Dave,
Would another 'IF' stage, or filtering, or 'nulling', or whatever you
want to call it, help? Sure. But then you start running into the
'practical' thingy again. It can get sort of complicated deciding
what is 'noise' and what is desired signal. DSP does a lot of that
when told how to do it by the controlling algorithms (or is that 'Al-
Gore-isms'? sorry, I know better, just can't help it). The mainest
problem is the time it takes to do that, it is not instantaneous. And
if you are going to make that controlling algorithm variable, the time
it takes makes things even more time consuming, not to mention
difficult. Keeping in mind that simply making the antenna larger/
longer can do about the same thing at less expense (time/work/$$$),
why not? Easy to do with a recording (sort of), very difficult in
real time. Manually doing all that is almost impossible. How do you
decide what to 'do' before it's too late? There are limits with
today's technology. So, put it off till 'tomorrow', right?
- 'Doc

(all puns intended, even the ones I didn't intend)