On 10/24/20 3:53 PM, paul swed wrote:
Antenna and filtering are not a problem for me. I use the 10' X 10' square
loop and about 800' of wire with a cap to resonate at 60 KHz and then a
preamp really to drive 140' of coax. Currently using a modified KD2BD
receiver frontend but using a 350 Hz xtal filter. Yes indeed that hamfest
find was amazing.
Looks like you have to build a costa loop SDR. Looked at lots of documents.
My first question to the group.
Can a single incoming sample be converted to I & Q through math. I sort of
think so. The original sample might be I and then use math to make Q. That
would save an entire analog chain. The teensy has a single chain for mic
level input. Though it does feed left and right channels. Granted there are
two audio chains at line level.
The teensy has a NCO that can create a quadrature output. The alternate
would be to use that to drive analog switches as a multiplier to form I & Q
samples.
Regards
Paul
WB8TSL
The classic way to get I/Q is to sample at 4 times the desired rate,
then, given that your input samples are x(1),x(2),x(3),x(4), etc. the
I/Q streams are
I(1) = X(1)
Q(1) = X(2)
I(2) = -X(3)
Q(2) = -X(4)
I(3) = X(5)
Q(3) = X(6)
I(4) = -X(7)
Q(4) = -X(8)
and so forth.
This will put your signal right in the middle of the sampling bandwidth.
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