GM4CXM gets 13cm! (/cont.)
Setting up the PA shouldn’t present any problems although it can be a bit tricky setting up the bias on the two output devices. Joe suggests 2.5A (at 26V) for the driver and 2A each for the output devices (Q1 and Q2). I found that with a supply voltage of 24V (Ray’s PSU only delivers 24V), setting the bias current to 2A was problematic and interdependent. Whatever the reason for this, I found that a bias current of 1.8A per output device was easy to attain and was thermally stable. Applying drive from the STM13 TX converter resulted in about 5A Drain current for each of the two output devices, indicating that the PA was working well. I fitted a switch and a meter for Ray to monitor the PA current.
Front and Rear views of the finished 13cm transverter