[Yaesu] FT-920 ultimate rejection (blow by)

[Cortland Richmond]

I had read, of course that there was a blow-by issue with the 920's, but
when I found a good deal on one I went ahead anyway.  For the 2005 CW Field
Day I installed an Inrad 400 Hz CW filter and together with the DSP that
did, as reports said it should, quite a good job.

Recently, I measured the selectivity of my 920's filters and the ultimate
rejection really is poor.  

400 Hz filter: 

+/-KHz	dB 
0		0
0.31		-3
0.44		-6
0.49		-10
0.59		-20
0.64		-40
1.56		-50
2.00		-60

The CW filter skirts get a lot wider after 40 dB down and though I couldn't
get below 60 dB down with my signal source, it looks like after that rolls
off only at about 9 or 10 dB per KHz. Put another way, coupling _around_
the CW filter looks like it's only about 34 dB down.

Has anyone on the list modified their 920 to improve this? I have in mind
filter control-line bypassing. and strategic application of copper tape in
the filter area.  Or do I have to spend the money for an Inrad Switchboard? 

FWIW, I checked the SSB filter too:

+/- KHz	dB
0		0
2.3		-3
2.6		-6
2.7		-10
3.0		-20
3.7		-40
4.1		-50
5.4		-60


Cortland
KA5S