If it is for testing the transceiver the best way is to connect up a dummy load with a sense port connection ,,and plug the counter into the sense port.

This will allow you to TX at full power into the load but the counter only see’s a small voltage, and thus it is protected.

The IM2410 I think has only a input connection , so its not easy to hook it in-line with the transceiver to monitor the frequency during normal operation.

There should be no need to do this anyway as the radio has digital readout , and it should be accurate enough.