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

[Cecil Bayona]

Murray Lang wrote:
> ***** High Performance Software Defined Radio Discussion List *****
> 
> Hi Ken,
> 
> No I don't, but I'll try to look it up. I've seen an article on (RX) 
> beamforming with "SDR" where they directly sample the RF using a separate 
> A/D for each line and synchronise the LO clocks. I believe a similar result 
> can be achieved by synchronising clocks on multiple QSDs/QSEs. But here the 
> phase adjustment is through RF PLLs.
> 
> My posting was actually a continuation of an earlier discussion where it 
> was proposed that beamforming could be manipulated via I/Q. I wasn't 
> comfortable with it at the time, but couldn't explain why beyond a vague 
> worry about I/Q frequency response.
> 
> Murray - VK6HL
> 
> At 08:36 AM 5/09/2006, Ken - N9VV wrote:
>> Hi Murray, I am probably way off base here, but there was an article in 
>> QEX this past month about what looks like what might be beamforming for 
>> microwave freqs using phased arrays and SDR/DSP. Do you have access to a 
>> copy of QEX?
>> de ken n9vv
>>
>>
>> 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
>>> _______________________________________________
> 

If you have multiple receivers with synchronized DDS LO's, you can steer 
the array by changing the phase differences between the multiple 
separate DDS chips. The DDS chips will allow you to do that easily, they 
have a phase register to shift the output clock by minute amounts.


-- 

Cecil
KD5NWA
www.qrpradio.com www.hpsdr.com

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