Dale: I was faced with doing the complex analysis of the individual
crystal
parameters when I was building my first superhet (W1FB's "Barebones"
aka
"Barbados" RX). I just skipped all of the analysis and used the same
capacitor
values that Doug had used in his version. I'm sure my filter's
passband wasn't nearly as pretty as it could have been, but it
definitely produced the
desired "single signal effect." I was happy.

As I mentioned in the earlier post, I have an 80/40 meter tube type RX
(Mate
for the Mighty Midget"). It has a 455 kHz IF. This makes homebrew
filter making difficult! I tried, but crystals were hard to come by
in that freq
range. In the end, I threw in the towel and just used a 455 Khz IF
can
in lieu of the filter. Great for listening to AM! But now I want to
narrow
it down a bit, so I'm thinking about yanking out the IF can and
replacing
it with a commercial 455 kc filter from the junkbox. I need to figure
out
how to handle the impedance matching issues (input and output).

73 Bill M0HBR N2CQR CU2JL
http://planeta.clix.pt/n2cqr




"Dale Parfitt" wrote in message news:Qx_1e.34384$oa6.2111@trnddc07...
"Bill N2CQR MOHBR" wrote in message
om...
I really enjoyed the message thread sparked by the pictures of
Dale's very FB HB RX. We need more of that kind of discussion...

Here is what I've been working on in London:

Hi Bill,
I have trouble keeping up with where in the world you are, but visit your
site regularly to see what you are up to.
I would encourage others to brew their own xtal filters. uP xtals are cheap
enough today that you can buy a pile and match up what you need. W7ZOI's
articles on crystal filters takes the mystery out.
Probably the most difficult part is characterizing individual crystals so
you can plug in the numbers. I use an HP network analyzer, but Wes also
shows a test jig for doing this. Alternatively, N2PK's VNA will do an
excellent job. In the end, you can make better filters than you can buy- and
for a heck of a lot less $$.
N2PK recently sent me 2 WAV files- one recorded with the 1000MP stock 250 Hz
filter; the other with a homebrew 250 Hz filter- it took no imagination to
discern which one was cleaner.
Now, I'll go have a look at Bill W0IYH's site.

Dale W4OP