SYSTEM DESCRIPTION | GENERAL INFORMATION |
MS4782X Test Set The Series MS4782X Test Set contains a Wilkinson type combiner that combines the two RF signals from Ports 1 and 3 (RF1 & RF3) of the Scor- pion. External preamplifiers can optionally be provided at the combiner input to boost the input RF power to the amplifier-under- test (AUT). The combiner has power input rating of 30-Watts maximum when terminated with a VSWR of 1.2:1. For an open or short at the combiner output, the combiner input power rating is 0.5 Watts maximum.
The output of the combiner is fed to a source selection switch that enables one of the following to be applied to the AUT:
The combined signal from the Scorpion sources.
A modulated signal from an optional external modulation synthe- sizer.
A provision for the insertion of an optional external pre-amplifier (after the combiner and source selection switch) is also provided. Refer to Chap- ter 7, “Preamplifier Operations,” for details.
The test set includes a bi-directional coupler at the input of the AUT that separates the incident signal from the reflected signal. The power rating of this bi-directional coupler is 100 watts average. The –30 dB portion of the incident and reflected signals are applied to the Scorpion reference port a1 and test port b1, respectively, for S11 measurement. The S11 mea- surement determined by the DRA Scorpion is simply the ratio of the re- flected signal to the incident signal.
The amplified output of the AUT is fed to a high power coupler in the test set. The power rating of this coupler is also 100-watts average. The –30 dB coupled arm of this coupler is routed to the test port b2 of the Scorpion through a 6 dB resistive divider and a 0-dB to 70-dB step attenuator (10dB/step). A limiter is also provided in this path provide added protec- tion for the Scorpion reference channel .
The divider enables the connections of a power meter or Spectrum Ana- lyzer, when desired, to measure the AUT b2 output.
The through arm of the 100-W coupler is routed to a high power
(100-Watt) termination through a circulator. In the MS4782A Test Set, the circulator is internal and has a rating of 100 watts average. This circulator has an isolation specification of 20-dB minimum. This means that the AUT output power is attenuated by 20 dB (plus other losses) be- fore reaching the Scorpion port 2. Since the maximum (no-damage) power level for this port is 27 dBm (0.5 watt), this establishes the maximum AUT output power at 50 watts.
In the MS4782D Test Set, the circulator is external as shown in Figure 1-2. In selecting an external circulator, the following criteria should be used.
Power rating: Should be no less than the power output of the ampli- fier-under-test (AUT). It should be noted that a 100 watt termina- tion is provided in the Test Set for the termination port of the exter- nal circulator.
