Potomac Instruments FIM-21 - Page 30

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SECTION 4. MAINTENANCE (Cont.)
4.10 R ecalibration (Cont.)
It is possible to maintain a rough calibration check by recording
th e reading obtained when th e known output of a signal generator is applied
to the external RF input, after first performing the self-calibration procedure.
Th is is not a satisfactory substitute for calibration in a known RF field for
two reasons: (1) Wh en the external input is used, some components are used
that are not used for field strength m easurements, while so me that are in the
circui t for field st rengt h m easure m ents are not used wi th the external input;
and (2) the outp ut level of the generator for all future checks would have t o
be maintained wi th i n one percent of the level for the first check, which is
not usuall y possible.
4-9