iFly GPS Forum

 Anyone know the size traffic puck  transmitted back from the ground to  an aircraft equipped with ADSB out.  Althougth I only  have ADSB  IN, and  Mode C txdr,  and yes i know it Mar 2019!   But I rarely fly to area which require ADSB  OUT.  I DO use  and like the  traffic and Wx  service  via Stratux which is  provide me back by those who have installed that OUT  service.  There are areas where that becomes marginal due to low equiped  traffic  out there. Just wondering how  large that coverage for those   who have installed the OUT equipment might be?

Thanks Cobra for the quick reply back, I should have also know and tried Google for the answer but personally  like the reply from common interest friends.   So, flying with ADSB  IN only should get better as we move closer and into the 2020s.  If I understand the words, anyone within 15 NM radius and 3500 ft above and below me having either UAT  or ES TXPDR providing ADSB OUT  should  show up for  me.  And I to him if we are in radar coverage.  Still use the "out the windscreen " method for others but  have learned  that unless they are within 1 nm  of you and 500+-  ft  you prob won't see them.

Dennis: your understanding is incorrect in a few ways.

If you have ADS-B In, you will receive direct transmissions from all aircraft that are transmitting ADS-B Out on the frequency or frequencies you are receiving.  Most ADS-B In receivers have an antenna for both the frequencies: UAT 978 MHz, and Mode S 1030 MHz.  As you noted, as more and more aircraft get equipped with ADS-B Out, this makes this part of the system work better and better because you don't need a ground station and its hockey pucks of TIS-B (traffic info).

But note that these ground stations will transmit (on the UAT frequency) only if triggered by an aircraft that is transmitting ADS-B out, and only if that aircraft has indicated that it can receive ADS-B In data (see the following paragraph).  The hockey puck of traffic they transmit is centered on that aircraft, not yours.  So, it is very possible that there is traffic around you that you do not get direct or TIS-B data on because they're not transmitting ADS-B Out and you do not happen to fit within an ADS-B out aircraft's puck; or if you do, you're only seeing a fraction of the traffic because you're at the edge of said puck; or the aircraft triggering the ground stations does not have ADS-B In, so the stations don't bother transmitting.

I don't know exactly what is transmitted in TIS-B data except for radar hits (assuming there is a hit) for traffic that is not ADS-B Out equipped.  For all other traffic: I believe that since one of the configuration options you set on all (I may be wrong on whether it's all) ADS-B Out transmitters is what frequency or frequencies you can receive on - if any.  This is transmitted as part of your ADS-B Out data.  To save bandwidth, I believe that TIS-B data leaves out info regarding all aircraft transmitting on frequency/frequencies that you have indicated you can receive directly.  (I might be wrong.  If I'm wrong, I'm sure someone else will chime in.)  But if true, this would further degrade the information that you would receive in your case since you don't know what part of the overall picture the ground station is leaving out since it's transmitting data meant for another aircraft.  The TIS-B data may contain only some or not any info about traffic that is around you that is transmitting ADS-B Out.  I guess that's probably fine, since you should receive from them directly.  But again, if the triggering aircraft has not indicated that it can receive ADS-B In, and there is no requirement that anyone have ADS-B In, then there's no hockey puck at all.