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general configuration and spacing of the transmission line, and no provision is made
for adjustment.
The validity of subsequent calibration steps is dependent on verifi-
cation of good v. s. w. r. over the full frequency range.
During manufacture a sweep
frequency method is used to achieve this, but another method can be used if tests are
made at a sufficient number of frequencies.
Connect the v. s. w. r. measuring device to the socket on the terminating load·
and check the v. s. w. r. at a selection of frequencies up to 1 GHz. The v. s. w. r.
should be better than 1. 05 over the whole frequency range.
With the INSERT PROBE control fully counter-clockwise, connect the v. s. w. r.
measuring device to the power meter input socket and check the v. s. w. r. of the
combined terminating load and in-line detector at a selection of
~requencies
up to
1 GHz.
The v. s. w. r. should be better than 1.1 over the whole frequency range.
5.4
CALIBRATION ACCURACY AT.L.F.
(Apparatus required: items d and e)
The power-reading accuracy is best checked at a low frequency - usually the
frequency of the local power supply - and then compared with that ·of a standardized
mean-reading power meter near the upper limit of the frequency range.
1)
Connect the dynamometer wattmeter between the a. c. supply and the power
meter under test.
The current and voltage coil connections should be arranged for
minimum error due to internal losses, and allowance should be made for the error
if it is appreciable.
Owing to the frequency response limitations of dynamometer
wattmeters the a. c. supply must have low distortion (less than 1 %) .
2)
Set the Range switch to 10 Wand set the power input until the dynamometer
indicates the input figure given on the label at the rear of the instrument.
3)
Check that the TF 2502 reading is 8 W ±0. 5%, if not adjust RV1 until it is
correct.
4)
Reduce the applied power to zero and allow sufficient time for the thermocouple
to cool.
5)
Set the Range switch to 3 W and set the power input until the dynamometer
indicates the input figure given on the label at the rear of the instrument.
6)
Check that the TF 2502 reading is 2. 5 W ±0. 5%, if not adjust RV2 until it is
correct.
16
2502 (1)
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