Section V. DETAILED FUNCTIONAL DESCRIPTION, CHANGE-OVER UNIT

TM 11-5825-271-34

Section V. DETAILED FUNCTIONAL DESCRIPTION,

CHANGE-OVER UNIT

transmitter. This removes the ac line and battery supply

2-26. Change-Over Unit

from the standby NDB transmitter, connects the battery

supply to the main NDB transmitter, and connects the

a. The change-over unit is used only in dual

main NDB transmitter rf output to the ATU.

transmitter systems. In the case of a shutdown of the

c. In the event of a failure of the main NDB

main NDB transmitter, the change-over unit

transmitter, the 48V supply at TB2-1 is not present and

automatically switches on the standby NDB transmitter.

relays K1/K2 are deenergized. This connects the ac line

The rf outputs of the two NDB transmitters (main and

and battery supply to the standby NDB transmitter and

standby) are applied to the change-over unit and the

connects the standby NDB transmitter rf output to the

switched rf output of the change-over unit is applied to

ATU. Diodes CR3 and CR4 provide isolation between

the ATU.

the + 24 Vdc supplies from the two NDB transmitters The

b. Relay K1 switches the NDB transmitter outputs

ATU supply is always taken from the NDB transmitter

to the ATU, and K2 provides control function switching.

that is on.

During normal operation, both K1 and K2 are energized

by the

48V

supply from

the

main

NDB

2-12