Please note that certain channels are intended for simplex operation, while others are intended for duplex operation.

SIMPLEX – uses the same frequency for both transmit and receive

DUPLEX – the transmit and receive frequencies are not the same (primarily for commercial use)

Your Cobra marine radio only operates in simplex mode.  Be sure to use only simplex channels.  These channels are for simplex operation:

1A, 3A, 4A, 5A, 6, 7A, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18A, 19A, 20A, 21A, 22A, 23A, 61A, 62A, 63A, 64A, 65A, 66A, 67, 68, 69, 71, 72, 73, 74, 75, 76, 77, 78A, 79A, 80A, 81A, 82A, 83A, 84A, 85A, 86A, 87A, 88A