dump1090-mutability - sample blocks dropped


#1

I have two RPI receivers with identical software configurations but different radio/antenna setups. One unit only rarely sees “sample blocks dropped” in /var/log/dump1090-mutability.log. The other has a huge number of blocks dropped, varying with time.

The one with the dropped blocks has a 12 element CoCo with an in-line amplifier on a 820T2 vs. an 8 element CoCo and no amp on a 820T. The 12 element antenna is about 5 ft. higher than the 8. Both are set for AGC.

Am I overdriving the RF on the unit with the dropped blocks? Even with the dropped blocks it is receiving about 30% more positions than the other one. Should I consider a filter or reduce the input levels?

Any thoughts are appreciated.

-Larry

Log from the dropping until:
Statistics: Sat Apr 11 11:56:15 2015 UTC - Sat Apr 11 12:56:15 2015 UTC
Local receiver:
55384 sample blocks processed
10533 sample blocks dropped
0 Mode A/C messages received
63448183 Mode-S message preambles received
39393068 with bad message format or invalid CRC
21700224 with unrecognized ICAO address
2219814 accepted with correct CRC
135077 accepted with 1-bit error repaired
-7.5 dBFS mean signal power
-0.6 dBFS peak signal power
237467 messages with signal power above -3dBFS
Messages from network clients:
0 Mode A/C messages received
0 Mode S messages received
0 with bad message format or invalid CRC
0 with unrecognized ICAO address
0 accepted with correct CRC
0 accepted with 1-bit error repaired
2354891 total usable messages
19 surface position messages received
82650 airborne position messages received
78520 global CPR attempts with valid positions
0 global CPR attempts with bad data
0 global CPR attempts that failed the range check
0 global CPR attempts that failed the speed check
107 global CPR attempts with insufficient data
3584 local CPR attempts with valid positions
3523 aircraft-relative positions
61 receiver-relative positions
565 local CPR attempts that did not produce useful positions
546 local CPR attempts that failed the range check
0 local CPR attempts that failed the speed check
0 CPR messages that look like transponder failures filtered
497 unique aircraft tracks
116 aircraft tracks where only one message was seen
CPU load: 47.9%
1450153 ms for demodulation
214431 ms for reading from USB
58648 ms for network input and background tasks

History of dropped samples over time:

