On 05/13/2018 08:45 PM, David Bengtson wrote:
On a side note, the combination of wideband LNA's in front of wideband
radios is generally something to be careful of, as strong signals out
of band can cause problems. Bandpass filtering in front of LNA's can
be a very good idea to think about.
The only caution I have about filtering *IN FRONT* of an LNA is that the
loss through the filter is usually enough to turn your
LNA into just an "A" :)
The approach that I use for radio astronomy is to place the
highest-dynamic-range LNA "out front", then immediately filter, some
more gain, some
more filtering, then the radio....
In some circumstances, of course, you simply have to pay the noise
penalty of having a filter between your antenna and the first gain stage.
We do this at CCERA for our 611MHz interferometer, because there's
just SO MUCH adjacent crap. I had some multi-stage cavity filters made
in China for me, and they're about 1.5dB insertion loss. But
followed by a 0.5dB LNA, it's still "low enough" noise to do what we
need it to do.
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