Peak Level and Ground hits


#1

Hi All, i notice that my peak level is high, as in over the -3. Is there a way to bring it down?

image

This may be due to me being near an airport and having a lot of hits on ground vehicles. While im on ground targets is there a way to drop their messages from over populating my stats/graphs but still keep them on the map? ( i like seeing them scuttle all over the airport).

I also see five ground stations that also get heaps of messages a day ie . image


#2

the easiest one would be to lower the gain, not by a big difference, and note the changes.
then adjust as required to be closer or under the red line. anything above the red line
appears to be an ‘overload’.

check this thread https://discussions.flightaware.com/t/read-set-gain-from-skyview-and-gmap/37140
for an easy way to set/check gain.

evangel


#3

Most definitively reduce the gain. One step at a time. Crossing the red line once in a while is ok, staying above it all the time is bad.

Another side benefit is that the noise level may go down by a greater amount, increasing the SNR.


#4

Where is that graph coming from?


#5

It is coming from the Performance Graphs you can add via the adsbreceiver.net install.sh script.


#6

I live in the approach path of an airport with planes flying less the one km away. To get no signals between 0 and -3, I had to lower the gain so much it had a negative impact on overall messages and planes, so I just left it as it was.

Lowering gain will always cost you a little in maximum distance, but then you might receive messages that are otherwise clipped. I think it is called the doughnut effect, but it is less pronounced with current hardware, according to a post from @david.baker in a thread here about someone having a similiar predicament, iirc.


#7

Thanks biekerc, I’m running the PiAware SD card image at the moment. I have a FlightRadar24 Gold sub which expires next month so I want to start feeding those guys too, so I’ll be looking at these kind of scripts shortly.


#8

The donut effect is that signals too close are not seen and signal too far are not seen. It creates an area of detectable planes that looks like a donut.

The graphs being shown are only showing detected signals. When you decode a signal at -3dB you actually got a signal at that level. When you see a signal at -0.7dB you actually got that signal too. In my earlier comment I was saying that signals near high end are hard to decode and lowering the gain will help you see the strong signals. You don’t know if the gain is too high unless you lower the gain and can then see those higher signal powered messages OR you lower the gain and don’t see any higher powered signals.

I suggest people look at the message rate when setting the gain. You can see the message rate in SkyView as messages decoded per second. Maximize the message rate will give you the best of close and far messages.


#9

To clarify, in the context of the above, is a message defined as an encoded transponder signal which was successfully decoded by dump1090? And if a signal is received but was not able to be decoded, for whatever reason, is that NOT shown or counted in the message count?


#10

I believe that the most of my > -3 db signals are coming from these unknown ids, they are always above -1.5. I have monitored actual aircraft flying near me and they are only at around the > -2 mark when passing.

Does anyone have any idea what these hex ids are for? They never come up with a distance, the height changes randomly and i receive constant messages from them 24/7.

image


#11

@coxyb76 They are probably fixed calibration beacons. We see the same thing around airports in the USA and elsewhere.


#12

is a message defined as an encoded transponder signal which was successfully decoded by dump1090?

Yes. Messages that do not pass the checksum are not counted (checksums are attached to the end of the ADSB message) . A large part of ADSB messages the checksum and it needs to match the message being sent to pass into skyview. There is a very very small chance that a message will pass the checksum and not be a real ADSB message.

And if a signal is received but was not able to be decoded, for whatever reason, is that NOT shown or counted in the message count?

The undecoded messages (messages that fail the checksum) are counted internally in dump1090 but not in the message count in Skyview. It will not be seen in Skyview.

There is a lot of online information about ADSB checksums if you want to know more.


#13

Thanks David, it all helps in analysing the data provided in PiAware