Quectel L70 GPS chipset and LoRa

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plugger

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I'd never heard of a Quectel L70 GPS chipset but this definitely caught my eye.

"Balloon mode, for high altitude up to 80km"

https://www.quectel.com/product/l70r.htm

The chipset seems to be integrated in a number of cheap GPS trackers with LoRa radios. Here's an example.

https://www.iot-store.com.au/products/lorawan-gps-tracker-accelerometer-lgt92

Given the pricing my gut tells me these would most likely be garbage but conversely given the price I'm finding it hard not to buy one to "play with".

Anyone have any experience with this GPS chipset?
 

jderimig

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I'd never heard of a Quectel L70 GPS chipset but this definitely caught my eye.

"Balloon mode, for high altitude up to 80km"

https://www.quectel.com/product/l70r.htm

The chipset seems to be integrated in a number of cheap GPS trackers with LoRa radios. Here's an example.

https://www.iot-store.com.au/products/lorawan-gps-tracker-accelerometer-lgt92

Given the pricing my gut tells me these would most likely be garbage but conversely given the price I'm finding it hard not to buy one to "play with".

Anyone have any experience with this GPS chipset?
The Quectel uses the MediaTek3339 chipset which supports dynamic modes similar to Ublox. Quectel doesn't make the chips they just integrate other maker's chipsets into modules.

You do not get balloon mode out of the box, it has to be set with an MTK command. The MT3339 also has some other interesting things in the datasheet that suggest that is doesn't have a velocity lockout below 18Km.

I have a MT3339 module that I am itching to fly in one of its airborne dynamic modes to see how well it tracks under acceleration. Remember a "balloon" dynamic is not that challenging an environment for a GPS receiver to maintain lock.

I played with an earlier MTK chipset many years ago and in the few flights I flew it performed reasonably well.
 
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jderimig

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Also how the module integrates the antenna with the chipset will make or break the performance of the unit. Many focus on the chipset but its the antenna which ultimately determines the performance in a rocket. Unfortunately that is where the cheap integrators skimp, badly. Look for a module that exposes pins for an active GPS antenna. Then you can integrate your own. You will find the good antennas (active quadfilar) will cost more than the GPS module sometimes.
 

plugger

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The Quectel uses the MediaTek3339 chipset which supports dynamic modes similar to Ublox. Quectel doesn't make the chips they just integrate other maker's chipsets into modules.

You do not get balloon mode out of the box, it has to be set with an MTK command. The MT3339 also has some other interesting things in the datasheet that suggest that is doesn't have a velocity lockout below 18Km.

I have a MT3339 module that I am itching to fly in one of its airborne dynamic modes to see how well it tracks under acceleration. Remember a "balloon" dynamic is not that challenging an environment for a GPS receiver to maintain lock.

I played with an earlier MTK chipset many years ago and in the few flights I flew it performed reasonably well.
Thanks for the detailed reply John, I really appreciate it. Furthermore thanks for the breakdown of the OEM that Quectel gets its chips from. I didn't know that and now I'm really excited! Why you ask? Because I've already got one! Late last year I picked up an Adafruit Ultimate GPS with an eye towards integrating it with my Pwnagotchi and I've yet to get around to it. PROJECT SHIFT!

So with reference to "Balloon mode" I expect that I'll have to configure that via UART or I2C? Looks like I've got some reading to do. I'd like to wrap my head around the specific modes the chipset supports to try and make sense around which mode will work best.

Do you think the integrated antenna on the unit I have will suffice for our use case or should I look to upgrade? The unit has a uFL connector and the ability to automatically detect an external antenna has been connected so I have a simple upgrade path if desired.

Thanks again for the reply, I genuinely appreciate it!
 

jderimig

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So with reference to "Balloon mode" I expect that I'll have to configure that via UART or I2C? Looks like I've got some reading to do. I'd like to wrap my head around the specific modes the chipset supports to try and make sense around which mode will work best.

Do you think the integrated antenna on the unit I have will suffice for our use case or should I look to upgrade? The unit has a uFL connector and the ability to automatically detect an external antenna has been connected so I have a simple upgrade path if desired.

Thanks again for the reply, I genuinely appreciate it!
The PMTK command manuals are kindof hard to find, its not a MT website and there seems to be different versions floating around. Here is one that describes balloon mode,

command Packet Type: 886 PMTK_FR_MODE

You can send the commands over UART using a terminal. Also you can use UBlox u-center as well. You will have to play and find out if the mode is saved in flash so it comes up in that mode after a power cycle.

As far as antenna, you will not know until you fly it.
 

mikec

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FWIW, as discussed in another thread, I've personally had issues with Mediatek GPS chipsets and don't use them any more, preferring Ublox instead. But I'd be interested in hearing about any flight experience with the Mediatek; I know John has had some success with them.
 

plugger

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Thanks for the response Mike. I did a bit of a search and I really can't find much on your experiences with Mediatek GPS. Was it the MT3339 chipset that you ran into issues with?
 
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