Although I have never tried it, I wonder about the possibility of brewing
your own ceramic filter from some of Murata's 455KHz ceramic resonators.
Although not the Q of a quartz crystal, it may be worthwhile. I have some

I've done this with ceramic filters in tube circuits. You definatly
need to match the impedence to the tubes wich is high both for plate
and grid. What I did for that was to use a transistor IF can, filter,
IF can wired so the high impedence side was to the grids and plates.
Worked very well in a tube RX like the mighty midget.

For transistors the matching for those filters is IF can to get the
high collector impedence down to 1k range then the filter into the
base of the transistor. FETs get treated like tubes.

Allison
KB1GMX

Dale - regarding homebrew crystal filters - I wonder if you or any others
here have looked at Elecraft's crystal filter implementation in the K2?
It's built with discrete crystals and the bandwidth is variable over a large
range. Haven't seen that design exploited elsewhere, but don't know why.
It sure works well.

K8AC

"Floyd Sense" wrote in message
...

Dale - regarding homebrew crystal filters - I wonder if you or any others
here have looked at Elecraft's crystal filter implementation in the K2?
It's built with discrete crystals and the bandwidth is variable over a
large
range. Haven't seen that design exploited elsewhere, but don't know why.
It sure works well.

K8AC

That filter topology was, I think, first used by Ten Tec in their Scout.
From a purist standpoint there can be problems:
1. Asymmetrical skirts
2. Changing IN/OUT Z with BW
3. Shifting center freq as the BW is narrowed ( capacity loading)
4. I am guessing here, but I would think the group delay would suffer at one
end or the other
5. Passband ripple can become excessive as BW is increased.

I looked at this approach, along with a method described in QEX last year
for dealing with the center freq shift, but came to the conclusion that I
could design a much better filter if I optimized each BW- even though it
took 3 filters.

One aspect of filters that has long been either ignored or overlooked (
even though W7ZOI details it in EMRFD) is group delay. A friend (N2PK)
recently sent me 2 WAV files of a Yaesu 1000 stock 250Hz filter and his
homebrew 250 Hz filter. The difference was remarkable- his filter was much
cleaner and crisper sounding, no ringing. Great care was taken with group
delay in his design.

Dale W4OP

It would be interesting to know what was different about his filter. Do you
know?

K8AC

"Dale Parfitt" wrote in message news:3Q03e.27300
snip

One aspect of filters that has long been either ignored or overlooked (
even though W7ZOI details it in EMRFD) is group delay. A friend (N2PK)
recently sent me 2 WAV files of a Yaesu 1000 stock 250Hz filter and his
homebrew 250 Hz filter. The difference was remarkable- his filter was much
cleaner and crisper sounding, no ringing. Great care was taken with group
delay in his design.

Dale W4OP

On Mon, 28 Mar 2005 21:19:44 GMT, "Dale Parfitt"
wrote:


"Bill N2CQR MOHBR" wrote in message
. com...
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

Dale & Bill,
Jim, K8IQY has the Precision VXO and Crystal test rig that uses the
PVXO as a driver for the candidate IF filter crystal under test. I'm
currently building both of those.

73,
Ted KX4OM

"Ted Bruce" wrote in message
...
On Mon, 28 Mar 2005 21:19:44 GMT, "Dale Parfitt"
wrote:


"Bill N2CQR MOHBR" wrote in message
.com...
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

Dale & Bill,
Jim, K8IQY has the Precision VXO and Crystal test rig that uses the
PVXO as a driver for the candidate IF filter crystal under test. I'm
currently building both of those.
Ted KX4OM

K8IQY web page for this test rig
http://www.k8iqy.com/testequipment/pvxo/pvxopage.htm

w9gb

On Mon, 28 Mar 2005 21:19:44 GMT, "Dale Parfitt"
wrote:


"Bill N2CQR MOHBR" wrote in message
. com...
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

Dale, I checked in late on this thread; what is Bill Sabin's site URL?
I've been Googleing to beat the band, but it doesn't turn up.

Ted KX4OM

Dale, I checked in late on this thread; what is Bill Sabin's site URL?
I've been Googleing to beat the band, but it doesn't turn up.

Ted KX4OM
Hi Ted,
Plug Bill's call, N2CQR into QRZ.COM His URL is there.
Dale