Garmin GPS AT575 with Pilotaware

[peteD]

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?
 

[Ian Melville]

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

[peteD]

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

[Ian Melville]

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

[peteD]

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!

[JCurtis]

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.

[peteD]

"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?

[JCurtis]

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.

[peteD]

 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 :-)

[Admin]

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

[peteD]

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!

[JCurtis]

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.

[Admin]

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

[peteD]

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!

[peteD]

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