Re: VLF: Earth antenna transmissions on a guide rail?!?? 2nd day...

[DK7FC <selberdenken@posteo.de>]

Hi VLF and ULF friends,

In the attachment you can find 3 spectrograms from transmission of the 
last weekend. For the 8270 Hz and 2970 Hz transmission i took the data 
of the 900m ground loop, 5170 Hz is from the 450m ground loop.
The 8270 Hz signal was very strong even in 3.8 mHz ('DFCW-600'). Some 
real QRSS-60 would have been possible!
The spectrograms also show that there was no trace on the frequency of 
interest before and after the transmission (no traces from the right 
channel ( 1 PPS) ).
A few minutes ago i built the switchable network for resonating the 
antenna properly. And i actually ordered 1000 m of that 0.75 mm^2 
loudspeaker cable. Thus, in the next experiment i think the Q of the 
antenna will be much higher and it will be possible to tune it 
accurately. Then, the tuning capacitance will tell us what the ground 
loop inductance is! And then, we can calculate the depth where the 
current is flowing backwards in the ground, asuming a simple model in 
first steps.
Next, we can see whether the inductance or depth stays constant at lower 
frequencies (hopefully it will increase!) by resonating the antenna at 
2.97 kHz for example.
BTW i measured the DC resistance of the wire i used last weekend, it is 
116 Ohm, so it agrees well with the calculated 120 Ohm...
The new wire should have 21.4 Ohm only.

The big advantage of this antenna is that no high voltage and large 
coils are needed. Usually the voltage is the limiting factor for a VLF 
or ULF TX antenna. But not here. Here it is the power of the PA. The 
antenna could easily handle 2 kW, which means 5.16 A, no problem for the 
wire. And it would be a 20 dB stronger signal than last weekend...
73, Stefan



Am 29.07.2018 23:11, schrieb DK7FC:
> 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

8270.jpg
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2970.jpg
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5170.jpg
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