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 openSPOT4 and the transmitter.
openSPOT4's oscillator has a frequency stability of 0.5ppm, and every openSPOT4 is factory calibrated during the assembly process, so you'll only need to use this special connector if your transceiver's transmit frequency is drifting. We suggest you to only run AutoCal if the openSPOT4 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 openSPOT4's built-in local echo service.
If the AutoCal does not enter Phase 2, then hold the PTT on your transceiver for at least the time it takes for the progress bar to go from 0% to 100%. Make sure the transceiver is transmitting on the AutoCal frequency (433.900 MHz by default). If the AutoCal still does not enter Phase 2, then the RX offset between the transceiver and the openSPOT4 is greater than 500Hz. What you can do is to switch frequency on the transceiver or on the openSPOT4, or enter an RX offset greater than 500Hz manually on the modem page and use the openSPOT4's built-in local echo service to find out the lowest BER.