PilotAware
British Forum => Technical Support => Topic started by: peteD on July 21, 2023, 05:53:47 pm
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I have a redundant Garmin GPS AT575 unit on my aircraft, can i use this to supply gps data for my PA?
Is it a matter of converting the coax connector to USB, or is there more to it than that?
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I cannot find any Garmin product that has used that name.
I suspect it is a GPS Antenna AT575 of which there are several variants. Is there a GPS unit on the panel? if so, you may be able to connect the PAW to that? Otherwise it is a no.
Cheers
Ian
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Apologies, should have been clearer, yes, it’s an antenna. Yes, I do have a GTN 650 in the panel, but as a certified a/c, I can’t really mess with that. Any reason why I couldn’t utilise the antenna as a part of a gps repeater to the PA?
Thanks
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Not without stopping your GTN650 from working and buying a second GPS. You cannot 'T' it off the lead to the GTN650, unless you pay an engineer to install a certified antenna spliter and second GPS Rx.
You would be far better off buying a USB GPS Mouse.
Cheers
Ian
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Maybe I didn’t make it clear, the garmin AT575 gps antenna is spare and unused at present (from a previous gps installation that has long been removed) I do not wish to interfere with my GTN 650 installation. At present my PA uses a gps mouse.
I was wondering whether it’s possible to use the redundant antenna to supply the original pa gps usb dongle with a signal, either by using it as a repeater
http://bytethebullet.com/geocaching/reradiating_antenna.htm
or direct connection to the patch antenna in the dongle
Thanks!
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Re-radiating GPS isn't a great idea, I'm surprised someone has tried it in that link you posted. The signal power is so low (~ -150dB), you can easily swamp it and degrade other GNSS receivers in the area if you take a 29dB amp and 'broadcast' the signal. Not a great idea in aviation. Been there, done that, never doing it again.
You can get USB GNSS dongles with a connector for an external antenna. You would need to check the datasheet for the antenna to see what power it needs. I can't find one after a quick search, so how old is it? It may have failed if it's not been connected to anything for a while, so you'd need to test it. Those take between 4.5v - 15v I think, depending on the actual part number (there are several AT575 variants). A USB dongle will provide a max of 5v DC bias and may be happier with a higher voltage.
You're making your own GPS Mouse with an external antenna.
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"You can get USB GNSS dongles with a connector for an external antenna"
That's really what i'm looking for but not been able to find one!
Any links/ideas where to look please?
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Search for GNSS dongle with external antenna connector.
This is one, power for the active antenna is only 3v, below the 4.5v min needed.
https://gnss.store/neo-m9n-gnss-modules/119-elt0103.html
You may need to use a bias-T to supply the power if the dongles can’t supply the power needs of the antenna. Those can take 60ma or more I think. It will be checking all the data sheets.
Suspect you’ll need to source from outside the UK, but beware that almost every GNSS dongle from China that says it has a U-Blox receiver it will be a clone that just uses the same commands. It’s pot luck basically how well it will work. They sell whole dongles for less than I can buy 10,000 of the raw U-blox chips for.
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The antenna is the 9 version and requires +5v( was connected to Apollo 820)
Thanks for your help and pointing me in the right direction!
PS have one of your power supplies, solved all my usb power-supply issues :-)
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You could try this
https://www.amazon.co.uk/Geekstory-Antenna-Supports-GLONASS-Compatible/dp/B07ZR8R17Q
I am assuming that it uses a usb-uart bridge which the OS has drivers installed for
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So bought this and works fine with pilotaware
https://www.amazon.co.uk/Geekstory-Antenna-Supports-GLONASS-Compatible/dp/B07ZR8R17Q
How does it know to switch between the built in patch antenna and the other connected antenna?
Also, the voltage on the device antenna is +3.13v, whereas the antenna requires 5v, can i use a bias-T to supply the 5v? Values?
Thanks!
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Plugging in an external antenna usually disconnects the internal. It's mechanically done within the RF plug itself.
I'd give it a try and see if it works. just cover the patch antenna and see if the AT575 gets enough juice, it might work.
You could use a bias tee, but you may also need a DC block before it to remove the original 3v from the module itself. It may not appreciate the reverse feed of 5v.
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How does it know to switch between the built in patch antenna and the other connected antenna?
Good question, and I have no clue!
However it does work
On Rosetta FX (shortly due for release), it has the option for internal/external antenna
Simply attaching/detaching the external antenna is detected automatically by the receiver
I know this because a status message is produced, indicating which antenna is being used
Thx
Lee
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Yes, it's not a mechanical switch on this GPS USB dongle as it still receives gps signal with the extension lead plugged in.
Good news is the garmin AT575-9 gps antenna seems to work with the lower than spec voltage.
Thanks all for your input!
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Lee Said
"Simply attaching/detaching the external antenna is detected automatically by the receiver
I know this because a status message is produced, indicating which antenna is being used"
How can I check that the attached antenna is being used, rather than the patch antenna?
Is there some software that allows me to do that?
Thanks
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Not sure about this particular gps receiver
But the one we use on Rosetta fx, produces an NMEA message
This is a $GPTXT message with text ANTSTATUS
To answer your question you need to plug into a PC or LINUX machine and connect a terminal (minicom or putty) and look for the above message when adding/ -removing external antenna
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Ok thanks, I’ll have ago!
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Could not see $GPTXT ANTSTATUS except on startup when ANTSTATUS=OK*25 with Putty,(at the limit of my knowledge here!)
So I used U-Blox u-centre which gave me a nice signal strength indicator display and responded positively to the connection of an active antenna,:-) , just need to try it on the AT575
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UPDATE
Works very well, signal strength 50-60db on AT575, compared to pilotaware internal gps mouse 30-40 db.
So if you happen to have a redundant gps antenna (ex garmin430 etc) on your airframe and wish to use it instead of an internal gps mouse, the above mentioned dongle works well!
Thanks for all the input that enabled me to reach my goal :-)