[ICOM] Icom 746 filter mod

[John Geiger]

I found this mod for stock filters for the Icom 746:

#  Upgrading Stock Ceramic IF Filter to a Crystal
Filter

The stock 455 Khz IF filter is a 2.4 Khz wide ceramic.
The PC board is drilled and traced for a full fledged
crystal filter (either from Icom or Inrad).  In
theory,
replacing the cheapo ceramic filter (Murata CFJ455K)
with a superior crystal filter should improve the
rig's
performance.  

One source of info claims that to do this mod requires
changing 2 resistors (R701 and R704) from 10K to 3.9K
to change the impedance seen by the filter from 2K to
about 1.2-1.5K.  Most do not bother.

------------------------------

Has anyone tried this mod?  Does it really improve
performance. It seems that if one didn't care about
Hi-Fi audio on receive (like me) then you could
install a 2.0khz or 1.9khz 455khz filter there and
really tighten things up.  

73s John W5TD


 
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