Topics ND6T AGC - how to verify / S-meter settings / RF gain control #ubitx

Rob French (KC4UPR)


I'm slowly upgrading my uBITX.  My latest add was the ND6T AGC from  I have it successfully (I think!) installed, but I'm thinking I may have missed something.  

I have all of the wires connected correctly, as far as I can tell.  I can listen just fine to signals pretty much as I did previously, so clearly I have managed to get a signal through the board (since I did verify that I had successfully cut the trace between the board input/output).  I did wire up the RF gain control, using RG-174 that I grounded at the panel (but not at the AGC; I do have a chassis ground).  

However, for the life of me, I can't tell if there's any difference between off/slow/fast.  If they are supposed to keep my signal level relatively even, that is definitely not happening.  I can definitely tune the volume to a comfortable level for one signal, and then have another strong signal pop in nearby, and it doesn't seem to gain anything down.  

How can I go about testing that this is working correctly?  I have verified (a) that I can receive signals, (b) that the RF gain control works, and (c) that the board is receiving 12 VDC.  I haven't been able to verify anything else though, i.e. that it's actually doing AGC.

Also, does anyone have a reasonable set of S-meter settings for the KD8CEC firmware, when used with the stock Raduino A7 pin connected to the AGC S-meter output?  Did anyone have to do anything special as far as connecting the A7 pin to the AGC?  When there are no transmitted signals on 40 meters, just static, my S-meter voltage is literally 0, which surprised me (maybe that's right?), and I haven't seen it go about 50 while listening to all the FT8 traffic on 7074.  Does that signal need to be amplified, or should it be fine as it comes off the board?

Finally, as mentioned, I did install an RF gain control.  I used a 1K audio taper pot... is that the right thing to use?  It seems like almost all of the change is in the last 1/4 turn.

Thanks for your help! 



On the agc, start with it off, find a dreadfully loud signal, and switch it on. It mostly acts only on big signals, you still need to manually operate the volume control for many signals. I find agc mostly useful to tune across a band without getting blasted.



On Sun, Oct 20, 2019 at 10:19 PM, Rob French (KC4UPR) wrote
The ND6T AGC acts more as a limiter, as it has no gain in its own right.
So it can reduce strong signal, but not boost low ones.

Philip G7JUR 

Rob French (KC4UPR)

Curt and Phillip, thanks for the replies.  I think maybe I just didn't have enough strong signals around.  I was using it today, and the AGC definitely had an effect, and I could definitely see a difference when I turned it off.

This may be a dumb question, but is it normal that I would not get S-meter readings when AGC is off?  (using the S-meter tap on the ND6T AGC board)



 Yes it must be on to get a S-meter reading.



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