Dear Stefan, LF Group,
I have been doing some receiving checks <9kHz, and althought the QRN level
is quite high, the level of man-made noise at my home QTH seems to be much
lower than during the last set of tests. So I should be able to have quite
good receiving conditions for DK7FC's tests tomorrow without having to go to
a /P location.
Around 6.5kHz there are some weak (n x 50Hz) spectral lines drifting around,
and a few more stable lines visible, which may be internal to the PC. This
is similar to the situation at 8.97kHz, so I am hopeful that at least the
receiver will be reasonably sensitive ;-)
Good luck with the test tomorrow,
Cheers, Jim Moritz
73 de M0BMU
----- Original Message -----
From: "Stefan Schäfer" <[email protected]>
To: <[email protected]>
Sent: Saturday, July 31, 2010 10:53 AM
Subject: Re: VLF: DK7FC's 6th VLF kite experiment
Hello Peter,
Better say 6,6 +-200 Hz. It is still not certain where the resonance will
be, sorry. There are to many assumtions, estimations and calculations.
On 137 kHz the measured C for 100m is 580pF (measured with a RC bridge and
by measuring the L and calculating C). But EZNEC shows a lower C. This
could be, since a 100m vertical is not absolutely short against Lambda and
so the sems to occur some impedance transformation which "looks/behaves"
like a higherC.
On <9 kHz the 100m wire IS short against lambda and so i loose this
benefit. There, the actual C is present. The L of my variometer part in
the BIG coil is estimated to be 30 mH. Maybe it is even more and the
overall L is higher than L(coil)+L(variometer) due to the better magnetic
coupling. So maybe i have less C and more L than thought on 8,97.
When doubling the antenna height from 100m to 200m and assuming 5 pF/m the
C is doubled as well. So i thought i will come out at 6,34 kHz
(8,97/sqrt(2)). But this may just a rough estimate. EZNEC says the C
factor is not 2 but 1,88 so i would come out some 100 Hz above.
So the question is:
What is the actual antenna C for 100m
What is the actual (maximum and average) L
What is the C factor when going from 100m to 200m
This are many uncertainties and so i didn't want to tap the coil at 70% of
the winding to come back to 8,97 kHz but first just to measure out where
the resonance will be, to solve these open Questions. Of course, another
important and very interesting issue is propagation in the 46km band! :-)
So, sorry for that coarse frequency range. Maybe the actual QRG will be
written here in the reflector and can be seen on my garbber2 but first
lets hope for proper WX!
73 and tnx, Stefan/DK7FC
Am 31.07.2010 11:23, schrieb pws:
Hi Stefan,
Question: do you have a realistic guess of the frequency window of your
transmission around 6.5kHz, e.g. +-100Hz?
You wrote:
....
on *Sunday, the 1. August*, i will make a new kite experiment.
...
i will transmit at arround *6,5 kHz,
...
Starting time is* 8 UTC*, maybe some time later
...
TX QTH is as usual in JN49IS, 49.77647N 8.699525.
Distance is 516km, heading 10deg. to Kiel.
Just modified the software running at ~17mHz of resolution. Antennas are
two crossed ferrite loops feeding some BC550 in parallel buffered by
NE5532. Both amplifiers are connected to a M-Audio Audiophile 192 running
at 24 kHz on an Intel Atom 330 "shoe-box" under Linux.
73 from Baltic Sea,
Peter
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