[time-nuts] Noise source measurement

Javier Herrero jherrero at hvsistemas.es
Sat Oct 22 19:21:51 UTC 2011

El 22/10/2011 16:49, Graham / KE9H escribió:
> Javier:
> When you say your Spectrum Analyzer bandwidth is set to 1 MHz, do you
> mean the frequency span width of the screen?
> I would think that your receiver bandwidth is the Video Bandwidth, 
> therefore 1 kHz.
> Correction for noise bandwidth is an adjustment for power, 
> proportional to
> bandwidth, therefore 10log(BW1/BW2)
> Correcting 1 KHz to 1 Hz is therefore a 30 dB adjustment, not a 60 dB 
> adjustment.
> I think what you are measuring is more like -75dBm/Hz.
No, with 1MHz bandwidth I mean the IF filter bandwidth, not the span. 
The 1kHz video filter processes the detected output, so it has no 
effect, other than to make the measurement less noisy. When changing the 
video bandwidth to 10kHz or 100Hz, the measurement of the noise does not 
change, however modifying the IF bandwidth to 100kHz, the measurement 
drops 10dB, as expected.


Javier, EA1CRB

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