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OPTION 006 Avionics
Annex-A-25
ACCEPTANCE TESTING
Introduction
The test procedures in this section enable you to verify that the electrical performance of the
avionics signal generator complies with the Performance Data given earlier. The test equipment
recommended for this purpose is listed in Table A-1. All tests may be performed with the covers
in place and are intended to be carried out in the order given. For convenience, the test equipment
and specification for each test are summarized before the test procedure. These tests are in
addition to those for non-avionics versions of the instrument.
These acceptance tests give a high degree of confidence that the instrument meets its specification,
without the use of specialised test equipment.
The avionics option uses a method of Direct Digital Synthesis (DDS) to generate the required
avionics waveforms. The accuracy of the generated waveform is therefore determined by stored
digital data and the AM performance of the signal generator. These tests check the waveform
generation and analogue and RF signal paths in the signal generator. Additional tests can be
undertaken using specialised ILS and VOR receivers if they are available.
Test equipment
The test equipment recommended for acceptance testing is shown in Table A-1. Alternative
equipment may be used provided it complies with the stated minimum specification.
Table A-1 Recommended test equipment
Test equipment
Description Minimum
specification Example
Spectrum analyzer
DC to 400 MHz
Level accuracy ±1 dB
IFR* 2382
Modulation meter
500 kHz to 1 GHz
AM accuracy ±1% of reading
Selectable ILS filter
IFR* 2305
Oscilloscope
100 MHz bandwidth
Tektronix 2235
*IFR Ltd was previously known as Marconi Instruments Ltd
Functional testing of ILS waveform generation
Test equipment
Description Minimum
specification Example
Spectrum analyzer
100 Hz to 400 MHz
IFR 2382
Oscilloscope
100 MHz bandwidth
Tektronix 2235
IFR uses a method of Direct Digital Synthesis (DDS) to generate the ILS waveforms. One DDS
generated waveform contains both the 90 Hz tone and the 150 Hz tone with 0% DDM (Difference
Depth of Modulation).
A second waveform is generated with 0% DDM but with the relative phase of the 150 Hz tone
reversed compared to that of the 90 Hz tone.
When small levels of the second waveform are added to the first, the resultant waveform has a
constant SDM and adding a proportion of the second waveform will result in the DDM of the
resultant signal changing.