[ICOM] Icom 746 filter mod

[Anders Janis SM4RNA]

I have done that. I found that I needed to put thin plastic spacers on the 
connector pins on the filter as otherwise the filter may short out some 
tracks on the PCB.

I put in a 2,4 INRAD  #109 and combined that with a 350Hz and a 1,9kHz 
filter in the 9MHz IF.

Big difference with a crystalfilter instead of the Murata. I think it would 
be boring to listen to some stations with narrower then the 2,4kHz in 455kHz 
IF. If needen I had the 1,9 in 9MHz IF and also the PBT if needed.

I do not have the 746 no more, but that is becaurse other issues,,,

de SM4RNA Anders


----- Original Message ----- 
From: "John Geiger" <johngeig at yahoo.com>
To: <ic746 at yahoogroups.com>; <icom at mailman.qth.net>
Sent: Tuesday, March 06, 2007 7:35 PM
Subject: [ICOM] Icom 746 filter mod


>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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