MLAT vs ADS ?

[jeepsandradios]

I have been running a ADSB receiver at home for a few years. Multiple times I have military aircraft fly over my house that dont come up on my ADS page at home. Last weekend we had a Blackhwk fly over about 700' high and it showed on ADS, but then 2 hours later 2 others flew over about the same area and neither showed up on ADSB. For reference I feed MLAT to all servers but I believe that needs multiple locations to show up ? How far apart do they need to be ? Just trying to get reliable military reception. Have not had issues in commercial or private planes and helos justm ilitary.

 

[RichM]

MilAir “usually“ have their transponders turned off. The exceptions are “usually“ heavy aircraft like C130’s and Stratotankers and sometimes helicopters - but not always. If they do have them on you’ll pick them up as evidenced by your experience with the lone Blackhawk. I run an ADSB system as well and this has always been my experience. Hope this helps.

 

[kayn1n32008]

How far apart do they need to be ?

MLAT depends on Time of Arrival differential, to calculate position, so the greater the time of arrival difference, the more accurate it will be. Also, the more stations that can hear it, the better the refined position will be.

 

[morfis]

For reference I feed MLAT to all servers but I believe that needs multiple locations to show up ? How far apart do they need to be ? Just trying to get reliable military reception. Have not had issues in commercial or private planes and helos justm ilitary.

Far enough to give meaningful differences in signal time of arrival. Realistically you need four or preferably more stations, and all MUST have accurate system clocks. If the aircraft isn't using Mode C then you are out of luck anyway*

*unless you are using a paid version of PlanePlotter software, know the Mode A 'squawk', that squawk is unique and have four or more stations in reception range of that unique squawk who are also using PlanePlotter software and opted in to share Mode A data....This works well in Britain and parts of Europe but probably not so much in America.

 

[kb5udf]

Pending a definitive response, I believe MLAT requires 4 stations to receive the signal. I am not aware of distance requirements between said stations in practice (obviously in theory if they receivers were all co-located that would not work).