[ICOM] Collins instead of Murata?

[Clark Savage Turner]

On Apr 13, 2005, at 1:07 AM, Alex Eban wrote:

> I replaced the 455kHz filter in my TS-140 with the Inrad 2.1 kHz 
> filter.
> Skirt selectivity went up beautifully but I got in trouble with the 
> offset,
> kind of shift in the zero beat point. Voices sound high pitched a 
> little and

Alex has an important point here, I've been through this time and again 
with my filter changes.  The correct carrier insertion point depends on 
the precise center frequency of the main filter in your rig.  Different 
filters will be close, but often not the same as the old filter.  This 
changes the IF shift behavior, and can change your SSB audio.  The 
carrier setpoint should be rechecked after a new filter is installed in 
place of the main filter (not for optional filters though).  This was a 
real procedure for older radios, but for the newer generation, go to 
the menu for carrier offset (or whatever its called) and move it around 
to get the right audio on transmit and receive and you're probably 
doing fine.

Alex also mentions the traces around the board holes when replacing a 
ceramic filter.  I've been there, too.  Be gentle and careful if you 
have to "wire in" a new filter and you'll be glad you did.

The CFJ 455 K12 (and K13) filters are the "best" for shape factor as I 
recall.  The K5 is pretty good, too.  The K12 and K13 are "wide" at 2.7 
and 3.0 respectively, but the skirts are really pretty darned good for 
such little, cheap filters.  The crystal filters are usually better, as 
are the 10 pole mechanical filters.  I now use some INRAD 2.8 filters 
as the "main" filter in some of my equipment - easier to listen to and 
still less QRM than most 2.4 filters because of good skirts 
(subjective, but based on a lot of hard listening, hi hi).

Clark
WA3JPG