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

To: [email protected]
Subject: Re: VLF: Earth antenna transmissions on a guide rail?!?? 2nd day...
From: DK7FC <[email protected]>
Date: Sun, 29 Jul 2018 16:01:32 +0200
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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

Am 29.07.2018 13:59, schrieb Roman:
Hi Stefan!

TNX!
Whats you TX? Ebnaut or carier?
Wait an other results.

Roman

Hi Roman,

Here are two spectrum peaks from 8270 Hz and 5170 Hz. I integrated the
complete transmission time into one bin. I also produced a wav file from
the recorded data (already resampled, mixed, filtered, blanked) and
postprocess this into SpecLab now, so we get a usual spectrogram
demonstrating that there was no trace before and after the transmission
on that frequency. The file starts 2 hours earlier and ends 2 hours later...
More tomorrow...

73, Stefan

Am 28.07.2018 15:54, schrieb Roman:

Congrats, Stefan!

Pse inform us with screens as possible!

73!
Roman

And another update: The 5170 Hz carrier was running from 10:13...11:19
UTC. The current was constant at about 555 mA.

Now my last transmission for today is on 2970.005 Hz, running 590 mA,
on air since 11:22 UTC, running for at least 1 hour...

73, Stefan

Am 28.07.2018 12:50, schrieb DK7FC:

Update: Since 10:13 UTC i'm TXing on 5170 Hz. The antenna current is
556 mA and the phase looks a bit less inductive but still inductive.
Despite beeing in the center of the Pfälzer Wald, i have mobile
internet access and so i reached my Linux PC recording the VLF stream
(both loop antennas). Using vlfrx-tools i managed to produce a spectrum
peak of 17 dB SNR after just 30 minutes!!!! (More later) So it is
possible with this ground loop TX antenna to transmit on 5170 Hz and
beeing detected in about 55 km distance! :-) These are two new
records for the TX earth antenna league :-)

I'm going to continue transmitting on 5170.000 Hz until 11:13 UTC, then
i'll do QSY to 2970.005 Hz which simply means i change the frequency in
SpecLabs signal generator driving my PA! :-)

73, Stefan

Am 28.07.2018 11:43, schrieb DK7FC:

Hi VLF,

I'm sitting in my car while writing this email. I'm in JN39WI96GX and i
transmit on 8270.000 Hz with a GPS locked signal generator into an
about 450 m long earth antenna using two guide rails as the earth
electrodes on both ends. On each end there are 16 (18) massive T-T
poles holding the guide rail, providing a super good earth coupling. I
measured that they are connected to each other.

The transmitter is on the air since 9:08 UTC running 550 mA with just
75 W DC inout power into my hand warm lossy linear mode VLF PA!

I'm amazed about the low losses! At DC i got 447 mA at 50.9 V. The wire
is 0.4 mm diameter so it has 63 Ohm. That means the ground loss is just
50 Ohm !!!! Amazing! And i have no efforts to build up a ground
connection here, i just need to connect the wire. Since the wire losses
are higher than the ground losses, i can get maybe 2 dB more signal
when buying some better wire. I already found a source that offers 0.75
mm^2 100 m loudspeaker cable (i.e. 200m wire)for just 13 EUR....

BTW i even have an ugly old scope here which is battery powered. I can
see that the phase of voltage and current is slightly inductive, maybe
30 deg or so. So i could series resonate the antenna with some C. This
is for the next experiment...

The signal becomes visible on my grabber now, in 424 uHz and also some
bright pixels in the 3.8 mHz window.

I'm going to stop the carrier at 10:08 UTC, after 1 hour. Then i'll
continue on 5.17 kHz!

BTW the antenna , if it works like a real loop, is beaming directly to
Paul Nicholson ;-)

73, Stefan

Am 26.07.2018 17:19, schrieb DK7FC:

...i just searched in the old emails and also on G3XBM's blog and found
this entry: 
https://g3xbm-qrp.blogspot.com/2010/09/vlf-dx-transmission-with-earth.html

So that is the best distance on a transmit earth antenna (or ground
loop) so far, at VLF, by amateurs.

I had a much lower earth resistance in mind but actually i just got
0.53 A at 250 W RF power, so the losses were rather 890 Ohm!

Will it be possible to make 55 km distance at 8.27 kHz, maybe in a
lower bandwidth like 424 uHz, with power levels in the range of 50 W
only?

73, Stefan

Am 22.07.2018 20:28, schrieb DK7FC:

Hi all,

During the weekend i am in the Pfälzer Wald again which is such a nice
place to be! I already installed a fixed E field antenna for VLF/ULF
reception in JN39XI06 :-)

Now i have the idea to use a guide rail (attachment!) as an electrode
for a earth electrode antenna! There is a perfect road which is not
much frequented and where no way is crossing so i could temporary
install a long wire on the ground between two of these guide rails. I
would assume they provide a good grounding. They are located on a
relatively high hill/mountain with stony ground. The mountain is very
steep there and in some distance, 200m deeper, there is a brook..

With some luck the ground losses can be near 200 Ohm? Maybe rather 300
Ohm. I'm going to prepare things and plan to transmit for some time
next weekend. If the ground loop actually acts like a loop, the bearing
should be 135 deg, so it will be in a 45 deg angle towards my QTH where
my grabber is listening in 55 km distance. That's quite a good distance
for testing! I'd like to try LF and VLF, maybe ULF it all works well.

A BTW the wire length will be 860 m! However there are two guide rails
in a shorther distance, about 450 m. I will try the shorter length
first, to get an impression of the loss resistance and to see if
something is visible at all :-)

73, Stefan




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