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From: <jrusgrove@comcast.net>
To: <rsgb_lf_group@blacksheep.org>
References: <004801cb04d6$e9740b80$0401a8c0@xphd97xgq27nyf> <CD190EC05BA84C1685A9A2F4A56DD284@JimPC> <004301cb0544$56965980$0201a8c0@Clemens04> <FF5414DBC74E45B69F5D9E01FDFB4A0C@White> <DFFD7B2AF9C74F0C9C1BFD90F8559389@JimPC>
Date: Sun, 6 Jun 2010 07:09:59 -0400
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Subject: LF: Re: Re: Re: VLF 9 kcs: preamp and antenna noise
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Jim

Sensitivity of the Perseus drops off below 10 kHz - see attached spectrum shot taken earlier this 
year. While the antenna in use at that time dropped off a few dB below 10 kHz the 'black hole' is 
mainly due to Perseus.

http://www.w1vd.com/vlf.html

Jay W1VD  WD2XNS  WE2XGR


----- Original Message ----- 
From: "James Moritz" <james.moritz@btopenworld.com>
To: <rsgb_lf_group@blacksheep.org>
Sent: Sunday, June 06, 2010 6:04 AM
Subject: LF: Re: Re: VLF 9 kcs: preamp and antenna noise


> Dear Clemens, Markus,
>
> Yes, what Markus wrote is exactly what I mean...
>
> In general, the SNR does depend on the source impedance. Also, the overall power gain of the 
> preamp/receiver depends on the degree of mis-match at the input, so the fact that the output noise 
> level stays the same in the Perseus does not imply that the SNR will also be the same.  But unless 
> the noise figure of the preamp/receiver is quite low, this effect will often be masked by internal 
> noise in practice. As Markus points out, with large RX antennas the source noise power at 9kHz is 
> spectacularly high, and preamp noise is not usually a factor anyway. But for small whips and 
> loops, preamp noise is important.
>
> The figures Clemens quotes for the Perseus RX are curious... With 732Hz bandwidth and T = 300K, 
> kTB would be -145.2dBm, so the -118.4dBm noise floor level indicates a noise figure of about 27dB, 
> which seems quite high. The QST review quotes -127dBm noise floor in 2.4kHz bandwidth, which would 
> imply about -132dBm noise floor in 732Hz bandwidth, so some discrepancy there.
>
> On a crude practical level, if you listen to your 9kHz RX output and hear mostly crackling QRN, 
> that is fine... if you hear mostly 50Hz buzzing and other man-made noises, you either have a 
> problem with local noise being coupled to the preamp or receiver input, or need a better antenna 
> location... If you hear mainly "white noise", your receive system is probably deaf!
>
> Cheers, Jim Moritz
> 73 de M0BMU
>
> ----- Original Message ----- 
> From: "Markus Vester" <markusvester@aol.com>
> To: <rsgb_lf_group@blacksheep.org>
> Sent: Sunday, June 06, 2010 8:38 AM
> Subject: LF: Re: VLF 9 kcs: preamp and antenna noise
>
>
> Clemens,
>
> I believe what Jim was suggesting is a comparison of preamp noise output with the antenna 
> connected versus a passive load, rather than between different passive load impedances. The 
> intention is to demonstrate that the receiver noise contribution is neglegible against external 
> noise...
>