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The reason for inreach mini poor gps performance compared to other units/phones

wildside
over 5 years ago

So like many people on this forum Ive found the time the Inreach mini takes to aquire a location fix to be ok but not great.  My mobile phone gets a location fix much faster than the mini.  (phone has all location assist services turned off and is in flight mode)

I think i found the reason.

The inreach has access to 34 orbiting satellites (GPS only)

My phone can communicate with 123 orbiting satellites to triangulate a signal (GPS, Galileo, BDS and GLONASS satellite constellations)

Thats a huge difference.

So can the mini be upgraded via software patch?  or can the garmin earthmate app be improved allow the mini to use the phones location for a fix when connected via bluetooth? 

This would speed up location acquistion time in an emergency and in general navigation and messaging.

It could make the difference between life and death in a scenaro where a person is located in a canyon and out of the line of site of the closest gps satelite orbit.  Then mini  would need to wait minutes or in a worst case scenario hours for another GPS satelites to pass directly overhead. 

In that time several of the satelites of the  other location service constelations like Galileo, BDS and GLONASS could have passed overhead but the mini currently cant talk to them.

Garmin says that adding just GLONASS 31 sats to the GPS's 34 sats decreases location acquisition time by up to 20%
https://support.garmin.com/en-AU/?faq=G ... ErPJevmbJ7

Imagine how much faster it would be if the inreach could talk to GPS, Galileo, BDS and GLONASS satelites either via a software patch or via the earthmate app using a phones location fix.

  • 0 over 5 years ago in reply to KEMITCHE

    2 minutes or less and I believe the Mini never shuts GPS radio off, so that is not it.....

  • 0 over 5 years ago in reply to atlas_cached

    Don't remember for sure about the Mini. For most iR devices, it's 30 seconds or less that results in GPS continuously on. Whatever it is, you will get an informational message when you set a value that's low enough to keep the radio on.

    However, the fact that the radio is on does not say anything definitive about the iterative computations required to refine the fix.

    I will say that I would not have expected a speed as low as 75 mph to cause problems. OTOH, I have no experience above about 50mph, where there is no observable problem.

  • 0 over 5 years ago in reply to KEMITCHE

    Additional questions just to clarify the circumstances.

    You say that the locations, weather conditions and mounting options were much the same. Where were the units mounted? And was this a side-by-side test, or different trips?

    How about time of day? In any given location, the GPS constellation repeats at (almost exactly) 12 hour intervals. A moderate difference in time of day can make a big difference in the available satellites, especially if the unit has a partially obscured sky view (for example, limited to forward view from the cockpit).

  • 0 over 5 years ago in reply to twolpert

    They were on different flights. Units were attached to the same point on my parachute chest strap.

    I feel there are too many variables, so I'm rather going to test both units in my car next time we do a longish drive (with both short and long track log intervals). So upright on each side of the dash. Not an ideal view of the sky, but it should be okay, and at least we are comparing apples and apples.

  • 0 over 5 years ago in reply to KEMITCHE

    I think there may be a problem with the unit. Based on prior experience, the Mini doesn't perform quite as well as the full-sized units. However, this situation really should have resulted in better performance than you report. I'd call tech support.

    For future reference, the ideal place for either unit is on the strap on the top of your shoulder. This isn't ideal from an antenna orientation perspective for either unit, but it gives the best sky view. The problem with the front strap is that your body blocks a substantial portion of the sky view.

    The only other suggestion I would offer is to be sure that the Mini (particularly) has a solid fix before you begin moving. I don't know if the Mini is one of the units that uses an EPO file. If not, or if the EPO is out of date, the unit will have to acquire ephemeris data the old-fashioned way. If you're moving, this can take much longer than you'd expect.

  • 0 over 5 years ago in reply to twolpert

    The chest strap is probably the best place when flying a sailplane as we sit (lie) in a fairly supine position. The antenna doesn't aim vertically, but I'm not sure how relevant that is (omni-directional antenna)? Anyway, I'll compare the performance of the Mini against a friends Mini before calling tech support. Thanks for the input.

  • 0 over 5 years ago in reply to KEMITCHE

    It does sound like there may be something wrong with your device based on the description of its performance. If you could contact our Customer Support we would be happy to further assist you. 

