via a type N connector on the front panel and one for use by the front panel forward
power metering circuit which uses a similar detector to process the RF signal. The RF
sample port, calibrated in coupling ratio versus frequency, permits independent
monitoring of CMPA output power levels through the use of an external spectrum
analyzer or portable power meter. High reflected RF protection circuitry is standard and
reflected power information is sent to the front panel for display. With forward power
metering comes user settable low and high RF power alarms settable via the front panel
access door.
The output and reflected power level readouts are also available for remote monitoring
via the optional CPI remote panel or the computer interface (CIF) port located on the rear
panel. RF drive is adjustable via these ports as well. The standard RF output interface to
connect the CMPA to the external waveguide run is a WR-75F (flange) termination. The
CMPA comes with a WR-75G (grooved, threaded) rear connector and a waveguide
gasket.
Power Supply Subsystem
Overview
The power supply portion of the CMPA provides all of the internal voltages necessary to
operate the TWT, RF driver (IPA), forced air cooling system and auxiliary circuits for
control, monitoring and protection of the CMPA. Only the AC input power is required for
operation. The travelling wave tube derives its operation from four DC power supplies: a
filament heater low voltage supply, a helix high voltage supply, and two collector high
voltage supplies.
The power supply design utilized in the VZU-6994 is of the switch mode power
conditioner (SMPC) type, which has an excellent reputation for reliability and stability.
An added advantage of the SMPC approach over outdated linear power supplies is its
intrinsic high efficiency and safe operation. By limiting the amount of the instantaneous
stored energy in the power supply, the risk of permanent damage to the CMPA due to
abnormal or transient conditions is avoided. The momentary level of stored energy
(measured in joules) is well below the maximum limit of energy that the tube can safely
dissipate during normal operation. A simplified block diagram of the power supply is
shown in Figure 3. The principal circuit modules are discussed in the following
paragraphs.
Power Factor Correction Module
Input primary power (single phase, 110-240 VAC) flows via a EMI filter and the main
circuit breaker to both the cooling system power supply and the Power Factor Correction
Module. This module provides a regulated 375 VDC to the Power Processor and allows
the CMPA to meet the requirements of EN61000-3-2 regarding total harmonic distortion.
In the event of a failure of this module, a DC bus fault flag is sent to the micro-controller
Ku-Band CMPA 04/08
TD-67 Page 4
