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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