The headphones being used for DEFCON talks are stereo FM, easily received on your SDR of choice CH 1: 920.1Mhz CH 2: 920.7Mhz CH 3: 921.2Mhz CH 4: 921.9Mhz CH 5: 922.3Mhz CH 6: 922.8Mhz CH 7: 923.4Mhz CH 8: 924.2Mhz CH 9: 924.7Mhz CH10: 925.9Mhz CHA1: 920.5Mhz CHA2: 922.4Mhz CHA3: 926.7Mhz