[Lowfer] Re: Filters recommendations: IC-R75A

[Steve Dove]

Hi Denis,

Well, the 9MHz/455kHz thing is the old one of you get what you pay for ;  the shape 
factor of the lower frequency filters is superior.  That said, a 455kHz CW filter without a 
corresponding 9Mhz one is a system-architectural disaster waiting to happen  -  ideally the 
selectivity should be as close to the front of the receiver as possible, else the pre-filter 
stages crash and burn inder the onslaught of signals that the filter should be getting rid of.

In the context of present-day QRSS operation, one could very well get by with no 
additional filter just by closing down the bandwidth using the pair of stock SSB filters with 
dual-BPF ;  this'd get down to maybe a kHz or so bandwidth.  This does leave one wide 
open for later on when there might be Big Hairy Monsters in the shape of close-by freshly-
minted 136kHz licensees.  A couple of years ago, we used to have a problem with CFH, 
a 10kW or so military station on 137kHz near Halifax NS which without decent filtering 
wiped out the band.

So, what is decent filtering?  If you want as a start just one decent general purpose aural-
CW / QRSS filter, I'd look at either the Icom IC-232 (9MHz, 350Hz) which is a nicer filter 
with better shape factor than their older 500/250Hz filters, or alternatively the 
International Radio 9MHz/400Hz filter.  The IR filters on the whole are better and 
cheaper than the YaeComWood ones, their only drawback (at least for the 9MHz filters) 
is that they are physically much larger, don't just plug in, and need wiring in and tucking 
away somewhere in the radio.  This last matter isn't a problem in the R-75, where there's 
room for a marching brass band.

Later on, an additional IR 455kHz/400Hz or 250Hz filter would give adequate enough 
selectivity for any reasonable person.  Unreasonable people like me do stupid stuff like 
have IR 455kHz/125Hz filters, to limited additional benefit.

http://www.qth.com/inrad/

for International Radio.  Say Hi to George.

        73,

                Steve        W3EEE