ADSB out Partial warning

[LouRubin]

I got several reports form the controllers my ADSB was inop and intermittent. Ive also encountered traffic which would cut out as well After investigation I noticed the ground plane in my Lancair was fairly small like 3 x 3 in The manual really isnt clear whats the optimum size however it does state under 12 x 12 in is to small. Any recommendations? Would to small a ground plane cause this issue or could it be a setup issue as well?

 

[airguy]

Two different issues here - ATC saying your ADSB is having an issue means you need to look at your transponder, the issue is there. They are seeing the "output" of your airplane from your transponder carrying your ADSB information out to the world.

Traffic cutting out is on the "inbound" side coming to your airplane, which is through the ADSB receiver, and may not be a problem within your airplane. Traffic on your screen comes from two different sources, either direct from the aircraft itself (displays ALL the time, as long as the airplane is close enough to be in range) and also from the ground-based ADSB uplink (limited to FAA/ATC being able to "see" that airplane, and retransmit its position back to you).

In the bottom right of your map screen you will see "ADSB OK" or "ADSB Partial", which tells you what information you are receiving. "OK" means it is receiving both transponders of other aircraft directly AND the ground re-transmit of data, while "ADSB Partial" or "ADSB No-Radar" means it has lost contact with the ground (FAA/ATC) retransmitted data and is displaying ONLY aircraft that it can see directly from the other aircrafts transponder.

If an aircraft transponder is weak or far enough away that you can't see it directly, and you are getting the ground re-transmitted data, that aircraft will show up on your screen. If you then "lose" the signal from the ground station you will see the display change from "ADSB OK" to "ADSB Partial" or "ADSB No Radar" (depending on software version) and the traffic target will disappear.

As to your original question - yes, a ground plane too small will result in a low-power output transponder signal, which definitely can cause the FAA/ATC to sometimes lose your signal.

 

[LouRubin]

Two different issues here - ATC saying your ADSB is having an issue means you need to look at your transponder, the issue is there. They are seeing the "output" of your airplane from your transponder carrying your ADSB information out to the world.

Traffic cutting out is on the "inbound" side coming to your airplane, which is through the ADSB receiver, and may not be a problem within your airplane. Traffic on your screen comes from two different sources, either direct from the aircraft itself (displays ALL the time, as long as the airplane is close enough to be in range) and also from the ground-based ADSB uplink (limited to FAA/ATC being able to "see" that airplane, and retransmit its position back to you).

In the bottom right of your map screen you will see "ADSB OK" or "ADSB Partial", which tells you what information you are receiving. "OK" means it is receiving both transponders of other aircraft directly AND the ground re-transmit of data, while "ADSB Partial" or "ADSB No-Radar" means it has lost contact with the ground (FAA/ATC) retransmitted data and is displaying ONLY aircraft that it can see directly from the other aircrafts transponder.

If an aircraft transponder is weak or far enough away that you can't see it directly, and you are getting the ground re-transmitted data, that aircraft will show up on your screen. If you then "lose" the signal from the ground station you will see the display change from "ADSB OK" to "ADSB Partial" or "ADSB No Radar" (depending on software version) and the traffic target will disappear.

As to your original question - yes, a ground plane too small will result in a low-power output transponder signal, which definitely can cause the FAA/ATC to sometimes lose your signal.

The ground plane on the transponder antenna is large The one on the ADSB is the small one What size do you recomend?

 

[jnmeade]

There are several threads on this forum discussing this question. I recommend you search for them. The consensus seems to be don't try to make the ground plane perfect in size or shape, rather make it bigger than necessary and not a circle. See the articles. I don't know how to cite a message number so can't help you that way.

 

[Stevec]

Here is the advice from the Trig transponder installation manual.


As the ground plane is made smaller, the actual dimensions of the ground plane become more critical, and small multiples of the wavelength should be avoided, as should circles. Rectangles or squares are much less likely to create a critical dimension that resonates with the transmissions. The smallest practical ground plane is a square around 120mm per side; as the size increases the performance may actually get worse, but will be better by the time the ground plane is 700mm on each side. Anything much larger than that size is unlikely to show significant further improvement.

 

[airguy]

The ground plane on the transponder antenna is large The one on the ADSB is the small one What size do you recomend?

Depends on which one is suffering the problem. If ATC is saying they cannot see your ADSB, then your transponder is the problem. If you cannot receive ADSB IN (traffic and weather) then it's your ADSB receiver antenna.

 

[LouRubin]

Ty for the info .I’m also wondering if shooting the ADSB signal thru fiberglass is degrading the signal ?
I understand the manual says mount it down which it is .I was advised by a Avionic shop to mount it up
preferably external but should work shooting thru the glareshield and windshield.