Masking
The phenomenon whereby certain sounds are not heard because of the simultaneous (or near-simultaneous) presence of other sounds of a similar frequency but at a higher level.

Back in the 1960's experiments were carried out to try and create UHF Masking to disguise [or hide] UHF Voice/Data transmissions.

The trials involved Fleet fitted UHF gear {692's and 696's - see Transmitter page}, an ordinary noise source, and a special aerial which was not named or branded.

The following pictures come from that time.

692 TX

696 TX

696 TX's

MASK NOISE SOURCE

MASK AERIAL REFLECTOR

MASK AERIAL