Calibration of Monitoring Antennas and Instruments

7/27/2019 Calibration of Monitoring Antennas and Instruments

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Calibration of monitoringantennas and instruments

Mr.Song KepingEngineer of Management of station and network Division

State Radio Monitoring Center

[email protected]+8610-68318264

Radio Monitoring and Spectrum Management Training

(China,23-31,May,2005)


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General considerations

Calibration of frequency

Calibration of measuring ormonitoring receivers

Calibration of the measuring

antennasCalibration of fixed monitoringrecording instruments

Calibration of monitoringantennas and instruments


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Calibration:

-Ensure the accuracy of the technical parameters

-Ensure the value is within the specified uncertainty

Technical parameters of the equipment

-Change over time

-Influenced by many factors



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Regular calibration of the equipment

-Decrease the risk of error

-Find the equipment need to be repaired

-Traces the technical parameters to standards

Parameters most frequently calibrated

-Frequency

-Signal level

-Antenna gain

-Values of legal significance



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Calibration documents

-Accompany with equipment

-Calibration report

-Indicate calibration status

-Incorporated in the equipment file

Calibration interval

-No generally applicable period

-Be chosen from a technical viewpoint



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High expense of calibration

-Because of the high demand of equipment used

-Make calibration in monitoring station more difficult

Calibration can be provided

-By service and support centers of manufacturer

-By external calibration lab



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-Check the accuracy of crystal oscillator

-Correct the error

Calibration task in monitoring station

-Exactly know the uncertainty of equipment

-Find the equipment need to be maintained

-Take action to avoid error



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Methods of check the accuracy of frequency

-Receive a HF standard frequency signal

-Receive a television signal as standards

-Use a GPS system

-Use a high accuracy frequency source



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Receive a HF standard frequency signal

-Standard frequency signals at 2.5, 5, 10MHz

-Other standard frequency signals

-Accuracy of 10-9 or better

-Receiving these signal

-Comparing the frequency to these signal



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Receive a television signal as standards

-High accuracy of television transmitters

-Accuracy of 10-11 or better sometimes

-Not all television signal are usable

-Receiving these signal

-Comparing the frequency to these signal



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Use a GPS system

-Caesium clocks on GPS satellites

-Time accurate of better than 1s

-Frequency accurate of better than 1011

-Signal is available everywhere

-Coded signals at 1575.42 MHz and 1227.60 MHz



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Use a high accuracy frequency source

-Calibrated frequency generator

-Caesium clock

-Rubidium clock

-Frequency accurate of better than 1011

-High cost of atomic clock



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Calibration of the measuringantennas





Calibration of fixed monitoringrecording instruments


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Antenna factor

-A part of calibration factors that determined bythe antenna system characteristics

-Gain, cable losses, adaptor losses

-Varies with frequency

Three basic method of calibration an antenna:

-Standard field method-Standard antenna method

-Standard distance (standard site) method



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All method deliver the antenna factors

-Valid for free space under far field conditions-Avoid influence of nearby object



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Standard field method

-Derived from the definition of the antenna factor-Direct calibrate in an accurately known field

-Limited to loop antennas



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Standard antenna method (substitution method)

-Measure a plane wave of unknown field-strength

-Using an antenna with known factor

-Replace it by antenna to be calibrated

-Determine antenna factor from the difference

-3 limitation



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Standard distance (standard site) method

-Mount 2 identical antennas at different distance

-Measure the attenuation between 2 antennas-Compare with calculated value

-Normally for directive antennas

-Distance should be far enough to avoid mutualcoupling



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Calibration of fixed monitoringrecording installations







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Initial calibration under controlled conditions

-Compare with calibrated field-strength meter and

antenna-Only valid when conditions remain unchanged

-Periodic calibration checks

-Calibration curve in the frequency range of interest

Calibration of fixed monitoringrecording instrument


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General calibration procedure

-Field-strength meter with a shielded loop antenna

below 30MHz-Field-strength meter with a dipole beyond 30MHz

-Substitute the recording antenna with the calibrateantenna

Calibration of fixed monitoringrecording instrument


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Thank you!

Calibration of Monitoring Antennas and Instruments

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