Time Records from FTP Output

[paday]

I am looking to use the RadarBox to provide an air track feed in my research project. I have connected my software to the FTP ports 30003 and 7879 but neither appears to provide every ADS-B transmission with the correct time; both feeds have the same error. I am using the AirNav 2010 - 3.13 software.

The ADS-B spec states that aircraft will transmit their data every second.

Looking at this sample capture shows the error:

MSG,3,0,0,4CA281,0,2010/06/01,09:19:21.557,2010/06/01,09:19:21.557,,10625,,,51.2149,-0.8238,,,0,0,0,0
MSG,3,0,0,4CA281,0,2010/06/01,09:19:21.557,2010/06/01,09:19:21.557,,10650,,,51.2153,-0.8246,,,0,0,0,0
MSG,3,0,0,4CA281,0,2010/06/01,09:19:21.557,2010/06/01,09:19:21.557,,10650,,,51.2158,-0.8255,,,0,0,0,0
MSG,3,0,0,4CA281,0,2010/06/01,09:19:21.557,2010/06/01,09:19:21.557,,10675,,,51.2170,-0.8279,,,0,0,0,0
MSG,3,0,0,4CA281,0,2010/06/01,09:19:21.557,2010/06/01,09:19:21.557,,10675,,,51.2177,-0.8292,,,0,0,0,0

What can be seen is there are 5 records for a single track (4CA281). Every record has the same time value (09:19:21.557) but the latitude and longitude value for each is changing. To me this indicates that there there is an error somewhere in the AirNav software that is not correctly recording or keeping the actual time of the data.

Can someone please provide some clarification?

Thanks

[DaveReid]

I am looking to use the RadarBox to provide an air track feed in my research project. I have connected my software to the FTP ports 30003 and 7879 but neither appears to provide every ADS-B transmission with the correct time; both feeds have the same error. I am using the AirNav 2010 - 3.13 software.

The ADS-B spec states that aircraft will transmit their data every second.

Looking at this sample capture shows the error:

MSG,3,0,0,4CA281,0,2010/06/01,09:19:21.557,2010/06/01,09:19:21.557,,10625,,,51.2149,-0.8238,,,0,0,0,0
MSG,3,0,0,4CA281,0,2010/06/01,09:19:21.557,2010/06/01,09:19:21.557,,10650,,,51.2153,-0.8246,,,0,0,0,0
MSG,3,0,0,4CA281,0,2010/06/01,09:19:21.557,2010/06/01,09:19:21.557,,10650,,,51.2158,-0.8255,,,0,0,0,0
MSG,3,0,0,4CA281,0,2010/06/01,09:19:21.557,2010/06/01,09:19:21.557,,10675,,,51.2170,-0.8279,,,0,0,0,0
MSG,3,0,0,4CA281,0,2010/06/01,09:19:21.557,2010/06/01,09:19:21.557,,10675,,,51.2177,-0.8292,,,0,0,0,0

What can be seen is there are 5 records for a single track (4CA281). Every record has the same time value (09:19:21.557) but the latitude and longitude value for each is changing. To me this indicates that there there is an error somewhere in the AirNav software that is not correctly recording or keeping the actual time of the data.

Can someone please provide some clarification?

Actually, the ADS-B spec says that Airborne Position reports should be transmitted twice per second.

And, as you rightly say (barring helicopters!) you should never expect to get two or more consecutive timestamps with the same coordinates.

The flight concerned, EIN233, was outbound from Gatwick when you logged it.  Assuming a groundspeed of, say, 300kt on the climbout, and given that the distance between the first and last coordinates is approximately 0.263nm, then there should be around 3 seconds between those two position reports.

Clearly, RadarBox is buffering consecutive messages and outputting them with the same timestamp - basically it's not designed for time-critical applications, nor for research projects such as yours.  Maybe that will change when RadarBox MLat comes along, I don't know.

PM me if you would like some accurately timestamped ADS-B data (though not from RadarBox) for your research.

[paday]

I have been looking round the options that apply to the program. It looks like the screen redraw rate which I did have set to 4 seconds (4000ms) may also drive the FTP output rate. I have now set it to 0.5 seconds and get more frequent data. The time would thus appear to be related to the time the data is written on the screen rather than received time - can this be confirmed?.