Recently installed PiAware and FlightAware feed this AM. Not showing any MLAT data. Wondering if I am missing anything here? I only have an indoor unit so not sure if it is due to the distance? I’ve attached screenshots of my stats showing 0 for MLAT.
MLAT data relies on critically accurate time and location information. Your Pi maintains time by connecting periodically with a NTP Network Time Protocol - Wikipedia server. Accuracy is close to a few nanoseconds.
The position is set at your AustonnL page and under the Settings “Gear Icon”. Looks like you have set the location already. The location needs to be VERY accurate, within 10’s of ft and the antenna heights matters too. I have used accurate GPS and online maps, even Google Earth locations to get the best location info I can. It does make a difference.
When the ADSB signal is received, it is relayed with the exact arrival time to FlightAware servers. By calculating the time of arrival between 4 or more locations, the source ADSB transmitter can be isolated and reported. When your site is one of the receiving sites, you get credit. At least that is how I understand it. Do a double check on your location, it can make a big difference, I have 5 digits to the right of the decimal point to get the best spot. At 45.6 degrees North, that is about 40 miles or so per degree. 4 digits is around 21 ft or so. 5 is better.
Have fun, get your system up and running, and make a few improvements here and there. It will be fun, interesting. Hang in there.
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“other” should show data as well…
Piaware doesn’t use ntp timing except with a few devices like the radarcape and airsquitter that have hardware GNSS/NTP built in. It can use GNSS for location information. There are other tracking applications that use NTP.
Dump1090 uses a clock(12mhz I think) signal on the sdr dongle for MLAT.
AustonnL ADS-B Feeder Statistics - FlightAware Shows very little traffic.
It looks like only two aircraft in the last 24 hours.
AustonnL ADS-B Feeder Statistics - FlightAware The other site looks better,
You will need more receivers in the area for MLAT. Like GNSS, four or more are required. In busy areas like NYC, I have over 500. https://www.flightaware.com/adsb/stats/user/jonhawkes2030#stats-99829
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Just to clarify, it doesn’t use ntp in that case for timing either.
The GPS receiver is integrated with the ADS-B receiver / demodulator.
That is a hardware demodulator / decoder which whill output beast with timestamps from the on-board GPS device.
That’s incorrect.
The timing reference used primarily is the SDR oscillator. (rtl-sdr used with dump1090-fa is a 2.4 MHz sample rate, the beast data coming out of dump1090-fa has timestamps recalculated as if it were a 12 MHz clock as that’s somewhat of a standard reaching back to the ModeS beast).
As the SDR doesn’t attach a timestamp, if you lose any samples on USB, the timing is off.
The clock not being off more than 0.1 seconds or so is still useful for mlat-server correlation of which identical messages in time from different receivers are gonna be calculated.
Edit: that sentence is atrocious. aircraft often send identical ModeS messages within 1 seconds. say multiple receivers receive those identical messages and send them to mlat-server. the system time is then used for mlat-server to know which of the copies belong into a group. such a group will be then used to derive a position (using the oscillator based timestamp associated to each message) (and knowing the relative frequency and offset between all the receivers. this sync is done using ADS-B position messages)
MLAT is green so it’s synced.
If all aircraft you receive have an ADS-B receiver, you won’t have any MLAT aircraft.
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I stand corrected on the timing aspects. Learning more every day. Thanks for clearing it up for us.
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