My optimization adventures

FlightAware ADS-B Flight Tracking
1

I can’t seem to leave this ADS-B thingy alone. I keep coming back to it again and again. Lack of better things to do, I guess? :grinning:

I had a ‘truckload’ of problems lately, some described in previous posts. Replaced every piece of hardware on both my stations at least once. Still no permanent fix, until late last week, knock on wood.

If this latest ‘solution’ holds, the problem had to do with weak wi-fi signal, either on the router side or on the RPi side. I would be most interested to hear from those that my have run into this situation as well.

I installed a brand new router in range extender mode half way between the ‘WAN’ router and the RPis.

In addition to replacing pieces of the stations when troubleshooting the connectivity problem, I also moved the antennas inside the garage a lot. I remembered where the antenna used to be when I received the largest number of planes since I setup my first station. Would you believe it that that location ‘worked’ again. There is a so called ‘sweet spot’ in the garage for best antenna siting. Then there was the N to SMA adapter issue mentioned in the past as well.

I had already mentioned many times before that indoor antenna siting can be very sensitive to literally inches of change, in all directions. I failed to record the different results as I moved the antenna around over the years. I have also concluded that when the performance went down a year or two ago, it was because of the N to SMA adapter. This made me change the antenna location many times, looking for a better place, and put me in this ‘wild goose chase’ kind of situation.

This is all to say that I think I may have maximized my stations for the highest number of planes possible in this location, with this setup. This would certainly change if the antenna moved outdoor and higher, for example, but that is not happening.

With plane seen maximized, I’m now looking at message numbers. I want to understand more about messages, and what kind of correlation it may have with the number of planes seen.

My first question then is: My two stations are only 20 inches apart now. They both see pretty much the same number of planes. However, the difference in the number of messages received, with pretty much the same number of planes, sometimes higher on the station receiving less messages, can differ by up to 80%, like at this very moment while writing this post. What could be the reason for this?

Sorry for the long winded post.

Thanks.

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2

Interference? …

3

That was my first thought, but wouldn’t interference impact both planes seen and messages, and on both stations, since they are only 20 inches apart?

I can live with this situation, asking just out of curiosity, since the discrepancy is noticeable.

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Not necessarily. External noise would likely affect both, but you can also get multipath interference caused by reflections off nearby buildings or other hard surfaces. The wavelength at 1090MHz is only 27cm, so half a wavelength change in position can make a big difference to reception.

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It’s the ‘black magic’ part, I get it.:wink:

Right now, same number of planes, with a 200% difference in messages.

6

Swap the dongles, leave the rest.

Or does the difference occur randomly and sometimes one station is better, sometimes the other?

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I did not try that yet. The dongle with the highest number of messages is the RadarBox one. The other is the FA Pro+.

Here is something ‘new’. The FA Pro+ also has an RTL-SDR Blog LNA connected to it. Without the LNA, the number of planes seen drops by 5-10% compared to the RadarBox dongle, but the message count difference almost disappears. Interesting.

The number of planes seen sometimes reverses by a couple of planes, literally, but not the messages.

Randomness is something that I was going to tackle next. I have seen that happen in the past, and was puzzled as well. The changes that I remember were substantial. Not happening now, but will keep my eyes open for the next occurrence.

After a few days reprieve, the heat is back. The garage is not where I want to be right now.:sweat_smile:

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Oversaturating the FA Pro internal LNA.

Probably doesn’t matter how low you go with the gain, it’s still not gonna work properly.
Gain doesn’t affect the internal LNA.

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That I can confirm, no lowering of the Pro+ gain changed the situation in a noticeable way message wise, but it reduced the number of planes seen.

This was basically my original question. Is the number of planes seen derived from the messages? How are they different or related? How does interference and/or saturation affect one and not the other in the same measure?

10

I’m not exactly sure how that big of an oversaturation affects the LNA.

Might be that it just goes deaf for short period when a strong signal comes in.
That would explain similar aircraft numbers, for short periods it gets all the signals, then nothing.
Alternating probably hundreds of times per second.

If you don’t receive a message from an aircraft, it’s not an aircraft that is counted.
Similar aircraft with positions need to have sent a position message recently.

If the aircraft count drops, you aren’t receiving any messages from certain aircraft.
(I thought that was very obvious).

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I think you may be onto something here. The SkyView refresh rate and persistence may mask these very fast changes.

That is obvious, except that it’s not what I’m seeing. The station with up to 200% less messages shows more planes. The previous quote from you post could be the explanation.

I think I’ll leave everything as is. I’m happy with the number of planes, my main interest. Got pretty close to my all time record from July 24, 2017. On that day I recorded 1121 planes seen. That’s nothing for most of you, but it was for me.:wink:

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Well less messages doesn’t mean no messages.

Do you have a dongle without internal LNA?

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True. Looks like SkyView keeps a plane on the map count for up to 60 seconds after the last message from that plane was received. That’s an eternity when dealing with hundreds, if not thousands, of messages per second.

I had an RTL-SDR Blog v3 until a week or 2 ago. Performance, using the planes seen measuring stick, was worse overall than the current setup. I had it both, with and without LNAs.

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What happened to it.

Where did you buy it, there are a lot of fakes of those floating around.

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It was the ‘real McCoy’, purchased from the RTL-SDR Blog directly.

I had it moved to my SatNOGS station, where it was until yesterday, when I replaced it with a NooElec SmarTee and an RTL-SDR Blog generic LNA for the sats. That is working great, but the current antenna leaves a lot to be desired. My next ‘challenge’, I guess.

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It should be (edit) a bit better than the FA prostick plus when combined with the filtered LNA if you are having low message rates.
Curious.

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There were so many changes recently that I honestly don’t remember. I don’t think so, as we tend to notice big improvements, and that seemed to jump at me with the current combination.

Best to let everything stay this way for now, and observe long term.

The RTL-SDR dongle is not defective, I don’t think, as it worked fine as a receiver in the SatNOGS station. It lost its position only because I wanted to add the LNA, and the SmarTee has bias-T always ON.

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So swap it with the pro stick plus.
What gain are you running the prostick plus at anyway?
I’d estimate you need to run it around 5, maybe 10.

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I’m back in the air-conditioning, enjoying a glass of red wine. Fall is just around the corner, let’s wait until then for cooler conditions.:grinning:

Right now, as I write, 49.6. I’ll lower it to 5.

Edit1: No 5 , so set it to 7.7.
Edit 2: Planes seen dropped by 20%. For messages, the difference dropped to 100% from 200%.

Not enough time, but the change was almost instantaneous.

20

Well then turn it up to 20.

I’d tell you to use messages >-3dB as a guideline, but i suspect you must have read that quite often following these forums.

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