Monroy ATD-300 - how can it possibly resolve target direction?

Peter wrote:

In that case it must be completely useless, because a TAS605 is accurate to say 20 degrees, so the Monroy will be accurate to 200 degrees

I think accuracy is ok… so you should use it as in front or behind you, from left or right, but nothing else. I think it is stupid to use information from this sort of systems (ZAON PCAS for example) to plot aircraft on a map. It just doesn’t make sense. It does slightly better than units without bearing information. If you expact this 200 degrees accuracy you will get what your expecting, if you expect 20 degrees of accuracy, you will be disappointed by this system, and shouldn’t install it with this directional antenna.

Peter wrote:

All one has to do, to achieve the same azimuth accuracy, is to switch all of them around within the duration of a transponder packet. And synchronously run the receiving circuitry of course (need to run an A-D on the amplitude of the L-band carrier).

It does not work like that.. The design of these systems is different.

Peter wrote:

In fact the switched system should be more accurate for azimuth because you are eliminating the cable length difference.

Not in this case, as system design is different. TAS systems can also transmit directionally.

Peter wrote:

The Avidyne TAS boxes are active so they will deliver good distance accuracy, but if the Monroy is 1/10 of that, that is also rather useless, because there is a big difference in what one does about a target 3nm away and 1/3 of a nm away.

The TAS boxes use timing, while the passive systems use signal strength. An airliner transponder can be 500 Watt while the lowest mode S transponder can be as low as 25 Watt. A 500 Watt intruder will show closer then a 25 Watt one. The one with more power is likely a bigger / faster aircraft, so not a real problem to show those earlier.

Peter wrote:

Have you installed the Monroy 300, Jesse?

Yes I have, and other systems, like ZAON PCAS systems, and Proxalert RX5. Whether customer is satisfied with this solution depends mainly of the understanding of the system. If they don’t like this 200 degrees of accuracy, I would recommend them to install another systems. Yet the TAS and GTS are out of budget for some. I think these systems are better then having nothing at all. I would not recommend to overlay information from these systems on a chart.

Peter wrote:

This is off topic, but as I wrote before, it is wrong to accuse me of being against FLARM. What I will point out is that it is unlikely to work as is often claimed – simply because almost no powered GA carries it. It would be disingenuous of me to suggest otherwise when my own flying with FLARM picked up almost nothing.

This is more or less the same, flarm uses a very small (ISM band) signal, so you can use it freely without license. With this very low power level, you don’t want an antenna in the cockpit, where it doesn’t have a clear view. An external antenna, especially on faster aircraft would be a must. The range is quite limited due to the ISM nature of the system. This is 10 milliWatt compared to the tens of Watts from these other active systems.

Peter wrote:

Can you post detail, Jesse?

These low cost systems use pseudo doppler on the carrier.

mm_flynn wrote:

Overall, it is not my best investment ever! Annoyingly, it doesn’t pickup 1090-ES data, so in that sense is less useful than say a powerflarm for decting mode-S traffic. I passed on the powerflarm because I hoped to have something ‘installed’ to display on the 530, but the European powerflarm manually says ‘do not install in US aircraft’ which makes it a bit challenging to get an avionics shop to install it anyhow !.

Could you clarify what you mean, it doesn’t pick up 1090-ES Data?

Peter wrote:

but it looks like this will give only front/back/left/right resolution, with the type of antenna likely to be used here. Like the old ZAON did.

It can do better then that in ideal situations, it is not ideal, and the result is this poor resolutions, which is basically is front / back / left / right… If you consider that is suiteable, then ZAON or Monroy will suite your needs, if you need / want better accuracy you should be looking at different systems, such as TAS or other types of systems such as Flarm / ADS-B.

Steve6443 wrote:

Could you clarify what you mean, it doesn’t pick up 1090-ES Data?

If you have an target which has ADS-B out, you will not benefit from ADS-B (GPS) data, as this unit does not process ADS-B data. It only reads mode A and C. So ADS-B or non ADS-B aircraft will be displayed with the same poor resolution.

mm_flynn wrote:

I passed on the powerflarm because I hoped to have something ‘installed’ to display on the 530, but the European powerflarm manually says ‘do not install in US aircraft’ which makes it a bit challenging to get an avionics shop to install it anyhow !.

The issue is with FCC IIRC. I vaguely recall that the frequency used by the European version can’t be used in the US. They eventually did a US version but it uses a different frequency. Just as a little side note if someone wants to investigate further.

Peter wrote:

ZAON never did anything better than just resolving the four quadrants, from various people I flew with who had it.

Anyway, it does look like the Monroy works a lot less well than most expected…

That 90 degrees is within the 200 degrees accuracy we defined before isn’t it? So it helps you finding your target in one or two quandrants, which is better then nothing, but a lot worse then TAS / GTS for example. So at 10x price difference, you get a 10x accuracy difference.

Which option is good for who, is up to the user to decide. Most people seem to have expectations which not meet up with the performance for these low cost systems though.