I don't think I said that. I imagine the onset of hardware AGC is determined
elsewhere. What I am saying is that the dB/V gain change is non-linear and
different from device to device. I assumed, mistakenly it appears, that the
bias voltage to the device was tailored via a lookup table to create a linear
dB/V (if you can call dB linear) scale factor. Lyle's description, if I
understand it correctly, says that they measure the gain control characteristic,
but leave it be and correct the numbers via a table.
A much better choice here (IMHO of course) would have been something like an
Analog Devices AD600 (See "A High-Performance AGC/IF Subsystem" by Bill Carver
in QST, May 1996.)
Another place where the designers' QRP DNA got in the way of robust design was
the choice of the second mixer. The oft repeated claim that hardware AGC is
protecting the DSP may be true, but the second mixer overload characteristics
are even worse.
Wes N7WS
On 12/14/2017 6:01 PM, Al Lorona wrote:
Wes stated that there's a component in the AGC circuit that changes the onset
of hardware AGC due to component tolerances. I suggested putting that theory to
the test by actually measuring it.
Al W6LX
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