FlightAware Discussions

For Beginners - How to Set / Change Gain

Yes, you used the correct case.

Whenever you want to check if you have used correct method and the gain has actually set to the desired value, give following command and read the LAST line of output. It will show what gain value is actually set.

sudo systemctl status dump1090-fa -l
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  1. The dongle gain can only be set to a value between 0 and 49.6
  2. The dongle does NOT accept any negative (-) value of gain.
  3. The gain value -10 is a special number. It does NOT sets gain to -10 . It SWITCHES dongle into AGC mode (Automatic Gain Control mode). In this mode the dongl dynamically adjusts gain according to received signal strength.

The -gain 30 given in the “How To” was an example only, and did not mean you adjust your dongle to it. The gain value to be used varies over a wide range, depending on antenna, location, dongle, amplifier etc. The optimum value for any setup is to be determined by trial and error i.e. try different values of gain and watch performance for each value of gain.

For your setup with 1/4 wave ground plane antenna indoors, the best is to keep it at the default setting of AGC (i.e. at --gain -10)

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Is there any case where auto gain mode is better than setting it manually?
I am in area with lot interference. I have a blue pro stick plus with FA antenna and external filter as well.

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It leads to gain value of around 55, which is higher than anything you can set directly (a bug, if you like), so if you need or want the highest possible gain value, it is the right choice.

AGC would work with a TV signal which is constantly transmitted, but does not with the many short and different ads-b signals.

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What gain are you at currently?

If you have really strong transmissions i can imagine that the ProStick is not performing well even with a filter. (External LNAs are usually better at handling strong interfering signals than the ProStick)

Anyway if you are blocked by houses all around and the antenna is not above them then there is little you can do.

Currently I am at 48 and definitely blocked by lot buildings.

Most likely you won’t get good range anyway because of the buildings.
It might be beneficial to reduce gain quite a bit further if you want to receive all the close-in signals.

See this thread for some advice on the topic: Thoughts on optimizing gain
(the first post of the linked thread is some more explanation on the topic)

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Thanks, one of my feeder is at 18%, will try optimizing and lowering it

I followed the guidelines in the mentioned thread(s) to reduce the gain but what should be the target maximum RSSI? I am under a flight path for Boston Logan inbound so there are jets coming over around 15,000 ft at an offset of less than a mile. I was losing track of these so I changed from -10 AGC and ended up at 30 to get the max RSSI to about -3 (range is now down to -39 for distant signals). Should I go higher than -3 for the strongest? My “Percentage of strong messages” is about 0.2 at this point but I am definitely seeing more local traffic, including takeoffs and landings at the local airport (KFIT, about 3 miles away as the crow-without-ADS-B flies but not quite line of sight).

I’d go higher, maybe -1.5.
Basically you increase gain until the local traffic gets worse and then you go back down one or two steps.

Ok, it does look like the local traffic is about -1.5 and the overhead jets go up to -5 or so. I’m getting over 80 flights, some close to 200 mi away so I’m happy and will leave it like this for a while. I’m running a RPi 3 B with the Pro Stick Plus and the FA green antenna in the peak of my attic.

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If you want all the local traffic you will have to sacrifice some range.
This can be especially true for an antenna in the attic as the attenuation differs by direction.

Yup, and that’s ok. Seems to be enough coverage in general, so the local contribution is a bonus.

Thanks.
Before reading this how to, I did not realize that there are 2 different methods, one for piaware sd card image, and other for raspbian image with package install.

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For me as beginner this explanation was very helpful. Thanks.

Also how to check the optimation on Thoughts on optimizing gain was interesting.

But for impatient people waiting after each change at least 5 minutes are quite long. So I found a workaround, not very exact, quick and dirty.

First, check the actual 1090 data, for example http://your-adsb-ip/dump1090/ or http://your-adsb-ip/tar1090/ and note the number of planes.
Then change the values, reload the page and re-check the number of planes.
The difference is a good indice if a optimation is necessesary and if you move in the right direction.
In my case with -10 gain I saw around 80 planes, with 30 gain there were only 4 planes left. Also gain 20, 10 and 0 marked less planes on the 1090 page. With -10 it was okay again.
So no optimation is necessary.
It looks that with a wrong optimation the results are even worse, so it is not necessary for all installations.

That’s just for the rough adjustment.
After that you just check the percentage the next day and adjust one step.

What is the percentage displayed for you at gain of -10?

That’s explainable, because 20, 10 and 0 means usually less planes as it’s less than 30

-10 in reality is higher than 49.6 which marks the maximum gain to be set manually.
Means, you need to step from -10 to 49.6 or lower to reduce gain, not to improve it.

After one week, the command
awk “$(cat /run/dump1090*/stats.json| grep total | sed ‘s/.accepted":[([0-9]).strong_signals":([0-9]).*/BEGIN {printf “\nPercentage of strong messages: %.3f \n” , \2 * 100 / \1}/’)”
marks
Percentage of strong messages: 0.274

My station is far away from a airport with a lot of traffic.
10 km away is Bern-Belp (LSZB) with low traffic.
1 km from my station is the hospital where ambulance-helicopters come to bring and get patients.
You can see my traffic on https://de.flightaware.com/adsb/stats/user/ChristopherRobert .

Should I try to optimize gain, or does it look like this will be worse?
If I should change, which setting do you propose?

Thanks, best regards from Switzerland
Christopher

No need to reduce gain with that percentage.
As written in the “Thoughts on gain” thread i’d normally increase gain with below 1 percent and reduce gain for values above 5 percent.
But as you can’t increase gain, no need to change anything.

What antenna are you using?
If you have magnetic base antenna, i’d recommend this thread: How to improve performance of whip antenna of DVB-T

Thanks.

I am using a set:

For beginners like me its quite good, no need to optimize, no too expensiv (90 Euros) but no cheap bullshit, and the support is very good.
I had the problem when I changed the place of the antenna while the system was running I feeled tingly that here was a static or inductive tension on the base of the antenna.
After a few hours the owner of the shop gave a very practical response to avoid these problems.

As I am living in a penthouse of a flat, I have mounted the antenna on the corner of the flat roof, there is also no room for optimation.
Next step will be to install a outdoor weather station and to put it online with the raspi.

If you ever feel like experimenting, try the blue FA ProStick Plus or the green Airnav Flightstick.
Both have an LNA and SAW filter builtin, one has the filter first and the other has the LNA first.

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