Telewave, Inc.
Model 44A/AP
Page 12
Directivity Error
5.07 Directivity error results from the effect of imperfect directivity in the
Dual Directional Coupler. Directivity is the ability of the coupler to
sense power fl owing in one direction and be insensitive to any power
which may be fl owing in the reverse direction. The directivity error
is included within the specifi ed instrument accuracy of ± 6%.
Insertion Error
5.08 When the RF load and RF source are well matched, any error con-
tributed by inserting the Model 44A/AP Wattmeter alone is negli-
gible. However, the use of a jumper cable to connect the wattmeter
in the system will change the characteristic impedance of the line,
especially in a system with high VSWR. Since the impedance on
either side of 1/2 wavelength is identical, the jumper cable added to
the input or output of the Model 44A/AP should be of an appropriate
length to equal 1/2 wavelength at the frequency of operation, thus
eliminating any error due to the additional length.
5.09 The chart shown in Figure 7-3 shows the required length (including
connectors) of RG-213/U cable to act as a 1/2 wave line section at
frequencies from 25-500 MHz.
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