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6.3 LEVELING USING THE 'EXT' MODE
When operating the amplifier in the External (EXT) mode, it is important to understand that the
power output levels are determined by the external voltage reference source and that the
applicable Calibration Data Sheets should be reviewed to determine the appropriate drive signal
level so that the amplifier does not exceed the specified power output rating. As described in
paragraph 6.1.2, due to the flatness curve tolerances at certain frequencies, the rated power
output power could be exceeded by an additional 40% and jeopardize the longevity of the
amplifier. The amplifier should not be over driven and should a particular application require
additional power beyond the rated power of the CMX25, contact IFI's Customer Service for
additional high powered amplifiers.
Detailed below are specific applications for using the External ( EXT ) Mode with a variety of
external inputs.
6.3.1 Constant RF Voltages Verses Frequency At A Remote Load
With remote detectors suitably rated for power and frequency, the CMX25 provides the means
for feeding a mismatched load with constant RF drive voltage over the entire frequency range.
Full leveling, at half the CMX25 rated output power, is realizable with most reasonable load
variations. Extremely mismatched loads, particularly those presenting near short circuit
conditions to the amplifier, will reduce the maximum voltage leveling capability of the system.
Load impedance variation from 50 Ohms to an open circuit will permit peak voltage leveling
within the VSWR capability of the amplifier. Variations in impedance from 50 Ohms down to a
short circuit will rapidly diminish the peak voltage leveling capability toward zero. Amplifier
VSWR limitations will, of course, further limit the maximum leveled voltage into mismatched
low impedance loads.
To operate in this mode, after selecting the desired band, place the ALC switch in the EXT
position. Connect the ALC on the rear panel to the detected output port on the remote detector.
Connect the remote detector in series with the CMX25 output and at the input to the load. The
system is now ready for operation. Amplitude adjustments can be made with the level control as
in manual operation.
NOTE:
When the CMX25 is used as a driver for higher power amplifiers, automatic level
control can be accomplished in the same manner but at the power and frequency limitations of
the driven amplifier.
