Re ARRL's test results, I wrote:
>Bottom line: it helps IMD and BDR for 5 kHz spacings,
but not much for 1-2 kHz spacings, as you would expect
since these signals still fall within the 4 kHz bandwidth.
RSGB came to a very similar conclusion with
very similar IMD numbers. Their words follow:
"The before and after results show a similar level of
intermodulation dynamic range at frequency spacings
well outside both roofing filter bandwidths. This is to
be expected and represents the dynamic range of the
RF front end. Similarly, at very close spacings well
inside both roofing filters the results are similar and
this represents the dynamic range of the second mixer.
However, at frequencies offset from the operating
frequency in the 3 to 10 kHz region, the INRAD filter
improves the dynamic range by up to 10 dB."
Now if I could only find one of those 3 kHz holes
in the CQ 160 CW, I would be a happy camper! ;-)
73, Bill W4ZV
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