Alarm Monitor 3A1

TM 11-5820-695-35

voltage at U1A-6 is derived from the +28 Vdc supply

2-87.

Alarm Monitor 3A1

through resistors R1, R2, and R3. It is set to a level of

+0.15 Vdc by adjustment of R2. When the signal at

Alarm monitor 3A1 (fig. 2-32) monitors status signals of

U1A-7 is normal, it is higher than the reference signal at

Converter-Multiplier Assembly CV-3633/GRC-144 (unit

UlA-6, and the output signal at U1A-1 is high (open

3). The characteristics, functions and sources of the

circuit). The supply voltage (+28 Vdc) through R4 and

input signals are described in (a) below. Output signals

R6 then reverse biases diode CR1. When the signal at

(b below) are routed to STATUS PANEL 3A8 (para 2-

UlA-7 drops below 0.15 vdc (fault status), the output

82). A converter summary alarm signal (c below) is

signal at U1A-1 changes to ground (O Vdc). Diode CR1

routed to orderwire assembly 1A13 and applied to

is then forward biased, with ground at the cathode

module 1A13A2 (para 2-8i). Figure 2-32 is a simplified

through R6.

schematic diagram that shows interconnections between

monitored circuits, alarm monitor 3A1, and STATUS

PANEL 3A8. Refer to figure 5-99 for the complete

(3) The signal at 3A1P1-25 comes from the

schematic diagram of alarm monitor 3A1.

local oscillator power monitor circuit in frequency

converter 3A2 (para 2-85); and it is applied to pin 11 of

voltage comparator U1C. The normal and fault levels of

a. Alarm monitor 3A1 receives input signals from

this signal and the operation of U1C are the same as

the monitored circuits at pins 14, 24, 25, 26, and 33.

those for U1A, as described in a(2) above. For normal

status +28 Vdc is applied to CR3 through R15 and R17.

(1) The signal at 3AlPl-33 comes from the

For fault status ground is applied to CR3.

thermostatic switch (S2) in amplifier-multiplier 3A5 (para

2-85f), and it is applied to the coil of relay K1. This

(4) The signal at 3ALPl-24 comes from the

signal is +28 vdc when the temperature in 3A5 is normal

chassis mounted reflected power detector 3A7CR1

and it is 0 vdc (open circuit) when the temperature is out

(para 2-82d(1)), and it is applied to pin 3 of amplifier U2.

of normal range.

A reflected power signal level of 70 mv corresponds to

an antenna VSWR of 1.5: 1, so the reflected power

(2) The signal at 3AlP1-26 comes from the

signal level is normally less than 70 mv. If the antenna

forward power monitor circuit in 3A5 (para 2-85e), and it

VSWR is greater than 1.5: 1, the reflected power signal

is applied to pin 7 of voltage comparator U1A. 'The

will be greater than 70 mv (fault). Amplifier U2 has a

signal level is 0.5 +0.1 vdc (normal) or less than 0.15

gain of 10 and the output signal at U2-6 is normally less

Vdc (fault). U1A is a high gain amplifier with positive

than 700 mv. An output level greater than 700 mv

feedback. The positive feedback through R8 prevents

indicates fault status. This signal is connected through

oscillations when the output signal switches states, and

resistors R35 and R37 to test point J2 (TP2 REFLD

also speeds up the transitions. The reference

PWR), and it is also

Change 6 2-137