Re: AW: LF: RE: Re: VLF_8.79 kHz

[Andy Talbot <andy.g4jnt@googlemail.com>]

Yes, but what is the gain / antenna factor of your Miniwhip? 

Measuing -115dBm means little in itself, you need to convert this to a calibrated V/m form.

 

IF the miniwhip were exactly 1m long and positioned over a good groundplane, fed an infinite input impedance, zero input capacitance voltage follower amp with unity voltage gain into 50 ohms, then -115dBm would equate to 0.4uV/m in 24Hz,  or  .08uV/m/ SQRT Hz.   

 

If the value quoted recently of 150dB kTB  is assumed, which is 25dB lower that my original calculation, it suggests a value  in the region of  4uV / m / SQRT Hz may be more typical.

Andy
www.g4jnt.com

On 25 February 2010 12:02, Roelof Bakker <roelof@ndb.demon.nl> wrote:

Hello Andy,

I measured the noise on 8800 Hz received on my mini-whip.
Receiver: SPM-30, BW = 24 Hz, noise level = -115 dBm

The same measurement with a PERSEUS SDR and a bandwidth of 20 Hz revealed a noise level of -122 dBm.
PERSEUS has an input isolating transformer, which rolls off below 15 kHz, hence the lower measured noise level.

It does not look too bad to me, really.

73,
Roelof Bakker, pa0rdt