I use a EZuhf-Immersion system for the control of my model.
The RSSI of my EZuhf receiver is a digital signal, and must first be converted into an analog voltage.
For this I use adigital -> analog converter of Microtronics.
The analog signal is fed to the second port of the modified super-simple OSD.
Now I can read the RSSI numbers on my Ezuhf, It works very well.
A GPS is not really necessarily in an environment you know well, sufficientbattery voltage, time, and now also RSSI value are important data.
With this setup I have a safe and 'cheap' UHF connection for the longer distances.
See the Video and read how I did it.