I didn’t feel this warranted a whole thread, but something I observed that is interesting and this thread seems as good as any.
I had noticed that for the past couple of weeks I have been seeing slightly lower message rates than normal, until just before noon today when things suddenly increased:
No changes have been made to either hardware or software, and I see a similar effect in @keithma’s graphs, so it’s obviously a real effect. There hasn’t been any significant change in aircraft numbers or range.
I can only assume that there is some change to aircraft interrogations that causes fluctuations like this - different radar operating mode, or a radar shutting down and starting again perhaps. It’s worth bearing in mind when making comparisons - sometimes you can get significant changes that are completely beyond your control.
looks like the traffic is really getting busy.
I’ve setup the feeder new on December 13th and today i achieved the highest number of aircraft. Haven’t seen >140 since months (including the previous feeder). But i also have to say that today the wind direction is my friend. FRA approach is passing my location.
@caius
A good description about what is going on in the air…
but I am not all with you…
normally the ADS-B messages sended out by aircraft are roughly 7-8 Messages/s
“At night, the number of messages per aircraft is a lot higher than during the day when it’s busy”
At night there is no reason for increasing the framerate. I believe that the reason is more or less that the receiver chain is overloaded during the day and can not process the mass of data …overlapping frames ect…I do not think that an aircraft is sending out with 20Hz …the phenomenon must cause in another reason…
Yes, the reason for the increase in received messages per aircraft is due to reduced message overlap, or at least a reduced ability to discriminate messages in a busy environment rather than an increase in the number of transmitted messages.
You have to remember that ADS-B is not the only cause of transmission. Those transmission rates you quote apply to automatic transmissions and do not account for responses to ground interrogation and TCAS, which can make up a considerable proportion of messages. For example:
DF 0 - ACAS/TCAS Air to Air anti collision.
DF 4 - Altitude Response
DF 5 - IDENT response
DF11 - Mode S All-Call reply/ADS-B Acquisition Squitter
DF16 - Long ACAS/TCAS Air to Air anti collision
DF17 - ADS-B Extended Squitter
DF18 - ADS-B Supplemenatary - non-transponder devices, TIS-B and ADS-R.
DF19 - Military Extended Squitter
DF20 - Comm B - Various navigation and status messages
DF21 - Comm B - Various navigation and status messages
Only DF17 is ADS-B (with minimal numbers of DF18 and DF19) which are transmitted automatically. DF0 and DF16 are TCAS messages which are responses to other aircraft, DF4, 5 and 11 are Mode S, and DF20 and 21 are CommB which are responses to ground interrogation.
From my knowledge TCAS is transmitted via the nose directional focused antenna. I do not think that TCAS can be received on ground.
But we have to recognize the 1030 MHz secondary radar which trigger also a transmission…but this is a rotating beam which will ping the aircraft additional every roughly 3 s. If it is silent… (traffic goes down) maybe a second, third …secondary radar far away is pinging also is received and getting a reply…who knows
It definitely can - the graphs I posted are stats from my receiver showing a large number of TCAS messages. Aircraft usually have two TCAS antennas, one above and one below the fuselage, with either one or both being directional.
There’s definitely multiple radar heads interrogating each aircraft. In Europe there will likely be many tens of radars in visible range of each aircraft due to the density of the airspace, but also radars in Europe seem to make use of CommB much more than in the US and they continuously respond to DF11 all call reply messages.
Yah…sure…may be I am misunderstanding…something
I am with you ADS-B on complete transmitter and antenna for the top and one for the bottom.
TCAS for avoid negotiation (Activ TCAS) …I believe you are talking about passiv TCAS right ?
Actual TCAS events and the negotiation can be received just fine by ground based receivers as well.
(i’ve seen loads of them going through large amounts of data)
The directionality for TCAS is more in the receivers i believe so the aircraft can determine which aircraft are possible intruders.
@wiedehopf
I have some questions regarding the graphs1090
There are some diagrams like “ADS-B message rate”
the result here is only ADS-B ? (long frames) or is Mode S included…
Same ADS-B tracked …does that mean only ADS-B ?
or ADS-B Signal level …does this include Mode-S ? or is that filtered ?
and of course ADS-B message rate …what is the meaning exactly ?
Just for understanding what exactly is shown in that graphs to avoid misintepretation.
thank you very much for your answers.
Avoiding further misinterpretation from my side i need to wait for the answer of Wiedehopf. I talked today with my engineers and it seems that we found a plausible answer for the interpretation of ADS-B messages/FA/s and the cause of increasing during low traffic periods. For information I have attached a nice picture.
It looks that I was wrong, that there is a third transmitter with a directional antenna for the TCAS and ADS-B mounted in the nose of the plane…looks that there is only the weather radar
I haven’t chosen the graph names really
Well maybe i changed them i don’t remember.
They are not very rigorous and the stats.json / aircraft.json aren’t rigorous all the time either …
Could maybe use some checking of source code and stuff but i’m happy with the graphs so i’m not particularly interested.
