Date: Sat, 23 Oct 2010 22:10:17 +0200 (CEST)
From: Jacek Lipkowski <sq5bpf@lipkowski.org>
To: rsgb_lf_group@blacksheep.org
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Subject: Re: VLF: here no results from DK7FC's 8th experiment
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On Sat, 23 Oct 2010, Horst St=F6cker wrote:

> [...] So I can find just one conclusion: All of you who could reveive=20
> Stefans transmissions must be living more or less on the countryside.=20
> [...]

i live in the middle of Warsaw, yet i can receive Stefan's signal using a=
=20
miniwhip-like antenna. try these things:

- experiment with bias, my antenna likes to be fed with a higher voltage.=
=20
it would be better to tweak bias directly, but this is the only way to=20
change it, since the antenna in on the roof now.

- use at least lowpass filtering, and preferably bandpass. sound cards=20
really don't like to be fed signals above their nyquist frequency

- use a 12v gel cell for power and a laptop running on batteries for=20
testing, and see if there are considerable changes in the noise floor.=20
i've found that my bench power supply is ok, there is no difference if i=
=20
use it or the battery. but connecting the laptops power supply ruins rx=20
completly, this can be solved with an isolating transformer.

- try to use the goodies that Wolf put into spectrum lab, the noise=20
blanker and sample rate calibration make a difference. this is the first=
=20
time i've used the sample rate calibrator and it is really great.

- listen to the audio that reaches your soundcard input. if you hear a=20
radio station - use even more filtering :)

- look at your soundcard noise floor. for example i can eliminate some=20
noise by changing the max_cstate parameter in linux. you can probably do=
=20
similar things under other operating systems.


e-probes are great. i've tried running loops here, and the last time i=20
could receive SAQ was in 2006, since then the magnetic field noise floor=
=20
is just too high.


hope this helps,

Jacek / SQ5BPF

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