D.K. wrote:
I'm considering to upgrade my receiver ICOM R75 with narrow CW filters. My
main interest is NDB listening in the LW band.
There are 2 possiblities:
a) ICOM FL101 (CW narrow 9mHz IF, 250Hz) + ICOM FL53A (CW narrow 455kHz,
250Hz)
b) INRAD 121 (CW narrow 9010.6kHz, 250Hz) + INRAD 122 (CW narrow 455kHz,
250Hz)
Which combination is the better one in terms of quality and efficiency.
Price does'nt matter.
Any advice is welcome!

Why? Do you hear more than one signal from adjacent frequencies? Or do you
hear broad spectrum noise?

250Hz CW filters are designed to be used by ham radio operators in
crowded bands. They often make listening difficult due to "ringing"
(noise).

They won't filter out broad spectrum noise because it covers the same
frequencies as the signal you want.

You might find that a DSP audio processor will give you better results. It's
easy to test, there are lots of DSP audio programs around for PC's, you
just record some signals and try it.

You could also ask around the local ham community and see if you can find
someone with a similar filter in a receiver that covers the LF bands.

Geoff.

--
Geoffrey S. Mendelson, Jerusalem, Israel N3OWJ/4X1GM