Measuring the transmit frequency.

The frequncy measuring is done by using a 12bit binary counter (74LV4040).
The output is then fed to the microcontroller section for further processing.
The input of the prescaler is driven by an LVDS line receiver.These driver provide 3V output signals and have a differential sensitivity level of around 100mV and have a 400Mhz bandwidth.
The datasheet can be found here.