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