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#40m #agc #calibration #qcxmini #40m #agc #calibration #qcxmini

kb9vno@...
 

So I just got done with my first build of the QCX Mini on 40m. So far it passed the smoke test. I did add on the TXCO and I was not sure about the AGC module as I could not find any reference at the time if I should install during initial build or after.
So I figured why not I can turn the AGC off  in the menu right? So I installed both at the same time to make things easy.

I'm trying to do the Calibration procedure on the radio. I'm stuck at the first procedure.
I'm thinking the AGC is effecting the signal meter on the radio, as its stuck at 11. No matter how much I turn the Band Pass Filter capacitor it does not change on the display. Yes I went slow I know the peaks are sharp.

I do hear the audio level changing in the headphones when I'm tuning the capacitor. And after a particular point where the volume starts to peak in the headphones what I can only think of is the AGC kicking in because it sounds like it dampens the test tone automatically for a split second then comes back. If I lower peaking value the volume stays constant.

So I'm guessing the AGC is not allowing me to Calibrate properly by using the display meter. And is not turning off like I suspected. (the always on jumper pad is not soldered)

I've checked to make sure the AGC was turned off in the menu. But seems like no effect.

Has anyone found a work around, Or am I going to have to unsolder the entire AGC board off to calibrate?

Thanks,
Robert

 
Ronald Taylor
 

Robert, the AGC has no effect on the BPF (8.7) alignment. The AGC circuit samples output audio and triggers the mute transistor Q7 on high audio levels. The audio sample used for the BPF alignment is taken at the wiper of R27, the IQ balance pot, so it is way before the volume control or Q7 in the circuit.

It would have been better if you had not installed the AGC board before testing as it covers up two ICs, but you can still do the voltage measurements on the ICs you have access to and see if the problem is in some other stage. 

Good luck ... Ron

On Fri, Mar 24, 2023 at 12:38 AM <kb9vno@...> wrote:

So I just got done with my first build of the QCX Mini on 40m. So far it passed the smoke test. I did add on the TXCO and I was not sure about the AGC module as I could not find any reference at the time if I should install during initial build or after.
So I figured why not I can turn the AGC off  in the menu right? So I installed both at the same time to make things easy.

I'm trying to do the Calibration procedure on the radio. I'm stuck at the first procedure.
I'm thinking the AGC is effecting the signal meter on the radio, as its stuck at 11. No matter how much I turn the Band Pass Filter capacitor it does not change on the display. Yes I went slow I know the peaks are sharp.

I do hear the audio level changing in the headphones when I'm tuning the capacitor. And after a particular point where the volume starts to peak in the headphones what I can only think of is the AGC kicking in because it sounds like it dampens the test tone automatically for a split second then comes back. If I lower peaking value the volume stays constant.

So I'm guessing the AGC is not allowing me to Calibrate properly by using the display meter. And is not turning off like I suspected. (the always on jumper pad is not soldered)

I've checked to make sure the AGC was turned off in the menu. But seems like no effect.

Has anyone found a work around, Or am I going to have to unsolder the entire AGC board off to calibrate?

Thanks,
Robert

 
kb9vno@...
 

I figured out my issue. Thanks for pointing me in the right direction with the schematics. And that the AGC had nothing to do with the alignment. 


Turns out my issue was I had my straight key plugged in and it was keying the radio. It dawned on me the next day because I remember the dummy load being warm.

So I took off the straight key and changed the menu setting configuration for the tip / ring settings. As I was using a mono plug.  Also please note I also figured out that some settings you may have to save before taking effect.
I was able to run the calibration procedure as normal after making these changes.

 

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