> >From a curve in an old 1981 copy of "Reference Data for Radio Engineers" ,
> at 10kHz (lowest value shown) atmospheric noise is given as being in the in
> the range 155 to 175 dB kToB. This will have risen over the intervening
> years due to the proliferation of industrial / domestic electrical
> junk-noise, so if just we take the upper figure it shouldn't be outrageous
> to start with.
>
> In a reference 1Hz bandwidth kTB = -174dBm, into a theoretical 0dBi
> antenna. Therefore, you could expect to see about 0dBm, or about 1mW of
> noise from such a beast
Why? It is for 175 dB noise level, not for lowest 155 dB level.
>
> 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)
For 155 dB it changes to 6.5 uV/m in 1 Hz. In 0.01 Hz (QRSS100) it yelds
0.65 uV/m. 2.5 uV/m is ~10 dB over noise. Right?
Regards,
Alexander/RA9MB
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