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  #1  
Old 12-13-2018, 07:17 PM
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Toobuilder Toobuilder is offline
 
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Question Is There A WAAS "Add On" Module?

Ok, hear me out. I have a 430 (non WAAS) and a 330 transponder. I can upgrade the 330 to ES and have the bones of an ADS-B out solution (lacking only the higher fidelity WAAS position source.

That said, I could throw a GDL-82 without upgrading the 330 and because the 82 has a built in WAAS reciever, I'm golden...

So it stands to reason that there should be a stand alone WAAS unit that can make a 330ES transponder and 430 work, shouldn't there?

Question #1. Does a "stand alone" WAAS unit exist?

Question #2. If I elect to upgrade my 330 to ES TODAY, and keep the straight 430 as a half measure for the next year, will I be throwing out an ADS-b signal?

Question #3. If the above answer is "yes" Is there a practical, discernable difference between an ADS-b position derived from a WAAS or non WAAS source, or is it a "legality issue"?
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Last edited by Toobuilder : 12-14-2018 at 07:37 AM. Reason: Changed "GDL 88" to "GDL 82".
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  #2  
Old 12-13-2018, 09:29 PM
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By the time you upgrade the GTX 330 to Extended Squitter and purchase a WAAS source, you would probably be better off to jump on the GTX 335 w/WAAS promotional deal. This will save you some weight over adding a stand alone WAAS module as well. The GTX 335 is $2995 and includes the Extended Squitter transponder, the WAAS receiver in the transponder and the WAAS antenna.

https://buy.garmin.com/en-US/US/p/140939

The FAA is sending letters to folks who are using non-compliant GPS sources for their ADS-B transmissions, so I would not recommend trying to use a non-compliant receiver.

Thanks,
Levi Self

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  #3  
Old 12-13-2018, 10:23 PM
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Ok, but why is this so? A WAAS chip is pretty inexpensive and weighs mere grams. If the GDL 82 can use (or not) use its internal WAAS magic based upon the availability of an existing WAAS navigator, why is a stand alone WAAS source for an already highly capable (and expensive) GTX330 such an endeavor? Based upon the GDL-82 and other WAAS enabled devices, such a product should cost about $100 bucks, weigh nothing and have a form factor similar to a postage stamp.

The bottom line is that I'm already highly invested in the 330, why does the WAAS GPS have to be the deal breaker that drives me to a whole new transponder?
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WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.

Michael Robinson
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  #4  
Old 12-13-2018, 10:33 PM
BobTurner BobTurner is offline
 
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Quote:
Originally Posted by Toobuilder View Post

So it stands to reason that there should be a stand alone WAAS unit that can make a 330ES transponder and 430 work, shouldn't there?

Question #1. Does a "stand alone" WAAS unit exist?

Question #2. If I elect to upgrade my 330 to ES TODAY, and keep the straight 430 as a half measure for the next year, will I be throwing out an ADS-b signal?

Question #3. If the above answer is "yes" Is there a practical, discernable difference between an ADS-b position derived from a WAAS or non WAAS source, or is it a "legality issue"?
1. I understood your question differently. Are you asking, ‘Is there a stand-alone box that will receive the WAAS signal, then port that data over to a non-waas gps, and get a corrected position out?” To my knowledge, no. The waas correction is different for each satellite, non-waas boxes won’t be equipped to handle the calculation.
2. I don’t think your non-WAAS box has the needed format for the 330 to read.
3. Maybe. The faa’s long term plans include automating ground control (that’s why the ground mode data stream includes wingspan, and distance from the gps antenna to the nose). This is also the reason for the very high accuracy specification. A non-WAAS box will too often tell the computer running ground control that you’re over the hold short line, or about to clip wings with the airbus on the adjacent taxiway.
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  #5  
Old 12-13-2018, 11:04 PM
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g3xpert g3xpert is offline
 
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Michael,

I probably should have more directly answered your question. The current price to upgrade the GTX 330 to ES is $1495 as shown here:
https://buy.garmin.com/en-US/US/p/596335

Garmin does offer a GPS 20A WAAS GPS receiver. This is typically used with a G3X system and would not really be recommended in a stand-alone installation as the G3X is what loads software to the GPS 20A. But for the sake of a comparison, you would need the GPS 20A and you would also need a GA 35 antenna. The combined cost of these two units is $1197. The total cost is $300 less than the GTX promotional bundle. This leaves you with a heavier, older, non-standard installation.

Another direction you could go would be to install a GDL 82 for $1795 if you are able to use a UAT solution versus the 1090 MHz Extended Squitter solution.

Regarding the GPS source for ADS-B, the GPS 20A and other GPS receivers used for ADS-B compliance in EAB aircraft have to meet the requirements of TSO-C146d. A typical commercial WAAS receiver does not meet these requirement. This drives cost and size when compared to the typical commercial GPS receiver.

Thanks,
Levi
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Last edited by g3xpert : 12-13-2018 at 11:07 PM. Reason: clarification
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  #6  
Old 12-13-2018, 11:13 PM
BobTurner BobTurner is offline
 
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Quote:
Originally Posted by Toobuilder View Post
Ok, but why is this so? A WAAS chip is pretty inexpensive

?
It’s more than waas. The spec writters went nuts; besides sending position, velocity vector, altitude, there are all kinds of error checking, error reporting, etc., requirements. But Trig, GRT, uAvionics, others are offering $500 gps boxes that meet the specs.
Now, why the S to S-ES upgrade is so expensive, that I don’t know.
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  #7  
Old 12-13-2018, 11:37 PM
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Quote:
Originally Posted by BobTurner View Post
...2. I don’t think your non-WAAS box has the needed format for the 330 to read...
This is the root of my confusion and certainly illustrates my ignorance of the ADS-B architecture. Curently, my 430 and 330 talk to each other in a significant way. The 330 provides TIS data which is displayed on the 430 and GRT EFIS. It "seems" the only thing lacking is the high fidelity WAAS position. Of course, I am hopelessly out of my depth on the technical details, but with the plethora of add on ADS-B solutions with built in WAAS, it "seems" (there's that word again) the addition of an auxiliary WAAS source should be an easy fix for the existing non WAAS navigators like the 430 (for ADS-B position at least).
__________________
WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.

