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Watsonville midair

Old 20th Sep 2022, 07:45
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Originally Posted by jimjim1 View Post
I have no idea where they get the data. I notice that Dave mentions Radar, however other discussion groups mention a different adsb radio frequency than used by "airline" grade (let me call it:-) adsb. There is certainly accurate looking height data. I think you can get that from a radar transponder.

Someone said:- "The C152 was pinging on 978mhz.
978 MHz is a reference to UAT (Universal Access Tranceiver) - an alternative (in the USA) to the more common 1090 MHz Extended Squitter. For either to be used for ADS-B (i.e. tracking) requires the aircraft to be equipped (usually) with a GPS source. Whether or not fitted with GPS, the aircraft will still send altitude data via Mode C or Mode S.

A number of the services we commonly use like FlightAware can't see 978 signals unless the plane is closer to 1800' in the Watsonville area"
Don't confuse what's available to crowd-sourced tracking sites like FlightAware or FR24 with what ATC (and hence the NTSB) has access to.
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Old 20th Sep 2022, 16:13
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Thanks for your replies. I did some Googling from your comments, and I see that there are indeed two ADSB-out frequencies in use, 978 and 1090. Well, thatís certainly interesting. And maybe the C150 was too low to be received by the open-source receivers in the area. I was not aware there were multiple frequencies.

The Webtrak site is interesting, seems to be able to track both frequencies, but that site is not available over the whole country.

Thanks!
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Old 20th Sep 2022, 20:49
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Originally Posted by Si Guy View Post
The Webtrak site is interesting, seems to be able to track both frequencies, but that site is not available over the whole country.
SJC WebTrak is driven principally by radar data.
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Old 21st Sep 2022, 01:41
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DaveReidUK - Ok, thanks. Been reading about it some more, seems it was primarily designed to allow for filing of noise complaints around major and medium size airports. But I can see it's useful for historical flight tracking as well.
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