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On 07/20/2020 11:42 AM, Brian Padalino
wrote:
Indeed second Nyquist
zone before decimation.
My thought was
143.05 MHz -> transpose by 100 MHz using the DDC (NCO at
100 MHz considering the
200 MHz sampling rate) to reach 43.05, and after
transposition, decimating to reach
8 MS/s (I do have Epcos B3607 SAW filters 140+/-3 MHz
frontend to select only the
signal I am interested in).
It is in the decimation process that I was thinking of being
in the third
Nyquist zone after decimation, which is incorrect because 8
MS/s is -4 to +4, so that
43.05 is in the 6th Nyquist zone after decimation
(\in[36:44] MHz).
This seems weird.
Sampling 143.05MHz at 200MHz real will produce the
desired signal at 56.95MHz and conjugated, won't it? Since
it's real, it'll appear at both positive and negative
frequencies, with the negative component being conjugated.
So if you mix with 56.95MHz, it will take the conjugated
negative signal of the conjugated desired signal and mix it
to 0Hz. Then you can go through the decimation filtering
however you want and everything is centered at 0Hz.
Right?
Brian
Certainly in older support for BASIC_RX, you could sort-of treat it
like any other daughter-card, and issue a tune request, and it would
deliver
a complex base-band centered at the desired frequency.
What I don't recall is whether this was completed for X310 or not...
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