[Icom] Filtering at 9 MHz vs. 455 kHz

Fri, 13 Sep 2002 15:30:33 -0700

In 1987, I obtained an IC-751A and put a 250 HZ filter in it.  Found it to
be very useful over the years although there was some 'ringing'.  Would
recommend it rather than a second 500HZ at 9MHZ.

73 de Jim [email protected]

-----Original Message-----
From: [email protected] [mailto:[email protected]]On
Behalf Of Clifford, Rick
Sent: Friday, September 13, 2002 11:33 AM
To: [email protected]
Subject: [Icom] Filtering at 9 MHz vs. 455 kHz

ICOM'ers,

I have an IC-746 (original, not PRO) and do primarily CW on 40m. After
suffering through several instances of adjacent frequency interference, I
decided to buy a filter. The IC-746 has two places where filters can be
placed, the 9 MHz and the 455 kHz IF stages. So now I needed to find out
which 500 Hz filter to buy. The suggestion from the HRO store was to filter
at the 455 kHz stage (naturally, the more expensive of the two options),
while a call to ICOM suggested that both stages should be filtered (an even
more expensive option).

I ended up installing the more expensive ($180) 455 kHz filter (500 Hz
bandwidth). I am quite pleased with the performance, but wonder if I will
get significantly improved filtering performance if I also place a 500 Hz
filter in the 9 MHz IF stage.

Since I have been wondering what the 250 Hz filter is like, an alternative
approach is to buy the 250 Hz filter and put it in the 9 MHz stage. Then, I
should be able to switch in either 250 or 500 Hz.

Does any have an opinion about how these filters should be used across the
two IF stages? And, is there enough difference between the 250 Hz and 500 Hz
filters to justify having both?

Thanks and 73,

Rick
KF6UEB
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