On 07/26/2020 03:15 PM, Koyel Das (Vehere) wrote:
Hi Marcus,
Good that you replied my email. Since you work on Radio Astronomy as I
heard from Neel, I want to ask you something. By using USRP I saw that
without any special configuration the phases of any two channels of
USRP 2955 are phase coherent and the phase difference value is
constant for a stationary source in one run of the application.
However, for phase aligned operation that is instrumental phase
difference between two channels to be zero we need LO sharing and time
commands. So suppose I don’t phase align the system and find delay-
rate spectrum then what impact the instrumental phase offset between
two channels will have on the delays of sources in the DR spectrum.
Will the offset add an additional delay to every source by a fixed
amount or this will have some random effects on the delays of the
sources in DR spectrum. You may be knowing but still, in delay-rate,
rate stands for Doppler shift.
Regards,
Koyel
Thinking about it for 30 seconds, I don't think it would have any impact
on perceived doppler shift--it's a one-time phase diference only. So
distance
estimates would be affected, but not doppler or doppler derivative, I
think.
In radio astronomy interferometry, if the phases aren't aligned, then
the "phase center" of the array isn't where you think it is, and that can
lead to sky-position estimates being a bit wrong. If your science
goals don't include high-quality position estimates, then as long as the
two sides "march together" (that is, are long-term phase-coherent,
without necessarily having a zero phase offset), then you can still
do science.
