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Old July 3rd 07, 05:30 AM posted to rec.radio.amateur.homebrew
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First recorded activity by RadioBanter: Jan 2007
Posts: 27
Default IF Freq for SDR sampling

On Jul 2, 10:35 pm, wrote:
That makes more sense. The selectable LC filters octave or fraction
of an octave?


I was looking at fraction of an octave, however I have yet to decide
anything more specific. Actually I started by playing with Ansoft
Designer to design the filters, keep being unhappy how they turned
out, and as a result keep having to increase the first IF to make it
easier to have good image rejection. I had naively started with 10.7
MHz as the first IF ... I may not have a lot accomplished, however
I'm certainly learning a thing or two. :-)

Generally it's antenna, a low loss selectivity, RFamp, Image stripping
filter then mixer.


What's the downside of doing the selectivity and image stripping as
one
filter prior to the RFamp?

I consider a RF amp at VHF/UHF of more than 1.5DB NF to be noisy.
This is because current technology for low noise amps are well under
1 DB to the 500mhz region maybe higher.


Care to mention a couple of model numbers?

-- John


 
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