In the absence of a Zaon response on this forum, an update.

Zaon responded through PM to the effect that the unit should be returned for testing.

Hello, I have a question? I continuly get false alerts from my mrx. I bought the unit in Jan 08. It shows alerts all the time from .4-.8 and anything between and anywhere from 00-400'. I fly all the time up and down the CA coast and inland all the way over to Tucson. The unit consistently gives alerts and nothing is there. I fly 90% ifr and in contact with atc. NO TRAFFIC!!!!!

Can u tell me what the problem is? Did I get a bad unit? What to do?
Dan

It sounds like your unit is detecting your own transponder, which can happen occaisionally with certain transponders. Our systems are "caged" to work with the vast majority of transponders, but it's important to note that not all transponders are identical. Because our systems attempt to establish an RF link with your transponder in order to not detect it as traffic, there's a certain threshold we set our units to that works for most transponders. If, however, your power output is less than we anticipate, your transponder signal may be outside this threshold and be treated as traffic.

There are two things you can do to alleviate this situation easily: 1) clean your transponder antenna. The belly of an aircraft, and therefore your transponder antenna, can pick up even a thin film of grease or dirt that can dampen the signal. 2) call us to manually adjust the suppression threshold to allow for your particular signal. Our techs can assist with this over the phone.

After receiving your unit, our techs have thoroughly tested the unit and have found it to be completely within factory specs. We have run it through 6+ hours of live traffic tests (we are located on a very busy general aviation airport near Dallas) and have found the accuracy to be a match with actual range, altitude and direction better than 90% of the time. Even the altimeter held to within 100 ft. of actual, which is well within expected norms. Supression level is exactly where it should be. The test conclusions lead me to wonder what other factors could be at play.

Are you flying in a pressurized aircraft?

In your first example of Alice Springs, you mentioned it showed an aircraft 2000' feet below ground level, which was 2000'. In other words, the MRX showed traffic at "-40", meaning 4000 feet below? Certainly this would be an erroneous reading, but the unit tests fine.

On the ground, all traffic systems are subject to occasional erratic readings due to signal bouncing and the fact that the earth is a giant ground plane and both absorbs and reflects RF energy. However, in our testing, this is very rare for the MRX, which has algorithms specifically designed to filter out redundant or erroneous signals. This is slightly more prevalent with XRX on the ground, but only with direction sensing and not altitude or range detection.

I am most interested in the answer to my pressurized aircraft question, as using MRX in a pressurized cabin will adversely effect accuracy in a way similar to what you have described. Otherwise, there's not much more we can do when our tests show the unit to be in fine working order.

Hi,

Thanks for your quick attention to this matter.

The aircraft that the unit is operated in are not pressurised.

Regarding the Alice Springs return, Alice Springs is 2000' AMSL. On climb out passing 4000' on local QNH ie. 2000' AGL, the unit showed traffic below me by 4000'.

But more concerning was the fact that during our AWK operations which are conducted at 400' AGL the unit displays near constant traffic below me and this fault last as much as 2 hours of the 3 hour sortie. As stated previously during these flights we were 300nm from ATC radar and only within TCAS range for intermittant periods of 10 minutes based on,- RPT overfly at 450 GS with 40nm radius range, 80nm/450 = 10 minutes and there are not many flights per day west bound.

Your response can only infer two possible reasons for these false returns.

1. The unit is indeed faulty and it is simply the case that the fault has not yet been detected.

2. The units can and do return false indications either generated internaly or from external sources.

I would be very dissapointed if #2 is the answer, given the marketing weight Zaon places on "zero false alerts".

Your statement regarding the fact that you are testing the unit in a very busy traffic environment sounds counter intuitive. Surely the best way to test for false alerts would be in an area outside radar/TCAS coverage with little or no traffic.


Regards
Mick

Of the two choices you present, the first is the only likely suspect, and we continue to test. Regarding our testing procedures, the best way to determine accuracy is around multiple threats where the environment presents the potential for overlapping, potentially distorted or garbled signals to work through. Also, even in the busy environment we're in, traffic is not constant, therefore we can test the wide range of congestion situations.

As for "false indications", indicated traffic can only be from a transponder source that presents a valid altitude code that can be decoded, and only after multiple hits. There is no other source that we know of that can present a valid 4-digit altitude code on 1090 MHz for us to decode and display. It would be like hearing a song on the radio without a broadcast source... not possible. Occasionally, systems can detect the local transponder, but the symptom is the display of VERY close traffic at or near the same altitude, which is not happening in your case. When you hit the local button, is the local altitude displayed (x100 ft) in agreement with your known pressure altitude?

We will continue to investigate this...