0 sample blocks dropped
0 sample blocks dropped
0 sample blocks dropped
0 sample blocks dropped
817 sample blocks dropped
7398 sample blocks dropped
10257 sample blocks dropped
10497 sample blocks dropped
10604 sample blocks dropped
9298 sample blocks dropped
10512 sample blocks dropped
10422 sample blocks dropped
10893 sample blocks dropped
11959 sample blocks dropped
12586 sample blocks dropped
12687 sample blocks dropped
12770 sample blocks dropped
11666 sample blocks dropped
11695 sample blocks dropped
10045 sample blocks dropped
8638 sample blocks dropped
5174 sample blocks dropped
0 sample blocks dropped
0 sample blocks dropped
0 sample blocks dropped
0 sample blocks dropped
0 sample blocks dropped
0 sample blocks dropped
4571 sample blocks dropped
10139 sample blocks dropped
12446 sample blocks dropped
12316 sample blocks dropped
12247 sample blocks dropped
10980 sample blocks dropped
11438 sample blocks dropped
11749 sample blocks dropped
11964 sample blocks dropped
12001 sample blocks dropped
12345 sample blocks dropped
12580 sample blocks dropped
12752 sample blocks dropped
10852 sample blocks dropped
10920 sample blocks dropped
10324 sample blocks dropped
8891 sample blocks dropped
4355 sample blocks dropped
0 sample blocks dropped
0 sample blocks dropped
0 sample blocks dropped
0 sample blocks dropped
0 sample blocks dropped
0 sample blocks dropped
5509 sample blocks dropped
10295 sample blocks dropped
12068 sample blocks dropped
12437 sample blocks dropped
11323 sample blocks dropped
10446 sample blocks dropped
10775 sample blocks dropped
12056 sample blocks dropped
13143 sample blocks dropped
12705 sample blocks dropped
13012 sample blocks dropped
12574 sample blocks dropped
13868 sample blocks dropped
11741 sample blocks dropped
10975 sample blocks dropped
9902 sample blocks dropped
9517 sample blocks dropped
3875 sample blocks dropped
0 sample blocks dropped
0 sample blocks dropped
0 sample blocks dropped
0 sample blocks dropped
0 sample blocks dropped
0 sample blocks dropped
5188 sample blocks dropped
9987 sample blocks dropped
11936 sample blocks dropped
12081 sample blocks dropped
12075 sample blocks dropped
11544 sample blocks dropped
11082 sample blocks dropped
11433 sample blocks dropped
13009 sample blocks dropped
11822 sample blocks dropped
13076 sample blocks dropped
12334 sample blocks dropped
13146 sample blocks dropped
11629 sample blocks dropped
11695 sample blocks dropped
10770 sample blocks dropped
10233 sample blocks dropped
7111 sample blocks dropped
94 sample blocks dropped
0 sample blocks dropped
0 sample blocks dropped
0 sample blocks dropped
0 sample blocks dropped
0 sample blocks dropped
3828 sample blocks dropped
10182 sample blocks dropped
12619 sample blocks dropped
12585 sample blocks dropped
12567 sample blocks dropped
11294 sample blocks dropped
11905 sample blocks dropped
11920 sample blocks dropped
13735 sample blocks dropped
13252 sample blocks dropped
14857 sample blocks dropped
13223 sample blocks dropped
14549 sample blocks dropped
13157 sample blocks dropped
11812 sample blocks dropped
11554 sample blocks dropped
10711 sample blocks dropped
8131 sample blocks dropped
475 sample blocks dropped
0 sample blocks dropped
0 sample blocks dropped
0 sample blocks dropped
0 sample blocks dropped
0 sample blocks dropped
4740 sample blocks dropped
9892 sample blocks dropped
11457 sample blocks dropped
11537 sample blocks dropped
10894 sample blocks dropped
11499 sample blocks dropped
11860 sample blocks dropped
11621 sample blocks dropped
13113 sample blocks dropped
12607 sample blocks dropped
13285 sample blocks dropped
12012 sample blocks dropped
12568 sample blocks dropped
10912 sample blocks dropped
12287 sample blocks dropped
9968 sample blocks dropped
10263 sample blocks dropped
8289 sample blocks dropped
222 sample blocks dropped
0 sample blocks dropped
15 sample blocks dropped
0 sample blocks dropped
0 sample blocks dropped
0 sample blocks dropped
3408 sample blocks dropped
9047 sample blocks dropped
10533 sample blocks dropped


#2

Dropping samples is a symptom of CPU overload more than anything. What else is the Pi running?

That said, dump1090 has a tendency to take more CPU when the input is over amplified (not to the extent of dropping samples, but it won’t help). The ‘signal power over -3dB’ is the stat to watch. Ideally you want this at no more than 1-2% of total usable messages. So I’d try dropping the gain a bit and see if that helps. With an amplified antenna, max/AGC is usually too high. I run mine at 40ish dB gain.


#3

Thanks for the response. Another difference is that the one with the dropped blocks is running the PiAware Debian package add-on to the basic Raspberry and the other is using the PiAware image.

They are both running the PlaneFinder client as well.

I’ll cut the gain down to 40 and see how it goes.

Any suggestions on monitoring CPU usage?


#4

If you are still using the nodejs planefinder client, that is very CPU heavy for a raspberry pi. They have just released a much lighter client which should help quite a bit: forum.planefinder.net/threads/ne … hread.253/

There are a few options for system monitoring on the raspberry pi - RPImonitor is one. I have monitorix installed on my pis, but there are quite a few alternatives. Both of those are lightweight and don’t have much overhead.


#5

@caius - Good catch. I upgraded the PF client on all of the devices except the one that has been giving me sample block dropped. I just updated it on that device as well.