FlightAware Discussions

Thoughts on optimizing gain

That’s fairly conclusive :slightly_smiling_face:

Is that with LNA or without?
And the airspy is that without LNA as well?

Both with uputronics 1090 mhz ceramic filtered preamp

One can definitely notice by the gain numbers that your antenna is quite obstructed :slight_smile:

Today i took the free time and played around with the gain.
I switched from 49.6 back to max/agc which did not change much except the number of messages > 3dB which increased again up to 8-12% in average

Then i changed the setting to a lower value of 42.1 and let it run for a while

Except the reduced number of messages >3, signal level and the CPU usage of ADS-B nothing seem to have changed.
The number of aircraft is the same, number of tracks seen etc is all the same/similar to previous hours/days with similar traffic. The range also did not change so far

I am using as you might know already the blue FA pro plus stick with a modified indoor antenna on a can.
Does this mean the changes does not have that much impact because i am not using an “optimal” physical setup? Or is the change between max and 42.1 that low?

EDIT: Just have seen this thread. seem to be that the values of 40 and up did not change a lot on the pro plus stick.

The change between max and 42.1 is actually quite large. It’s possible however, that if your antenna is blocked by obstacles or terrain, you are already receiving everything inside that range, so increasing the gain isn’t increasing the signals significantly - any increase from getting marginal signals could be easily offset by losses from oversaturating the strong signals.

I take it from your previous post that you are using the mag-mount antenna cut down to the correct length? If so, then you can likely increase your receiver performance a lot by swapping it for a simple home made antenna (or one of the pre-made options you can get).

See one of abcd567’s many threads on building and optimising antennas - the spider based on a chassis socket is a good place to start:

And some graphs showing it.

Until 0900 the gain was set to 49.6, between 0900 and 1300 it was at max/-10 and changed to 42.1 since 1300



As said before I would leave it at 49.6. :innocent:
Just out of curiosity regarding the amount of messages compared to mine, what is in your /etc/default/dump1090-fa? (I never get more than > 800 msg, unless I enable "Mode-AC.)

So can you post the output of cat /etc/default/dump1090-fa, please?

Sure, here we go. Still with setting the gain to 42.1

# Generated automatically by /usr/lib/piaware-support/generate-receiver-config
# This file will be overwritten on reboot.
ENABLED=yes
DECODER_OPTIONS="--max-range 360"
NET_OPTIONS="--net --net-heartbeat 60 --net-ro-size 1000 --net-ro-interval 1 --net-http-port 0 --net-ri-port 0 --net-ro-port 30002 --net-sbs-port 30003 --net-bi-port 30004,30104"
JSON_OPTIONS="--json-location-accuracy 2"
RECEIVER_OPTIONS="--net-bo-port 30005 --fix --device-index 0 --gain 42.1 --ppm 0"

From the number of messages it’s almost all the time shown as factor 10 compared to the aircrafts seen. Sometimes more, sometimes less. No idea if this is good or bad.

I’ve had up to 1400 using the rtl-sdr v3 stick with LNA.
And with the Flightaware ProStick+ i believe my maximum message rate was 1200.

It’s not unusual for Europe.
Seems your receiver can’t quite see in all directions, normally you should get lots of messages/s being in the Netherlands.
Might also be a problem with interference.

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Can you add a text at the end of the run to point to the location address of the plot?

rtl-sdr stick with the rtl-sdr LNA gives me a peak message rate of about 1780 messages/s. I’ve never seen it crack 1800 however.

What script do you want that adding to?

I am using the unmodified one.
$ wget -q -O plot.sh https://raw.githubusercontent.com/wiedehopf/adsb-wiki/master/caius_scatter_plot.sh

the max amount of messages i’ve seen since the device is running was 1150 today where it was busy in my area west of Frankfurt Airport.
Normally i am not getting > 1100

Right.
It seems to me (when looking on FlightRadar24) the airspace around FRA/EDDF is a bit more busy ATM than where I live (GRQ/EHGG - in the north of the Netherlands).
Besides I have some high-rise buildings blocking my view to the north / northwest.

I’ve added a modification to give the output:

Graph available at http://192.168.0.201/dump1090-fa/data/graph.png

When @wiedehopf sees it he can update the script on github. The ip address will be for your own pi.

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Thanks. I kept scrolling trough this topic for that address…

Yes, the buildings, trees and even other frequency can be the reason. While i am living in a small village with not that much “noise” i can reach almost the range which is geographically possible. A friend of mine in the middle of Vienna is always struggling with the range due to environment.

In your airspace there’s much traffic, but it depends on the range you see.
Did you check http://www.heywhatsthat.com/ for your max range?

A little bit hard to understand but it give you a good idea what is possible as maximum.

Edit: Looking on your profile you already have a good range. So it seem to be less traffic.

3 nmi from his position someone has 7 times the position count in the FA stats.

Either it’s terrain or his setup is just not that good.
(might be interference related)

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I was looking at his range rings only in the profile.