RE: [linrad] Detecting phase modulation with undersampling

["Robert McGwier" <rwmcgwier@xxxxxxxxxxx>]

If your assumption that bandpass sampling will work on this
signal, then you will simply do the PM on the undersampled
signal.  The MODULATION will not be undersampled and straight
PM detection will work on the sampled signal.

Bob
N4HY
 

-----Original Message-----
From: owner-linrad@xxxxxxxxxxxxxxxxxxxxxx
[mailto:owner-linrad@xxxxxxxxxxxxxxxxxxxxxx]On Behalf Of Dr. David
Kirkby
Sent: Friday, October 22, 2004 10:46 AM
To: linrad@xxxxxxxxxxxxxxxxxxxxxx
Subject: [linrad] Detecting phase modulation with undersampling


Hi,
    I has anyone any experience of demodualting phase modulated signals?

I am tryiing to measure the phase shift between two signals, when they 
are derrived from the same source? I guess you could say this is a form 
of phase modulation, but whereas for normal 'PM' receiver you don't have 
access to crystal developing the signal in the first place, I do in this 
case.

The problem is I need to undersample this. I have an A/D that can do 65 
MS/s, but the input can be upt to 200 MHz - in pracitce I will use 70 
MHz. However, since the bandwidth of the signal is narrow (< 1 kHz), I 
am not breaking the Nyquist criteria, which states you need to sample at 
no less than twice the *bandwidth* of the signal, and not twice the 
frequency as most people seem to think.

I then intend doing the processing on a dedicated DSP chip (TI 6701), 
rather than a PC's CPU.

I realise this is not exactly what the Linrad project is, but i though 
some here might have some ideas.

-- 
Dr. David Kirkby PhD CEng MIEE
Senior Research Fellow
Department of Medical Physics
University College London
11-20 Capper St
London WC1E 6JA
Tel: 020 7679 6406 (direct line)
Tel: 020 7679 6262 (office)





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