Pete wrote:
Pete KE9OA Apr 14, 12:57 pm show options

The Inrad unit would be good. About those Murata filters..........the
older
Murata databook I have specifies those filters as having a 2k
impedance.
That is the design spec I have been using for the last several years,
and
the do work ok with that impedance. The 4k spec seems more in line with
the
natural impedance of many of the commercially available crystal
filters.

Pete
----------------------------------------
By 4K I meant BW, I have been using 2K (OK 2010 Ohm metal film,
"low noise" Dale mil surplus) for my load.
I use a BFO from teh ARRL circuit desing handbook circa 1975.
It uses a back to back varicap-diode and a DC voltage for tuning.
I use a MOSFET buffer to couple the out put to our HP SA at work.
My BFO tunes from 450~460KHz and is very clean. I have a HP DFC
and Tektronix scope to verify the Fc. Crude but very stable.

The BFO is routed through a emiter follower to give me 50 Ohms and I
add a 2K resistor in series.

The BFO was from my R392/URR days. That reciever is the little brother
to the R390. It has a 455KHZ IF out and I built my own product detector
using a motorola balanced modulator. The BFO is all that remains of
that
project. It is in a metal Sucretes cough drop box and it was too good
to
toss.

Today I use Altoid metal tins for a lot of my projects. The tiny ones
make
good Reverse & Overvoltage Protection cases because they are RF tight,
the larger ones make either good project boxes, or are great for
holding
sub-modules. It is so much easier to build a "complex" project if the
sections can be built and tested individualyu. Plus it makes "major"
changes a piece of cake. Build a new whatever module.

I am debating building something like the non longer available Kiwa
MAP outboard IF strip complete with a good selection of different BW
filtters, a stand alone BFO, a synch AM detector would be nice, but
I really don't know enough to try to design one from the ground up,
and my search efforts have been a mixed bag.

A seperate IF strip /detector audio conditioning would be very do-able
and this fitler research may well turn into that. I liked Craig's
discription of his "tone tilt" tone control, and found a good circuit
on a electiic guitar site. They had their's set for 1K, but it was
simple
to scale the parts to give his 700Hz tilt point, I like it much better
then the simple hi-cut, or complex trebble/bass boast HiFi tone
controls.

I have a couple of mil-surplus 300-2500HZ AF filtes that are very
narrow
with no ringing. For my needs a outboard detector/etc is looking like a
winner. I really only need one "perfect" IF/BFO/Fitler so I could
switch between my 2 R2000s and use the standard on board/in radio
detector/BFO for back ground monitoring.

I am mainly into utility comms and I almost never have to really dig on
two
freqs at the same time.

As to the source and load resitances when using Murata ceramic filters,
I have found higher Z sources and lower Z loads improve the skirt. But
very
much off on either the in or out really ups the loss.

Terry