Tue, 23 Apr 1996 16:25:46 -0500
I received several requests concerning information on the FT-1000 Mods,
so I will have to post several messages, This is the filter mod.
The FT1000D comes equipped with additions including I.F. Filters for the
455khz. c.f. The narrowest of these has a 500hz. bandwidth, but no
matching filter for the 250hz. bandwidth for the 455khz. I.F. This
means that if you select the 250hz. bandwidth filter in the second I.F.,
it is paired with the 2.4khz. filter in the third I.F. It is a simple
modification to have the control section select the 500hz. filter in the
third I.F. instead. This modification requires the addition of a
switching diode (1N4148, 1N918 etc.) between the select line on the
250hz filter spot and the 500hz. filter. First access the filters on
the I.F. board, and clip the diode as indicated for the installation of
the 250hz. filter in the manual. Then remove the 500hz. filter, note
that the I.F. filter position for the 500hz. filter is the second from
the front of the radio. Then solder the diode between the cathode end
of the 250hz. select diode, and the cathode end of the diode under the
500hz. filter. This diode should be oriented with the cathode toward
the 250hz. select diode's cathode end. Now when the 250hz. third I.F.
control pulls the select line low, the new diode will pull the 500hz.
filter select line low, selecting that filter in place of the 2.4khz.
filter. When you finish this modification you will note that the 500hz.
filter reduces the wideband noise, and the "Width" control works when
the 250hz. filter is selected. Because of the mismatch in the filter
bandwidths, the first few detents on the width control act as an I.F.
shift, when the 500hz. filter is offset enough to "catch up" with the
bandwidth of the 250hz. filter, the action changes to a bandwidth
control. On my radio, the first three detents act as an I.F. shift, and
the next three reduce the bandwidth to under 100hz.