[Icom] Filtering at 9 MHz vs. 455 kHz
Guillermo
[email protected]
Thu, 12 Sep 2002 23:59:13 -0300
Hello Rick, I've read all other reply messages posted until now (six
answers, mine the seventh). I agree mostly with Jordan's reply, and want
to add this: in my humble opinion, it would be better to have 500 Hz in
9 MHz, and then another 500 Hz or if you want a 250 Hz filter at 455 KHz
IF. You "pre-shape" incoming RF signal first with the 500 Hz filter at 9
MHz, and then make more "vertical" skirts with the 455 KHz 500 Hz filter
and even a narrower BW with the 250 one.
The skirts of the second filter (500 Hz at 455 KHz), won't add too much,
if something, if you install the already narrower 250 Hz BW filter. My
choice would be to add another 500 Hz filter at 9 MHz.
Best regards
Guillermo - LU8EYW.
"Clifford, Rick" escribi�:
>
> 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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