Feedback on any improvements


#1

Hello all.
I’m feeling pretty good about my antenna setup, but I would like some feedback on if there is anything I can do better. Below are my stats from the last 2 hours. I’m planing on raising the antenna up to get better coverage in the coming months. It’s a long term project…adding a better tower for this and other antennas. Is there anything that can be done to reduce the bad message count? Signal power looking ok?
In the past, I’ve had issues with power supplies and USB connection errors, but I believe those are now resolved.


Statistics: Sat May 23 11:31:11 2015 EDT - Sat May 23 12:31:11 2015 EDT
Local receiver:
  65925 sample blocks processed
  0 sample blocks dropped
  0 Mode A/C messages received
  87868276 Mode-S message preambles received
    55601052 with bad message format or invalid CRC
    30488152 with unrecognized ICAO address
    1682405 accepted with correct CRC
    96667 accepted with 1-bit error repaired
  -4.8 dBFS mean signal power
  -0.6 dBFS peak signal power
  459315 messages with signal power above -3dBFS
Messages from network clients:
  0 Mode A/C messages received
  347 Mode S messages received
    0 with bad message format or invalid CRC
    0 with unrecognized ICAO address
    347 accepted with correct CRC
    0 accepted with 1-bit error repaired
1779419 total usable messages
14 surface position messages received
75923 airborne position messages received
73770 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
104 global CPR attempts with insufficient data
1939 local CPR attempts with valid positions
  1850 aircraft-relative positions
  89 receiver-relative positions
228 local CPR attempts that did not produce useful positions
  214 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
567 unique aircraft tracks
158 aircraft tracks where only one message was seen
CPU load: 49.3%
  1486985 ms for demodulation
  233585 ms for reading from USB
  52687 ms for network input and background tasks


Statistics: Sat May 23 12:31:11 2015 EDT - Sat May 23 13:31:11 2015 EDT
Local receiver:
  65924 sample blocks processed
  0 sample blocks dropped
  0 Mode A/C messages received
  87060454 Mode-S message preambles received
    55049254 with bad message format or invalid CRC
    30192877 with unrecognized ICAO address
    1725505 accepted with correct CRC
    92818 accepted with 1-bit error repaired
  -4.6 dBFS mean signal power
  -0.4 dBFS peak signal power
  540815 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
1818323 total usable messages
18 surface position messages received
66862 airborne position messages received
64971 global CPR attempts with valid positions
1 global CPR attempts with bad data
  0 global CPR attempts that failed the range check
  1 global CPR attempts that failed the speed check
91 global CPR attempts with insufficient data
1726 local CPR attempts with valid positions
  1653 aircraft-relative positions
  73 receiver-relative positions
182 local CPR attempts that did not produce useful positions
  164 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
501 unique aircraft tracks
184 aircraft tracks where only one message was seen
CPU load: 49.2%
  1486198 ms for demodulation
  232905 ms for reading from USB
  53294 ms for network input and background tasks


#2

The number of signals received with levels above -3 db as compared to the number of usable signals is running, in your case, 25 to 30%. Some have suggested lowering this ratio to 1 to 2%. For me, I’m happy with less than 10%. This can be done by lowering the gain setting in dump1090.

What is your present gain setting, MAX or AGC?

If you make any changes, make them small and observe before making more.
…Tom


#3

Ah, ok.
Today I reinstalled a VBFZ-1065-S+ filter. It got removed after I installed the perfect vision amp a month ago (I ordered the wrong cable to use both). With the amp only, I found a gain setting of 30 to yield the highest positions per second. After I put the amp back in, it appeared that the “max” was the setting that yielded the highest positions per second. The highest positions per second was determined by watching the web interface, then changing the gain setting and restarting dump1090-mut. I then watched to see if it appeared better or worse. It was very subjective.

To clarify…
Stats with “messages with signal power above -3dBFS”: These are overpowering signals, so the receiver ends up missing a % of data, correct? The solution is to lower the gain?

Update: Just tried using AGC. If using it, it sets it a 0 dB. (Why? Does this mean there is a strong signal outside of the targeted 1090mhz?)
Going to give it a go back at 30.


#4

The way I understand it there’s three parts to the tuner each are affected by the MAX, AGC or fixed gain setting differently. AGC stands for automatic gain control, but I’m sure you knew that. Just because the dump1090 log says it is set to zero doesn’t mean it stays at that level. You’ll have to search around a bit to find some more info on the subject. I’m not an authority.

…Tom


#5

It’s just a misleading message - the manual gain setting is not used when AGC is enabled so it gets logged as 0.


#6

This thread does a good job of explaining.

http://discussions.flightaware.com/ads-b-flight-tracking-f21/actual-gain-when-gain-10-t26976.html

…Tom