TECHNICAL NOTE – OPERATION OF MT4400 TWTA
08/10/2004
TN4400-3
MCL, INC.
27 of 36
4.8 Optional
Linearizer
If the TWTA was supplied with the optional linearizer, it may be necessary, or desirable, to fine
adjust the linearizer for the specific application. The linearizer is preset at the factory to yield a
6 to 10 dB improvement in intermodulation distortion at an output power backoff of 4 dB for
two carriers spaced 10 MHz apart across the band.
MCL offers Linearizer Sub-Band tuning for optimizations over a narrower band. Please contact
MCL for details.
4.9
Switchover Interface J8
Switchover Interface J8 is dedicated to use with various redundant systems. Refer to TN4400-2
– Technical Note, Installation Guide for MT4400, paragraph “Connection to the Switchover
Interface,” for a detailed signal description.
4.9.1
MT4411 1:1 Redundant System
A 1:1 redundant system will consist of two HPAs, a RF switch interface box, and a RF switch
(Waveguide or Waveguide/coaxial). The controlling logic for the switchover is built into every
MT4400 and is accessed through the control line of the switchover interface connector (J8).
Either HPA in 1:1 redundant system can act as the switchover logic depending upon the current
waveguide switch position. As a result the HPAs must pass information back and forth so that
switchover operation is continuous and uninterrupted. The switchover logic will use inputs
from the Remote Interface, Computer Interface and Switchover Interface. The MT4400
contains several controls and indicators for a 1:1 switchover, they are as follows:
•
This HPA to Antenna, puts the HPA on the Antenna port during manual.
•
This HPA to Load, puts the HPA on the Load port during manual.
•
Auto Switching, puts both HPAs into the Auto Switching state.
•
Manual Switching, puts both HPAs into the Manual Switching state.
•
RF Low Switching Flag, indicates that a switchover will occur on a RF Low
alarm.
For details on the function of these controls, see Section 3.4.16 – Section 3.4.21 of this manual.
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 MT4412, MT44PC, . . .)
use only a small portion of the signals on J8. Depending on the system type the Switchover
Fault relay output will indicate the state of the MT4400, 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.
