Jacek and group,
That are really interesting responses here. That's what i like in this group!
Well, perhaps it is not necessary to reach a "DX", DX becomes very relative in
that frequency range. 50km sounds like a really good DX here.
But what about that WSPR mode, everyone was using before some weeks? Wouldn't
that be a nice tool to try what's possible, for a first step?
If 750m is possible with 2W TX power and 4m*14m loop then it should be possible
to reach some km with a grounded dipole of abt 2x500m. And if the ends are
grounded, the impedance will decrease. Bandwidth will increase due to the
resistive end loading and the voltage over the coils will decrease. That will
depend by the end capacity and conductivity, of course. Something like a
vertical loop with the second half as the earth. Maybe, if the formula RA9MB
showed is correct, it would be better not to place it on the ground but hung it
up on some trees. Sure, everything in the near will be lossy but that's the
case at each commercial VLF transmitter as well. The losses are simply a part
of the job.
Important is the achieved fascination, isn't it? What would you feel if you
would get a contact in QRSS10 to your next VLF interested neighbour, say in
20km? I expect the biggest problem on VLF is to find a person who is fascinated
in the same manner than one self ;-) I do not know someone in a radius of 50km
who is interested :-( But i will discuss it in our club...
BTW, why exactly choosing 8,79 kHz (Horst?)?, why not 8,9 kHz?
We all have a great hobby, really!
73, Stefan/DK7FC
________________________________
Von: [email protected] im Auftrag von Jacek Lipkowski
Gesendet: Mo 22.02.2010 17:25
An: [email protected]
Betreff: LF: Re: Beaconing on 8.79 kHz in QRSS
I've done some tests on VLF also, like many others on this group.
For antennas i've used a 1.5m x 2.5m 3-turn loop, a 4mx14m 1-turn loop,
and coupling to external structures (i won't disscuss this bit here :).
Using the third antenna i can receive my vlf beacon abt 750m from here.
The power was abt. 2W from a TDA2030:
http://acid.ch.pw.edu.pl/~sq5bpf/ham/vlf/20100203/vlfcapt3747.jpg
The receiving antenna was a 100turn loop in a hula-hop toy with a dia. of
90cm. This loop was tuned to resonance and amplified.
Using the 4x14m loop and abt. 40w from a TDA1562 i can receive it from
930m:
http://acid.ch.pw.edu.pl/~sq5bpf/ham/vlf/capt0706082213.jpg
The receiving antenna was a 50turn loop in a hula-hop toy with a dia. of
80cm. This loop was connected to the amplifier virtual ground (broadband
design like "easyloop").
If i remember correctly i could receive 40W into the 1.5x2.5m 3-turn loop
at about 500m.
Unfortunately i haven't had an opportunity to play with e-field antennas,
which should be much more efficient. I've noted that for b-field antennas
nearby installations (power lines, phone lines etc) can carry the vlf
signal far away (hint :)
VY 73
Jacek / SQ5BPF
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