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05-31-2012, 11:45 AM
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Join Date: Jul 2006
Posts: 145
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Mode S Transponder/ADS-B Sanity Check
I'm ready to replace my inoperative Mode C xponder with a new Mode S, so I've been wading through info on transponders and ADS-B capabilities and limitations. This is what I think I know - please give me a sanity check before I place an order for a Trig TT21 or TT22 (both transmit/receive on 1090 MHz). I fly day VFR.
...The Mode S transponder signal satisfies FAA requirements for transponder use regardless of the status of the ADS-B network deployment.
...Connecting my Garmin 496 to the Trig will allow a more accurate fix on my position (but the 496 doesn't provide the position integrity required for IFR).
...Sending the GPS-enhanced signal MAY allow me to receive TIS-B traffic info and display it on the 496 (not sure about this one).
...Traffic info is transmitted by the ground system on both 1090MHz and 978MHz.
...Weather info is transmitted only on 978MHz, so I won't receive any weather with the Trig.
...If I decide later (after the ADS-B network is built out) to utilize the weather info (FIS-B), I will need a universal access (978MHz) receiver, and will somehow have to signal that I can receive on 978MHz.
...I read somewhere that the FAA may require the higher power transponder (i.e. TT22) for all planes by the 2020 deadline. Any truth to this?
Thanks for your input ... Joe
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05-31-2012, 12:01 PM
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Join Date: Oct 2007
Location: Sacramento, CA
Posts: 3,351
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Here is what I know about Mode S and ADS-B and hope it is accurate:
Mode S is entirely different than ADS-B. It allows you to receive traffic info from a ground base (TIS) and only in selected metropolitan area. I have it and the coverage is very limited. The cost for certifiying (transponder check every two years) is almost double the cost of a regular transponder with mode C.
Garmin makes a squitter for its mode S transponder that satisfies the ADS-B requirement. I believe it gets installed inside of the transponder and it needs to be done by Garmin.
If I was going to do it again, I would not get a Mode S transponder as I end up adding a Zaon so I can receive traffic info at all times and not only in busy air space.
Hope this helps.
__________________
Mehrdad
N825SM RV7A - IO360M1B - SOLD
N825MS RV14A - IO390 - Flying
Dues paid
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05-31-2012, 01:18 PM
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Join Date: May 2005
Location: Canby, Oregon
Posts: 1,786
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496.
The 496 can only handle FIS-A. This not only doesn't have weather, but the traffic information is more restricted than the FIS-B.
I can't remember the details, but fewer targets and targets need to be closer.
You can get more details from http://www.navworx.com/
My plane is setup with Navworx, AFS EFIS, 496 and mode C transponder.
Kent
__________________
Kent Byerley
RV9A N94KJ - IO320, CS, tipup
AFS 3500, TT AP, FLYING....
Canby, Or
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05-31-2012, 01:54 PM
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Join Date: Jan 2005
Location: Peoria, AZ
Posts: 1,053
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Quote:
Originally Posted by JoeLofton
...If I decide later (after the ADS-B network is built out) to utilize the weather info (FIS-B), I will need a universal access (978MHz) receiver, and will somehow have to signal that I can receive on 978MHz.
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No signal output necessary to receive ADS-B weather.
__________________
Regards,
Thomas Velvick
Goodyear, AZ (KGYR)
2020 Donation sent.
N53KT RV-6a finished 2018, Flying
N7053L RV-4 Wife's RV
N56KT RV-4 Finishing
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05-31-2012, 03:17 PM
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Join Date: Oct 2009
Location: Fort Myers
Posts: 370
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I have the Dynon transponder which is really a Trig. It's mode S and extended squitter. I have a 978 UAT receiver but get very limited TIS B traffic. Main issue is awaiting Trig to do a software update that will allow for 1090 traffic to be received on a 978 receiver. Certified stuff so it's been taking them quite a while.
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05-31-2012, 05:44 PM
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Join Date: Mar 2008
Location: Reno NV
Posts: 542
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Mode S Transponder/ADS-B Sanity Check
It is my understanding that a Mode S (ES) txp, including the Trig, in order to transmit to ADS-B, must get it's position data from a "Certified" WAAS GPS system to be legal. Dan
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06-01-2012, 11:08 AM
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Join Date: Jul 2006
Posts: 145
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Back to the Drawing Board
Dan, you're right. The Mode S transponder with extended squitter (gotta love the terminology) may not even recognize a GPS interface unless the GPS is certified for IFR.
So a Mode S transponder won't do anything more than a Mode C for me at this point. I may go with a Trig anyway because of very limited depth behind the panel. Would like to get my transponder control head onto the panel instead of down on the floor behind the stick.
Thanks for the input. I'll worry about ADS-B sometime later.
...Joe
RV-3
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06-01-2012, 11:47 AM
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Join Date: Oct 2006
Location: Garden City, Tx
Posts: 5,145
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According to Dynon, their Mode S transponder (which is made by Trig) will trigger ADSB-IN through it's own non-WAAS gps location data, but will likely not qualify for the ADSB-OUT mandate unless there is either a certified WAAS signal given from another source or the rules are changed. Currently they send a "reduced reliability" bit (if I understand it correctly - I may not) telling the ADSB receivers on the ground that the GPS location is from a non-certified source, but it's enough to trigger the ADSB-IN traffic data to be transmitted back up to the aircraft.
I don't pretend to know this stuff for certain, if you have better knowledge please enlighten all of us....
__________________
Greg Niehues - SEL, IFR, Repairman Cert.
Garden City, TX VAF 2020 dues paid 
N16GN flying 700 hrs and counting; IO360, SDS, WWRV200, Dynon HDX, 430W
Built an off-plan RV9A with too much fuel and too much HP. Should drop dead any minute now.
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06-01-2012, 01:42 PM
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Join Date: Jan 2005
Location: KASH
Posts: 498
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SDA
You pretty much hit the nail on the head, Greg.
One of the bits of data in the messages broadcast by an ADS-B transceiver is a parameter called System Design Assurance (SDA) level. SDA is preset by the installer based on the certification status of your ADS-B transceiver and attached GPS. It basically tells ATC and the rest of the world how reliable your ADS-B transceiver and GPS are.
Right now the FAA's ADS-B ground infrastructure apparently lets some users get away with using non-certified ADS-B transceivers and GPSs to access TIS-B by setting the SDA "reliability flag" to show that those boxes and installation haven't been certified. This won't always be the case; if the FAA doesn't close this loophole sooner, anybody equipping with ADS-B for the 2020 mandate will be required to have TSOd/certified equipment.
Dave
__________________
Dave Setser
RV-7 N701ED FLYING!
Nashua, NH (KASH)
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