BIRD Thruline 43, Инструкция

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Bird Model 43 Wattmeter
6
Coupling Circuit
The coupling circuit that samples the travelling waves is in the Bird
Plug-In Element. The element circuitry and its relationship to the rest
of the Bird 43 are illustrated in Figure 3.
Current is produced in the coupling circuit by the travelling waves in
the line section. Both inductive and capacitive coupling contribute to
this. The inductive current flows in the direction of the travelling
wave. The capacitive current is independent of the direction of the
travelling wave. Therefore, the inductive current produced by one of
the travelling waves will add in phase with the corresponding capac-
itive current, while that produced by the wave travelling in the oppo-
site direction will subtract. The additive or “arrow” direction is
assigned to the forward wave.
The electrical characteristics of the element are carefully adjusted so
that, for the reverse travelling wave, the inductive current will com-
pletely cancel the capacitive current. The result is directivity greater
than 25 dB. Thus, the element is sensitive at either of its settings, but to
only one of the two travelling waves. Thruline Wattmeter measure-
ments are also independent of position along the transmission line.
Like similar diode devices, the Bird 43 indicates the carrier component
of amplitude modulation, with very little response to side band compo-
nents added by modulation.
Figure 3
Thruline Wattmeter
Schematic