AirRadioUK

Civil & Military

Radar

ADSB

ADSB  is a replacement for traditional radar based surveillance of aircraft. Instead of using ground based radar to interigate aircraft to determine its position, each aircraft use GPS to find its own position and then automatically report it.

There are many reasons to use ADS-B. GPS positions reported by aircraft are more accurate, ADS-B is more easily deployed and less expensive as ordinary radar, ADS-B is a broadcast service and can be received up by other aircraft and ATC on the ground.

To support ADS-B “Out”, the aircraft must have a GPS receiver as the position source, and a datalink transmitter to actually send the ADS-B data.


The datalink transmitter that most aircraft will use is a Mode S transponder, using a feature called “Extended Squitter”. This is often referred to as 1090 ES, because the Extended Squitter (ES) transmissions are transmitted on the 1090 MHz frequency. The Mode S transponder with Extended Squitter is the international standard for ADS-B output. Specific to US airspace – and not approved elsewhere – is the UAT datalink transmitter as an alternative to the Mode S transponder. UAT transmitters may only be used on GA aircraft flying at lower altitudes in the USA.


The GPS receiver used must be an IFR certified receiver. Although that GPS is not required to be WAAS capable, that may be a moot point. Many legacy GPS receivers that were designed before ADS-B was planned do not include the necessary calculation of integrity and accuracy that ADS-B needs to operate. It is unlikely that these older devices can be upgraded, and therefore a new GPS receiver would be required. This does not necessarily mean discarding an existing GPS navigator - a secondary receiver can be used to provide ADS-B data without disrupting the existing installation - there is no rule that requires a single common position source.