Finally had time to get back to this for the second time. I accidentally deleted the first post I made of this a week ago.
Here is another set of test results with the AGC board vol-hi connected to to TP21 on the uBITX via a resistor.
(remember this is a V4 board)
I made three sets of measurements
1. AGC off
2. AGC-slow and a resistor value of 11.5 ohms
3. AGC-slow and a resistor value of 5.75 ohms
11.5 ohms is the closest I had to the 10 ohms Tim suggested.
Hoping to get a little higher levels for the S-Meter a 5.75 ohms (2x11.5 in parallel) was tested to see if it would increase the bias voltage and in turn the ADC reading.
Interestingly the measurements was almost exactly the same with both resistors. There looked like a very slight instability on the oscope with 5.75 ohms. after the fact that may have been due to a poor connection. In any case I'm going to stick with the 11.5 ohm resistor
From the measurements its pretty clear the AGC is doing its job and is pretty effective for about 50db. It looks like it kicks in by S9+10
and continues to work to at least S9+50. By S9+60 it has given up. Maybe someone else can use the measurements to come up with some useful numbers.
Bottom line is -- connecting the AGC board to TP21 through a resistor of about 10 ohms works for me and I'm a happy clam, I mean ham. I would though love to see some one else replicate these tests.
73 digger AB3XU