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  #161  
Old 03-12-2019, 04:32 PM
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DanH DanH is offline
 
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Ok, have a buddy with very good connections into the ADS-B world. He was kind enough to do a bit of research regarding the time intervals:

Each UAT message frame consists of exactly 1 second and is synchronized to UCT using GPS timing. The beginning of the frame is reserved for "uplink" from the ground station - 176 msec with guard bands on either side. The final 800 msec is reserved for ADS-B aircraft broadcasts. As stated in the document excerpt, "Each UAT-equipped aircraft makes exactly one ADS-B message transmission per frame". So, the data rate for UAT messages is always 1 Hz.

It reconciles with the ADS-B Pro app developer's "logs as soon as data is ready" comment because...

...while the overall data rate of UAT ADS-B messages is 1 Hz, the instantaneous message rate may be more or less due to the pseudo-random nature of the messages. They may occur anywhere within the ADS-B message segment of the frame. But the average will be 1 Hz, as only one message per frame per aircraft is allowed.
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Last edited by DanH : 03-12-2019 at 05:34 PM.
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  #162  
Old 03-12-2019, 04:53 PM
moosepileit moosepileit is offline
 
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Where is the, "like" button? Nice update, thanks for the research, Dan.
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  #163  
Old 03-12-2019, 05:28 PM
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Quote:
Originally Posted by moosepileit View Post
Where is the, "like" button? Nice update, thanks for the research, Dan.
Credit goes to my bud, who prefers to be, well...anonymous. Which is pretty darn funny given he helped bring you ADS-B.
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Last edited by DanH : 03-12-2019 at 05:35 PM.
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  #164  
Old 03-12-2019, 05:37 PM
moosepileit moosepileit is offline
 
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Word parsed to find a 2004 era FAA .pdf.

Has the same wording of timing messages.

It has nothing about anonymous.

Not a reader's digest:

1.5mb .pdf

Department of Transportation
Federal Aviation Administration
System Specification
Ground-Based Transceiver (GBT)
For
Broadcast Services
Using the Universal Access Transceiver (UAT) Data Link
FAA-E-2973
01/15/04

https://www.google.com/url?sa=t&sour...9ynSAFLCG9rSA_
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Last edited by moosepileit : 03-12-2019 at 06:47 PM.
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  #165  
Old 03-12-2019, 06:07 PM
GWZ GWZ is offline
 
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Hi Dan, any chance your buddy has any insight into the 1090ES anonymous mode technology demonstration that’s supposed to take place “early 2019”.
Also any chance he’s involved in writing the spec and if so can we request that this “brief transmitting in the clear” be eliminated for 1090ES anonymous mode?
Yea, I know, not likely but a guy can ask can’t he....
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  #166  
Old 03-13-2019, 12:04 PM
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nomocom nomocom is offline
 
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Default GDL behavior and anonymous switch

I’ve had my GDL82 installed for over a year. Startup, anonymous switch on and monitoring its behavior via the Stratux (ads-b in, build your own), it’s behavior is consistent with what has been described. There is a few seconds on startup of unique and specific icao and n number. Any local receiver and perhaps Aerion * would see me and then a few seconds later not see that aircraft, but an anonymous aircraft in the same location. A simple algorithm could bond the two ID’s for the flight duration.
As a general practice, a few minutes before asking for ATC services, I switch to non-anonymous since it will help with correct ID and I’ll loose the anonymous anyway when not on 1200.

*aopa article reports Aerion only 1090, so should not see the 978 transmissions
https://www.aopa.org/news-and-media/...-the-high-view
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Last edited by nomocom : 03-13-2019 at 01:03 PM.
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  #167  
Old 03-15-2019, 10:55 AM
Ted RV8 Ted RV8 is online now
 
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Default Is this applicable?

https://www.aopa.org/news-and-media/...privacy-policy
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  #168  
Old 03-15-2019, 11:22 AM
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DanH DanH is offline
 
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Not really. You can request that the FAA not release your flight information to outside vendors. Your ADS-B transmissions (1090 or 978) need not be anonymous to request privacy under the policy.

You will remain identifiable by the FAA, any other governmental agency, and by anyone with a smart phone and a cheap radio dongle. For that you'll need a true anonymous mode.
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  #169  
Old 03-18-2019, 07:02 AM
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Quote:
Originally Posted by jliltd View Post
I leave my Mode C transponder in standby until ready to taxi, which I think leaves the GDL 82 in standby during its GPS acquisition and start up. Jim
Got to that question yesterday.

Powered up a GTX-327 transponder in STANDBY, squawk set to 1200, with the GDL-82 unpowered. After a few moments, I applied power to the GDL-82 while monitoring for signal. No ADS-B packets were transmitted with the transponder in STANDBY.

However, subsequently switching the transponder from STANDBY to ALT caused the GDL-82 (with pin 5 grounded, and supposedly anonymous) to momentarily broadcast initial "real ID" packets (true ICAO and N-number) before switching. I only noted the text traffic display. I did not save the packets to a .csv file to look at number of packets or specific content.

Perhaps it is time to hear from our friends at Garmin.

Quote:
Originally Posted by moosepileit View Post
The GDL goes quickly anonymous, from what Dan posted. Today you would have to be at one of the 35 or so major airports that use ASDE-X on the ground and have GBT installations- The FAA's UAT towers.

Or, you would have to be receivable by a GBT anywhere else, on the ground, at power up. Slim chance on average, today.
Maybe, maybe not. An official ADS-B ground installation is not required. Consider we're recording the initial real ID data with a $20 dongle radio receiver coupled to a $15 frequency filter. Any cell tower would do.
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  #170  
Old 03-18-2019, 05:47 PM
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Alan Carroll Alan Carroll is offline
 
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FlightAware already has coverage down to the ground at my home base, a small uncontrolled field, apparently through the PiAware network. This seems to be limited to 1090 for now, but looks like 978 could be coming soon (see newsletter linked below).

Welcome to the FlightAware ADS-B newsletter for February 2019!
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