 Hz : 08:12...09:33 UTC
2970.005 Hz : 09:42...11:15 UTC
Sorry for the confusing email ;-)
73, Stefan
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