search

antirez / dump1090

Dump1090 is a simple Mode S decoder for RTLSDR devices
2.41k stars 1.32k forks source link

Position and velocity messages getting repeated 2 to 3 times #124

Closed sekarchandran closed 6 years ago

sekarchandran commented 6 years ago

Hi

Thanks to creators of this wonderful tool ..which helped me lot in my work.

I am developing a tool which will compare my Radar data with the ADSB (from dump tool) data for bias calculation.

I am using the "NooElec NESDR Mini 2 SDR & DVB-T USB Stick " and dump1090 .

I have following problems

  1. Many times, Messages are getting repeated with in short time.. 100 ms ( maximum three times) same values ..only small time difference...?

I tried following methods ...but not able to solve the problem a) changed the buffer size and number of buffers in rtlsdr_read_async function.. b) changed the receive using "rtlsdr_read_sync " c) removed mutex and signals ...instead i used POSIX message queue bet receive and process threads...

still data is repeating some times .

Is it the bug in rtlsdr library which makes repeated messages OR ADSB system itself broadcast messages like this ...?

Kindly help me.

Thanks and Regards K.Chandrasekaran

yuvadm commented 6 years ago

It's definitely possible the aircraft broadcast the same message several times in response to different interrogations.

sekarchandran commented 6 years ago

ADSB messages( position -lat,long,altitude, velocity - speed,heading, call sign..) are broadcasted without any interrogation at regular intervals ( one second once) ....correct me if i am wrong ..

I just added some code to display the messages in console continually ....there i noticed that both position and velocity messages are repeated with in some milliseconds interval...same values only time is the different.

I verified the code thoroughly with various ways...in my understanding ..these messages are coming in different times ( different reads ) have you ever noticed that the position and velocity messages repeated ..?

yuvadm commented 6 years ago

As far as I understand ADSB messages can either be periodical (as is the case with extended squitter) or respond to secondary radar interrogations.

Regardless, unless it can be shown that there truly is a software bug that causes erroneous repeated messages I'll have to close this issue.

sekarchandran commented 6 years ago

as of now i am not having the dongle with me ... i will come back with the log data after getting the dongle ..probably two to three days ..