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Date: Fri, 20 Oct 2006 15:18:01 +0200
From: =?ISO-8859-1?Q?Jean-Pierre_M=E9r=E9?= <jpm.f1afj@online.fr>
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Subject: Re: LF: Re. TA Last Night
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Hello Markus , Wolf   and LF'rs ,

If I can allow myself , how I found best in SL against the sferics, it=20
is a fast AGC behind a narrow filter! to see my configuration at :
http://jpmere.online.fr/Grabber/Setup/Setup.htm  . Many Thank  Wolf for=20
your very good software .

73's Jean-Pierre f1afj


Wolf DL4YHF a =E9crit :
> Hello Markus,
>
> Just a suggestion...
>
> Instead (or in addition to?) of the "old" noiseblanker (inside SL's=20
> "DSP" blackbox), try the noise-limiter in the FFT-based filter, with a=20
> small FFT size for the filter. I tried it a few weeks ago at the club=20
> and found it worked even better than the classic noiseblanker. The=20
> trick is to set the limiter values (in the FFT filter control panel)=20
> just a few dB's above your usual noise level. Then everything above=20
> that level will be cut off, before transforming the signal back into=20
> the time domain. Note that this must happen with a low FFT size (256=20
> points or less) to let it react fast enough for sferics. After this,=20
> the signal will be fed to the main spectrum analyser which of course=20
> runs with a larger FFT size (16384 points, plus decimation).
> This "spectral limiter" also works nice for other kinds of local QRM=20
> which is "normally not there", and would otherwise spoil the=20
> spectrogram. Of course, when the noise is very strong, it will deafen=20
> the receiver.
> If you like, I can search for some screen shots taken in dual-channel=20
> mode (with and without limiter+blanker). They must be somewhere on the=20
> club's "LF computer" ;-)
>
> Cheers,
>  Wolf .
>
>
> MarkusVester@aol.com schrieb:
>> Dear John and LF,
>>
>> yes my grabber seems to be plagued a lot. Most of the QRN is=20
>> currently emanating from the Mediterranan sea area. I believe the=20
>> unilateral directivity of the K9AY E-H-loops does help a lot for=20
>> Hartmurt and Jean-Pierre. However up to now my own attempts on=20
>> H-field reception have always resulted in decreased SNR due to all=20
>> sorts of local QRM.
>>
>> The QRN was probably emphasized a little by the increased dynamic=20
>> headroom which was required here to cope with the Budapest telegrams.=20
>> Apparently these have also affected the software noise blanker=20
>> performance, which I have tried to improve now by inserting a=20
>> bandpass filter before the trigger.
>>
>> Judging by the fat CFH trace last night, LF propagation looks quite=20
>> favorable in the aftermath of the recent period of geomagnetic=20
>> activity. On the 100 kHz monitor, all stations from the the Far East=20
>> Loran chains (including Minami Torishima island) were well visible=20
>> this evening.
>>
>> 73 and best wishes
>> de Markus, DF6NM
>
>
>
>

--=20
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