Mode-S (1090MHz)Bearingless Target

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Similar to Mode-C, Mode-S transponders are devices which only transmit (at 1090MHz) when interrogated by a ground radar signal or an aircraft TCAS System. Therefore, if an aircraft is not being interrogated it will not transmit a signal. This can happen at low levels and or in remote areas.

Mode-S is an onward development of Mode-C which adds additional features. The most important additional feature is that it transmits more information. The most significant of which is the unique airframe ICAO number.

PilotAware detects this code which allows simpler techniques to be used to uniquely identify the target aircraft(s).  The signal from an approaching Mode-S transponder will increase non-linearly as it gets close to and diminishes non-linearly as it retreats from your aircraft. The absolute signal strength at any particular distance is not consistent for all installations so detection can only work with changes in relative strengths. This is shown in the following illustration.


When a Mode-S transmission is detected by PilotAware and compared with a group of pre-set heights and strengths (selectable by the user in the PilotAware CONFIGURE page) it will trigger a voice alert direct from the PilotAware audio output and also send a message to your chosen navigation software package. The absence of a GPS co-ordinate means that a directly detected Mode-S target cannot be plotted on a screen as that of a target with a bearing, however its separation from the host aircraft and its approximate distance will be shown. Its bearing cannot be shown.

PilotAware uses the smaller of the two antennas provided to receive Mode-S signals.