David, I would suggest checking several settings before you try modifications
on the receiver itself. The symptom that you're describing could come from too
much RF amplification.
A number of selections on the FT-1000 effect RF levels. Audio distortion is a
hallmark of over driving the RF amplifier. The following controls all interact
with one another so any one or a combination of several could be the source of
the audio distortion from too much RF amplification.
The two noise blankers (NF, and NBW), the Front END control, the AGC control.
And of course, the RF gain control. Keywords: that you mentioned include
"strong signals". Given conditions such as this one should be using they some
level of attenuation. The NOR position adds further RF amplification to a
signal (RF preamplifier is switched in). With the switch in the IPO position,
the signal bypasses the radio's preamplifier and it is injected directly into
the first mixer. As mentioned earlier, one of the positions for attenuation
should be selected.
The AGC control also affects RF amplification as well as possibly adding
interference to the audio signal. Under the conditions you described, the AGC
control should be set to on. The AGC control in tandem with the RF Gain control
can add interference in both the RF and IF (amplifier) stages. The following
settings guarantee audio distortion: the AGC control set to OFF, the RF gain
control set to a high level (turned clockwise).
With a single side band mode selected the AGC control should be set to the
medium or slow position. When the mode is set to CW the AGC control should be
OFF or set to the fast position.
The above gives the idea: too much RF amplification gives audio distortion.
Dick Zseltvay, KC4COP
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