Having a passing familiarity with the inner-workings of the FT-817, one of the problems with it is that its AGC is not well-designed.

Unlike most AGCs, the time constant appears to be different for weak signals (<S9) than above, but this has to do with the unfortunate "volts/dB" curve of the AGC control voltage: For weaker signals, it is reasonable, but for strong signals a small change in voltage = more dB. The net effect of this is that the AGC seems to be inconsistent in the manner described.

When I use my FT-817 - particularly on a busy or noisy band - I make use of the attenuator to keep the S-meter in the "lower half" (<S9). In this way, one avoids the de-facto audio compression that seems to occur when the AGC is in its upper range where the time constant - even on "slow" - is faster than what one would ever choose intentionally.

Interestingly, I've not see this AGC problem discussed much as its cause isn't immediately obvious and I have not ever seen any attempted fixes but it does explain the sometimes "heavy" sound attributed to this radio. If nothing else it can serve as a cautionary tale to someone designing their own AGC loop.

73,

Clint
KA7OEI

Bitx definitely the best sounding of the lot.?

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