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From: Jean-Louis.RAULT@fr.thalesgroup.com
To: rsgb_lf_group@blacksheep.org
Date: Thu, 25 Mar 2010 09:03:10 +0100
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Subject: LF: RE: Re: Mini-Whip
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Dear all
Please get a look on figure 3 at
http://www.vlf.it/F6AGR/meteorsignatures.html
Such a receiver is the one I'm happy with on ELF/VLF.
With a vertical 1 m long cylinder antenna, it allows to detect the Schumann
resonances down to 7 Hz and the 82 Hz ZVEVS russian transmissions, but also
the RSDN 11 and 12 kHz transmissions.
So the 9 kHz band is also fully covered.
Regards
Jean-louis Rault F6AGR
> -----Original Message-----
> From: owner-rsgb_lf_group@blacksheep.org
> [mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of James Moritz
> Sent: Wednesday, March 24, 2010 9:50 PM
> To: rsgb_lf_group@blacksheep.org
> Subject: LF: Re: Mini-Whip
>
> Dear Roelof, LF Group,
>
> Thinking about your mini-whip design, it seems to me it might
> benefit from
> modification for VLF use. The circuit is a high Z buffer
> driven by the
> capacitive probe - the source impedance might be 10 - 20pF ,
> if one includes
> the JFET follower input capacitance with the probe
> capacitance as part of
> the source. The reactance of 15pF at 9kHz is about
> 1.2Megohms. This is
> shunted via the bias resistors, totalling 1.5Megohms, so
> nearly 3dB loss of
> signal amplitude will occur relative to higher frequencies at
> 9k, or more at
> lower frequencies if one were to use the antenna for "natural radio"
> purposes - the resistors will also add to the input noise
> voltage. So for
> VLF use, higher value bias resistors might be appropriate.
> Alternatively,
> the probe capacitance could be increased. The band noise
> level may be so
> high that this doesn't make much difference in practice
> though, as far as
> SNR is concerned.
>
> Cheers, Jim Moritz
> 73 de M0BMU
>
>