Chapter 2 - Theory of Operation
General
The forward power meter acts as a continuous monitor of forward power output. This provides
a reference against the reflected power value enabling determination of power ratios and VSWR.
Alarm Condition
An alarm condition occurs as the result of the reflected power being greater than the reflected
power set point for longer than 50ms. If enabled, an audible alarm will sound.
An alarm condition will also activate the interlock. An active interlock will cause the normally
open terminals to close and the normally closed terminals to open.
Fail-Safe/Non Fail-Safe
In the fail-safe mode an alarm condition will also occur if the Wattcher is not powered. The non
fail-safe mode requires power for an alarm condition.
Element
The function of the element is to detect (sense) the forward or reflected RF power in the line
section at any given time. The direction in which the “arrow” on the element cap is oriented
indicates the direction in which it is sensing the RF power flow in the system.
Traveling Wave
Viewpoint
The best way to visualize the Thruline Wattmeter idea is from the Traveling Wave viewpoint on
transmission lines, which illustrates that the voltages, currents, standing waves, etc., on any
uniform line section are the resultants of two traveling waves, forward and reflected.
Coupling Circuit
The coupling circuit which samples the traveling waves is in the Plug-In Element. Energy will
be produced in the coupling circuit of the element by both mutual inductance and capacitance
from the traveling RF waves of the line section. Of course, the inductive currents will flow
according to the direction of the traveling waves producing them.
The capacitive portion of these currents is naturally independent of the direction of the traveling
waves. Therefore, it is apparent that the inductive portion of the current produced from the waves
of one direction will add in phase to the capacitive portion of the current, and those of the opposite
direction will subtract in phase. The additive direction is the forward or
arrow
direction of the
element.
Figure 4
Element Schematic
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