William E. Sabin wrote:
"AndyS" andysharpe@
A large increase in a receiver amplifier load impedance just outside the
passband of a crystal filter (or other types of filter) can cause adjacent
channel susceptibility. The network between the amplifier and the filter
should be designed to prevent this occurrence. There are networks that can
reverse this effect, so the impedance drops instead of increasing.
Simulations and impedance measurements can verify.

Bill W0IYH

Andy comments:

A good point. But I am not aware of any passive networks than
can roll the impedance off ( or bring it up) fast enough to handle
the adjacent channel problem. Adjacent channels are usually
(in my experience) only a few Khz away while the xtal filter is
usually many Mhz, and a passive network just doesn't change
the impedance that quickly. For those problems, I have always
had to go to a passive resistor source, such as a collector resistor,
or use a coil with a Q low enough to provide the same effect.

If I am incorrect in this, could you please elaborate on what
passive matching circuit you are reccommending. ?

Andy W4OAH