    Garmin Support

  • 0 over 3 years ago

    I know this is an old thread but I thought I would update this with the correct information. The reason that your mobile phone can get a faster GPS position has very little to do with the number of satellites but a lot more to do with its other features. For a GPS receiver to get a lock, it needs an up to date almanac. The almanac consists of coarse orbit and status information for each satellite in the constellation, an ionospheric model, and information to relate GPS derived time to Coordinated Universal Time (UTC). The GPS also needs an accurate time and date. Your mobile phone can get a rough position from the mobile phone network, it can get an accurate time from the mobile phone network / internet and it can download the GPS almanac from the internet. This mean that your mobile phone has a short cut to getting a GPS location that isn't available for a Garmin unit. If the garmin unit has been switched off for a long time or has moved in location significantly since it's last use then it will need to download the almanac through the GPS network which is fairly slow ( minutes ).

  • 0 over 3 years ago in reply to Neutronstorm

    Yes, almanac is a potential issue  for the Mini, as well as for GPS receivers in general. Unlike some iR units, I do not believe the Mini has an EPO file. The Mini cannot take advantage of AssistedGPS, which is what your phone is doing to decrease acquisition time.

    You are correct that the onboard almanac ages out of usefulness if the unit is off for an extended period of time. I don't recall the exact limit, but it's on the order of a few weeks. And the almanac is for a particular area - after all, it reflects "satellites overhead HERE at a particular date/time". Again, I don't recall the geographic limit - perhaps on the order of 200 miles? If you move far enough with the unit off, the onboard almanac will be useless when you power up again.

    If the onboard almanac is out of date, the unit will eventually fall back to a full-sky search, which is time consuming.

    If in doubt about the quality of the onboard almanac, turn the unit on, place it on the ground with a clear sky view, and step away. Allow the unit to "soak" this way for about 20 minutes. This will allow it to build a complete, up to date almanac. Do not hold the unit in your hand, and do not move it. Doing so may interfere with the acquisition of the almanac. (It actually takes just over 12 minutes for the constellation to transmit the full almanac. 20 minutes gives plenty of time just in case there are interruptions in line of sight.)

    There are special considerations for the Mini, which tends to shut down the GPS radio to conserve battery power. Set the logging interval to 30 seconds or less to keep the radio on. 

    Note that even devices which HAVE an EPO file will suffer the same fate if the EPO file ages out of usefulness. Although it's not always easy to find, the device usually shows the EPO status somewhere. For example, it's on the About screen for the Montana. The EPO file is typically maintained "out of band" - for example, by syncing the device. The above method for rebuilding a current almanac will work on any device with a clear sky view.

    Yes, the unit needs relatively accurate time and date. This is unlikely to be the source of any acquisition problem, The device maintains a clock even when off. Worst case, it will get the time from the first GPS satellite it finds.

    Once the unit has a valid almanac, it will maintain it incrementally while the unit is switched on. So if you don't move it too far and do not leave it off too long, the almanac stays up to date - and an additional soak is not required.

  • 0 over 3 years ago

    I own a Mini and GPS reception is really bad. It takes too long to fix position. I also own a GPSMAP 64s and a Colorado 300. When these two are put into GPS only mode, they take some time (never more than 2-3 minutes), but never too much as the Mini. In some cases the Mini will never get a fix, which is annoying, at first.

    Communication via Iridium is really good. Even when you cannot get a GPS position, you can send messages and they are sent most of the time in really short times (the manual says it can take up to 20 minutes. I have been in many harsh scenarios and never experienced more than 5 to 10 minutes for a message to be sent).

    I stopped fighting with this issue because let's be honest. We cannot pretend such a small device to be used as a navigation tool. For me, the Mini IS NOT intended to be used as a standalone devide. It MUST be complimented with a "real" GPS device. Yes, you should not go to a place where you would eventually need satellite communication without a proper compass/map and/or another GPS device.

    Here is my recommendation:

    -Never go with a Mini alone. A real GPS is a MUST.

    -Forget navigation capabilities of the Mini. They are as useful as the stopwatch in other Garmin devices. I mean, if you need to navigate, you should rely in map and compass and a real GPS.

    -If you need to send a message, just bypass the position-not-fixed alert and just send the message.

    -If you really need to send your position, read it form your "real GPS" and send it in the message. Same applies if you need to send the position in a SOS message.

    -If you are in a perfect condition for the Mini to get a position (a really clear sky), use its position.

    I live in Chile and I have been using the Mini in this way in very isolated and intricated places especially in the Patagonia and the Mini works like a charm. Don't get unmotivated as I did feel in the beginning (complaining myself for such a waste of money). Just consider the Mini as a communication device and forget the "free" navigation capabilities which as I said before I consider them as useful as the stopwatch or the sunrise/sunset times available in other GPS devices.

    Regards.

    Pablo.