FON808 GPS altitude limit

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nmaretas
 
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FON808 GPS altitude limit

Post by nmaretas »

I am a schoolteacher in Greece.
We intend to create a high altitude ballon as a school project, using for GPS (and gsm) the FON808 breakout board.
Our target altitude is 30Km (about 100.000 feet).
Are there any operational altitude limitations in the MT3337 GPS module inside the fon808 breakout?
Thank you.

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adafruit_support_mike
 
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Re: FON808 GPS altitude limit

Post by adafruit_support_mike »

We don't have any specs for that, so it's best to assume the GPS module will shut off at the standard legal limits of 18km and/or 1000 knots.

Our standalone GPS module has firmware we've requested specially, which should go higher than 30km:

https://www.adafruit.com/product/746

We've gotten reports from people who've used them in high-altitude balloons and had them cut out below that level, while other people have gotten output above the 18km limit. We don't have any way to test the speed or altitude limits, so we can't say for certain where they'll cut out.

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nmaretas
 
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Re: FON808 GPS altitude limit

Post by nmaretas »

Thanks for the quick reply.
Are the conflicting reports about altitude cutoff you are mentioning about the fon808 or the standalone?
By standalone i assume the mtk3339 with your tailormade firmware.
Hopefully there is "and" and not "or" in the firmware.
I 'd hate to change from the adafruit module we have been using the last 2 years, library works like a charm.
If there is any way for me to find out more, please let me know.

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adafruit_support_mike
 
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Re: FON808 GPS altitude limit

Post by adafruit_support_mike »

The Ultimate GPS module (pid 746) has been programmed with firmware options we selected:

https://www.adafruit.com/product/746

I don't know of any non-baseline features for the GPS module in any FONA.

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devilstower
 
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Re: FON808 GPS altitude limit

Post by devilstower »

Hi, I purchased an ultimate GPS breakout in both the normal and featherwing versions to build flight comps for high altitude balloons, because somewhere along the line I thought that the 60,000 foot limit was not longer in the firmware. However, not that I've checked the data sheets, it seems like I may be in trouble and may have to go back to my uBlox.

Is the limit still in place?

The legal limit is not 18,000 meters or 1,000 mph. It's knots, and it is AND. That is, GPS need only disabled at a speed greater than "1,000 knots (1,900 km/h; 1,200 mph) at an altitude higher than 18,000 m (59,000 ft)." that's the COCOM GPS regulation, as set by the US Department of Commerce. While a lot of GPS firmware seems to take an easy out and use an OR condition, that makes them pretty useless for high altitude purposes.

There is no limit on altitude at all for a device moving less than 1,000 knots.

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adafruit_support_mike
 
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Re: FON808 GPS altitude limit

Post by adafruit_support_mike »

We've requested firmware settings that allow the GPS modules to continue to track position above 18,000m, but we don't have any way to test that spec.

The only responsible answer I can offer is that you should look for a vendor who does have some way to guarantee high-altitude performance. We can't, and we won't ask you to risk the time and resources on a high-altitude flight to find out.

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devilstower
 
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Re: FON808 GPS altitude limit

Post by devilstower »

Well ... darn. Back to the uBlox, which seems to have removed the limits a couple of years ago.

Thanks.

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devilstower
 
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Re: FON808 GPS altitude limit

Post by devilstower »

Oh, I should mention -- I'd be happy to put the Feather-based solution (I have an Express MO and a GPS featherwing together) in the next launch along with Nano / uBlox / SD Card solution that I'm counting on to record top altitudes.

So if you want to know where it really cuts off, or test new firmware, that can happen.

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devilstower
 
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Re: FON808 GPS altitude limit

Post by devilstower »

I’d been wondering how I got it in my head that this would work for me, started back tracking, and found this answer to a question about altitude on Amazon.

What is the max Altitude this unit would operate at? (for high altitude ballooning)
The module is not designed for high altitude use. That said, in theory, it will work up to 40 km altitude, but we do not guarantee operation at that altitude.

Chicago Electronic Distributor… Seller · August 7, 2015
I realize this isn’t you, and I should have checked the data sheet. Just wanted to make you aware this is out there.

https://smile.amazon.com/ask/questions/ ... _ql_al_hza

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adafruit_support_mike
 
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Re: FON808 GPS altitude limit

Post by adafruit_support_mike »

I appreciate the offer to test a unit, but we've had mixed reports from other people who've tested them in the past. Some report normal operation above 18km, others report cutoff at different altitudes, some higher than 18km.

Given the variation and the cost of failure, it's best to stick with something that has a guarantee.

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