So, should I, would I be better served to remove the external filter that I installed onto the FA Blue Dongle??
All you can really do is try, to see what happens. I have cellular interference in my area, so I am using the FA 26" antenna, the FA light blue filter, and the blue FA pro stick.
If you don’t have interference in your area, the filter could possibly be reducing your results. There is a great “Do I need a filter” thread here (which I don’t have a link handy for) that gives step-by step directions for running a scan on your system which will show the frequencies that you are receiving signals on. That can be very helpful in determining your need.
Note that if you remove the filter you will probably have to play with lower gain settings in order to get the best results. The gain setting adjusts the internal amplifier in the dongle, effectively “adjusting the volume” on what is received from the antenna. When you remove the filter, more of the original signal (good and bad) arrives at the dongle, so less amplification is needed.
Edit: Here is the thread: Do I Need A Filter?
Try it, monitor it for some days and compare the result. You might also need to change gain probably.
Lower would mean from a 42.1 to say a 38 or?
Rough guidelines.
Just try and look at the graphs, don’t ask for specific gain values.
Yes, correct. In the thread @wiedehopf linked you will find all possible values.
Without a very special setup it is very unlikely that you’re improving something with less than 40
the sticks do have steps like 49.6 48.0 44.5
But it does not matter, if you select a value not in the list, it will change automatically to the nearest valid value.
(e.g. using 48.5 will set the receiver to 48.0 )
I’ve seen the map with the aircraft and the blue ziggy lines embedded withing the distance rings.
How do you get this blue ziggy line to show on your map??? I’ve never been able to see it on mine.
I ran the script… 5.58% strong messages
The blue lines are the boundaries specified by your geographical location. It’s a graphic generated by heywhatsthat.com and copied over to your site pages. There’s a guide on how to do it at the end of the project page:
GitHub - wiedehopf/tar1090: Provides an improved webinterface for use with ADS-B decoders readsb / dump1090-fa
heywhatsthat.com range outline:
- Create a panorama on http://www.heywhatsthat.com/
- You an use up in the air on the map and set altitudes to view the outlines
- For use on the tar1090 map the altitude will be set by changing the download URL
- Near the top of the page, an URL for the panorama is mentioned.
- Replace teh XXXXXX in the following command with the ID contained in your panorama URL
sudo wget -O /usr/local/share/tar1090/html/upintheair.json "http://www.heywhatsthat.com/api/upintheair.json?id=XXXXXXXX&refraction=0.25&alts=12192"
- You should now have a range outline for the theoretical range for aircraft at 40000 ft on your tar1090 map
- It might be interesting to compare to http://192.168.x.yy/tar1090/?pTracks which will by default will display the last 8 hours of traces.
5.58% is a bit too high. You should target for < 5%
Looks like the FA antenna is too close to the 8 element or at least the coax that feeds it. Seems like it must be reacting with it some. It would be interesting to try mounting it a few feet away and then compare.
I removed the filter and the errors rose then I reset the gain to 30 just to start over.
Errors fell.
Ran the script and I am getting “strong messages of 1.47%”
They’re not errors, just a metric of stronger messages as stated a few times already in this thread. This misnomer needs to be clarified since it appears to be spreading like a virus and is confusing new users. Errors and strong(er) messages are not synonymous.
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Sorry, they appear in RED and someone had called them errors.
As an attempt to put them into perspective: Think of these stronger messages the same as having speakers close to you. If they are too loud, they will be a greater % of what you hear and you wont be able to hear the music or conversations in the background. This is the red metric in your charts. There is no perfect value, just rule of thumb as this is greatly impacted on your location from stage (close airports, cell towers, etc).
Logically, you’d want to turn them down to allow you to hear as much other ambient noise as possible because if they are too loud, they will overwhelm your senses. IE: Too much volume (gain) will make them too loud and overwhelm your radio to the point where it wont be able to hear much else. 
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Simply change it to green, blue or whatever you prefer
There a lot of attention to % of strong signal statistics. Is there a reason to look at the other end of the RSSI scale and ask what % of weak but detectable signals are below the AD quantization threshold?
The 1090 MHz downlink signals are encoded as pulse position modulation so there is no amplitude information beyond 1 bit for a given downlink frame. Additional bits could serve to distinguish overlapping signals on the basis of RSSI.
Setting up the gain of an 8 bit SDR so that the top of the quantization equals the strongest signals means that the weakest detectable signals will be at most 48 dB below the strongest.
Turning down the gain to move the AD window higher desensitizes the system. I assume that’s why gain reductions usually reduce both % strong signals and message rates.
It “seems to me” that the AD converter ought to be set up to quantize a bit or two into the background noise floor, and the AD should have enough additional bits to span the RF dynamic range. 14 bits ought to work…
In practice we mostly have 8 or 12 bit SDRs with fixed gains and have to work within those limits. I don’t have a way to access the AD output directly anyway. So, I have adjusted for maximum message count averaging over a few weeks at a time.
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In practice the demodulator needs more than 1 bit / 6dB SNR, but otherwise the logic is sound - you are moving the approx 48dB ADC window around. Usually you can just about make that stretch to cover the range of signals you see within line of sight (signal levels drop sharply as soon as the aircraft crosses the radio horizon) even with only an 8-bit ADC, but there’s some tradeoffs to be made. 42dB will cover roughly a 128x range of distances (e.g. 2-256km) for the same transmitter power. There’s also a 4x 6x or so difference in transmitter powers, but lower power transmitters also tend to be flying lower (and so fall below the radio horizon at closer distances) so that cancels itself out to some degree.
Trying to measure the rate of signals that you would have received but can’t because of the ADC resolution is tricky because, well, you didn’t receive them…
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That’s would be way too expensive for the 1GHz frequency.
I switched to Airspy because they use a 12 bit ADC @ 20 MSPS (10.4 ENOB, 70dB SNR, 95dB SFDR).
Is that much better than the 8 bit ADC? It depends of everyone’s conditions (traffic pattern, bigger difference with higher numbers of signals) and expectations.
PS: The Effective Number of Bits (EONB) should be more advertised in ADC/DAC products. I see people claiming they have 24 or 32 bit in digital audio, but when you actually look at the EONB they barley scratch 20-20.5. Some even go as low as 18 EONB on a product that claims “32 bit DAC”.
It’s a hobby so who is to say what some might pay?
Anyway, the point is that the dynamic range of the ADC, however many bits, should be set to best cover the 1090 MHz signals’ amplitudes. Adjusting to reduce % of strong signals is not necessarily an optimal approach.