Message-ID: <BFF6723B062BFF40B4B7A6CF670160B40334626B@argos2.clb.tcfr.thales>
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
> 
>