[hpsdr] DDC Noise Figure

[h-hartfuss at t-online.de]

Edson,
please see for more details as well p 631 ff in Rohde, Whitaker,
"Communications Receivers", 3rd edition 
(sorry, Ulrich)
73, Hans, DL2MDQ.


-----Original Message-----
Date: Mon, 28 Mar 2011 14:12:44 +0200
Subject: Re: [hpsdr] DDC Noise Figure
From: KA2WEU at aol.com
To: h-hartfuss at t-online.de, ewpereira at gmail.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: *****    High Performance Software
Defined Radio Discussion List *****

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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