Bird Technologies 4308 - Manual (Page 18)

currents will flow according to the direction of the travelling waves producing them,
whereas the capacitive portion of these currents is independent of the direction. Therefore,
in either position of the Plug-In Element, the coupling currents produced from the waves
of one direction will add in phase, and those produced from waves of the opposite
direction will accordingly subtract in phase. The additive direction is indicated by the
arrow.
The electrical values of the element circuits are carefully balanced and designed so that
the inductive current produced from the reverse wave will cancel its portion of the
capacitive current almost completely. The result is a directivity greater than 25 dB, which
means that the element is highly insensitive (i.e. produces little or no signal) from the
reverse direction wave. By being so highly directional, the Detector element is sensitive
at either one of its settings, but to only one of the two travelling waves. Thruline
Wattmeter measurements are also independent of their position along the standing waves.
Bird Model 4308 Thruline Wattmeter
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