500 WATT RADIOBEACON TRANSMITTER
ND2000A-02X-xx0
Page
3-3
15 January 2005
3.4.2.6 Press-To-Talk
Control:
The press-to-talk
switching circuit should be the equivalent of a
normally open, single pole, single throw switch.
When set to its closed position (press-to-talk), it shall
apply a ground to TB4-19. If the press-to-talk
information is phantom fed on the audio input, this
switching circuit will not be required (see note on
figure SD-2).
3.4.3
EXTERNAL STATUS MONITORING:
Outputs that may be used to identify or verify the
status of remotely controlled functions are available
on terminals of TB3 and TB4. These outputs include
forward power, reflected power, modulation
percentage, audio monitor, internal standby and SWR
standby.
3.4.3.1 External Forward Power Monitoring:
The external forward power output is intended to be
monitored by a remote maintenance monitoring
(RMM) system. A buffered dc voltage that is
representative of the forward power level is provided
at TB4-14. This voltage is a non-linear function of
the forward power level and will be 7.8 ± 10% V dc at
500 watts. Any other terminating device must have
an input impedance of not less than 100K ohms.
3.4.3.2 External Reflected Power Monitoring:
The external reflected power output is intended to be
monitored by a remote maintenance monitoring
(RMM) system. A buffered dc voltage that is
representative of the reflected power level is provided
at TB4-15. This voltage is a non-linear function of
the reflected power level and will be 8.6 ± 10% V dc
at 500 watts. Any other terminating device must have
an input impedance of not less than 100K ohms.
3.4.3.3 External Modulation Percentage
Monitoring:
The external modulation percentage
output is intended to be monitored by a remote
maintenance monitoring (RMM) system. A buffered
DC voltage that is representative of the modulation
percentage is provided at TB4-16. When operating in
CW, at 500 watts RF output, 4.3 ± 10% V dc will be
applied to TB4-16. When operating in MCW, at 500
watts carrier power and 95% modulation, 8.2 ±10%
volts dc will be applied to TB4-16.
3.4.3.4 Audio
Monitor:
A transformer coupled
600 ohm audio output is provided between TB3-22
and TB3-23 for external monitoring.
3.4.3.5 Internal
Standby
Monitoring:
The
internal standby output is the normally closed contact
of a relay. The relay is held energized when the
selected side (main transmitter) is operating and an
open circuit is applied to TB3-9. When the main
transmitter has been shut down and the standby
transmitter has been enabled, the relay will de-
energize and apply a ground to TB3-9.
3.4.3.6 SWR Standby Monitoring:
The SWR
standby output is provided by a CMOS inverter that is
protected from negative voltages by a series diode.
When the reflected power is satisfactory, an open
collector is applied to TB3-10. When the reflected
power is excessive and causing the carrier level to be
cutback (reduced), a current sink-to-ground is applied
to TB3-10.
3.4.4
EXTERNAL ALARM MONITORING
CIRCUITS
(see figure SD-1)
:
Alarm signals that
identify malfunctions or conditions that require
response from a maintainer are provided.
3.4.4.1 Standby-Alarm:
A standby alarm output
is provided by the normally closed contact of a relay.
The relay is held energized when the selected side
(main transmitter) is operating and an open circuit is
applied to TB3-15 as the standby alarm status. When
the selected side has shut down and the standby side
has been enabled, the relay will de-energize and apply
a ground to TB3-15 as the standby alarm status.
3.4.4.2 Shutdown-Alarm:
A shutdown-alarm
output is provided by the normally closed contact of a
relay. The relay is held energized when either side
(main or standby transmitter) is operating and an open
circuit is applied to TB3-16 as the shutdown alarm
status. When both sides have been shut down and the
transmitter is off-the-air, the relay will de-energize
and apply a ground to TB3-16 as the shutdown alarm
status.
3.4.4.3 SWR-Alarm:
The emitter/collector
impedance of a switching transistor to ground is
applied to TB3-13 as the SWR-alarm output. When
the reflected power is satisfactory, the transistor will
be reverse biased and apply an open collector to TB3-
