"radio_rookie" wrote in message
ps.com...

doesn't anyone use zero IF now a days. What is the problem of brining
the RF signal directly to baseband? Does the IF stage conditions the
incoming signal? What are the advantages of the IF stage?

Actually, it is fairly common -- it is called direct conversion and it is
very popular for simple rigs.

It is not without issues. Converting down to audio means that you cannot
eliminate the "other sideband". Also, since the RF amp needs to be
broadband, you can only get limited gain, so you end up needing a lot of
gain in the audio stage. This is achievable, but it is a little tricky to
manage oscillations, ringing and the like. In addition, getting narrow
bandwidth at audio is also a little dicey, and you can't have it at RF
unless you tune the RF ... also tricky.

Which is why most receivers these days are still superhets. You can choose
an IF that allows you to manage the bandwidth, and even so, multiple
conversion is pretty popular. Many commercial rigs are triple conversion,
typically with IF's around 60 MHz, 10 MHz and 455 kHz, with a very liberal
interpretation of "around" g

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