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LF: Re: 9kHz noise level

from [James Moritz] [Permanent Link][Original]
To: <[email protected]>
Subject: LF: Re: 9kHz noise level
From: "James Moritz" <[email protected]>
Date: Thu, 25 Feb 2010 18:50:46 -0000
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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" <[email protected]> 
To: <[email protected]>
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)
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