GPS Data Source

Discussion in 'Avionics and Upgrades' started by Rob58, Oct 12, 2020.

  1. Rob58

    Rob58 Pre-takeoff checklist

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    Looking to better understand how GPS data is shared and learn more about the data bus technology. To start with I have a Stratus ESG xpdr which is working well. Now I want to add a Garmin GPS-175 (or possibly the 355) and I am wondering what the options are for acquiring GPS data. Should these two systems use independent GPS data (two antenna)? Or can one of the units be the master source for the data and pass it on to the other device? What technology or standard is used to let these devices talk to each other? Just trying to learn how the backend works. Thanks!
     
  2. asicer

    asicer Final Approach PoA Supporter

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    If both receivers are active, yes.
    You can do this too.
    In this particular instance, either "GPS Aviation Format" or NMEA data over an RS-232 serial line.
     
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  3. Ryan Klems

    Ryan Klems Pre-takeoff checklist

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    The ESG cannot be fed a GPS data source from another device, it'll only use its internal data source, only the ES can take an external source. The GPS175 also will not take an external GPS data source, it must be connected to an antenna. There are expensive splitters that could potentially be used to share the antenna (it's not like splitting a nav signal to two receivers), but it's generally not worth going down that route and it introduces a common failure point.
     
  4. MuseChaser

    MuseChaser Pattern Altitude

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    To add on to what Ryan (who is a genius and I'm an idiot by comparison) just said, I was/am faced with the same dilemma. I installed a Stratus ESG a while back as I had no GPS source in my plane, and now want to put in a GPS175. After looking over the ESG installation and pin-out documents repeatedly and comparing them to the ES pin-outs, I thought that there MIGHT be a chance the GPS data was available on a slightly ambiguously labeled pin on the ESG, so I called the folks at Appereo who were very helpful. They confirmed what Ryan has already said... it can't be done. The only course available is to either mount a second antenna (and run another cable) or replace the ESG with an ES and let the new GPS feed it. To add insult to injury, according to the person I spoke with at Appereo, there IS a way to change the ESG to an ES via firmware, but it's not approved by the FAA (maybe the rep meant in the field, or in general...I don't know). When I start the GPS175/G5 installation, I'll contact Appereo again to see if there's any program they offer for exchange of ESG to ES, but I'm not hopeful.
     
  5. asicer

    asicer Final Approach PoA Supporter

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    That's an interesting tidbit of information. I did not know that. Seriously twisted, but interesting.
     
  6. jrcox19

    jrcox19 Pre-takeoff checklist

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    You'll probably end up installing a new antenna anyway. Odds are the ESG antenna/wiring couldn't be reused by the GPS 175
     
  7. bnt83

    bnt83 Final Approach

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    The ESG antenna is kind of an oddball IMHO, If this ship was my project you'd need a new antenna installed for the GPS-175.

    If you had picked a GTX-335 or 345 with internal GPS receiver it would have had a GA-35 antenna which is pretty much the go-to antenna for most Garmin products. Then you could have disconnected the GTX from the existing GA-35 antenna and hooked the new GPS-175 to it and ran RS-232 to the GTX from the GPS-175. (at least I think the 175 can do the RS232, the 6xx series can)
     
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  8. bnt83

    bnt83 Final Approach

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    I'm not sure if a guy could successfully use this on two separate boxes, I assume this would only work on radios that are GPS and com radios in the same box like a GTN 650/635 or GNC 355

    upload_2020-10-13_10-55-44.png
     
  9. MuseChaser

    MuseChaser Pattern Altitude

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  10. jrcox19

    jrcox19 Pre-takeoff checklist

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  11. MuseChaser

    MuseChaser Pattern Altitude

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    No concrete plans right now. When I installed the ESG, I had considered using Jim's antenna above just to minimize drilling holes in my airplane and reducing the size of the antenna itself, but ended up using the regular Stratus antenna. I don't see any reason why it wouldn't work for a gps175 or any other device requiring an active gps antenna, but if there is a reason, hopefully someone who knows for sure will chime in....
     
  12. jrcox19

    jrcox19 Pre-takeoff checklist

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    Up to you if I "know for sure" -- but that antenna isn't in the GPS 175 list of approved antennas.
     
  13. Ryan Klems

    Ryan Klems Pre-takeoff checklist

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    ESG antenna is typically a RAMI AV-801, which is certified to TSO-C190, which superseded TSO-C144. It should be a perfectly a antenna for the Garmin, other than the fact that Garmin doesn't offer verbiage like "Or any antenna meeting the performance requirements of TSO-XXX", their standard verbiage is "The XXX must be interfaced with one of these antennas to achieve acceptable performance", followed by a table of acceptable antennas... Which paints you in to a corner when installing per the STC for the unit, unless one felt that was a minor deviation from the STC, or wanted to field approve the deviation. As far as Jim's antenna on a Garmin, while it might perform perfectly, I would say that definitely wouldn't be acceptable per the Garmin STC.
     
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  14. chemgeek

    chemgeek En-Route

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    It's not usually that big a deal to install a second GPS antenna. I put in an NGT-9000 which required a GPS antenna and there was plenty of room on the top of the fuselage to do so to avoid interference. If you are installing GPS in your aircraft you should probably move one of your COM antennas on the bottom of the fuselage if you haven't already.