This material is included as a reference for existing equipment. It does not require modification of an existing radio or loss of communications capability. Continuous monitoring of 121.5 is possible with the built-in silent alarm system. External antennas are required for the proper operation of this system. Antenna installations are illustrated on the aircraft antennas page with detailed information in the Installation Information section from the manuals.
Crystals are of a plug-in type and easily accessible for additional capability.
Units are equipped with 121.5, 121.6, 121.775, and 243.0 MHz. A 10-second delay before the alarm sounds prevents activation on tests. Reset is automatic when the signal goes off. Auxiliary Receiver DF capability allows DF on any channel of the regular AM communications receiver to which it is attached. In many cases, no modification to the comm radio is required.