FlightAware Discussions

For Beginners - How to Set / Change Gain

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

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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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So I am feeling pretty dumb here… How do I adjust the gain in dump978-fa? I have replicated what works for dump1090-fa, and that’s not working on dump978-fa.

Are there any differences in tuning gain for UAT I should be aware of?

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@dmandrell
Please see this post:

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The UAT demodulator doesn’t like having too much gain (more so than the 1090MHZ demodulator), there is a more pronounced donut effect.

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What does this mean? I may have fallen into the donut!

What would be a good gain value to start at? And then a best guess direction to head?(more gain, less gain?)

The donut effect is where you have the gain set too high, and you can’t hear nearby aircraft (the hole in the donut) because they’re overloading the receiver.

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for 978 gain what config takes priority? the above one or this one?

As you are using Piaware sd card image, changing gain by editing file /etc/default/dump978-fa will be lost at reboot. This is noted in the file itself:

pi@piaware:~ $ cat /etc/default/dump978-fa
# Generated automatically by /usr/lib/piaware-support/generate-receiver-config
# This file will be overwritten on reboot.

For Piaware sd card image, use this command to set/change gain:

sudo piaware-config uat-sdr-gain xx

.

Only if you have Raspbian image with dump978-fa package install, changes made manually in file /etc/default/dump978-fa will persist.

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I have the Raspian Buster image (Sep 2019). And my brain got turned around when I read this post. Thank you!

@abcd567 - Thank you for mentioning -10 is special for turning on AGC!

Now it all makes sense and I’ve got my system tuned up nicely. Had a big hole around my location once I moved my antenna to the roof. Signals were way too strong at my local airport so aircraft there were dark until they got out far enough to not oversaturate the receiver on the stock -10 setting.

I’ve been backing off gain, now down to 22.9 dB, and can see aircraft wake up, taxi, and takeoff at my local airport, and out past the 200nm ring on the local PiAware display. Still adjusting but that one bit of information was crucial to understanding how to interpret and use those gain values.

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@SFRobert
Just one more clarification. In my post to which you have replied, I have mentioned:

The last sentence above is wrong. The gain -10 does NOT dynamically adjust gain according to signal strength (as it is supposed to do). Due to a glitch, it actually sets gain to about 55dB, which is 5dB higher than the manually setable max gain of 49.6dB.

The gain -10 (i.e. 55dB) is good for locations not very close to an airport, or where planes dont fly very low overhead, or with a simple indoor antenna like the mag-mount whip of a stock DVB-T.

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Thank you for the clarification! Even being slightly wrong, your post was still a great help. I just assumed (wrongly) lots of planes/messages far away were making it keep the gain high - at somewhere close to 55.

At 55 dB fixed, -10 doesn’t work right for me anyway. It seems I have a fairly wide range of acceptable gains just as long as it isn’t set too high. I was surprised I even could see a Canadian jet into Mexico. But next step is more refined looking at the stats to see what they say.

Just being able to fix the hole in the donut was great. It’s fascinating to watch the activity at the local airport. I didn’t want to lose that. Now I don’t have to.

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For the RTL SDR, I have been using the following list of gain settings: -10, 49.6, 48, 44.5, 43.9, 43.4, 42.1, 40.2, 38.6, 37.2, 36.4, 33.8, 32.8, 29.7, 28, 25.4, 22.9, 20.7

Would anyone know where I can find the complete listing, extending also below 20.7?