SparkFun Forums 

Where electronics enthusiasts find answers.

Tips and questions relating to the GPS modules from SFE
By mbrocketry
Ok here it is, I have an em-406 gps module that I would like to use for a high altitude balloon project. Is/are there unlock codes in the SiRF III chipset or with the EM-406 to unlock the 18kmeter/60kfoot limit. I would like to track the balloon upwards of 80k feet. I believe that the current unit without modification will just peak at 60k even if the balloon goes higher. Anyone know or have any ideas?
By jandirks
allthough, at 60k, a few meters of is not a big problem I think: You are aware of the fact that GPS altitude is not very accurate? It's always of a few meters.

Have you thought about barometric altitude, you would need a good resolution though...
By mbrocketry
Yes I have even built altimeters for my rockets but Baro pressure is only good to about 42,000 MSL. Our flight computer also has an accelerometer which we can add to steps to the baro and get good accuracy to about 67,000 feet but it only works good in something that moves fast like a rocket so right now GPS is the only way to go that I can think of.

I have a friend that has an older GPS that he launched on a balloon to 84,000 with very good accuracy (before they started locking the altitude to 60k). The newer ones are just locked out so you can't use them for guidance of say a destructive device, but GPS is accurate up much higher than 100,000 feet. You just have to be able to unlock them with a manufactures code or hack it somehow. The 60k is a number some government picked because all GPS's seem to be capped at 60K.
By henryhallam
I wrote to the manufacturers of the EM-406 and they said that the limitation is built into the SiRF chipset, so wasn't something that they could change (their hardware and firmware are at a higher level).

I am going to fly an experiment on the next Cambridge University Spaceflight balloon to test five different GPS modules at more than 30km and see which, if any, work. If you email me at hallam at mit dot edu I will send you the results (expect it to take a couple of weeks)

I also have about 20 units of the GPS-MS1E module, which is older technology. I've successfully tested it to 32km. It does draw a little more current than the EM406, it takes about 150mA at 3.3V and you need an external active antenna. Excluding the antenna it is a little bigger than the EM406 but not enormous. I can sell you an unused one for $40 if you like (I paid about twice that much a year ago...)

User avatar
By ohararp

You should include the EB-85A in your testing. Its a great little module and will allow for 5Hz data collection. Power draw is stupid low at ~30ma.
By henryhallam
It's already on there :)
The modules we'll be flying are the MS1E (for reference), EB-85A, EM-406A, EM-402 and Lassen iQ.
I'll post the results here.
By mbrocketry
Great to hear Henry, I would love to see how the EM-406A performs in reading altitude above 60K feet. Please do let us know.

Question have you tested or read anything on the NEO-4U unit?
By henryhallam
I can already tell you that the EM-406 (plain, not A version) quits above 24km, at least in one test.

I hadn't heard of the NEO-4U unit, I've mainly been looking at modules that have built-in antennae or at least an easy connection rather than having to route RF on the PCB. But I guess we'll look into those if none of the modules we're trying end up being satisfactory.
By BigRedBee
I can positively confirm that the Lassen IQ works above 60K MSL.

-- Greg
By NorHighAltitude
henryhallam wrote:It's already on there :)
The modules we'll be flying are the MS1E (for reference), EB-85A, EM-406A, EM-402 and Lassen iQ.
I'll post the results here.
Hi. I am doing some preliminary research on a GPS for a high altitude balloon. (Very new to this, learning embedded electronics at the moment, but the goal is making a data logger fore a HA balloon :) ). Is it possible to view the results from your GPS altitude tests?

Best regards

By edmoore

I am part of the same team as henryhallam. We never flew the gps experiment in the end but can positively confirm that the lassen iQ works up as high as we have got (32+ km)

...and it's very simple and friendly to use. A nice GPS. We'll be experimenting with the uBlox 5 series soon.