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External antennas for Fona 808
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External antennas for Fona 808

by oudevolvo on Fri Apr 20, 2018 11:58 am

I have an Adafruit Fona 808 breakout module that I want to use in a project in a car.
It will be installed underneath the dashboard in a plastic enclosure.
But there is a lot of metal around.
So I am afraid keeping the antennas inside the box won't give me very good signals.
So I am looking at possibilities to install external antennas.

For the GSM part I found that I can use the SMA to uFL Adapter Cable (product 851) and than any antenna that at least supports 2G (GSM/GPRS) and has a SMA connector.
For example this one ANT-TBARQB-SMA RF Solutions - 2G (GSM/GPRS), 3G (UTMS) Antenna Adhesive Mount, SMA
Is that correct?

For the GPS part I found it a little more difficult to find the right one. Is my understanding correct that I can use the same SMA to uFL Adapter Cable and then any passive GPS antenna with a SMA connector?
For example this one External GPS Antenna - Cabled SMA connector
Will that work?

Or do you have any other suggestions?
Thanks in advance for thinking along and your responses.

oudevolvo
 
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Re: External antennas for Fona 808

by adafruit_support_mike on Sat Apr 21, 2018 2:13 am

Both of those should work with the FONA. A long as the coax cables are long enough to get from the FONA itself to a good antenna location you should be okay.

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Re: External antennas for Fona 808

by oudevolvo on Thu Apr 26, 2018 1:04 am

Thanks!

oudevolvo
 
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Re: External antennas for Fona 808

by ze51 on Fri Apr 27, 2018 1:14 am

Are there any other guidelines when selecting an antenna from outside the Adafruit store? I am planning on sending sensor info via FONA in an area that has spotty cellular coverage and have started to look at larger antennas for my project.

One spec I have seen listed for some antennas is power, some listing up to 50 W. For example: https://www.digikey.com/product-detail/en/taoglas-limited/GA.107.201111/931-1044-ND/2332671

Is this generally the power the antenna requires, or just a maximum rating? Would an antenna such as the one in the link overdraw current through the FONA and burn it out?

Thanks for the help!

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Re: External antennas for Fona 808

by adafruit_support_mike on Sun Apr 29, 2018 1:18 am

50W is a rating for how much power the FONA can send into the antenna when transmitting to the cell tower.

The FONA's burst current during those transmissions can be as high as 3A for a few milliseconds, but even at that level, the power is 3A * 3.3V =~ 10W. That's well within the limits of the antenna.

As long as it's a passive antenna for the right frequency bands and has the right connector (or you can find an adapter), it should be fine.

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Re: External antennas for Fona 808

by oudevolvo on Tue May 01, 2018 9:25 am

Do you perhaps also have a suggestion on positioning the external GPS antenna?

Would attached to the inside of the roof the car above the headliner be a good idea?
Image

Or is a position where the receiver can “see” through a window required?
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Re: External antennas for Fona 808

by adafruit_support_mike on Wed May 02, 2018 12:16 am

The receiver part needs to be outside the car, or at least under the windshield or rear window so it can see the sky.

Test it with the microcontroller and see if it can get a fix.

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