[Lf] [Fwd: LF: VLF Sensitivity - Noise Levels]

[Andre' Kesteloot]

James Moritz wrote:

> Dear LF Group,
>         Regarding the recent comments about receiver sensitivity at
> VLF - I did some measurements with my 'SAQ' ferrite rod antenna,
> and some Helmholz coils I made for 136kHz measurements to
> generate a known field strength.
>
> The atmospheric noise is all of an impulsive, thunderstorm type, so
> it's difficult to measure in a meaningful way, but I can say that a
> 30uV/m field strength is audible at 17.2kHz, and 50uV/m at 9kHz,
> with the current QRN levels - presumably this situation would be
> improved during the winter, but I don't know by how much. I was
> using 100Hz bandwidth - spectrogram would do better of course.
>
> By way of comparison, SAQ measured in at about 750uV/m. I
> reckon this means about 20kW ERP, very approximately.
>
> I found that having either the ferrite rod, or the tuned whip antenna,
> near the mains wiring of the house produced significant 50Hz
> QRM, but moving both antennas 5m away from the house reduced
> the noise on the rod to an inaudible level, but still detectable on the
> whip, although not serious.
>
> Cheers, Jim Moritz
> 73 de M0BMU