Re: load ver.4 original firmware into ubitx ver.3
The v4 code has a different calibration scheme, which is actually pretty easy if you have a second receiver. The code is posted at: https://github.com/afarhan/ubitx4
You can get the needed Arduino IDE compiler for free at: https://www.arduino.cc/en/main/software
Using the Arduino IDE program, you can read the ubitx_v4.3_code.ino code, compile it, and load it into the Raduino with a USB cable.
While I now understand this, I'll admit the process was not so obvious when I started. Another "geezer" (AA4PG) posted some very clear instructions here: http://radman.no-ip.ca:96/wordpress/?p=2747