Chapter 3. FUNCTIONING OF EQUIPMENT

TM 11-5825-270-23

CHAPTER 3

FUNCTIONING OF EQUIPMENT

Section I. FUNCTIONAL DESCRIPTION

3-1. General

are above a predetermined threshold and the keyed

modulation is present, the operation is considered to be

a. The monitor receiver is a flux-tuned, non

normal.

However, if some abnormal operating

conditions cause the transmitter carrier level and/or

directional beacon (NDB) monitor specifically designed

modulation to fall below the predetermined threshold or

to verify continuously the operational readiness of an

the keying becomes continuous, the monitor receiver

associated NBD transmitter.

The monitor receiver

generates the following alarm output

consists of an antenna assembly and a receiver

(1) Visual alarm (red light on front panel).

assembly.

b. The antenna assembly comprises a one meter

(2) Aural alarm (3 kHz tone from built-in

loudspeaker).

long whip antenna and a matching module. The signal

(3) Alarm contacts (form-C contacts for remote

transmittal by the NBD transmitter is picked up by the

monitoring).

whip antenna and fed to the receiver through the

matching module which transforms the antenna

3-2. Block Diagram Description

impedance to 50 ohms (nominal).

c. The receiver is a crystal-controlled, single

a. Figure 3-1 is a simplified block diagram of the

conversion superheterodyne unit, providing high degree

monitor receiver. The rf signal from the NBD transmitter

of selectivity and sensitivity. The receiver is fix-tuned to

is picked up by the whip antenna and applied to the

the same frequency as that of the associated NBD

matching module which transforms the antenna

transmitter, over the range of 160 kHz to 535 kHz. In

impedance to approximately 50 ohms There is no signal

operation, the receiver continuously monitors the rf

gain in the matching module and its output is fed to the

carrier level and keyed modulation of the NBD

receiver through a coaxial cable.

transmitter signal. As long as the amplitude of the rf

carrier and modulation level of the signal being received

3-1