FlightAware Discussions

Is This A Sign My Gain Is Set Too High?

I think I may have my gain set too high on two of my setups - I’m guessing the signal level should be more dynamic, like on the left of the screen shot?
The right side looks to be possibly clipping / compressing?

Any input folks?

Screenshot 2021-06-16 at 09-36-12 graphs1090 Performance Graphs

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Why not reducing gain for a day and checking the results?

What device are you using? FA stick or Airspy?
Without beeing an expert it might be bit high

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This is my gain on the indoor receiver with blue Pro Plus stick and the dark blue FA Filter - set to 49.6

And this is the gain of my outdoor device with the Airspy and the Uputronics filtered LNA - gain set to 18

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@PhilDoggo
To give you one more to compare:
Rtl_SDR dongle+ Uputronics
Gain RTL-RTL 49.6

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You need to go that high with the Uputronics? Are you sure it’s working properly?
I’ve attached it to my FA stick which is internal until the Airspy arrived.

Any gain on the FA stick higher than 35 caused a high amount of messages > -3dbFS

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tried different gain settings. But perhaps the Uputronics is not working correctly, but I don’t know how to check it.

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It’s not attached to an FA stick, those have an extra LNA already on board.

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I think we can (and should) compute the RSSI (or SNR) in a smarter way than what we do today. How about building a small curve with the Y axis being the RSSI, and the X axis being the distance? Once a position is known, the ICAO will be used to map the RSSI to a point on the X axis.
The evolution in time could be done with some javascript widget. One can select a point in time and the detailed view will display the RSSI/Distance graph.
More: Imagine the same with a heatmap where the color corresponds to the RSSI. This can help optimizing the gain or the antennas for a specific region or angle.

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You’re absolutely right. Forgetting that…

That’s not so different to what I did with my heatmap script which use rssi to produce coloured plots: Signal Strength Heatmap - #499 by NigelRichardson

I did a quick bodge to produce a bearing/range plot:

And here is a plot of range against rssi with bearing used to colour points (colour bar title is wrong):

It might be more useful to be able to colour the dots by gain on the second one, but that data isn’t collected anywhere at the moment so it’s not as easy to implement.

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Thanks chaps! Nice to see a reference too.

My two setups in questions are…

Uputronics+Mini-Circuits splitter feeding:
Blue FA Stick @ 33.8
RTL-SDR 49.6

I also presume that having too many aircraft in the > -3dBFS region isn’t good?
Should I be trying to get that number down without compromising too much?

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I’ve reduced my gain now and I think it’s all looking healthier :+1: :+1:

I adjust gain to maximize the spread between the weakest and peak signal level. That seems to work better for me than setting gain to 5% of strong signals.

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That will usually lose you some range which people are very keen on :slight_smile:
But your route is certainly not a bad approach if local stuff is more important to you than long range stuff.

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I’m going for slightly hotter, biasing towards range, as I have multiple setups running in tandem, one of which is better at local aircraft.