Question about dump1090 timestamp frequency


#1

Hi everyone! I’ve got a fast question regarding the ticks frequency of the timestamp provided through the Beast format. Is it 2 MHz or 12 MHz? I found both values on the Internet and I don’t understand which one I should consider to make the calculations and get the number of nanoseconds contained in one tick.


#2

The demodulator samples at 2.4MHz (dump1090-fa, dump1090-mutability) or 2MHz (most other versions)

The timestamps that are included in the Beast output are scaled to 12MHz for compatibility with the actual Mode S Beast which produces 12MHz timestamps. So it is a 12MHz value but the resolution is worse than 12MHz.

An alternative format you may run into is that the Radarcape can produce Beast-format output with timestamps that are seconds and nanoseconds since GPS-midnight (see the beast/radarcape wiki for details, the two fields are packed separately into the timestamp); dump1090 doesn’t produce that format.


#3

Got it, thank you!