[hpsdr] DDC Noise Figure

[KA2WEU at aol.com]

This is correct. ( Friees formula)
 
73 de Ulrich N1UL
 
 
In a message dated 3/28/2011 8:06:57 A.M. Eastern Daylight Time,  
h-hartfuss at t-online.de writes:

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Hi Edson,  

If the noise figure of the ADC is dominated by quantization noise,  it's
noise figure Fadc is given by
Fadc=((DV)^2)/(6kTRfs)
with DV the  voltage quantization step and fs the sampling frequency (see
for example  Frerking's book "Digital Signal Processing in  Communication
Systems").
So only by reducing the quantization step size  (more bits) or by
increasing the sampling rate fs you can reduce the noise  figure of the
ADC. You cannot improve this figure with measures in the  signal
processing pass.

In the Mercury case the effect of increasing  the sampling rate and/or
the number of bits will, however, be very small  since a preamp is
involved which has 20dB gain.

Generally, when  cascading stages characterized by noise figures F1 and
F2 the overall total  noise figure Ftot is always:
Ftot= F1 + (1/G)(F2-1)
where G is the gain  of the first stage. The noise figure F1 of the first
stage dominates the  overall behavior and that the more the higher its
gain G is. 
It is  completely independent of what you are cascading.

73, Hans,  DL2MDQ.

PS: In this context my paper on Mercury noise temperature  measurements
in TAPR / psr109 might be interest for  you.




-----Original Message-----
Date: Mon, 28 Mar 2011  01:06:16 +0200
Subject: Re: [hpsdr] DDC Noise Figure
From: Edson Pereira  <ewpereira at gmail.com>
To: KA2WEU at aol.com

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