OPTION 010 DME Modulator
Annex-E-16
The instrument has its DME mode RF calibration carried out with modulation
disabled. Press [MOD ON-OFF] key. Absolute level accuracy in this mode,
measured using a calibrated power meter, should be that of the instrument in
standard mode (e.g. single modulation) ±0.5 dB.
(4)
ON/OFF ratio
Set up the equipment as follows:
Unit under test:
Modulation mode Avionics, DME
RF level 0 dBm
Pulse pair spacing 9 µs (Invalid Pulse message displayed)
Modulation Disabled (press [MOD ON-OFF] key)
Spectrum analyser:
Centre frequency 1025 MHz
Span 100 kHz
Ref level 0 dBm
The analyser should display an un unmodulated signal at the centre frequency
with an amplitude of 0 dBm. Press the [MOD ON-OFF] key, and the signal level
should fall to less than -80 dBm.
Note: depending on the analyser used, it may be necessary to reduce the reference
level or input attenuation in order to lower the noise floor of the analyser to less
than -80 dBm.
Repeat the above process with the unit under test and analyser frequencies set to
960 MHz and 1215 MHz. The ON/OFF ratio should not be less than 80 dB.
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