Re: ND6T AGC Troubleshooting

Albert Peter

Hi guys,

The new JackAl board for uBITX uses a hybrid JFET circuit for AGC control.  Have a look on    and download the User Manual Section 2.  There is a complete AGC circuit in there which works very well.  You do have to break the IF chain in one spot, but nor other modifications and the uBITX reception is not changed.


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From: Curt via Groups.Io
Sent: Thursday, January 10, 2019 9:54 PM
Subject: [BITX20] ND6T AGC Troubleshooting


I am beside myself that I cannot get this simple circuit doing something with the ubitx.  I am starting with the simple version with a single MOSFET, and I may add the series one later. 

I built one unit - nada.  So I build a second one, and left off the MOSFET.  I have its input attached to high side of the volume control pot (I think it is 10k in the Sunil case version), the ground attached to a connector in the closest corner of the board, and 5 volts from the raduino.  No matter how huge the signal -- I get no rectified voltage output.  What could I be doing wrong?  With hundreds of these boards in uBITX I am surprised by my result thus far. 

I am using a 2n2222A for the NPN, I have tried 3 different devices.  Yes the diodes each work on the DVM, and they are proper orientation. 

I also could not get the VK3YE AGC to work either.  The ubitx receives wonderfully and I am testing on 40m. 

73 Curt

PS - I do have a hybrid cascode but I am thinking to use it in a homebrew Rx -- not sure I wish to 'break' one of the bidirectional amplifiers here.  my goal is just to AGC the very largest signals. 


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