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Idea for Satcom tests of the BTO method

09 Feb 2019

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On aircraft 9M-MRO it is possible that the air temperature and the electrical voltages may have become significantly non-normal. This article suggests simple tests of the BTO (Burst Timing Offset) method. They are designed to determine whether the assumption of constant processing delay is accurate, when the SDU (Satellite Data Unit) operates in significantly non-normal air temperature or voltage conditions.

With satellite communications equipment similar to that installed on the missing plane, but located at a fixed location on the ground, it should be possible to perform the following tests. The extra equipment required is: a temperature controlled enclosure, and a variable power supply.

Here I refer to the test equipment as the AES (Aircraft Earth Station), because that is what it simulates.

Each individual test would consist of transmitting a standardised message from the GES (Ground Earth Station), via the satellite, to the AES, and measuring the elapsed time until the GES recieves the response from the AES. The two momentary distances involved, and the processing delay within the satellite, should all be known, therefore the processing delay within the AES can be calculated.

1. Tests as above to be performed with the AES SDU in constant normal air temperature, but supplied with various voltages in the range 100v ac to 122v ac [1].

2. Tests as above to be performed with the AES SDU supplied with constant normal voltage, but in various air temperatures, ideally covering the range -55C to +70C [1], but in practice covering a smaller temperature range which is easily achievable by the enclosure.

If the test results are that the AES SDU processing delay is constant, for all tested voltages, and for all tested air temperatures, this would provide evidence that the satellite to AES distances calculated for the missing plane are accurate (even if the plane experienced significant electrical or temperature problems).

If on the other hand the test results show that the AES SDU processing delay significantly varies with voltage or with temperature, this would enable alternate satellite to AES distances to be calculated for MH370, for various patterns of on-plane voltage or temperature variations.

Caveat: This is written by an amateur, therefore please independently check everything yourself, as it may contain factual or logical errors.

Sources:

[1] (The suggested voltage and temperature test ranges are based on the operating requirements of this different but similar SDU)
https://usermanual.wiki/Honeywell/HS-720/html
See table 1-11: "AC Voltage at SDU terminals 100 to 122 V ac" "Operating temperature -67°F(-55°C) to +158°F(70°C)"


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