ZAON XRX

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PRICE £1056.33 (INC VAT)

THE XRX is the latest in a line of portable traffic awareness systems from Zaon Flight Systems and features the ability to indicate the direction of detected traffic as well as range and relative altitude.

The latest version of the firmware also supports a data interface that allows traffic information to be sent to and displayed on a Garmin 496.
The system is designed as an aid to visual detection of traffic. As well as showing traffic information on screen, it can output audio traffic alerts. It will track up to 10 target aircraft simultaneously, and display the three most ‘threatening’.

Even though the XRX has a built-in LCD screen we were keen to try out the interface to the Garmin 496. This requires the use of the optional power and data cable to connect the two units together and to connect both to a power outlet.

HOW IT WORKS
The XRX is a transponder based passive detection system, which means it listens for the replies from nearby transponders that have been interrogated by ground-based radar or by active airborne systems such as TCAS.

This transponder signal is then processed and decoded to provide range, bearing and relative altitude of the target aircraft.

However, there are so many ways in which the received signal can be distorted – everything from multipath echoes and airframe shadowing, to a dirty transponder antenna on the target aircraft – that some sophistication is required to adequately compensate.

To that end, the XRX includes a built-in solid-state compass and altimeter, bank angle sensor, temperature monitoring and a cooling fan.

I have to admit to having been a bit sceptical that all this wizardry, packaged up in a cockpit-mounted, selfcontained unit weighing 250gm, would hang together well enough to provide usable accuracy and reliability.

ON TEST
We installed the XRX in a CAP-10, and to ensure that we could verify the traffic information displayed by the unit we flew in company with an RV-6A. We used GPSmeasured distances along a common course line to check the accuracy of the range information.

Getting the best out of the XRX requires a little more than just slapping it up on the glareshield and switching it on. The unit needs to be placed at least 6in away from obstructions (including the magnetic compass) and must be horizontal. A number of different sized silicone feet are provided to facilitate this, but in the CAP the glareshield itself is horizontal so we only needed a couple of the provided Velcro ‘buttons’.

A simple menu system is used to set the size of the ‘detection window’ that the XRX monitors for traffic. The maximum size corresponds to a radius of 6nm and an altitude of 2500ft above and below.

The Garmin displays traffic information using simplified TCAS-style symbols – a hollow diamond which changes to a solid yellow circle if the traffic gets close enough to be regarded as a threat.

For Mode-C or -S equipped targets, a number beside the symbol indicates the relative altitude of the target and a small arrow indicates if it is climbing or descending. While the integral LCD in the XRX is adequate, it is small, and can sometimes be hard to read. So having traffic information displayed on the big, bright moving map of the 496 is a revelation. It provides instant awareness of where to look for detected traffic and so helps to reduce head-in-the-cockpit time.

Furthermore, while the XRX’s LCD shows bearing information in 45º increments, the unit can actually provide bearing resolution of 20º, and the 496 uses this improved resolution.

IN THE AIR
We let the RV take-off first then lined up behind it. Shortly after take-off , a target appeared on the Garmin at 12 o’clock, a mile ahead and 500ft above. That is exactly where the RV was.

We manoeuvred around so the RV was in different relative positions and at different ranges, and while the bearing shown by the display wasn’t always exactly correct it was easily accurate enough to help locate the traffic visually.
Several times during the test we lost visual contact with the RV but on every occasion we were able to use the XRX to find it again. The Zaon documentation highlights a possible limitation with accurately determining the range of targets in the rear quadrant.

However, we didn’t experience this – most likely a benefit of testing in a wooden aeroplane with a huge bubble canopy. In fact, we found range accuracy was within 0.5nm for traffic about 5nm away, and improved to 0.2nm as traffic came closer than 2nm.

CONCLUSION
We found the performance of the XRX to be first-rate. It is well thought out and impressively engineered. Like TCAS, though, its major limitation is that it can only detect transponder-equipped aircraft.
Nevertheless, particularly when combined with a Garmin 496, it provides a remarkably effective traffic awareness system at a realistic price.

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