VLF,
The LOPT still works, seems to be no problem. Just a FET was sk.
Somehow all the previous problems are gone now and i am getting about 2
kV rms from the transformer. So i stopped my LF beacon on 137 and QSYed
to 8.97000 kHz. I also found the problem why my last transmission had
so many phase glitches. Now the PC is locked to GPS again. The PA takes
about 15 W input power, no not much DX is to be expected, just a local
test. I do some tests with the VLF active E probe now, receiving my own
signal in some distance and compare the S/N from the forest and a flat
field.
I think Paul can't receive my weak signal but we've often been wrong
with such assumptions :-)
BTW i'm transmitting DFCW-600 centered at 8970.00000 Hz, so i should be
outside eventual other VLF tests by DF6NM.
73, Stefan/DK7FC
PS: If all works well with the transformer over a longer period, i
intend to run a stable carrier over several days or transmit ma full
call in DFCW-60000 or so :-) But the signal is 20 dB stronger with the
big coil and another 20 dB stronger with the 300m kite...
Am 01.04.2012 23:47, schrieb Stefan Schäfer:
Hi Roger,
Well, they are not as suitable as i expected. Just a few kV can be
generated and applied to the wire. But that's fine for local tests. I
didn't measure the L but rather tried to find a resonance. I took two 1
nF capacitors and a 50 Ohm resistor in series to make an equivalent
circuit of my antenna for tests in the shack. I built a class D PA out
of the transformer, running at low input voltage and tried to find the
resonance. But there was no clear resonance. The output waveform looks
very different to a sine wave :-) Probably this is due to internal
winding capacitances, no idea. At least i spend a lot of time and do
not want to spend even more time on the LOPT project.
A few weeks ago i tried some local tests with WOLF10 and got a decode
in 950m distance, which is close in the near field, so not really
exciting. I just want to go on a bit with these tests but i won't go on
much longer with the tests. The standard QRSS or DFCW or MFSK analog
modes, readout by a human is just the best in my opinion.
73, Stefan
Am 01.04.2012 22:35, schrieb Roger Lapthorn:
Stefan et al,
Not being too familiar with LOPTs what inductance are the windings? Are
there particular non-encapsulated types that would be more suitable for
compact loading coils for lower powered 8.97kHz E-field TX antennas?
73s
Roger G3XBM
--
http://qss2.blogspot.com/
http://g3xbm-qrp.blogspot.com/
http://www.g3xbm.co.uk
https://sites.google.com/site/sub9khz/
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