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ADSB (Read 796 times)
Jun 19th, 2017 at 7:09am

dwightsmall   Offline
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I have the dual band receiver but had the single band till a month ago. I operate in the Tucson/Phoenix area and should have solid ADSB reception but targets regularly disappear. My system reverts from ADSB "OK" to TIS "OK".  When that happens my targets disappear even when I'm in the Tucson terminal area. This also happened when I was single band equipped.  This happens frequently when I'm about mid way between the Tucson and Phoenix ADSB towers. Perhaps it's an issue of the towers not properly "handshaking" with my system when I go from tower to tower?   I'm attaching a screen shot showing 43 sentence errors from my SV-472 dual band receiver so perhaps my receiver isn't working properly?   Anyone help me on this?
 
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Reply #1 - Jun 19th, 2017 at 5:26pm

Tyler Pattison   Offline
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Hi dwightsmall,

What you are describing sounds like a symptom of poor ADS-B reception. This is normal at low altitudes, or when outside of good ADS-B coverage areas. Other users of the ADS-B system have reported poor coverage in areas between Phoenix and Tuscon.

Please provide me with a little more information to help me understand your situation:
What kind of ADS-B IN antenna are you using with your receiver?
Where is your ADS-B IN antenna mounted?
How long is your ADS-B IN antenna coax, and what kind of coax is it?
Do you have any other antennas mounted near your ADS-B IN antenna?

In response to your comment about tower 'handshakes': The ADS-B towers do not hand-shake in a way that would cause the symptoms you are describing (a switch to TIS OK).

In response to your comment about the 43 sentence errors: It is normal to get sentence errors when the GPS is still acquiring a GPS lock during startup. 43 sentence errors is not an indication of a problem
 
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Reply #2 - Jun 19th, 2017 at 6:21pm

dwightsmall   Offline
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I'm using a factory installed blade antenna that came with my new airplane in 2013. I suspect it may be a 1090 antenna. I don't know what coax I have but the run is short, only about 6 feet and the antenna is bottom mounted just ahead my Cub's main landing gear.  There are no other antennas mounted nearby. The comm antenna is on top and the xponder antenna is on the bottom a few feet forward of the tailwheel.  The sentence errors are from my SV-472 receiver, not from the GPS.  I've checked the GPS sentence errors and they are zero and the transponder sentence errors are also zero.  The sentence error count from the SV-472 receiver continues to slowly count upward during flight. It's hard for me to think that I may have  poor reception when I'm at 4,000 AGL and can see the ADSB tower (group of towers) about 10-15 miles away on the Tucson Mountains.  I really appreciate your input and am most receptive to suggestions.
 
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Reply #3 - Jun 20th, 2017 at 8:24am

Tyler Pattison   Offline
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It is normal for the SV-ADSB-472 to generate a handful of sentence errors when the GPS has not provided SkyView with valid position information. It is normal behavior for users to observe some sentence errors on the SV-ADSB-472 serial port config page on startup when the GPS has not finished acquiring a position lock.

However, your description of sentence errors in flight (when the GPS presumably has a solid lock) is not expected. This are several things that could cause this. If you are seeing less than 1/second it does not seem like a serious problem.

Some follow-up questions:

Is your cub fabric?
If so, do you have a conductive ground plane mounted to the blade antenna?
 
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Reply #4 - Jun 20th, 2017 at 9:06am

Andy Karmy   Offline
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So I'd like to jump in with another view. I had the original SV 470 unit for 2 years and it always worked perfectly. It is installed in a RV-8 us a DeltaPop ADSB tuned blade antenna with a short (4ft) RG400 run. I installed the SV-472 a couple of weeks ago and since installing have had multiple instances of no ADSB in signal. I get TIS-OK and when checking the serial port config I see I am talking ok to the unit, but it says "no signal" on the ADSB status page.

I'm located in the Seattle area and am flying under the ClassB just a few miles from the airport. (between Auburn, and Puyallup) is where I've see the issue. The first time it happened I power cycled the SV-472 and it picked up signal within a min or so. This last time it never did come back until I shutdown and restarted, then took off again and it was working.

I've not flown it enough yet to feel like I understand what makes it fail and what makes it work. I'll gather more data.
 
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Reply #5 - Jun 21st, 2017 at 8:05am

dwightsmall   Offline
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Yes, my Cub is fabric. The antenna is mounted on a rather large aluminum panel but I haven't checked to see if the antenna has good electrical contact with it.  I've established  dialog with the FAA so they are looking into it. There has been problems with the Tucson ADSB tower but they found a problem and fixed it but maybe there's still an issue.
 
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Reply #6 - Jun 21st, 2017 at 12:10pm

Tyler Pattison   Offline
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dwightsmall wrote on Jun 21st, 2017 at 8:05am:
The antenna is mounted on a rather large aluminum panel but I haven't checked to see if the antenna has good electrical contact with it.


Having a ground plane/counterpoise is quite important. Most types of ADS-B antennas are designed to be installed with a conductive surface under them. For fabric, fiberglass, or other aircraft with non-conductive skins installing a conductive ground plane below the antenna usually works well.

It is important that the conductive ground plane has a good connection to the shield of the antenna coax at the antenna.
 
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Reply #7 - Jun 21st, 2017 at 4:05pm

GalinHdz   Offline
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This antenna is a bit pricey but works extremely well on non-conductive (fabric, fiberglass) surfaces:

http://www.aircraftspruce.com/catalog/avpages/antennasystems1.php?clickkey=22844

I use one for the transponder and another for the SV-ADSB receiver in my fiberglass airplane.

Cool
« Last Edit: Jun 22nd, 2017 at 7:52am by GalinHdz »  

N819PR
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