Bird Technologies 4331 - Manual (Page 52)

Model 4431 Thruline Wattmeter
The Model 4431 RF Sampling Wattmeter is essentially the same as the Model
43 Thruline Wattmeter described in this instruction book except for the extra
provision of the adjustable RF signal sampler probe.
Theory of Operation
The RF sampler, as its name implies, provides a low level signal or sample
of the energy being transmitted through the line section of the wattmeter.
This signal is available at a Female BNC connector located on the right side
of the meter housing, labeled “RF SAMPLE”, and the level of this signal can
be varied by means of the control knob located on the front of the meter
housing. This adjustment is accomplished by means of mechanical linkage
connecting the sample adjustment (control) knob to the RF probe, so that
turning the knob varies the proximity of the RF probe to the center conductor
of the line section. Placing the probe closer (clockwise) to the center conductor
increases the coupling and the signal level at the RF sample port, and moving
the RF probe away from the center conductor (counterclockwise) decreases
the coupling. Refer to table 1 for an approximate guide for the levels of
coupling, and for a note on the maximum suggested adjustment of the
sampler. In the operation of the unit, the sampler output may be fed to any
suitable RF signal monitoring device; i.e., frequency counter, spectrum ana-
lyzer, oscilloscope, etc.
Bird Model 43 Wattmeter
38