Owner’s Manual | PCAS XRX
UNDERSTANDING PCAS 17
How does XRX work?
XRX is a stand-alone, passive system. Passive systems are different from active systems such as TCAS, Skywatch®, etc.
Active systems can be found in commercial airliners, corporate jets, and higher-end general aviation aircraft. They
actively interrogate aircraft transponders within a specific range. Passive systems like your XRX listen for the replies to
these interrogations, as well as ground-based RADAR interrogations.
How is direction obtained?
The key to providing directional information is the antenna design. XRX uses a specially designed antenna which uses
a combination of signal amplitude and/or phase cancellation, which is the only way to accurately detect direction from
inside the cockpit. Other methods of directional detection do exist, but antenna array installation is required.
Difficulties with detection inside the aircraft include airframe echoes, multipath, phase cancellation, and signal path
loss due to airframe shadowing. The XRX design overcomes most of these issues. However, direction resolution is
limited to 45° increments. Inside your XRX is a highly-specialized antenna array. This array is made up of four precision
tuned directional antenna elements which are coupled to four individual super heterodyne RF receivers. Several years
of testing and the use of our custom-designed RF anechoic chamber allow the XRX to overcome reception issues and
accommodate a wide range of airframe types. The traffic bearing information displayed is directly related to the
internal solid-state compass to accommodate changes in heading so that at any given moment the bearing you see is
relative to your heading. This design allows the unit to “hear” which direction the aircraft is approaching and display the
information on the screen. Multiple aircraft are tracked at once using this method.
Bearing information shown is directly related to the angle at which your XRX system is placed upon your glare shield.
Changing the forward angle of the unit greater than 20° to accommodate viewing is not recommended without using
the 45° screen option (see page 43, “Screen Options”).
The Importance of Relative Information
The key to displaying smooth, understandable traffic information is relativity. If the information is always relative to your
aircraft, you are your own point of reference. Range is relative to your location, as is the relative altitude (ie +600 above
your altitude) and relative bearing (ie: to your right). For instance, if only the altitude of the other aircraft is known, you
would have to find out your own altitude by another glance at your altimeter, then do the math. Likewise, to find out
the target’s relative bearing, you must glance at your own heading indicator. However, XRX contains these instruments
and will do these calculations for you. You will see a live, relative representation that requires no translation, whenever
you glance at the XRX screen.
Alerts and advisories are determined by the range of the aircraft
converging, and what range setting you have selected.
Changing the angle of the unit greater than 20 degrees to accommadate
viewing is not recommended without using the 45-degree screen option.
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