Thanks Marcus.
The reason why I do not want to attenuate is because I want to receive a
high-powered signal and low-powered signal at the same frequency.
If I attenuate then the low-powered signal will be reduced and if I go
beyond the noise floor, I might see it. The goal was to stretch the
difference in power between the high-powered signal and the low-power. But
now if I think about it no matter what I will be limited to my Dynamic
Range.
Yes, given that perfectly-acceptable signals can arrive at the front-end
at -90dBm or lower, and you want to be able
to "see" +30dBm at the same time, you'll need roughly 120dB of
dynamic range. But +30dBm is about 7.07VRMS, or
about 10VP. There's no way on gods little green earth that you're
going to find an ADC that can sample at 100Msps or
more, and have a peak input voltage of +10VP (+7VRMS), and have a
120dB dynamic range. Let alone a receiver
front-end RF chain that can tolerate anything more than about +15dBm
or so.
For 120dB dynamic range, you'd need a 20-bit ADC, *and* it would need to
run at a fast sample rate, *and* it would need to be
able to handle +10VP input. Not gonna happen.
I'm curious about why you need to inject +30dBm into a receiver. You're
getting no more information out of that signal than if
it arrived at -30dBm.
--
Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org
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