Telewave, Inc.
Model 44L1/L1P
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4
FUNCTIONAL DESCRIPTION
4.01
The Model 44L1/L1P Wattmeter is made up of two major sections.
Refer to the schematic diagram in Figure 3-1 for this description.
(a) A Dual RF Directional Coupler with directivity of greater than
25 dB.
(b) A voltmeter circuit. Five ranges are provided.
4.02
The 50 ohm Dual Directional Coupler A1 samples a small amount
of the incident or forward RF power delivered to the load. The cou
-
pler incorporates two RF detectors which produce a DC voltage
proportional to the sampled RF power. A small amount of power
reflected from the load is also sampled.
4.03
Mode Switch S1 determines which of these voltages is displayed on
the meter, M1. The RF Power Range Switch S2, selects the appro
-
priate range and calibration resistors for the power to be measured.
Each range is provided with an adjustable internal potentiometer for
range calibration.
4.04
Meter M1 displays five scales which correspond to the RF Power
Range Switch positions. The lower third of the meter scale is shaded
red, alerting the user to switch to a lower power range for improved
accuracy. An OFF position is provided on Mode Switch S1, which
shunts out the meter movement. This provides protection for the
sensitive meter when the instrument is being transported.
4.05
Model 44L1P provides an RF sampling port with an output of -40
dB (+/- 2 dB) below the transitional line level to use for measure
-
ment of frequency, spectrum analysis, to inject a signal for measure
-
ment of receiver sensitivity, or other applications. The port coupling
is not directional; in a high VSWR system, the sampling port output
will be -40 dB below the
total
power passing through the instru
-
ment.
