Mode-C (1090MHz) Bearingless Target
It is important to understand that Mode-C devices 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-C is similar to Mode-A but is equipped with an onboard altitude (Height relative to 1013.2mB) encoder that can be used to calculate the vertical separation between the host and the target aircraft. The relative horizontal distance of the target aircraft from the host aircraft can only be estimated from the signal strength and the rate of change of signal strength. This is explained further in the following section on Mode-S transmissions.
When a Mode-C 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-C target cannot be plotted on a screen like that of a target with a bearing, however, its separation from the host aircraft and its approximate distance will be shown. IMPORTANT its bearing cannot be shown.
PilotAware uses the smaller of the two antennas provided to receive Mode-C signals.