The Rockwell-Collins Torsional Mode mechanical filters are right around 90
dollars, shipped. This is the low-cost
526-8695-XXX series that many of the manufacturers are selling as optional
filters for 120 dollars and up.
If you do look for one of the old coffin style mechanical filters, people
are selling those items for very silly prices so I would avoid those. A
disadvantage of the older style vs the Torsional Mode units is that the
older style filters require terminating capacitors at the inputs and
outputs. The Torsional Mode units don't require any external terminations,
as long as the stray capacitance on the PC board and its switching is below
30pF. These filters also have an Input/Output Z of 2k, which means that you
can replace one of the Murata ceramic ladder filters without any
modification to the existing circuit.
Buy them directly from Rockwell Filter Products Division, Costa Mesa,
California.
Lee Cornett is the sales person that you want to speak with.
As far as the buffer amplifier, what kind are you using? Source follower?
Common source with or without bypass capacitor?
If you use a JFET as a common source, you can use it is self-biased mode.
Use a 2k gate resistor to ground. The drain resistor should be 6.8k and the
source resistor should be 2.4k. This will give a Thevenin resistance of
around 1.7k...........close enough for matching the I/O characteristics of
the filter. Remember, the input capacitance of the JFET will be around 8pF,
but this will have minimal effect on the filter response.
Arthur is correct about that shape factor; crystal and mechanical filters
will have a much better characteristic.

Pete

"Arthur Pozner" wrote in message
...
Murata filters are not known for good shape factor(6db//60db) . When
stacked in series losses mount rapidly. And they seem to have a lot
more noise when compared to crystal or mechanical IF filters. Have you
tried to build a crystal ladder filter? Very effective and MUCH cheaper
than any other IF badpass filter ,and Inrad is not the costliest-
KVG,Collins etc.may set one back many hundreds of dollars...