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Is There A WAAS "Add On" Module?

Toobuilder

Well Known Member
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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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

Team X Project Manager
 
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?
 
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.
 
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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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.
 
...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).
 
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.
 
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?).
 
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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I got one of those letters from the FAA. I have a G3X non-touch and a GTX-23ES transponder. I will eventually be installing a GPS-20A. I spoke with the FAA and the idea is, if you broadcast ADS-B it has to be completely compliant including the GPS source, even though the ADS-B deadline is 2020. The G3X system allows you to disable the ADS-B out, leaving you with a basic Mode S transponder. The FAA specialist agreed that would comply with the intent of the letter.
 
the rest of the story.....

Ok Michael, now that we have the ins/outs' of the ADSb dilemma, would you care to share the info on the L-39? I thought about buying one but the fuel burn...... was rather bloody discouraging...

By the way, I went the uvionics adsb route with the tailbeacon. About 5 minutes to install and two wires (positive and negative) and your done. I was able to keep my Garmin 327 so no panel work needed.
 
Ok Michael, now that we have the ins/outs' of the ADSb dilemma, would you care to share the info on the L-39? I thought about buying one but the fuel burn...... was rather bloody discouraging...

The jet was an unplanned purchase. It was one of those right time, right place things that I could not turn down. Long story short, it arrived at my house on a flatbed, but its undamaged, and I've even flown it. Once I screw it back together I will fly it a bit and likely sell it off for a real airplane - one powered by a piston radial.

I have to admire the engineering on this one though. Aside from it being WAY too heavy (by western standards), its a very clever bird and has certainly proven the design's effectiveness over the decades.
 
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