For probably very silly reasons, I would like to install a FrSky 2.4GHz DIY TX module in an old but functioning Hitec Focus 3 SS AM. With no buddy box option, it is not clear at first glance where to pick up the signal on the main circuit board (containing both the encoder and the RF broadcast electronics). I would greatly appreciate input from anyone familiar with these venerable radios who could direct me to the proper point to pull the signal. Many thanks for the bandwidth.

Of course you realise the conversion will cost more than the Tx present value. If you have access to an oscilloscope its not too hard to trace were the ppm goes from the encoder to the RF part of the Tx. If you can post a picture of the inside of that transmitter it might even have a separate board fot the RF section since Focus were sold in many different bands for NA,Europe and Asia. Here is the manual if you don't have one:
http://www.hitecrcd.com/files/ManualFocus23AM.pdf

The Focus FM version has a single circuit board with a single IC and several caps and tunable inductors. It appears the chip may have custom part number on it since I can't find a cross reference. I assume the AM version is the same.

As far as the PPM, I have no idea. I would suggest checking the pins on that single chip to see if there is PPM coming out of it.

Originally Posted by WERA611

For probably very silly reasons, I would like to install a FrSky 2.4GHz DIY TX module in an old but functioning Hitec Focus 3 SS AM. With no buddy box option, it is not clear at first glance where to pick up the signal on the main circuit board (containing both the encoder and the RF broadcast electronics). I would greatly appreciate input from anyone familiar with these venerable radios who could direct me to the proper point to pull the signal. Many thanks for the bandwidth.

WERA611; did you ever manage to convert your Focus 3 SS TX? I have one that I would like to do as well.

Mark.