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IC-746 FAQ
Starting with both filters in their center, detented, position (widest effective bandwidth), and
tune in your desired signal as accurately as possible.
Grasping both IF shift knobs simultaneously, simply turn and adjust for the best sound. If
you have a nearby, interfering signal, then you'll probably have the best results shifting your
bandpass away from it.
Now, adjust just the 455Khz IF shift (the inner knob) in the opposite direction for the best
sound.
There's a whole document describing the theory and mechanics behind TPBT at:
http://groups.yahoo.com/group/IC746/files/ic746_tpbt.txt
4.16
How do I configure the IC-746 to use an optional filter?
After you've installed a filter, you need to tell the radio about it. Using the SET menu, tell
the radio which filter you've installed (by Icom part number) and which slot it is in. Then,
hold in the FILTER button for two seconds to bring up the filter selector. Cycle through your
available filters by mode and by wide/narrow until everything is set up the way you want.
See the operator's manual for details.
4.17
How do I configure the IC-746 to use a non-Icom filter?
You have to lie to the rig.
All of the IC-746 filter settings are on the basis of Icom part numbers. (This is supposed to
make things easier for new operators.) Just tell the rig you've installed the Icom crystal that
most closely matches the one you're actually using.
Lying to the rig does have a side effect.
The 746 cannot actually shift the IF filters' passbands. Instead, the 746 shifts the local
oscillator frequencies of the 2nd and 3rd IF stages to shift the signal back or forth, aligning
the edge of the desired signal with the computed edge of the filter's passband.
Small lies generate small effects, like when you tell the rig that a 2.1Khz wide filter is
actually 1.9Khz wide, yielding a 100hz offset in the control. Larger lies generate larger
effects, like when you tell the rig that a 400hz filter is actually 2.4 Khz wide, yielding a
1,000hz offset in the TPBT control.
4.18
How do I use a CW filter in SSB mode to receive PSK31?
Icom took their ease of use one step further, and programmed the rig to prevent the use of a
CW filter while in SSB mode; probably to prevent what they considered to be a foolish user
error. They didn't know about PSK31 at that time. So again, you lie to the rig during setup,
telling it that the crystal is wider so that the rig will allow you to select it for SSB use.
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2003-02-08