[hpsdr] My doubts about I/Q beam-forming

[Murray Lang]

Hi Bob

My doubts were confined only to the concept of beamforming using the I/Q 
signal to adjust the phase. I just can't see how a signal from a sound card 
(say) can possibly accurately adjust the phase of an RF carrier to within a 
small fraction of the RF wavelength. I don't doubt that it can adjust it, 
just not to any useable accuracy.

Murray
VK6HL

At 10:49 AM 5/09/2006, Robert McGwier wrote:
>Murray:
>
>So long as the total bandwidth of the signal or band of interest is small 
>compared to the carrier,   beam forming by adjustment of the LO's by 
>analog phase shifters or by simple phase rotations in software all will 
>work to do beam forming.   If you want you can read all sorts of 
>literature about "narrow band" phased arrays.  Beam forming by simple I/Q 
>rotation will indeed work so long as all the LO's, A/D's,  etc.  in the 
>system of coherent.   They cannot be wandering around or independent of 
>each other and still have the rotation by multiplication do beam 
>forming.  So while not completely trivial in hardware,  it is a pretty 
>simple concept.
>
>Bob
>N4HY
>
>
>
>Murray Lang wrote:
>>***** High Performance Software Defined Radio Discussion List *****
>>
>>My doubts about the ability to do RF beam-forming via I/Q have clarified 
>>somewhat.
>>
>>Beam-forming would seem feasible given that you can modulate a carrier 
>>any way you like with I/Q. However, the *resolution* of that modulation 
>>is limited by the I/Q bandwidth and dynamic range. To accurately and 
>>steadily control the phase of an RF carrier to within a small fraction of 
>>its wavelength would require an I/Q  bandwidth of the same order as the RF.
>>
>>Would it not?
>>
>>Murray - VK6HL
>>
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