WAAS GPS/ADS-B question

I have decided upon the uAvionix echoUAT unit to provide ADS-B in and out for my RV-4. My aircraft has an existing GPS antenna connected to a Garmin SL-60, but I don't have a WAAS GPS source, so had planned to install the integrated (antenna + receiver) SkyFYX unit offered by uAvionix.

Now, I am second guessing myself and would like to know whether or not I could use the existing GPS antenna (or a new one in its place) with a GPS splitter to provide signal to both my SL-60 and the SkyFYX variant that requires an external antenna.

The benefit to me is that I would not need to install another antenna, and would avoid running the associated wire(s). The downside is that I would need to buy and install a splitter something like this:

https://www.gpssource.com/collections/gps-splitter/products/s12-1x2-standard-gps-splitter

Thoughts or recommendations appreciated.

Thanks,

Dean

You answered your own question:
- SL60 uses and external GPS antenna
- The SkyFLX is an integrated GPS antenna and receiver in the one puck.

These are two different animals and not compatiable.

The SkyFLX that has an external antenna might work with a splitter, but I’m very skeptical. Considering the gross price of a GPS splitter along with odds that it would not meet the WAAS requirement I would look at other options.

If you ever plan on using this plane for IFR work, this might not be the best path.

Carl

Carl Froehlich said:

The SkyFLX that has an external antenna might work with a splitter, but I?m very skeptical. Considering the gross price of a GPS splitter along with odds that it would not meet the WAAS requirement I would look at other options.

If you ever plan on using this plane for IFR work, this might not be the best path.

Carl

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Hi Carl,

Thanks for the reply. The SkyFYX with the external antenna is the one I am considering for use with a splitter in this scenario.

Every so often, I consider a major panel upgrade to incorporate IFR capability, but the task is so large given my current equipment that "throwing away" the uAvionix ADS-B solution does not bother me.

Thanks again,

Dean

don't split

I will let you decide which avionics is best for your situation, but I don't agree with splitting a GPS signal. I know they make the splitter and charge $300. But a gps signal is very very weak by design. Splitting it further risks poor performance.

It?s potentially much worse than just losing half the signal. Some antennas have built in amplifiers requiring dc voltage running up the coax. Some have different gains than others (look at the mess the early 4xxW Garmins had when they used an OEM antenna). Unless you are absolutely sure you know what you?re doing I would never suggest a splitter for this application.

IIRC the GA56 NON waas antenna is quite popular and used with the SkyFYX that requires an external antenna. They can be found on Ebay or here VAF classified for not much money, far less than a spitter that will probably not work. I know of at least 2 RVs using this same set up as you with this antenna. Recommend checking with Uavionix of course.
When upgrading the 430/530 to WAAS the GA56 became surplus so they sell pretty cheap and now used on several ADSB systems like Uavionix.

Larco said:

IIRC the GA56 NON waas antenna is quite popular and used with the SkyFYX that requires an external antenna. They can be found on Ebay or here VAF classified for not much money, far less than a spitter that will probably not work. I know of at least 2 RVs using this same set up as you with this antenna. Recommend checking with Uavionix of course.
When upgrading the 430/530 to WAAS the GA56 became surplus so they sell pretty cheap and now used on several ADSB systems like Uavionix.

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Pretty sure you need a WAAS gps for proper adsb out reporting, no? Or does the SkyFyx put out a proper WAAS signal with a non-waas antenna?

G56 antenna works well with uAvionix

No issues, with several FAA reports asked for and rec'd ---- always clean. Always worked fine with Navworx, previously.

Ron

RONSIM said:

No issues, with several FAA reports asked for and rec'd ---- always clean.

Ron

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As has been discussed previously, the fact that a gps is working today, or last week, or on a hundred straight days does not mean that it will work under the worst case scenario where it is still supposed to work. e.g., Does it meet the performance spec? Almost no RV owners can answer that question. I?d call uAvionix and ask them if their promise of meeting specs is still valid with this antenna.

Thanks to all for the posts. The questions, concerns, and advice have helped with the inquiries made to the various suppliers.
So far, I have had preliminary conversations with Garmin, uAvionix, and GPS Source the division of General Dynamics that makes this splitter.

flightlogic said:

But a gps signal is very very weak by design. Splitting it further risks poor performance.

