On Sat, 26 Jul 2003 21:55:40 +0100, Paul Burridge
wrote:

On Sat, 26 Jul 2003 18:50:45 +0100, Don Pearce
wrote:

This is a strange way of achieving your aim. You should be going for
adjacent channel selectivity in the IF, not the front end. That way
you can use a fixed frequency filter, and it can be as lossy as you
like - and it will be lossy to achieve these kinds of selectivity with
achievable unloaded Q.

If you put this filter at the RF stage where it will help with
adjacent channel selectivity,m it must be before the first amplifier,
and that will have killed your hoped-for sensitivity increase. If you
put it after that amplifier, then you may as well leave it where it
belongs - in the IF.

Thanks, Don. I'm aware this is a daft way of doing it, but I don't
have much choice. The IF stages of this rx are not accessable and no
schematic is available, either. The makers have declined to make them
available and threatened any service personel who do so with
termination of their contracts. Faced with these obstacles, I don't
see any other option, apart from boosting the tx power instead; a
solution which just brings a different load of problems.
--

"I believe history will be kind to me, since I intend
to write it." - Winston Churchill


Hello Paul,
it is time to dump that receiver and start again. It is too
small and tiddly and I know you do not like surface
mount size components. I would imagine that you
have plenty of room inside that robot of yours to
take a fairly large die cast box. My suggestion is
find a radio control receiver that you can get
circuit diagrams for or build one from scratch
on large pieces of printed circuit board using
"ugly construction" or "dead bug construction".
Google those terms and you will see what I am
talking about.

You can then build the various stages of the
receiver on separate boards and try all the
different things you have been wishing to do
but couldn't due to miniature parts, lack of access
and lack of information.
After you have a prototype ugly construction
receiver working, you can miniaturize if you
wish on the the next unit. You will need spares
anyway. Heh heh heh......it is fighting machine.

Have a look at National semiconductor application
notes for radio control receiver, they might even give
you half a dozen chips as free samples.

Google search for radio control receiver schematics.

"Buy" is a dirty word for me, but you might be able
to buy a receiver in kit form with all the information on
construction and alignment as well as a "how it works"
description.

Have Fun,
John Crighton
Sydney