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From: "James Moritz" <james.moritz@btopenworld.com>
To: <rsgb_lf_group@blacksheep.org>
References: <38A51B74B884D74083D7950AD0DD85E82A1B18@File-Server-HST.hst.e-technik.tu-darmstadt.de> <Pine.LNX.3.95.1100225172510.244A-100000@noname.nodomain.nowhere> <fc7eccec1002250322x41754c42y7790481401b25a83@mail.gmail.com>
In-Reply-To: <fc7eccec1002250322x41754c42y7790481401b25a83@mail.gmail.com>
Date: Thu, 25 Feb 2010 18:50:46 -0000
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Subject: LF: Re: 9kHz noise level
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Dear LF Group,

As a quick experiment to estimate noise level at 9kHz, I coupled a sig gen 
into my broadband RX loop antenna using a "current transformer in reverse" 
arrangement to induce a known EMF into the loop. I used Spectrum Lab to 
monitor the RX output, set up for QRSS3 reception (0.46Hz noise bandwidth). 
I reduced the signal level to give what I imagine would be an "M" copy 
trace, and from the induced EMF and loop area worked out the equivalent 
field strength - this was 35uV/m. It is a bit difficult to say what the SNR 
is, due to the constantly varying impulsive noise, but 6dB is probably not a 
million miles from the mark, which would imply a noise field strength about 
25uV/m per sqrtHz. I don't know if the noise level on VLF this evening is 
particularly high or low. The Alpha beacons are clearly audible here.

Cheers, Jim Moritz
73 de M0BMU




----- Original Message ----- 
From: "Andy Talbot" <andy.g4jnt@googlemail.com>
To: <rsgb_lf_group@blacksheep.org>
Sent: Thursday, February 25, 2010 11:22 AM
Subject: Re: LF: AW: 9 Dreamers


> To get the V/m value from this, first calculate the effective area of a 
> 9kHz
> isotropic antenna :
> At 9kHz, lambda = 33333m,   G = 4.pi.A/lambda^2,   G = 1,   so  A =
> 88*10^6  m^2
>
> 1mW of noise per Hz bandwidth, received in this aperture means noise 
> density
> Nd = is  1.1E-11 W/m^2
> Field strength E volts/metre, == SQRT(Nd. 377)
> = 65uV/m in 1 Hz bandwidth,    or 65uV/ (ROOT Hz)
>