Thanks to Esa, Steven, and others for their replies.
I examined my FT-1000 over the weekend and discovered that the IF board has the
updated AGC component values. The tech at Vertex/Standard (Yaesu USA) with whom
I discussed the problem had never heard of it, but perhaps I just had the wrong
person.
I made quite a few measurements of the AGC in operation over the weekend. One
issue is overshoot on the AGC line - on voice peaks the AGC drives a bit further
than it should, then quickly recovers, the net effect being that some amount of
modulation appears on the AGC line (not desired). I was able to reduce the
audible artifacts in SLOW agc mode by shorting out the 10K resistor that's in
series with the 2.2 uF cap (the cap for the SLOW time constant)- the artifacts
aren't completely eliminated, but they're much less noticable. Time allowing, I
hope to be able to perform some additional experiments this next weekend. I'll
also try to incorporate the W8JI noise-blanker mod.
One curious thing about the latest Yaesu agc ckt is that the series resistors
for all of the caps are the same value (10K), which means that the charge times
(which affect agc attack), will be *different* for the three different agc
positions. By contrast, the Drake R4-C has the same charge-times, irrespective
of AGC setting. I wonder why Yaesu did it this way?
By the way - has anyone tried the Tuning-Upgrade available from International
Radio Service Division? How well does it work, and are there any
idiosyncrasies?
73,
- Jeff, WA6AHL
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