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Chapter 1 Introduction
The Model 4391A is a multi-purpose Radio Frequency
wattmeter designed around a microcomputer. A program
stored in permanent memory controls the operation of the
instrument at all times, permitting the detection and
correction of various error sources and the refinement of the
raw data produced by the directional detectors. The
instrument can compute VSWR, amplitude modulation, and
various decibel variables reducing the odds of error and
making such measurements consistent or repeatable
regardless of who makes the measurement.
Other benefits include extended range using standard
elements in some modes of operation, continuous monitoring
of maximum and minimum readings, a peaking aid, and
error messages.
Because of its complexity, the proper use of the 4391A is not
always obvious. For this reason it is strongly advised that
this manual be read in its entirety before using the device.
Purpose and
Function
The 4391A RF Power Analyst is an insertion type digital RF
Directional Thruline® Wattmeter designed to measure peak
or average power flow, load match, and amplitude
modulation in 50 ohm coaxial transmission lines. It is
intended for use with CW, AM, FM, SSB, TV, and Pulse
modulation envelopes. The instrument directly reads PEP or
CW power in watts, milliwatts, or kilowatts in 9 ranges from
2.5 to 1000 full scale forward power and 0.25 to 100 full scale
reflected power depending on the Plug-in Element. In
addition it reads SWR directly over the range of 1.00 to
99.99, percent modulation directly over the range of 0.0 to
99.9, and return loss over the range of 0 to 36.1 dB. For
convenience, forward and reflected CW power can be
displayed in dBm (dB above 1 milliwatt) from 6 dB above to
24 dB below nominal element range.
Power range and frequency band are determined by the
Plug-in Elements used. Two switches on the front panel of
the instrument are set by the user to correspond to the
nominal power range of the forward element. The reflected
element is assumed to have a nominal range one tenth that
of the forward element.
In any mode of operation, the instrument can recall from
memory the lowest or highest reading taken or tell the
operator whether the newest reading is less than, equal to,
or greater than the previous reading.