Click to expand...

BobTurner said:

It?s potentially much worse than just losing half the signal. Some antennas have built in amplifiers requiring dc voltage running up the coax. Some have different gains than others (look at the mess the early 4xxW Garmins had when they used an OEM antenna). Unless you are absolutely sure you know what you?re doing I would never suggest a splitter for this application.

Click to expand...

The GPS splitter I'm investigating amplifies the received signal. It can be configured to use a DC voltage provided on the coax by the GPS receiver or can accept an external supply.

The Garmin aviation tech rep I spoke with said the use of a splitter in this application is common. (Though, to be honest, I have not heard from anyone who has done it.) He admonished me to make sure to get the correct voltage for the splitter. The antenna that came with my SL-60 uses 5VDC according to the drawing I found for it on the internet.

Veetail88 said:

Pretty sure you need a WAAS gps for proper adsb out reporting, no? Or does the SkyFyx put out a proper WAAS signal with a non-waas antenna?

Click to expand...

BobTurner said:

As has been discussed previously, the fact that a gps is working today, or last week, or on a hundred straight days does not mean that it will work under the worst case scenario where it is still supposed to work. e.g., Does it meet the performance spec? Almost no RV owners can answer that question. I?d call uAvionix and ask them if their promise of meeting specs is still valid with this antenna.

Click to expand...

The SkyFYX unit is a WAAS GPS receiver. According to uAvionix, the SkyFYX unit will work with my installed GPS antenna. This is a key issue and I will probably have a 2nd conversation with uAvionix to confirm, once I have all the details specified for the splitter.

I need to have a deeper conversation with GPS Source to determine connector specifics, EMI issues, and so forth. I also need to confirm the 25dB of gain provided by the splitter is acceptable to both receivers. There are probably other issues I have not yet considered, but this is what make this fun.

Thanks again for all the help.

Dean Pichon said:

I also need to confirm the 25dB of gain provided by the splitter is acceptable to both receivers. There are probably other issues I have not yet considered, but this is what make this fun.

Thanks again for all the help.

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This was exactly the issue with the 430 to 430W upgrade - the antenna had too much gain, resulting in the requirement to install with a specified minimum or more coax length, to introduce a deliberate loss.

BobTurner said:

This was exactly the issue with the 430 to 430W upgrade - the antenna had too much gain, resulting in the requirement to install with a specified minimum or more coax length, to introduce a deliberate loss.

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Interesting. Were you able to find maximum allowable gain levels for the GPS receiver? How was the minimum length of coax determined?

Thanks,

Dean Pichon said:

Interesting. Were you able to find maximum allowable gain levels for the GPS receiver? How was the minimum length of coax determined?

Thanks,

Click to expand...

Cannot answer your questions. The minimum needed insertion loss was specified by Garmin in the installation instructions, for their specified antenna.

engineering questions aside, my question would be legality. the manufacture has shown that the system meets the TSO for adsb using approved equipment listed in the manual. unless they spell out the use of a splitter in the manuals, does the install meet the requirements of the TSO? only the manufacture can answer that. from what i have been told, meeting the TSO is quite complicated and requires testing of the whole package, not just the box.

bob burns
RV-4 N82RB

BobTurner said:

Cannot answer your questions. The minimum needed insertion loss was specified by Garmin in the installation instructions, for their specified antenna.

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Yesterday, I spoke with an Applications Engineer at GPS Source. I expressed your concern and he said this issue is typically dealt with through the use of a unity gain splitter. (The output is amplified only enough to offset the losses associated with splitting the signal.) With this set up, neither receiver should know they are sharing the GPS signal. (Though, one receiver will have to supply an additional 15mA to power the splitter.)

n82rb said:

engineering questions aside, my question would be legality. the manufacture has shown that the system meets the TSO for adsb using approved equipment listed in the manual. unless they spell out the use of a splitter in the manuals, does the install meet the requirements of the TSO? only the manufacture can answer that. from what i have been told, meeting the TSO is quite complicated and requires testing of the whole package, not just the box.

bob burns
RV-4 N82RB

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That's an interesting point. When I spoke with uAvionix they said there would be no issue using a splitter, but I did not specifically as about the legality of it. I will add that to the list of questions.

Thanks,