Radar
It's the indicator for an RDS81/82/84/86 radar. You'd need to look at the scanner to see what system you actually have. It's the scanner that matters as this determines power output, range etc. This is a two-box radar system, so no separate transmitter/receiver unit - it's all in the scanner.
You can replace this indicator with an Avidyne EX600 MFD and get full moving map display (if you have a compatible GPS), charts, etc.