[CQ-Contest] Re: Choice of CW Narrow filters

Guy Olinger, K2AV k2av at qsl.net
Fri Apr 16 19:14:33 EDT 1999

Quite some number of excellent replies here, responding to all of them
in general, so no quotes below...

One of the nice things about TR in S&P is it's keeping a bandmap. What
I see is an average 500-600 hz between CQing stations in a CW contest.
I happened on the 400 hz because INRAD was offering it at the time I
got my MP. I had already gotten INRAD filters for my trusty ole 101ZD
with excellent results.

I got the 455 IF filter early and was pleased. I got the 8 Mhz
matching 400 hz filter when it became available and was struck by the
huge difference it made in 160m tests.

It took the +- 500 hz stations out of hearing, and improved the crud
factor. Several things, and I think this should apply whether INRAD or
not, whether MP or not, if one can install matching filters in both

1) Using the matching narrow filter in the 8/9 mhz IF keeps signals
just outside the 455 khz IF filter from overloading and making IMOD &
klix in the early IF stages. 

2) Using the matching filter vastly improves the ultimate rejection,
if the skirts are matched with the translated 455 filter skirts. It is
this phenomenom that *removes* the guy up 500 hz. 

3) The 400 hz plays a little better in the spread-by-500hz-increment
contest CQ frequencies because the guy up 500 is really up 400-600. So
you are needing to reject stuff up 400 and down 400 even if the
centers are +- 500.

In the two filters I have, the rejection at +- 400 hz (not +-200) is
-65 Db for the 455 Khz filter, and -45Db for the 8Mhz filter. That's
-110 combined at +- 400 Hz. In addition to increasing the ultimate
rejection, the 8 Mhz filter reduces the just out of band signals by
45+ Db cutting down on the crud and klix made by the RX first IF
between +- 1200 hz and +- 400 hz otherwise. (That assumes a "default"
filter in place selected with the CW low IF filter. If not it's even

73, y'all,  Guy


73, Guy
--. .-..

Guy Olinger, K2AV
k2av at qsl.net
Apex, NC, USA

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