Dump1090-fa options default values

Is there a way for me to have dump1090 spit out a list of the values its using for all of its options/parameters? In particular I’m interested in the values its using for its adaptive burst mode. I live near a large airport, which means I have a near/far issue with the close aircraft blinding me to planes further out. I’d like to try to fine tune the burst parameters to see if a faster adaptive response will help.

I can see the list of parameters using “dump1090-fa --help”, but not the default values.

You can find the config file which installs during setup on Github:

# dump1090-fa configuration
# This is sourced by /usr/share/dump1090-fa/start-dump1090-fa as a
# shellscript fragment.

# dump1090-fa won't automatically start unless ENABLED=yes

# SDR device type. Use "none" for a net-only configuration
# serial number or device index of device to use (only needed if there is more than one SDR connected)
# Initial receiver gain, in dB. If adaptive gain is enabled (see below) the actual gain
# may change over time

# Adjust gain to try to achieve optimal dynamic range / noise floor?
# Target dynamic range in dB (leave blank to autoselect based on SDR type)
# Reduce gain when loud message bursts from nearby aircraft are seen?
# Gain range to allow when changing gain, in dB (empty = no limit)

# Turn on options to reduce load on slower CPUs, at the expense of slightly worse decoder performance.
# Setting "auto" will enable these options only if the CPU appears to be a slow CPU (currently this
# means armv6 only, e.g. Pi Zero)
# Local wisdom file used to select DSP implementations; uses built-in ranking if the file is missing

# Correct CRC errors where possible

# Receiver location, used for some types of position decoding. Provide the location as
# signed decimal degrees. If not given here, dump1090 will also try to read a receiver
# location from /var/cache/piaware/location.env (written automatically by PiAware, if installed)
# Maximum range, in NM. Positions more distant than this are ignored. No limit if not set.

# Network ports to listen on for connections

# Accuracy of location written to JSON output

# Additional options can be added here:

# If OVERRIDE_OPTIONS is set, only those options are used; all other options
# in this config file are ignored.

# This is a marker to make it easier for scripts to identify a v6-style config file

The documentation for the various options can be found on Github.

Yes - I’ve seen that doc. But it does not show the values for the parameters. It doesn’t even show the full list of adaptive gain or burst parameters, which you only see if you issue the “dump1090-fa --help” command. I’m wanting to do some tuning of those parameters which are less commonly used.

These parameters are listed in the help command:

  Adaptive gain

–adaptive-burst Adjust gain for too-loud message bursts
–adaptive-burst-change-delay s Set delay after changing gain before
resuming burst control (seconds)
–adaptive-burst-alpha a Set burst rate smoothing factor
(0…1, smaller=more smoothing)
–adaptive-burst-loud-rate r Set burst rate for gain decrease
–adaptive-burst-loud-runlength l Set burst runlength for gain decrease
–adaptive-burst-quiet-rate r Set burst rate for gain increase
–adaptive-burst-quiet-runlength l Set burst runlength for gain increase

This is the parameter listing, but notice no default values are listed.

Yes I edit this file to make adjustments to the adaptive burst gain range. But it does not contain a full list of the available parameters you can see in the help command.

@obj might have answers to your questions…

Thanks - I’ve sent @obj a message. I think these lower level parameters are hard-coded into dump1090, and they’re only changed if the user specifies a different value. So they don’t normally appear in the /etc/default file.

I found the answer - should have thought to look at the source code for dump1090-fa fork. The values are in the source listing:

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Stefan, did you figure out what “loud-rate” and “loud-runlength” do?

I saw the default values below …


Is “loud-runlength” the number of seconds the gain is reduced by the “loud-rate” dB? This would mean the defaults are set to reduce the gain by 5.0 dB for 10 seconds.

If I’m near a runway and never want to miss an ADS-B message from a landing aircraft, what burst settings should I use so the gain is automatically adjusted down before the landing aircraft ADS-B signal gets too strong and is ignored?

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I’d like the option to set the “loud dBFS” trip level and to set the temporary GAIN value the receiver uses until the trip level is no longer exceeded. For example …

GAIN is running at 48 but an aircraft on final has a -7dBFS ABS-B signal and the trip level was -10 so the GAIN shifts down to 24 until there are no more aircraft at or below -10dBFS.

No, it is the number of seconds that the smoothed rate of loud messages needs to exceed the threshold before gain is reduced.

This is not possible with the burst-mode implementation.

@obj, what’s the definition of “loud” - anything less than -3dBFS?

Can I change the definition of “loud”?

Can I change how much the gain is reduced? I believe there is a receiver dynamic range setting that’s defaulted to “30” - would reducing this to 20 cause the loud gain change to be more significant?

“Loud” is “undecoded bursts of >-3dBFS with a length matching a potential 56/112-bit message”. You cannot change this.

No, it decreases one gain step at a time until the loud rate stops exceeding the threshold.

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