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

[Murray Lang]

What's still niggling me is the resolution, or granularity if you like, of 
phase shifts applied by I/Q. Sure, you can swing the phase around but what 
are the step sizes at RF. We know it's not going to be continuous, so what 
is it?

Anyway, I think it's time to retreat and consider what people have said.

BTW Nyall I don't think you clicked on "reply all" so your posting might 
not have reached the group. I'm forwarding it.

Cheers
Murray
VK6HL

At 05:35 PM 5/09/2006, Nyall Davies wrote:
>It is worth remebering that :
>Phase is retained through mixers - 360 degrees sahift at 1000 MHz is 360
>dgrees at 10 MHz IF or baseband.
>An antenna is a spacial filter - so there is a direct parallel in filtering
>in the frequency domain.
>A set of antennas give a set of spacial samples we need to reduce them to IF
>or baseband and use these samples to form the beams (or null)
>It does mean we need a set of identical Rx front ends - A/Ds down converters
>etc down to the DSP
>The AD6636 that someone drew our attention to recently has a number of 
>channels for this purpose.
>A SDR does make the production of a set of channels somewhat easier - 
>think of trying to match crystal filters for phase
>
>I trust this helps a bit
>
>Nyall G8IBR
>
>----- Original Message ----- From: "Murray Lang" 
><murray.lang at metoceanengineers.com>
>To: <hpsdr at hpsdr.org>
>Sent: Tuesday, September 05, 2006 1:36 AM
>Subject: [hpsdr] My doubts about I/Q beam-forming
>
>
>>***** 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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