GPS Flight telemetry

Project to send a balloon into lower space with payload
Rris
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Joined: Mon 12 Oct 12 2009 9:17 pm

GPS Flight telemetry

Postby Rris » Fri 08 Jan 08 2010 6:42 pm

http://www.gpsflight.com/index.php?opti ... 5&Itemid=2

i think we need to replicate this. It's UBX based and they claim it works at 60,000ft. So i think that's our answer for the gps unit.

Rris
Posts: 66
Joined: Mon 12 Oct 12 2009 9:17 pm

Re: GPSFlight telemetry

Postby Rris » Fri 08 Jan 08 2010 6:57 pm


Daniel Wee
Site Admin
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Re: GPSFlight telemetry

Postby Daniel Wee » Fri 08 Jan 08 2010 10:05 pm

I've got one of those UBX coming from SFE (won it on free day!).

Daniel

Daniel Wee
Site Admin
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Re: GPSFlight telemetry

Postby Daniel Wee » Fri 12 Nov 12 2010 11:26 pm

Mark, I don't think the UBX module from SFE uses the NEO-5 chipset. I believe it uses the LEA-5 chipset and I'm not sure if the specifications are the same. You may want to check on that.

In the meantime, this one looks promising:-
http://inventeksys.accountsupport.com/s ... V0004.html

I would also talk to Locosys about getting a module without the said limitations. I think there is a possibility that they may play ball.

Daniel

chris1seto
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Joined: Thu 02 Dec 02 2010 3:05 pm

Re: GPS Flight telemetry

Postby chris1seto » Thu 02 Dec 02 2010 3:12 pm

Limit is an AND not OR.

If you meet (or exceed) the speed limit AND altitude limit you will have exceeded the device's operational limit.

If you only exceed the speed OR altitude limit, you are within the device's operational limit.

Rris
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Joined: Mon 12 Oct 12 2009 9:17 pm

Re: GPS Flight telemetry

Postby Rris » Thu 02 Dec 02 2010 3:19 pm

That's only confirmed for the SkyTraq units Chris, as i told you. Other companies may implement it differently (especially non-cn/hk/tw companies)

chris1seto
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Re: GPS Flight telemetry

Postby chris1seto » Thu 02 Dec 02 2010 3:30 pm

Rris wrote:That's only confirmed for the SkyTraq units Chris, as i told you. Other companies may implement it differently (especially non-cn/hk/tw companies)



Then why stray from Skytraq? I have had excellent results with my Skytraq Venus 6 devboard, fix acquisition is rapid and it's usually accurate to a few feet, or at least it's accurate enough that it's hard to tell if there IS any "significant" error from the GPS.

The unit is fairly compact, however it does require an external antenna.

The SUP500 is based on the same chipset, however it doesn't play well with high refresh rates. The antenna is sitting directly above the chipset, so when the clock is increased to accommodate the higher refresh rate, you start to get interference leaching into the antenna.

The balloon doesn't need a high refresh rate, so the SUP500 should be fine.

Rris
Posts: 66
Joined: Mon 12 Oct 12 2009 9:17 pm

Re: GPS Flight telemetry

Postby Rris » Thu 02 Dec 02 2010 3:35 pm

The limitations may be different from other brands due to how they interpret the COCOM rules. The asians are very liberal in their implementation, others may take it more as it is implied rather than so literally.


Talking with Daniel on Skype, we prefer an external antenna solution anyway. The SUP500's have antenna quality issues anyway. Having an external antenna would get the antenna outside of the box (assuming it can handle the cold) and allow it to be outside any shielding we add against solar radiation.

I'm trying to get 5x Venus638 chips off SkyTraq for the system, 1 spare in case of reflow issues (it's BGA), 2 for ground station, 2 for payload. This would allow us to have spare boards incase something happens. Its much easier to switch out a board rather than debug it in the field.

chris1seto
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Joined: Thu 02 Dec 02 2010 3:05 pm

Re: GPS Flight telemetry

Postby chris1seto » Thu 02 Dec 02 2010 3:56 pm

Just out of curiosity, do you know of any OTHER issues the SUP500 antenna has besides the clock issue?

SFE sells two versions of external antenna:
* A "raw" one
* A "rugged" one

The rugged one is out of the question due to weight issues, so the "raw" model may be the way to go, but I'd like to see if there are any other good sources for GPS antennas. So far, I'm not finding many.

Daniel Wee
Site Admin
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Re: GPS Flight telemetry

Postby Daniel Wee » Thu 02 Dec 02 2010 5:55 pm

I have tested both modules and the SFE one without antenna works fantastically when used with an active antenna. The SUP500F, unfortunately, has dismal performance (cannot acquire at all.) Nate at SFE has posted that they no longer encourage people to use the SUP500F for the myriad of issues related to its' performance. The reason for this is unclear though but if could be a poor antenna design, or as you suggested - interference.

As for the CoCom limits - there are some differences in how different companies interpret the constraints. While some (few) implement it as AND, most actually implement it as OR. You can also Google this.

Daniel


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