Dittos. Also most electrically tuned circuits suffer from lower Q
and strays. It is hard enough to build hi Q cavities let alone try
to emulate one. It might be more worth while to build a motorized
cavity or electrical band switching of helicals, but who has room for
all that? Many manufacturers have concentrated on making RF stages
that can withstand very high levels without intermod. Of course none
of this will help you if you are at a congested site with mixes in
transmitters without circulators.

At HF it is practical to build a bandswitched set of bandpass filters
much like the ones found in some radios. Toroids can make them small
enough, but again you need to be careful not to overload them.

wrote in message
oups.com...
I think part of the reason for little information or enthusiam is
the
diodes tendancy for IMD on strong signals. This increases the
complexity of the circuit. You might check with the ARRL and see if
any
information is available from past QEX articles. I am researching
the
same thing for a HF preselector. I am going to experiment with
solid
state relays. Just a suggestion. Try the Vishay site
as(http://www.vishay.com/solid-state-relays/). I have found little
info
on varactor tuned pre-selectors