[Icom] InRad 9MHz filter in IC-746

[Martin Davies G0HDB]

I've just installed an InRad 400Hz b/width 9MHz filter (#111) into my IC-746, 
in the position suggested by InRad so the connecting leads (I've used 
RG178 sub-min PTFE coax) are about 22-23ins long.  I'm finding that there 
seems to be some leakage around the filter - I can hear a low-level residual 
signal as I tune up to a few kHz HF of the frequency of a strong carrier (eg 
S9+).

Has anyone else experienced this effect with a narrow InRad filter and found 
a way to improve the isolation between the filter's input and output, and 
hence achieve the ultimate rejection specified for the filter (>90dB)?

73 and thanks in advance,
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Martin, G0HDB