Michael Robinson
______________
Harmon Rocket II -SDS EFI - Flying
RV-8 - Flying
1940 Taylorcraft BL-65 -flying
1984 L39C - flyable, available for sale
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  #8  
Old 12-14-2018, 12:05 AM
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Toobuilder Toobuilder is offline
 
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Quote:
Originally Posted by g3xpert View Post
Michael,

I probably should have more directly answered your question. The current price to upgrade the GTX 330 to ES is $1495 as shown here:
https://buy.garmin.com/en-US/US/p/596335

Garmin does offer a GPS 20A WAAS GPS receiver. This is typically used with a G3X system and would not really be recommended in a stand-alone installation as the G3X is what loads software to the GPS 20A. But for the sake of a comparison, you would need the GPS 20A and you would also need a GA 35 antenna. The combined cost of these two units is $1197. The total cost is $300 less than the GTX promotional bundle. This leaves you with a heavier, older, non-standard installation.

Another direction you could go would be to install a GDL 82 for $1795 if you are able to use a UAT solution versus the 1090 MHz Extended Squitter solution.

Regarding the GPS source for ADS-B, the GPS 20A and other GPS receivers used for ADS-B compliance in EAB aircraft have to meet the requirements of TSO-C146d. A typical commercial WAAS receiver does not meet these requirement. This drives cost and size when compared to the typical commercial GPS receiver.

Thanks,
Levi
I appreciate tha candor. Perhaps I have an outlier case, but if some manufacturers can provide a WAAS position source AND ADS-B magic as an add on to a legacy transponder for less than $1000, it stands to reason that my legacy 430 and a 330 (with the ES upgrade) should benefit from an inexpensive add on WAAS "magic box". Offer that for $200 bucks and I'd be all over it like a fat kid on cake.

Please note that I'm not complaining about the cost of Garmin equipment... I'm heavily invested as it is. It is what it is. But I am trying to come up with the best value solution for the equipment I have on hand. As I posted in another thread, I have two airplanes which need ADS-B systems (three, actually - if I count the L-39). Not counting the jet, one airplane has the legacy 430 and 330, the other has a 650 and a 327. Yes, I could throw GDL-82's at both airplanes, but doing so "wastes" the (potential) capability of the 330; the other "wastes" the WAAS capability of the 82. I guess the best thing is to pair the 650 and 330 (with ES upgrade) on one airplane and do a 430,327 and GDL-82 on the other. Swapping transponders is not something I'm looking forward to, however.
__________________
WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.

Michael Robinson
______________
Harmon Rocket II -SDS EFI - Flying
RV-8 - Flying
1940 Taylorcraft BL-65 -flying
1984 L39C - flyable, available for sale
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  #9  
Old 12-14-2018, 02:07 AM
BobTurner BobTurner is offline
 
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Quote:
Originally Posted by Toobuilder View Post
This is the root of my confusion and certainly illustrates my ignorance of the ADS-B architecture. Curently, my 430 and 330 talk to each other in a significant way. The 330 provides TIS data which is displayed on the 430 and GRT EFIS. It "seems" the only thing lacking is the high fidelity WAAS position. Of course, I am hopelessly out of my depth on the technical details, but with the plethora of add on ADS-B solutions with built in WAAS, it "seems" (there's that word again) the addition of an auxiliary WAAS source should be an easy fix for the existing non WAAS navigators like the 430 (for ADS-B position at least).
The WAAS signal basically is a bunch of numbers which describe the current state of the ionosphere, in various locations around the US. (The ionosphere is electrically active, and radio signals propogate thru it at less than the speed of light.) But now the gps receiver has to go back and recalculate the position, adjusting each satellite’s time delay for the ionosphere near that satellite. This is a lot harder than it sounds. Recall that when Apollo came out with the waas-enabled 480, Garmin had their engineers working overtime, and it still took something like a year to transition from the 430 to the 430W. It just isn’t as easy as feeding WAAS correction data into a non-WAAS 430. I seem to recall they had to go to a whole new processor board.
Now, communication is another story. The 430 and 330 communicate via an rs232 format, which means the 430 sends a string of numbers, and the 330 knows that the first set of numbers is the latitude, next string longitude, next string the north component of velocity, etc. If the numbers are sent in any other order it will look like nonsense to the receiver. Garmin wrote their own format specs specifically to handle adsb data, and named this format ‘adsb+’. The 330 looks for data with this format. Unfortunately, you cannot use a $500 GRT gps to send the data to your 330, because GRT doesn’t know how to send adsb+ format; Garmin keeps the details of this format secret (‘propriatary’).
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  #10  
Old 12-14-2018, 08:54 AM
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g3xpert g3xpert is offline
 
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Quote:
Originally Posted by Toobuilder View Post
I guess the best thing is to pair the 650 and 330 (with ES upgrade) on one airplane and do a 430,327 and GDL-82 on the other. Swapping transponders is not something I'm looking forward to, however.
This seems like a very reasonable approach if you can do the work yourself. If you have some avionics installation experience, this is a simple job.

Thanks,
Levi
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Last edited by g3xpert : 12-14-2018 at 09:42 AM. Reason: grammar
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