[ICOM] Narrow CW Filter (FL-63) Filter "Blowby"

[Philip Atchley]

Hi,

I have an recently acquired IC-751 (not A) with the optional FL-63
Narrow CW filter (MHz IF).  The rig seems to work fine, EXCEPT that
there is a fair amount of "Blow-by" around the CW filter.

I use it down in the LF range chasing Beacons that are using the MCW
(modulated CW) mode and of course each beacon has a steady carrier
associated with it.

The nominal bandwidth of the filter as measured in the set is somewhere
between 250 and 300 Hz, about what I'd expect.  HOWEVER, strong carriers
may be heard up to 2-3 KC or so away, indicating MUCH wider skirts than
I'd expect.  Tuning the PBT (true Variable Bandwidth PBT) to one side or
the other helps some, but not much.  HOWEVER, if I select the "wide"
filter (which is cascaded 9MC and 455KC FL-44A SSB filters) and use the
PBT to narrow the bandwidth down (to about 800 Hz measured bandwidth)
those carriers 2-3 KC away become totally inaudible, though I may then
have the strong carrier associated with the beacon being monitored quite
loud.

This seems to indicate to me that strong signals are 'somehow' making
their way around the 250Hz filter.

DOES THIS INDICATE A FAULTY FILTER OR PERHAPS A BYPASS CAPACITOR ETC
GOING BELLY UP IN THE FILTER SELECT CIRCUIT?

73 de Phil,  KO6BB
991 Different NDB's heard to date.

http://www.geocities.com/ko6bb/
Merced, Central California, 37.3N  120.48W  CM97sh