FlightAware Discussions

Trying to understand message rates

Good afternoon,

I am trying to understand why my message rate dropped. Since some time I am using an Airspy mini and my messages rate went up to 1800+
The last few days, even today with no clouds at all, the best message rate was 1386, still a little bit more than with my RTL-SDR dongle. But far from the 1800+
I have been reading in all kinds of threads in this forum, but cannot find an understandable answer.

I really hope someone can explain the difference.

I haven’t changed my setup.

Gain 18
Sample rate 12
OPTIONS= -v -f 1 -b


Is your LNA working properly?
Your green area seem to be low
This is mine with active Uputronics and gain set to 19. Have you tried it with this setting as well?

This is my seven day chart where i changed from 18 to 19, but it wasn’t that much impact in message rate

What’s the amount of aircraft you see? Just the message values do not give a picture

Your profile doesn’t show any significant impact:

`thank you for the help.

The number of aircrafts has increased a little bit.

I did try to set gain to 19, but will do it again and see if something will change. First impression, only the weakest signal goes from -30 to -25. The green area just moves the same amount.
From what I see in your graphs the green area stays as wide with gain 18 and 19, just “moved” up.
But it can be that I do not interpreted that correctly
Schermafbeelding 2021-07-18 om 18.46.30

Will figure out if my Uputronics is working properly, but as said did not change anything. Did not disconnect or something.


Show some more graphs.
Could just be a different distribution of aircraft over the area you receive.

Thank you.

here are some more graphs. Hope this will help

From what to what? We need absolute numbers, not relative statements.
For my peaks of 1600 msg/second i need at least 90 aircraft with ADS-B positions.

All below is approx. 20 messages per aircraft which is also shown in the graphs of your instance. Check if these values have been changed as well.

Sorry, did not see your updated reply

here are mine: Not even close to your 1600.

Sorry, did not see your updated reply

No problem

This is just a number on that moment. I think also stations are not 100% comparable.

This is mine, right now:


You see it’s not that far away. I have some closer traffic today based on wind coming from east.

These are the last eight hours. For 1600 messages there were 100 ADS-B positioned AC required:

So one possibility is that there is interference and it got worse.
If you have a blue FA filter, you can try it in front of the uputronics.

Really it’s hard to say why people have different results.

What pi do you have and what threshold do you run for airspy_adsb?
As in the -e value.
It’s explained in the settings file.
Reading will increase knowledge. Well sometimes it takes repeated reading and googling and stuff like that :slight_smile:

#-e: preamble filter sensitivity, values: 0.1 to 11.0 (higher values increase CPU load and can improve detection)

There should be the airspy CPU load in the graphs, increase -e step by step until you get a load of around 80% for that graph

I have forgotten to mention this. Mine is set to “-e 11
ADS-B CPU load is hovering around 80 with a total CPU load of 25 - 28

How is it going for you today? Here it’s pretty busy and these are my values since tonight:

@foxhunter and @wiedehopf

All the help is very much appreciated.
Your githup airspy is bookmarked and do not worry I read it over and over. Did not want to bother you before reading it :slightly_smiling_face:

I will increase the e value

the graphs of today:

But I still do not understand, why the message rate dropped. My settings haven’t changed.

But will do as advised

Your ADS-B CPU utilization can be increased using the “-e” option in the settings of the airspy config file.

I would suggest you start with “-e 10” and leave it for a moment. But don’t expect that it now doubles the ratio :slight_smile:

If you compare your ADS-B aircraft/messages with mine, it’s not that far away.
And again, it could have to do with different approach directions.

Just because your setup doesn’t change, doesn’t mean the weather, interference and air traffic doesn’t change.

All that can affect the message rate.

Say there is a mobile phone tower that overloads the uputronics LNA while it’s transmitting.
Normally it’s not too busy and not sending with a high duty cycle.
Then it gets used more and the duty cycle increase.
Thus your reception suffers in more time slices than before.
Basically your station isn’t as sensitive when that transmitter is on but it’s not on all the time but switches on and off really fast.

There are all kinds of possible explanations.


Thank you very, very much for the explanation. This does make sense and I had never ever thought of that.

In Europe the message rate can also change considerably depending on what responses are being requested by ATC interrogations. I have occasionally seen a sudden drop or increase in message rates that aren’t attributable to any other changes in hardware or software.


Thank you for the additional information. Still trying to understand what is happening, but I have a looooong way to go.


I have been running my system with the new settings for two days. It seems there is hardly a difference with the “old” settings.
Gain 18
Sample rate 12
OPTIONS= -v -f 1 -b

Gain 18
Sample rate 12
OPTIONS= -v -f 1 -b -e 11

Changed -e as @wiedehopf suggested to set CPU Airspy use to 80%, overall CPU use around 25%
Added graphs to show the “small” differences.

My naive question, or ignorance, should I still use the “new” settings or not and what would be the benefit?

The benefit would be a lower/higher messsage rate.

This can also impact your FA stats.

That was my was my question at the beginning of this thread, but the messages rate has hardly increased. 1386->1475

Here my 30 days graphs