The MRX the smallest portable collision device weve seen yet, measuring 2 1/2 inches wide by 4 1/4 inch long and only 3/4 inches high a cigarette pack, basically. Its a bare bones device, shipped with an onboard antenna, accessory power cord and some Velcro bits for mounting. Price, on sale as of press time, is $474. The MRX also has an excellent, large-format manual which clearly explains how the gadget works and how to use it.

The MRX is one of two products Zaon now sells, the other being the XRX, which we reviewed in the August 2006 issue. The XRX currently at $1695 is the more sophisticated of the two products, providing both range information and, according to our trials, relatively accurate azimuth information, something unique for a portable. Zaon ne SureCheck is unique in the portable field for having entered the market early and having remained in it, offering improved products. Two competitors Monroy Aerospace and ProxAlert have remained in the market with essentially the same products they first introduced. Zaon, on the other hand, has evolved a number of products, each of which has performed better in our trials, including the diminutive MRX.

Like all of the portables, the MRX is a passive transponder listening device. It depends on ground-based radars or active traffic systems to interrogate nearby transponders, then listens to the reply to make sense of range and relative altitude, but not azimuth. Like the more expensive XRX model, the MRX has a built-in electronic altimeter to provide relative altitude and trend data.

Control and display wise, theres really not much to this device. It has a simple two-element front display, a power and a mute button and a multi-function rocker-type switch that controls volume for the aural alerts, brightness and a simple set up menu. Speaking of brightness, the MRX display is a bit of a throwback, using LEDs rather than the more popular LCD-type display. But theres an advantage in this: The red digits are very bright and easy to see in almost all light conditions, much more so than the low-contrast LCD used in the more expensive XRX product. The exception is direct sunlight, where the LEDs wash out and the LCD doesnt.

The MRX is equipped with audio alerting through an internal 3.2 KHz tone generator which can be heard even through noise-canceling headsets. In addition, theres also a miniature audio jack into which you could plug a headset or hardwire the output into an aircraft audio system.

The MRX can operate on a pair of AA batteries about five hours, by our estimation or run on 14- to 28-volt ships power. The antenna is a tiny rubber ducky-type that screws into the left side of MRX or, as an alternative, Zaon also offers a

remote antenna suction-cup setup with an extended antenna wire. Given the units small size, running it on batteries is a plus, since you just plop it on the glareshield, switch it on and it does the rest.

Controls are minimal. The upper left button powers up and powers down, the lower left button mutes the audio alerts. The rocker switch on the right has multiple functions, including alert volume control, brightness control, menu access and something called “local” which displays your squawk code and Mode-C altitude from your encoder or, if none is present, from its own built-in altimeter. It also briefly shows a battery check screen before returning to the traffic display.

The menu screens there are two allow you to deselect altitude sensitivity to reduce nuisance alerts in congested airspace and to do the same with range settings. The selectable ranges are 1.5, 3 and 5 miles and the altitude choices are 500, 2000 and 5000 feet above or below the aircraft.

Like other passive devices, the MRX detects nearby transponder returns but it only displays what it calls the “primary” by sorting through these criteria: relative altitude, vertical trend, host aircraft vertical trend and range to closest target, if multiple aircraft are detected. Although it has no azimuth information, the device displays range and relative altitude in unambiguous terms. If a second airplane enters the picture that represents a larger threat, the MRX displays “NEW” for two seconds, then the target information of the new threat.

According to the MRXs manual and confirmed by our flight testing the range accuracy improves the closer the target is. At 2 to 5 miles of range, the value displayed is in whole-mile increments. Traffic detected closer than 2 miles is shown in .1-mile increments. Altitude is displayed in 100-foot increments above or below the host aircraft. The MRX uses the host aircraft transponder as an altitude reference or its own built-in electronic altitude. Further, the device is smart enough to fall back on the internal altimeter if the host Mode-C isnt received.

There are two levels of audio alerts, an advisory and an alert. The former consists of two beeps, the latter four beeps both are sharp, easy-to-hear tones. Advisories and alert performance depends on the devices range setting. At 5 miles, for instance, it advises of traffic within 1000 feet vertically and within a mile. It alerts within a mile and 700 feet vertically. This logic cuts down on nuisance alerts without blinding the thing unnecessarily.

To test the MRXs mettle, we flew it in a Piper Tomahawk equipped with an Avidyne TAS600 to give relatively accurate range comparisons. We flew in traffic patterns above and below targets acquired visually and we flew away from airports in less congested airspace. Setting up the unit is easy, thanks to a first-rate owners manual.

The bright LEDs are quite visible but you have to shade the display to see it well in direct sunlight. This is rarely an issue, however, because the display is recessed to shade it somewhat. The multi-function rocker is easy to use, although small for those with fat fingers. It can be toggled to accurately show the host squawk and Mode-C, a useful crosscheck, in our estimation.

We conducted our test flights with the MRX set at 5 miles range and 2000 feet for altitude sensing. There was enough traffic around such that the MRX screen was rarely blank. Although it was difficult to accurately correlate targets between the MRX and TAS600, when this was possible to do visually, the MRX had surprisingly good accuracy, rarely varying by more than .1 mile. The MRX has one advantage over the TAS600 it only worries about one target, likely the one youd most be worried about, too. To see the second and third targets on the TAS600, buttons must be pushed and held, which is actually a bit clumsy.

Above the horizon, the MRX tended to show the target closer than actual range. Conversely, below the horizon, it showed the target farther away than it actually was, when compared to the TAS600. This tended to bias the display to show targets above the horizon.

Unfortunately, a closer target below the horizon is not displayed if theres a target above the horizon. Still, these are minor criticisms. Generally, the unit didnt miss many targets, nor did it false alarm annoyingly. We circled over the airport at 1000 feet above pattern altitude and the MRX continued to display traffic directly below the airplane, albeit at a greater-than-actual range. Impressive performance, in our opinion.

Altitude agreement was generally 200 feet or better. Worth noting is that we tested the MRX under the best possible conditions with an active interrogator (TAS600) to ping everything within sight. Without that, acquisition time would increase to the time required for two full sweeps of an ATC ground antenna (about 12 seconds) and the update rate would be one sweep of the antenna.

One feature we didnt like was the long period of time that the MRX would show the target range and altitude after signal reception from the target was apparently lost. This could be a bit disorienting. The range would increase and then suddenly freeze. A few seconds later, the display would stop showing the target.

One technical problem we encountered was heat soaking. We left the unit on the panel until mid-morning on a warm Florida day and after we took off, its tracking became wildly inconsistent with false alarms and possibly missed targets. Once it cooled, it returned to normal operation. We dont think this will be a problem in a comfortably ventilated cabin but its best not to leave it on the glareshield when parked.

Were impressed with the MRX. We think its a vast improvement over SureCheck/Zaons (and anybody elses) early efforts. The package comes with the right accessories and a good manual makes it easy to set up and use, all at a bargain price. Its especially impressive in accurate ranging.

We hear from owners of high-priced traffic systems who tell us how much traffic is out there that we dont see. True. But what we like most about the MRX is that it doesnt worry about traffic thats not a factor and concentrates its limited electronic eyeballs only on the one that matters the airplane thats about to T-bone you. That alone makes it worth the asking price, in our view.

Tomahawk owner David Ansley assisted with the preparation of this review.

CONTACTS…

Zaon Flight Systems
800-496-9430
www.zaonflight.com