Dear LF group,
Tomorrow, the wind forecast is excellent! See
http://www.windfinder.com/forecast/frankfurt
It is almost to much wind but i have the new kite braid with a strenght of
500kg... So the antenna will be in a high angle and stable for tests. That is
the first positive news.
Yesterday i got such a air coil. It has not 85mH but even about 100mH but It's
Q is bad at 8,9kHz, just about 38. Anyway, i will easily handle 20kV rms. This
will be the maximum voltage on my single wire. There are several possibilities
to increase the maximum antenna voltage, well known and applied in the high
voltage power fields but this may be very difficult at a kite antenna. So i
will start with a first test at only 20kV, if the PA will give a proper power
;-)
That coil is very heavy, about 50kg, really no fun to carry that and there are
better ways to realisethat. But it is available i get the chance to resonate
that 100m vertical at 8,9kHz. I tried to resonate it in the living room of my
parents since it it to heavy to carry it in my room in the first floor ;-) It
was successfully resonated with 6x22nF/6kV plus a lower voltage C in series,
about 33nF/2kV and a DDS VFO with a sinus output, loosely coupled by another
air coil (in this way i will be able to make a transformation of the resonated
loop!(varying the coupling)). The 8,9kHz are well audible so i am excited how
the antenna and coil will sound when some 100W applied;-)
The last problem is the PA since it is not yet available. I will try to built
it today or tomorrow in the morning but i have also to spend some time with my
YL. I hope that can be arranged...
On the hill i have no internet but i will at least inform Markus/DF6NM to give
those who are interested a information here...
I have to go now, and will inform you...
73, Stefan/DK7FC
________________________________
Von: [email protected] im Auftrag von Alexander S. Yurkov
Gesendet: Sa 27.02.2010 20:37
An: [email protected]
Betreff: RE: LF: Fwd: Special Permits for Amateur Radio Operation below 9kHz?
> when back in the mid 90's the initial request for a longwave amateur
> segment (what later turned out to be 137kHz) was discussed, one of the
> big telecom "bobo's" stated that they saw no harm that amateurs would
> transmit there with max. 1 W EIRP as with that power one wouldn't be
> able to get any further than the other end of the town.
> It turned out a bit different, unless you see the world as one big town ;-)
Rik, after some theoretical estimations done i am absolutely shure
QRSS communications at few 100s km (may be more) is posible on 9 kHz.
There is lot of problems on TX side but them to be solvable. Main problem
is high voltage on the TX ANT. I expect 100 - 200 kV is reachable with
some 'tricks' wellknown for power ingeneers. For example one should avoid
free end of a wire with such a voltage. On should use 'protecting rings'
on the ends. With voltage abt 100 kV seems to be posible use not too high
antenna. Seems 20-30 m high well top loaded marconi designed specially for
high voltage is adequate. Remember effective height of 60m kite antenna
used in DK8KW experiment was 30m (if wire was absolutelly vertical, does
it was?). With not too high voltage and not too large ANT capacity 4.5 km
was reached. Another key problem is noise level on this freq. Now we see
huge discrepancy on the noise level got from different sourses. What is
the real noise level is not obvious now. Can it be much lower time to
time? Experements to be usefull. Look at DK8KW web side where 4.5 km
experiment is described. Waterfall background is too smooth. Where
spherics are? This is why i expect RX sensetivity was not as
high as posible. One should remember 4.5 km is begining of the wave zone
on 9 kHz. At distanses more then 4.5 km field decreases not too fast with
distance. Another critical distance is abt 100 km where 'waveguide'
propagation starts. At such distances one shold increase TX ANT voltage
only in 3 times to reach distance 10 times more. Anyway Stefan's
experiment will be very intesesting. And i hope it will be not the last
experiment.
Regards,
Alexander/RA9MB
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