AutoCal is a special connector - it does not connect to anywhere. It analyzes an incoming transmission from the modem and tries to find out the frequency difference (RX offset) between the openSPOT2 and the transmitter.
openSPOT2's oscillator has a frequency stability of 0.5ppm, and every openSPOT2 is factory calibrated by us, so you'll rarely need to use this special connector. We suggest you to only run AutoCal if the openSPOT2 shows BER above 1% for your radio's transmission, as errors in the voice stream usually won't be noticeable if the BER is below 1%.
To use AutoCal, set the modem mode to the mode your radio uses and the modem frequency to the radio's transmit frequency, then click on the Save button. Hold the PTT button on your radio until all 3 phases are completed. The found RX offset will be displayed at the Last found offset field and it will be automatically saved for the current modem mode.
Keep in mind, that you can always check your own voice quality by using the openSPOT2's built-in local echo service.