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TAS620 with GDL-88 ADS-R reception issue

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jburns3 View Drop Down
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    Posted: 07 Aug 2016 at 10:30pm
I visited Tom Hass and Mike Jensen in Park Rapids, MN on Friday for some troubleshooting and flight testing regarding ADS-R receptions issues in my Cessna 340 equipped with an Avidyne TAS620, Garmin GDL88, Flight Stream 210, GNS530W/430.

Airplane to Airplane GDL-88 ADS-B is not an issue, works perfectly. Avidyne active traffic system feeding through the GDL88 also works perfectly.

What we notice is the Service level of the ADS-R traffic drop from excellent to marginal/poor/none when the Avidyne TAS is operational, even at high numbers of ground stations being tracked or available.  When we pull the breaker to the AvidyneTAS the ADS-R service level ramps right up to excellent.  With the Avidyne TAS operational only 0 to 1, at the most, ADS-R traffic targets are being relayed, and weather loads very very slowly, if at all.

Both the GDL-88 and the Avidyne TAS620 are installed per the manuals with suppression of both my GTX330 Transponders (one ES one non ES).  Latest firmware update to the GDL-88 installed with no improvement.

We've reviewed the installs, the install manuals, and are now looking for any similar reported incidences that we may be able to learn from. 

Has anyone run into this?  


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khuffine View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote khuffine Quote  Post ReplyReply Direct Link To This Post Posted: 07 Aug 2016 at 11:52pm
I have a GDL88/waas and went to OSH ...Had no weather graphics on the way until south of the lake. Then graphics popped up. This has been an issue with me so I updated to 3.33 on the 88. Seems to work hit or miss but only seems to get the regional within 250 miles. Do not get the conus on the GMX 200. I think either the ADS system is in and out or all stations are not reporting. I had Sirius xm the whole time thank goodness. Wx at Oshkosh was not good on sat Arrival. Seems we are still having growing pains...
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jburns3 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jburns3 Quote  Post ReplyReply Direct Link To This Post Posted: 29 Aug 2016 at 9:26pm
Update of everything we've tried... TAS still kills ADS-R/FIS-B reception on 978Mhz.

 1-swapped gdl 88(non diversity)
> 2-swapped top and bottom coaxs
> 3-with coaxs swapped disconnected and terminated bottom antenna(used too antenna without connection to bottom antenna)
> 4-wrapped both tas 620 and gdl 88 in mu-metal
> 5-verified all coaxs
> 6-verified gdl 88 and tas 620 wiring
> 7-swapped tas 620
> 8-removed bottom tas antenna and terminated coaxs
> 9-replaced bottom tas antenna with new, verified skin under antenna is clean.
> 10-used gtx 327 and transmitted through the both gdl88 antennas, verified health of coax and antennas
> 
> During tests flights pulling tas 620 breaker, Adsb ground reception returns to normal. Seeing poor reception on portable equipment verified on g500 by slow fis-b upload.
> 
> Gdl 88 has no issues with 1090mhz reception.
> 
> Verified with ifr6000 ground reception against one of our airplanes with gdl 88 installed(with tas 620 operating).
> 
> Using handheld consumer grade spectrum analyzer can see spikes around 980 MHz while tas operating. On the ground.
With lower TAS antenna leads terminated on the ground the spikes at 
980MHz were greatly reduced, however, in the air, with leads terminated, 
issue remains.
 
We have not terminated the antenna outputs on the TAS directly on the 
TAS unit.. this is upcoming this week.
>   
> Have not tried swapping transponder couplers for tas 620
> 
> Have not swapped top tas 620 antenna
> 
> Tas 620 has double shielded low loss coax
> 
> Gdl 88 has rg-400 coax
> 
> Tas 620 to gdl 88 distance approx 30"
> 
> Bottom tas antenna to original bottom gdl 88 antenna approx 24"
     Moved antenna lead for bottom antenna to a transponder antenna 
further forward, verified correct GDL88 (with TAS circuit breaker pulled 
and transponder operation with ATC, antenna separation distance now 
around 43" from bottom TAS antenna.
> 
> Top tas antenna to top gdl 88 antenna approx 50"
> 
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