Re: ND6T AGC Troubleshooting

WA6PXC Rich <sigma@...>

Hi Curt,
I have tried a number of the AGC circuits floating around out there.
They all seem to work, but do not handle large (>1000 microvolts) signals.
Out of frustration, I have developed an AGC controller which controls the RF path
instead of the audio path. It begins to control the signal at about 30 uv and continues
to provide very good control up through about 7000 uv.
It essentially uses a BS170 FET in place of R12.
I have a neighbor 2 blocks away running 500 watts on 40 meters. His signal is not distorted
If you are interested I can lead you through the process of building one...
Kind Regards..

-----Original Message-----
From: "Curt via Groups.Io"
Sent: Jan 10, 2019 6:54 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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