AR 10012510, Operating And Service Manual

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Model 200T8G18A/250T8G18
10 Rev D
3.2.5 RF Connections
The RF output connector is type WRD-750 waveguide flange.
CAUTION:
Never operate the TWTA without a matched output load rated for at least
350 watts, continuous. The TWTA is not provided with an output
isolator. Full reflected power may irreparably damage the TWT. Even
with no drive, "looping" oscillation can result in RF output high enough
to damage the tube if it is operated without a load. The VSWR detection
and foldback circuit is provided to protect the tube from progressive
failure or mismatch of the output load; it should not be relied on for
protection from the absence of a load.
If an external isolator is installed at the output of the TWTA, either the isolator should have a load capable of
dissipating the full output of the TWTA or the isolator load should be provided with a temperature-sensing
switch. The temperature switch should be normally closed, self-resetting, and with a temperature rating such
that there is no possibility of damaging the load by overheating before the switch opens. The TWTA may be
interlocked with the switch by connecting it between pins 3 and 4 of the external interlock connector (J3). If
no external isolator is used, install a jumper between pins 3 and 4. See section 3.2.6, External Interlock
Connector, below.
3.2.6 External interlock connector
The TWTA is provided with external interlock capability via a 15-pin female D-sub connector, J3. To enable
the high voltage power supply, it is necessary to provide continuity between J3 pins 3 and 4. If the amplifier
shuts down because the interlock was opened, it will be necessary to reset the system to return to standby (see
System shutdown screen in Section 3.4). In addition, there is an external inhibit capability via the same
connector, J3. To enable RF ON (beam on), continuity must be provided between J3 pins 10 and 11. If
continuity is broken, the TWT beam will shut off until continuity is restored. No reset is required to return to
RF ON. Users may adopt the interlock and inhibit features to disable the HPA for either equipment protection
or as a backup for personnel protection.
CAUTION:
Do not rely solely on the external interlock or inhibit features for
personnel protection. Use proper operating and safety procedures to
insure that power is removed as necessary for personnel safety.
The amplifier has an internal jumper between J3 pins 1 and 2 that may be used by the customer to verify
installation of the HPA in the overall system by means of a continuity string.