wrote:

Sorry for the botched who wrote what, but I haven't
had time to hunt up a better news reader.
-------------------------------

Arthur Pozner Apr 9, 9:31 am show options
Newsgroups: rec.radio.shortwave
From: (Arthur Pozner) - Find messages by this
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Date: Sat, 9 Apr 2005 12:31:37 -0400
Local: Sat,Apr 9 2005 9:31 am
Subject: Question for Pete KE9OA
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455KHz resonators are commonly used in remote controls. Have not tried
building a lattice or a ladder filter with them yet. But, what if
it just might be succesful-- that's why experimenting is fun.
Collins mechanical filters do have very good rejection just as Pete has
stated, in fact, at 455KHz it might as well have better
selectivity/rejection/low distortion/phase linearity than any other
filter type. I believe R-2000 is a triple conversion receiver, has
anybody ever try changing out the first (roofing) filter.Just for the
sake of experimenting.
------------------------------------------------
Sadly the R2000 uses a variable first IF. Or at least that is what
I tink after a long study of the service manual.
My large diagram is at work, I was in a hurry when I left Friday.

But looking at the service manual that I have at home:
Thefirst ceramic fitler is centered at 9.875, but is rated at +/-
130KHz for the 3db points, and +/- 2MHz! for -30dB points.
The manual says the first If 45.85~45.90MHz then that is
converted to 9.850~9.90 MHz.

I doubt if there is enough market numbers for anyone to make
and market a 9.865MHz +/-15KHz filter. Ihave looked, but have
found one. Building a latice filter is in my dream book.

I tried Pete's suggestions and a set of three stacked 555Is in
series may do the trick. I put the widest one first, followed the
narrower, ending with the narrowist. They are all within spec,
but after measuring 11, I went with the narrowist, that had the
proper center freq. 1 had the center freq at 453.8.

I am listining as we speak and the results are well worth the effort.
It pays to have frineds with well stocked junk rooms. I was given
12 older maxon MCB25 CBs. One was still in the plastic, so I
decided to add that one to the RF stable. That is just what I need,
another radio!

I tried to use the 455 3 pinresonators and found they make great
CW fitlers. The bnadwidth is too naroow, and by stacking them you
get pretty decent skirts.

Terry


There are Murata (and clone) 455 KHz ceramic filters in old cordless
phones and pagers as well. i always ttake the junk cordless phones
people offer and I am trying to get the scrap circuit boards from a
local pager and cell bhone rebuilding company.

--
Former professional electron wrangler.

Michael A. Terrell
Central Florida

Why does your name sound familiar? Do you belong to one of the LW/MW radio
clubs?

Pete

"Guy Atkins" wrote in message
...
Hi Pete,

Craig Siegenthaler and I have been friends since 1988, so we go back a
ways, and I'm very partial towards his design abilities and products.
Apart from my bias, there's a great value in Kiwa's Premium Filter
Modules-- $75.00 for a filter with typically greater than 100 dB USB
ultimate rejection and shape factor typically 1 to 1.65 is money well
spent. The final, resulting performance depends on the entire receiver
system and PCB layout/shielding, as you mentioned.

The very best filters I've encountered (before I went IF-DSP with the
756Pro) were matched-pair INRAD crystal filters, and the crystal filters
in my RA6790GM.

BTW, before Craig offered filter modules using cascaded ceramics, he tried
the same idea in the Kiwa Multiband AM Pickup (MAP) accessory in the
1989-1991 timeframe. This device provides outboard synchronous detection
plus two IF bandwidths, notch, tone tilt, IF output, low distortion
speaker, and other features. The closest competitor is (was) the Sherwood
SE3.

The filter characteristics in my particular MAP are excellent-- the actual
measurements from the Certificate of Performance show an ultimate
rejection at 3.5 kHz of -108 dB and shape factor of 1 to 1.53 in the
narrow bandwidth (3.0 kHz @ -6db nominal) for my particular serial number.
The passbands are also kept flat within +/- 2.0 dB for both the wide and
narrow IF bandwidths, something you don't always find in discrete crystal
& mechanical filters.

73,

Guy


"Pete KE9OA" wrote in message
...
Craig's filters are very good, with good ultimate rejection, but
Mechanical Filters have an ultimate rejection of 120dB. True, this figure
is better than the dynamic range of most receivers, and also true, you
have to have very good shielding/ground in your PC board layout scheme in
order to obtain this 120dB figure.
100dB ultimate rejection is a good figure to shoot for. I have spoken to
Craig a few times.....he is a very good designer.

Pete

"Guy Atkins" wrote in message
...
Craig at Kiwa Electronics seems to have figured out how to make quality
filter modules from series-cascaded Murata ceramics. He uses low noise
buffer amps as part of the package in Kiwa's Standard and Premium Filter
Modules (PFMs). The latter are particularly good, with ultimate
rejection figures exceeding Collins mechanical filters and better shape
factors than quality crystal filters... and at a very good price for the
performance.

I've used a number of PFMs over the years in various receivers, and
they've performed excellently for DXing and program listening.

http://www.kiwa.com/kiwa455.html

Guy Atkins
Puyallup, WA USA


"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...

"Michael A. Terrell" ) writes:


There are Murata (and clone) 455 KHz ceramic filters in old cordless
phones and pagers as well. i always ttake the junk cordless phones
people offer and I am trying to get the scrap circuit boards from a
local pager and cell bhone rebuilding company.

But those will be quite wide, given that they are for narrowband
FM.

The suggestion of CB sets is good, since those should tend to be
narrower than AM broadcast receiver filters. The sad part is
that the digitally tuned Delco car radios that I use as
everyday radios use a 450KHz IF (presumably because of the math
for the synthesizer), so one can't simply move a CB filter to
the car radio.

Sadly, it's easier to scrounge up wider filters than narrower
ones. Old clunky cellphones are also a good source of "roofing
filters" and 455KHz filters, but they too will be wider than
desired for AM reception. You're much more likely to come across
something that uses FM than AM or even less likelier SSB. By
the time you find something that has an SSB filter in it, you
have to think carefully about whether it's more valuable
as an intact piece of equipment. I've found CB sets in the garbage,
but never an SSB set (and never junked shortwave receivers, either.

One line of pursuit might be cascading wider filters, at least of
the bandwidth found in the average AM broadcast receiver. People have
talked about doing this, though I've not seen much detail. Can you
get much variation in bandwidth by fiddling with the termination (and
without adding bad ripple to the passband)? Use small coupling capacitors
to link a few of the filters together, getting something narrower
than just a few cascaded filters (which generally just improves the skirts).

Michael