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Re: [linrad] RE: Detecting phase modulation with undersampling

Krzysztof Kamieniecki wrote:

>I'm probably confused but with the processing power of the DSP that you have why
>not just create a digital version of the analog circuits you have used in the
>past. You may need to downconvert and decimate the input signals first.
In theory that sounds good, but it is not too obvious (to me anyway), 
the best way to do that. The DSP is fast, but not fast enough to do 
real-time processing of a 70 MHz signal directly. The key will be the 
undersampling, but that, along with the fact I can't continuously pass 
data from the A/D to the DSP due to the limitaitions of the bus between 
them, causes even more complications.

>You may also want to look at GNURadio, if you haven't yet, it is a Software
>Radio Toolkit. 
I will do that.

>Although it is PC based you could prototype your design using it. You can post this question to the GNURadio list as well, there seem to be a
>lot of people there with a wide range of signal processing interests and
Knowing GNU stuff, it will probably run on any UNIX system, which is a 
good thing. I rather have an aversion to PC's - especially if they run 
Windoze. At home I have UNIX computers from Sun, IBM, SGI, Dec, HP (plus 
any I forgot). I find testing software on lots of platforms a very good 
way to find bugs.

One of my programs for analysing transmission lines


has been built on various UNIX systems, but including a very old Cray 
supercomputer and a Sony Playstation 2!!! I personally built it on the 
Cray (which caused a few problems due to the fact the size of a short is 
8 bytes, rather than the 2, which it has been on any computer 8, 16, 32 
or 64 bit computer I have come across). Someone else went to the trouble 
of building it on a Sony Playstation 2. It wil also build on Windoze.

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)