BIRD 43 Instrukcja Obsługi Pobierz pdf (Strona 19)

Theory of Operation

 NOTE: Attenuation, measured in dB, can be derived from the

power ratio by the equation N

= 10 log φ.

VSWR scales and their attendant controls for setting the reference

point have been intentionally omitted from the Bird 43. Experience

using the Thruline Wattmeter for transmitter tune-up, antenna

matching, etc. will show that the power ratio measurement is as

useful in practice as the standing wave ratio.

A trial is suggested – forget about VSWR for a few days and think

in terms of

φ = W

/ W

. The two meter readings, W

and W

, give

a useful, approximate picture of the results without bothering to

calculate the power ratio exactly. Consider that, for an antenna

matching problem, the main objective usually is to minimize W

Anything done experimentally to this end will be seen when the

element is turned to the reflected power position.

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BIRD 43 Instrukcja Obsługi Strona 19