Hi Chris,
Well, in the last experiments my ERP was increased each time. But now i
am reaching some limits. 300m is one limit. Now i can just reduce the
losses and/or increase the TX power. Thus i have thought about what is
possible. My coil losses are about 180 Ohms but the overall losses are
above 500 Ohm so the major part is the earth losses! So this is why i
indeed planned to reduce the losses in the next step.
There is a (metallic)street sign about 130m away. Next i will try to
use it as a earth rod and will add another copper earth rod nearby. I
will use a thin copper wire to connect it to the coil, probably some
0.4mm telephone copper wire which will have a R of 18 Ohm but anyway i
assume to reduce the losses hereby. I have to be careful about
hammering too much rods into the soil there since the land is used by
farmers who can be very angry sometimes. Another idea would be /p earth
rods but there are a lot of stones in the soil so it is difficult
sometimes. Anyway i will try to reduce the losses some 100 Ohms. If i
would wind a second TX coil, rather compact and out of bigger wire, i
think i could reduce the coil losses by 100 Ohm as well!
So, if i can reach the goal of reducing the losses by 50 %, which seems
realistic, i will get another 3 dB ERP and by using a 2 kW generator i
will get another 6 dB. So maybe my absolute limit will be 0.5 W ERP
on 8970 Hz some day (which is nothing compared to 2 kW ERP on 137
kHz, theoretically ;-) )! Then i am back at 30 kV rms on the 300m wire
which is the limit for this wire as well! Sounds like a challenge :-)
73, Stefan
PS: On VLF/(LF) it is rather important to have a good ground connection
instead of (insulated) wires directly lying on the ground since the
wire length is always << Lambda. This connection can be achieved
by galvanic coupling, i.e. earth rods or by capacitive coupling, i.e. a
metallic foil on the bottom. My copper plate i a combination of that
but one can clearly see that the capacitive coupling works worse on
VLF, as expected.
Am 10.12.2010 15:46, schrieb Chris:
Thanks Stefan.
Nice way of showing your excellent results, again, well done!
The pictures your site visitor took are very good also, which gave me
an idea - there seems to be a very large amount of ground at your /P
site, have you thought of trying some long radials (2 maybe) laying on
the ground? I know this would be extra work, especially if you wanted
to resonate them(!), but I wonder what the effect would be. I know for
sure this works well on topband.
Vy 73,
Chris, G4AYT.
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