|
Dear LF,
Stefan DK7FC just called me on the phone. He asked
me to inform the group that because of much heavier winds than expected, he will
not be able to transmit from the kite antenna today. He also mentioned
that the output matching of his PA (a converted SMPS circuit) will
require some more work.
Kind regards,
Markus (DF6NM)
----- Original Message -----
Sent: Saturday, February 27, 2010 3:33
PM
Subject: LF: VLF TX experiments this
sunday becomes more probably
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
|
