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Aircraft Data Decoding - A forum to discuss decoding the various data transmissions such as ACARS, Mode-S, ADS-B, etc.

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Old 09-16-2017, 11:10 AM
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Default backcountry ads-b

I am wondering if low-flying aircraft in backcountry areas (if equipped with ads-b) utilize the 1090 mhz range or 978 band? I am asking the question in the specific context of mountain-flying in the Bitteroot Mountains of the Northern Rockies.

I understand some aircraft may not be ads-b equipped, and some perhaps use only one band or the other. If using an USB dongle for reception which band would one use or would a dual freq/dongle lash-up be in order? Perhaps there is some official or unofficial convention regarding a particular band for mountain flying?

My ignorance is manifest, so perhaps someone has an enlightening comment.

This seems like a fun mountaintop radio thrill to me.
Thanks Guys!
p1879
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Old 09-16-2017, 11:15 AM
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The FAA's objective is that aircraft operating exclusively below 18000' will be equipped with the 978 MHz device. Just how many aircraft are so-equipped I can't say as it is not a mandatory installation yet. Matter of fact, I've never seen anyone here post anything that leads me to believe they've tried capturing data on that frequency to see just how active it is. Give it a try and let us all know what you're seeing!

More here:

https://en.wikipedia.org/wiki/Automa...0%93_broadcast

https://www.faa.gov/nextgen/programs/adsb/faq/

Cheers!
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Old 09-16-2017, 11:25 AM
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I've tried capturing data on 978 here in the highly traffic Northeast US. There was very little. 978 does have fixed rebroadcasts from FAA sites, but both are far enough away I can't receive them from home. I went to both tower sites and lost the reception about a mile away...probably the antennas are radiating upwards.
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Old 09-16-2017, 2:44 PM
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Just for giggles I started ADS-B decoding on 978 MHz using an RTL dongle, MultiPSK and only a discone. I didn't expect to see anything much being about 60NM northwest of the KBUF, but I am receiving this exact pattern a few times per minute for well over an hour now. There is no ident of any sort and no data, so presumably just ADS broadcasts from VFR aircraft in western New York state.

09/16/17 19:34:26 UTC (00000000): DF=0 / VS:airborne / CC:0 / SL:0 / RI:0
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Old 09-18-2017, 9:36 AM
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Interesting that there is no ICAO hex code. I wonder if it's coming from a unit on a lab bench somewhere.
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Old 09-18-2017, 5:39 PM
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Interesting possibility Dave, except that Canada hasn't adopted the 978 MHz system and I'm a long way from the U.S. border to expect a discone to receive anything sitting on a test bench. It's possible that somewhere in-range of me there's an avionics facility that might be working on ADS equipment or an aircraft in a hanger at the local (5NM south of me) G/A airport. Hopefully someone here on RR will try the same simple experiment with a dongle and MultiPSK or similar to see what they receive.

On a lighter note, maybe there's an active unit in a box at the nearby Amazon distribution center. In my working days we chased down more ELTs that got activated in repair shops and in shipment than I care to remember. Perhaps ADS transponders will be added to the list.

Cheers!

Bob
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