Yes, the audio 'thump' is caused by the audio AGC being derived from the
audio waveform rather than the IF itself. However there are numerous
benefits to this scheme including the fact that the audio filters (the
primary source of CW bandwidth limiting) and the notch filters remain
inside the AGC loop itself which (if you read the Orion threads) is a
very good thing.
Many have played with the AGC time constants but my general opinion (as
an RF engineer) is that no matter what constants you choose you will
always be working with a compromise, depending on changing operating
conditions. Probably the best 'fix' is to add the RF Gain mod. Ten-Tec
has a Technical Note on this mod although they no longer provide the
parts. Basically you replace the AF Gain control with a concentric
control (requires concentric knobs like found on the Scout, 526,
Paragon, Omni V, etc.) and insert the new variable resistance with a few
other parts into the AGC system allowing you to decrease the GAIN of the
Argosy for very strong signal reception. The 'thumpin' you are referring
to is only noticeable with very strong signals so reducing the gain
reduces and/or eliminates the thumping.
There was an Argosy with this RF mod on a commercial auction site this
past week. I think it is gone now but you can look at past items and see
what I am referring too.
73,
Jerry, KG6TT
Fairfield, CA
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