Power Probe A1A6 - TM-11-5825-271-340009

TM 11-5825-271-34

ent filter configurations, set up by installing appropriate

below the threshold level set by R2. Shutdown does not

links on terminal blocks on the rf filter A1A5, cover the

take place if the carrier level falls below the threshold

complete operating frequency range of the NDB

setting of R3, however, the NORM light DS1 is turned

transmitter.

off, the ALARM light DS2 is turned on, and the

transmitter status monitoring contacts (K1 contacts 2-5)

become open-circuit When the special shutdown circuit

2-9. Power Probe A1A6

is used, the special link must be in, and the normal link

The power probe AlA6 detects the level of rf output and

must be out

performs the following functions.

d. The modulation detector monitors the rf level

(1) Supplies a current limit signal to the monitor

and provides the modulation reading for the metering

assembly A1A2 which keeps the rf current within safe

circuit With the modulation removed, the zero set control

limits in the event of a malfunction (e g, partial or

R1 is adjusted td provide a meter reading of 0%. The

complete short circuit) at the output of the NDB

tone level detector monitors the output of the one

transmitter

oscillator located m the exciter assembly A1A2. The

(2) Supplies the rf level signal to the monitor

output from the tone level detector is also fed to the

assembly A1A7 for modulation and carrier detection

metering circuit.

circuitry

(3) Provides forward and reflected power

2-11. Metering

signals for use by the metering circuits.

(4) Provides final output from the NDB

The TEST switch S2 and TE ST meter M1 are used to

transmitter (50 watts maximum) The output from the

monitor all pertinent parameters of the NDB transmitter

power probe AlA6 is fed to the ATU through TB1-2/3 and

Calibration controls R5 and R6 are provided to calibrate

J3 using a 50 ohm coaxial cable.

the meter for forward/reflected power and dc current

respectively. The TEST switch S2 also permits checking

of the modulation % (percentage), unregulated and

2-10. Monitor Assembly A1A7

regulated voltages, tone level, dc current and the rf drive

a. The monitor assembly AlA7 contains the

level

normal/special shutdown control circuits. The rf level

from the power probe A1A6 is routed to the monitor

2-12. ATU

assembly A1A7 through R2 and R3, which set the

a. The ATU matches the antenna impedance to the

threshold levels for the modulation and carrier re-

spectively When the NDB transmitter is operating

50-ohm impedance of the NDB transmitter, automatically

properly, shutdown relay K1 is energized, normal light

compensating for variations in the antenna reactance

DS1 is on, alarm light DS2 is off, and the transmitter

caused by environmental changes The power radiated

status monitoring contacts are closed (K1 contacts 2-5)

by the antenna is dependent upon the relative values of

The shutdown circuits have a time delay which causes

the antenna loss resistance, the antenna radiation

shutdown to occur 20 to 35 seconds after the out-of-

resistance, and the ATU coil loss resistance.

b. The rf output (50 watts carrier maximum) from

tolerance condition is detected.

b. The normal shutdown control circuit deenergizes

the NDB transmitter is connected to the ATU through a

relay K1 if keying is lost, modulation falls below the

50-ohm coaxial cable Power for the ATU (+24 Vdc) is

threshold level set by R2, or if the carrier falls below the

obtained from the NDB transmitter. The ATU has a

threshold level set by R3. When the normal shutdown

POWER ON/OFF switch S1 and a POWER light DS1

c. The ATU power probe Al operates TEST meter

circuit deenergizes K1, the rf oscillator in the exciter

assembly A1A2 is turned off, the NORM light DS1 is

M1 to provide a reading for the forward power, reflected

turned off, the ALARM light DS2 is turned on, and the

power, and rf current. The TEST meter has a meter

transmitter status monitoring contacts (K1 contacts 2-5)

calibration control RI and an on/off switch S3. The on/off

become open circuit. When NORM/BYP switch S1 is in

switch S3, located on the side of the ATU cabinet, is

the NORM position, the BPY light DS3 is normally off.

used to switch the meter off when not required, without

When switch S1 is set to the BPY position, the normal

opening the cabinet.

shutdown circuit keeps the shutdown relay K1 in an

d. The servo probe A2 monitors the phase

energized state and prevents a shutdown, the BYP light

relationship between the current and voltage of the rf

DS3 comes on and the NORM light DS1 flashes at the

output. When an off-tune condition exists (voltage and

keying rate.

current out of phase), the servo probe A2 actuates the

c. The special shutdown circuit is similar to the

tuning motor to raise or lower tuning slugs in the loading

normal shutdown circuit except that it causes shutdown

coils This maintains a tuned condition to compensate for

only if keying is lost or if modulation falls

changes in the antenna reactance caused by environ-

2-4