Marconi Instruments TF 2502 - Page 19

5.5 CALIBRATION ACCURACY AT R.F.
Calibration is difficult at r. f. since, unless great care is taken with impedance
matching, substantial errors can be introduced. If it is essential to make checks at
r. f. , then connections should be made with a wide band directional coupler having a
directivity of at least 35 dB and the power level monitored with a low level power
meter. Such an arrangement must, of course, be calibrated by reference to a
standard power meter.
NOTE If either a terminating load or a detector unit is to be returned to Marconi
Instruments for repair or recalibration, it is important to send the complete
detector /load assembly. This will enable the item to be recalibrated as an
assembly, which will ensure a better performance, e.g. v. s. w. r. and fre-
quency response, than can be obtained by recalibrating the detector and load
separately.
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