TECHNICAL NOTE – OPERATION OF MT4000 TWTA
10/24/03
TN4000-3
MCL, INC.
39 of 46
4.7.4 Filament Delay During Local Override
There is not a "Filament Off" or "Transmit Selected" state while in Local Override mode. There
is no Proportional delay while in the Local Override mode. The Filament Under fault will be
disabled while the HPA is in the Local Override mode. Either of the following events can start
the filament delay over again (always a 3 minute warm up delay).
•
When the HPA was switched into Local Override mode while it is not in the
Transmit state.
•
Every time the HPA is turned on while in Local Override.
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 at mid-band.
If operating with more than two carriers, near the band edges, or at an output power backoff other
than 4 dB, a slight increase in performance may be obtainable with a slight adjustment of the
Phase control behind the accessory panel. The Phase Voltage test points may be used as a
reference during the adjustment. The factory preset Phase Voltage can be found in the MT4000
test data, which was supplied with the unit.
The linearizer Mag control is set for the specific TWT characteristics and should not be moved
from the factory preset position unless the TWT is replaced.
4.9
Switchover Interface J7 and Front Panel Controls
Switchover interface J7 is dedicated to use with various redundant systems. Refer to TN4000-2
Technical Note, Installation Guide for MT4000 paragraph “Connection to the Switchover
Interface” for a detailed signal description.
4.9.1 MT4011 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
MT4000 and is accessed through the control line of the switchover interface connector (J7).
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, Local panel interface, and Switchover interface. The
MT4000 front panel contains several controls and indicators for a 1:1 switchover; they are as
follows.
Antenna button/LED, puts the HPA on the Antenna port during manual.
Load button/LED, puts the HPA on the Load port during manual
Auto button/LED, puts both HPAs into the Auto Switching state
