AR 10009284, Operating And Service Manual

Page: 23 / 62

Model 40T26G40A
Rev A 9
3.2.3 Cooling Requirements
The TWTA is provided with a cooling fan. It is important that air movement around the rear of the unit be
unobstructed.
CAUTION:
For either bench-top or rack mounting, do not position the TWTA in such
a way that the air intake or air outlets are blocked, or that the exhaust
flow is directed into the air intake. See section 3.5 for the locations of the
air intake and air outlet. If the unit is rack-mounted, make sure that the
intake air is 45°C or below. If necessary, fabricate a short duct to direct
the hot exhaust air out of the rack enclosure. Great care must be taken to
minimize any flow restrictions. Avoid mounting heat-producing
equipment in the same rack, especially below the TWTA. Failure to
provide adequate cooling can result in the unit’s shutting down from over-
temperature conditions. The TWTA dissipates approximately 700 watts
when it is in the Operate mode.
3.2.4 AC Line Power Connection
AC line power connection to the TWTA is made at the AC inlet J1, which is a female IEC-320 connector. A
line cord suitable for the type of AC outlet used, and consistent with local electrical codes, must be obtained
to mate with J1. Minimum wire size for the line cord is 18 gauge.
TWTAs destined for the North American market are provided with a terminated 3-wire cord. It plugs into
normal 120 VAC single-phase outlets. The amplifier will operate from any line voltage between 99 and 260
VAC.
3.2.5 RF Output Connection
The RF output is a WR-28 waveguide flat flange. Output flange alignment is critical for proper operation of
the amplifier. Use #4 hardware equivalent. Align the two output flanges and secure the mating waveguide,
while maintaining flange alignment.
CAUTION:
Never operate the TWTA without a matched output load rated for at least
100 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 (J2). If
no external isolator is used, install the factory-supplied connector with the jumper between pins 3 and 4 and
pins 10 and 11. See section 3.2.6,
External Interlock Connector .