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FT-847 and 38.4k baud modifications

Hi All,

I'm mulling over ways to get the FT-847 going on 38.4K baud. The SYMEK IFD
board is under active consideration but I had another idea and would welcome
your comments...

The FT-847 has separate 2nd IF filters for FM-N and FM-W modes. The FM-W
mode selects the normal 15khz filter in the second IF, but the narrower 8khz
filter for FM-N is pretty much useless (to me).

I was thinking that perhaps the 8khz filter could be swapped out with a
suitable 50khz filter for use with 38.4K? Everything downstream would remain
the same, so radio and modem connections would remain intact. Also, it would
be a trivial matter to have the tuner software select FM-N mode via the CAT
for 38.4K operation.

In other words, 38.4k baud operation would be identical to 9600, and 1200
baud operation except for selecting FM-N instead of FM-W. As an experiment,
I was thinking of bypassing the FM-N filter with a capacitor just to see how
it would work until I can locate a proper 50khz wide filter...

The only hitch I can see is the whether or not the first IF filter is wide
enough for all this to work. The specs for it are not called out on the
schematic, and I don't have the FT-847 service manual. Could someone look
this up?

Can anybody see why this wouldn't work? Where could a compatible 50khz IF
filter be found?

--Bob Carlson, n0aot@amsat.org

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