The antenna has just one cable coming out of it.
How do they do it?
The other TAS/TCAS products use four antennae and thus four cables. One antenna is a 2-blade antenna with the 2 blades side by side. The other antenna is also a 2-blade antenna but the 2 blades are one in front of the other and they are overmoulded to look like 1 blade.
But Monroy have just the one…
I guess it uses phase shifting, two small antenna’s inside the housing, instead of a blade which is used for DME/Transponder in this form factor.
Powering the switching electronics over the coax.
Do not expect a huge deal on bearing of distance of these units. There is more than 9 dB variation between different transponders due to different output power, and different cable loss. Up to 3dB loss is allowed
That, however, would resolve only front-to-back, not side-to-side.
It would have a sense of direction (sideways as well) only it could not tell which of the two possible bearings is trough. A sense antenna could solve this. The hardware is different for the ANT-300 and non ANT-300 model.
Again, don’t expect anything usefull. Resolution is 45 degrees, expect accuracy of about 180 degrees.
On the other portable systems, this is not much better. Resolution of maybe 30 degrees, and accuracy of about 90 degrees.
The larger fixed installation perform little better.
I personally don’t think the portable systems should be allowed to give map positions, accuracy is just so bad. Just a nice gadget to know their is traffic in the vincinity. The larger fixed installations like you have are a little better, and ok for plotting on a map. ADS-B or flarm positions are spot on so they are very suitable for plotting on a map.
I have called Monroy and spoke with the designer. He confirmed that there are more antennae in the housing and electronic switching is going on between them, feeding into one coaxial cable. Does this sound realistic? Could anybody with practical experience of the Monroy+ANT-300 installation PLEASE report on their real life experience re: direction & distance accuracy? handling several targets / choosing the most critical target?
And one more technical question: they claim that Monroy is a PASSIVE TAS. I understand that this means that it is not actively interrogating the other transponders, but rather waiting for them to respont to interrogation by another aircraft or the ground station. But if this is the case, how can they measure the distance, if they have not interrogated themselves?
Centurion_Flyer wrote:
But if this is the case, how can they measure the distance, if they have not interrogated themselves?
Strength of the signal, I guess. However, as Jesse wrote, there is a big variation. So you get a similar problem as with stormscope.
I have called Monroy and spoke with the designer. He confirmed that there are more antennae in the housing and electronic switching is going on between them, feeding into one coaxial cable
That would be damn clever… but not impossible.
Centurion_Flyer wrote:
Does this sound realistic?
Peter wrote:
That would be damn clever… but not impossible.
Why? This is almost the standard methode for direction finding techniques? Yes this is realistic.
Centurion_Flyer wrote:
Could anybody with practical experience of the Monroy+ANT-300 installation PLEASE report on their real life experience re: direction & distance accuracy? handling several targets / choosing the most critical target?
It kind of works, it works fair, if you understand the limitations of such a system. Don’t expect miracles from these. They are NOT accurate at all, you should think of sectors rather then bearings, and as in close range or not. I think price wise they are quite ok, again if you understand the limitations. IMHO it is more useable then these systems kind of passive systems which only give a unaccurate range (and altitude difference)
Why? This is almost the standard methode for direction finding techniques? Yes this is realistic.
I don’t have an issue with multiple antennae. I have the TAS605 system myself.
What somewhat surprises me is that Monroy appear to claim they are switching different antenna elements, using control signals sent up the single coax cable. And they would be doing this quite quickly – cycling through all the various elements within the duration of a Mode A/C transponder response packet which is, from vague memory, about 100us.
It would be quite neat, as it would avoid having multiple cables of closely matched length which the Avidyne (Ryan) TAS boxes need.
