[Elecraft] K3 / RF gain - S meter issue - Similar issue

[Wes Stewart]

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