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Thread: Automated Installation of Dump1090-Mutability, Data Feeders, and Performance Graphs

  1. #71
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    Quote Originally Posted by abcd567 View Post
    FOR WIRED LAN/SSH TO WORK IN RASPBIAN
    The SSH no more works by default in Raspbian releases since end of 2016. Creating a blank file named ssh or ssh.txt in /boot sector of microSD card enables SSH.

    To enable SSH in headless operation (i.e. no GUI, no hdmi/monitor, no mouse & no keyboard), follow these steps:

    (1) Remove microSD card from Pi and insert into a card reader and insert card reader into Laptop/ Desktop (on which you wrote the latest Raspbian image).

    (2) Open command prompt console of desktop/laptop, and give command

    echo >E:\ssh

    Note: Instead of letter E, use drive letter of your microSD card.

    The above command will create a file named ssh in /boot directory of your microSD card.

    (3) Reinsert the microSD card in RPi and power up. SSH will start working.

    Attachment 8566
    Much easier than connecting monitor+keyboard, thanks!

  2. #72
    Captain abcd567's Avatar
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    Step 2 in my previous post is open command prompt and give command echo > E:\ssh.

    An alternate to this step is to double click on drive E in windows explorer. This will open a folder showing all files in /boot folder of microSD card. Right click, and select New text document. Rename the new text document ssh (or ssh.txt if file extension is shown).

    Note: Replace letter E in my post by actual drive letter of microSD card as shown in your Windows Explorer.

  3. #73
    Captain abcd567's Avatar
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    ABOUT AGC

    Following are comments by Oliver Jowett (obj), who is the author of dump1090-mutability:

    Turning on the tuner AGC sets a fixed gain for one gain stage and hands control of the other stages over to the AGC.

    The AGC works by measuring the amplified signal power over a period and using that in a feedback loop to control the gain to try to get an amplified signal power that is somewhere in the middle of the usable range - i.e. if the amplified power is too low, it increases the gain, and vice versa. The AGC is designed for the dongle's original purpose - receiving digital TV signals. For a digital TV signal you are receiving a continuous signal from a single transmitter so this works fine.

    ADS-B signals are bursts that are much shorter than the measurement period, and they originate from many transmitters of different power at different ranges. So the AGC measurement is basically useless and in practice the AGC sees it as a very weak signal and ends up setting the gain as high as it will go.

    Due to a quirk in librtlsdr, the combination of the manually set gain stage + the AGC-controlled gain stages results in a total gain that is higher than what librtlsdr will let you set directly.

  4. #74
    Captain abcd567's Avatar
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    Dump1090-mutability: About gain -10

    Question: What does gain -10 actually mean?
    Answer: Enable the tuner AGC.

    Question: So that is the same as having GAIN="agc" in /etc/default/dump1090-mutability ??
    Answer: Yes, if you look at the init script you will see that AGC is translated to -10 and if you look at the dump1090 source then you will see that -10 turns on AGC.

    -10 is a special value meaning "turn on AGC" (for ADS-B, the AGC doesn't actually give auto-gain, just a high gain. Usually AGC will behave like "more gain than max")


    -10 and agc are identical, they both end up passing "--gain -10" to dump1090, see the /etc/init.d/dump1090-mutability script:
    Code:
    pi@raspberrypi:~ $ cat /etc/init.d/dump1090-mutability
    #!/bin/sh
    ### BEGIN INIT INFO
    .............
    .............
    case "x$GAIN" in
     x|xmax) ;;
     xagc) ARGS="$ARGS --gain -10" ;;
     *) ARGS="$ARGS --gain $GAIN" ;;
    esac
    .............
    .............

    For regular gains, you want a positive value in the 0..50 range (nominally in dB). It will pick the closest gain step to the value you give. If you specify any negative number (other than -10), then the closest gain is 0dB: minimum gain!

    AVAILABLE GAIN VALUES:

    pi@raspberrypi:~ $ sudo systemctl stop dump1090-mutability
    pi@raspberrypi:~ $ rtl_test
    Found 1 device(s):
    0: Realtek, RTL2838UHIDIR, SN: 00000001

    Using device 0: Generic RTL2832U OEM
    Found Rafael Micro R820T tuner
    Supported gain values (29): 0.0 0.9 1.4 2.7 3.7 7.7 8.7 12.5 14.4 15.7 1 20.7 22.9 25.4 28.0 29.7 32.8 33.8 36.4 37.2 38.6 40.2 42.1 43.4 43.9 4 49.6
    Sampling at 2048000 S/s.

    Info: This tool will continuously read from the device, and report if
    samples get lost. If you observe no further output, everything is fine.

    Reading samples in async mode...
    lost at least 16 bytes
    ^CSignal caught, exiting!

    User cancel, exiting...
    Samples per million lost (minimum): 0
    pi@raspberrypi:~ $

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