FlightAware Discussions

For Beginners - How to Set / Change Gain

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?

Mine says 0.0 0.9 1.4 2.7 3.7 7.7 8.7 12.5 14.4 15.7 16.6 19.7 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 44.5 48.0 49.6

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pi@piaware:~ $ sudo systemctl stop piaware dump1090-fa dump978-fa  

pi@piaware:~ $ rtl_test -t 

Found 2 device(s):
  0:  Realtek, RTL2838UHIDIR, SN: 00001090
  1:  Generic, RTL2832UFA, SN: 00000978

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 16.6 19.7 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 44.5 48.0 49.6
[R82XX] PLL not locked!
Sampling at 2048000 S/s.
No E4000 tuner found, aborting.


pi@piaware:~ $ sudo systemctl restart piaware dump1090-fa dump978-fa  

 

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@abcd567

Sorry for troubling you again. Tried to change my gain ( using SDR-RTL Dongle). After using your sudo nano /etc/default/dump1090-fa command I noticed a small difference.
RECEIVER_OPTIONS="–device-index 0 --gain -10 --ppm 0"

DECODER_OPTIONS="–max-range 360 --fix"

NET_OPTIONS="–net --net-heartbeat 60 --net-ro-size 1300 --net-ro-interval 0.2 $

JSON_OPTIONS="–json-location-accuracy 1"

In your example the max-range 360 does not show --fix.

If I want to change my gain to 43.9 do I have to delete --fix as well?

Thanks for your time and advice

You couldn’t have just tried?
After all you know how to change it back to the old state.
It’s a completely unrelated option.

I did try it. Changed gain to 30 and after that I did not see any plane! That is why I asked you.

Why did you change to 30 if you want to try 43.9?

Thoughts on optimizing gain

It’s very likely btw with your SDR that only the maximum gain (-10) makes sense.