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[Yaesu] FT-1000 AGC Problem...

To: <yaesu@contesting.com>
Subject: [Yaesu] FT-1000 AGC Problem...
From: jeffa@ix.netcom.com (Jeff Anderson)
Date: Sun Feb 9 09:19:52 2003
I recently purchased an FT-1000.  I love the radio, but there is one issue which
has been bugging the heck out of me:  There is a very subtle audible distortion
on received SSB signals that seems to occur during AGC attack.  If I turn the RF
gain down below the AGC threshold, the audio sounds cleaner and, to my ears,
much more pleasing (but the radio's internal noise comes up as a consequence).

The sound is subtle but noticable.  It sounds like a slight "crunching" or
"crackling" sound (very noticable when someone says "ahhh."), and can be made to
stand-out (when looking for its presence) by rotating the "Shift" knob to
accentuate high frequencies.  When the shift is in the normal position, the
distortion is still present, but it tends to be masked (in most cases) by the
higher level of the voice signal.

The AGC rates don't seem to affect it because it occurs during agc attack, not

I just received the Tech manual for the FT-1000 from Yaesu (it's on CD now,
rather than being printed), and I immediately noticed that there has been a
change made to the component values in the AGC circuit in this schematic
compared to a previous schematic I have.  For example, on the IF board R2318 has
changed from 4.7K to 0R ohms, C2120 has been replaced with a 0.22 uf cap and 10K
resistor in series, etc.  (Interestingly, these component changes are not listed
in the "Modifications" chapter of the Tech manual).

Does anyone know why Yaesu changed the AGC circuit values?  Perhaps to fix this
problem?  Is anyone aware of other reports of this type of AGC issue?
Admittedly, it's very subtle - a friend's FT-1000D has the same distortion, and
although it doesn't bother him, it has been bugging the heck out of me, and I
didn't expect it in a radio of this caliber.  I have other, less expensive
radios, that, frankly, sound cleaner.  I'm hoping that updating the component
values will improve the sound (although I haven't yet verified if the radio has
the older, or newer, component values), but I don't want to undertake this until
I have a clearer understanding as to why these changes were made.

Thanks for any information you can provide!

- Jeff Anderson, WA6AHL

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