TECHNICAL NOTE – OPERATION OF MT4000 TWTA
10/24/03
TN4000-3
MCL, INC.
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Manual button/LED, puts both HPAs into the Manual Switching state
RF Low Switching LED, indicates that a switchover will occur on a RF Low
alarm.
For details on the function of these controls see the O&M manual for the MT4011.
Once the HPA is in the Auto switching mode, the amplifier on the dummy load will continually
monitor the primary amplifier for failures. If the primary HPA (the one on the antenna) or its
exciter fails the secondary amplifier will switch itself to the antenna.
4.9.2 Other Redundant Systems
All other redundant systems whether they are MCL systems (such as MT4012, MT40PC, ..) use
only a small portion of the signals on J7. Depending on the system type the Switchover Fault
relay output will indicate the state of the MT4000, the RF Off input would be used during
switching, and/or the RF Low Switching input would be used to turn on switching for a RF Low
alarm.
4.10
User Interface J6
User interface J6 is supplied to allow various earth station equipment (such as exciters) to be
wired into the MT4000. Refer to TN4000-2 Technical Note, Installation Guide for MT4000
paragraph “Connection to the User Interface” for a detailed signal description. The Interlock
fault & Waveguide Pressure fault inputs will shut down the high voltage power supply and will
require a fault Reset to clear. The RF Off input will shut off the HPAs RF switch but the high
voltage power supply will remain on.
4.11
Prevention of Excessive RF Input Power
As is well known, driving a TWT past saturation will damage the tube. Saturation is the point
where further input results in no further increase in power out.
It is requested that the user immediately investigate the possibility of overdrive in his installation.
If this possibility exists, the following is suggested to protect the TWT:
4.11.1 The Exciter
The exciter output must be limited to less than or equal to 2 dB greater than the level required to
drive the system to rated output power. This level can be found on a warning tag (see the figure
below) attached to the front of each unit as well as in the system test data.
