Here is an excellent microphone for use with the HP 8920 family of units. It works well with the 8920A, 8920B, 8921A and 8924C units. It's not the original OEM microphone but a high quality after market unit. This is a new mic with 90 day warranty with a cost of $120. To use this or any mic with the 8920 units, go to the RF Generate screen, set the 'Mic In To" field to FM and 4 KHz. ( or you can set it to AM) You can then set your frequency, RF level out, CTCSS or DPL tone (on AF Gen #2), press TX test, set receive frequency. The 8920 unit can now function as a radio. It will receive until you press the mic PTT key.