Hi everyone,
I’ve been reading the forums recently and I’m new to ADS-B and feeding FR24, so I’m hoping someone can answer this for me?
Why is there often such a large discrepancy between aircraft total and with positions on dump1090?
I can understand having a few missing, but if my system knows there is an aircraft then why would it be missing it’s position data?
This morning was a classic example, where I had 102 aircraft, but only 52 with positions - screen grab attached:
Many thanks!
Most of those are squawking 7000 which means they are VFR and probably light aircraft that don’t transmit ads-b. They aren’t transmitting their position so don’t appear on the map. The way to get them to show up is to use mlat, which calculates the positions using data from several receivers.
If you installed dump1090 from FR24 it’s an ancient version and you’d be better updating to a more recent one. If you use one of wiedehopf’s scripts it will reconfigure FR24 for you as well: Automatic installation for dump1090 fa · wiedehopf/adsb-scripts Wiki · GitHub
Many thanks calius!!!
So my ADS-B system will pick up non-ADS-B transmitting planes, but obviously no position data?
I’m a noob at this, but I’ll have a look at wiedehop’s scripts for sure!
So much to learn… 
Yes, most aircraft carry a mode s transponder these days, which transmits its Id and altitude in response to a ground radar interrogation. Dump1090 can decode mode s, so displays those aircraft but can’t show their location on the map.
FR24 doesn’t return mlat results, so if you want those you need to install piaware or something else like the adsbexchange feeder which do.
Now this all makes sense - thank you so much for answering this!
After trawling websites, blogs and forums, you can’t beat asking an actual human 
If I reconfigure FR24, will it still recognise me as a feeder with my stats etc?
Seeing my stats and chart position motivates me to keep improving my equipment and learning more.
You can run fr24, piaware, adsbexchange, RadarBox, planefinder and whichever other feeders you want alongside each other. If you install fr24 first, it uses an old dump1090 though. The script above will install dump1090-fa which is much newer and reconfigure FR24 to use it instead. You will keep the same receiver ID.
Most of the data sharing sites will give you stats of one sort or another, but you could also install Graphs1090 which will give you stats you can track independently.
Specifically … ADS-B is an extension to Mode S, an older transponder system. ADS-B transponders transmit with the same frequency and modulation scheme as older Mode S transponders (with the ADS-B data transmitted as a new message type within the same basic message format that Mode S uses). dump1090 will hear and decode messages from both types of transponder.
Thanks for this guys! Everything is starting to make a lot more sense now 
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