[linrad] Detecting phase modulation with undersampling

["Dr. David Kirkby" <drkirkby@xxxxxxxxxxxxxxxxx>]

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)


LINRADDARNIL