[hpsdr] Infinite precision, phased arrays,and us

[Murray Lang]

Thanks again Bob,

Just to take a step backwards, this all came about from discussion in 
another thread a while back where the topic of beamforming arose. At one 
point I flippantly discounted controlling the RF phase shifts via I/Q but 
was pulled up and reminded that with I/Q you can do anything. OK, you can 
do phase modulation so why not a steady phase shift? I was uncomfortable 
with it but couldn't put my finger on exactly why so I let it go. Now I'm 
grabbing it back again.

Yes, I knew that their would be more than one QSD/E with synchronised 
(English) clocks. I also understood that the HPSDR dudes were already 
catering for synchronised clocks - it's not new. I'm just trying to 
understand why the concept of achieving phase shifts via cunning 
manipulation of IQ is not sitting quietly in my head.

It's one thing to shift the phase to accurately represent a modulating 
audio signal, but to have such fine control as to be accurate to within a 
fraction of a wavelength of the RF carrier seems to me a lot to ask of a 
sound card. Consider a phase modulated signal applied to such a phase 
shifted carrier. I/Q would have both shifts encoded into it: a component 
accurate at AF and a component accurate at RF.

Murray
VK6HL





At 12:33 PM 7/09/2006, Robert McGwier wrote:
>***** High Performance Software Defined Radio Discussion List *****
>
>Baaa.  You are doing it justice.  Believe me.  There are 100 hundred
>people reading this that wanted to ask the questions and didn't.
>
>As I said in the previous,  for a phased array in the HPSDR system,
>we are not likely to use only one QSE for transmit or QSD for receive.
>  We are not likely to use a single sound card.   You will need one QSD
>and one sound card pair for EACH ELEMENT in the phased array and the
>QSD oscillator<<S>>  must all be the same source just as the sampling
>clock on the A/D's must all be derived from the same clock.   But they
>are separate devices, one per element in our narrow band phased array.
>   If we chose to use only one QSD and sound card, then the combing of
>the elements must be done before it and there must be a phase shifter
>in each antenna element.
>
>I think you are getting there.  You are asking the right questions to
>understand the system.
>
>Bob
>N4HY
>
>
>
>At 09:41 AM 7/09/2006, Murray Lang wrote:
> > ***** High Performance Software Defined Radio Discussion List *****
> >
> > What about the situation where QSE is the only "mixing" stage and I/Q 
> is from a sound card? Where does frequency response come into it? You've 
> only talked about word size. You seem to be saying that phase is a DC 
> component of I/Q.
>
>Sorry Bob, I realise that I haven't done justice to what you've
>posted. I can see that the commutative nature of mixing helps but I'm
>having trouble relating that to the situation I've identified above.
>The only oscillator is the 4xoutput carrier and it's being modulated
>by a sound card.
>
>Murray
>VK6HL
>_______________________________________________
>HPSDR Discussion List
>To post msg: hpsdr at hpsdr.org
>Subscription help: http://lists.hpsdr.org/listinfo.cgi/hpsdr-hpsdr.org
>HPSDR web page: http://hpsdr.org
>Archives: http://lists.hpsdr.org/pipermail/hpsdr-hpsdr.org/



 1157608626.0