I am new to running my own adsb flight tracking. I started with a basic dongle from noelec which doesnt have filtering but then upgraded to pro stick plus but when I run Do I need a filter it would appear I still need more filtering do as I still get a lot of interference from mobile signals in the 900 range etc
I ran the same test with the old dongle and it does show that the flightaware pro stick filters out stuff which obviously the noelec one does not
So then I read I should get the 1090 band pass filter as that should filter out even more?
Just wondering so exactly what is the filtering part of the pro stick plus and why does it say you have a filter in it when in reality its not very good? And you still need there external filter as well?
And that makes me wonder if I got the band pass filter did I really need the pro stick plus then? And would I get the same results if I just added the band pass filter to the old stick?
because I am about to setup another one at my parents place and I will get the band pass filter for them but do I also get a pro stick plus as well? Or just use the band pass filter with the old noelec dongle and get the same results?
and I have attached the output of Do I need a filter (my understanding of running this check though is that it uses its own gain setting 29.70db) so should I also change that gain for the test as well?
I have attached my scan at 29.70 decibals showing the interference I have
and here is my stats of the dump1090-service (when running sudo systemctl status dump1090-fa -l)
rtlsdr: tuner gain set to about 58.6 dB (gain step 29) (tuner AGC enabled)
adaptive: using 50% duty cycle
adaptive: enabled adaptive gain control with gain limits 0.0dB (step 0) .. 58.6dB (step 29)
adaptive: enabled dynamic range control, target dynamic range 30.0dB
adaptive: enabled burst control
Allocating 4 zero-copy buffers
adaptive: available dynamic range (29.0dB) < required dynamic range (30.0dB), switching to downward scan
adaptive: changing gain from 58.6dB (step 29) to 49.6dB (step 28) because: probing dynamic range gain lower bound
rtlsdr: tuner gain set to 49.6 dB (gain step 28)
adaptive: available dynamic range (38.2dB) >= required dynamic range (30.0dB), stopping downwards scan here
Thanks a lot!
EDIT: I tried changing the RECEIVER_GAIN=60 &
ADAPTIVE_BURST=no
Ive done just some more testing… I ran the Do I need a filter scan at 49.6db and yes I get more interference than when I run it at 29.7 but I get more aircraft
I ran it scan again at a lower gain 20db and yes less interference but hardly any aircraft (and confirmed this with the live feed on the map)
So it would seem I need that high gain that its being set at automatically at 49.6 to see aircraft and so then a filter might hopefully remove that interference in the lower bands so I see more aircraft?
The filter in the prostick plus is located after the internal amplifier. This means you first increase the out of band signals and then filter the adsb signals out.
With an additional external barrel filter you filter out the out of band signals before they are amplified and that reduces the interference.
So if you have external noise sources like mobile cell towers then if might be a good idea to use the external filter as well.
thanks a lot tom thats the answer I needed. Well explained
so the prostick plus is trying to filter out amplified signals which is a lot harder to do when the interference is strong?
And if the interference was not strong the stick would be enough?
I think thought the prostick plus is not a waste then because it does have the amplifier?
Because this is the stick I previously had:
for sure the prostick plus + the external filter is going to be much better than just using the old stick + the external filter isnt it because the prostick plus has the amplifier and additional filter?
just want to justify the cost of the stick was worth it lol!
The Prostick plus has an internal amplifer and a filter indeed. It amplifies first and filters next.
Decoder<-Filter<-Amplifier<- Antenna
With the external filter added you get this:
Decoder<-Filter<-Amplifier<-Filter<-Antenna
This enables you to filter out more noise leading to a cleaner signal into the amplifier and into the decoder.
If you have little interference then the stick itself would be enough indeed.
In terms of performance the Prostick Plus will certainly outperform the Nooelec SDR so it was well worth the money
My understanding is that gain of -10 is a very, very high setting that you can’t set manually otherwise (something close to 60dB, it appears your test shows it at 58.6dB). You can’t set your gain above 49.6(?) unless you have it set to -10. It’s possible you’re blasting your decoder with so much noise and such high-power ADS-B signals that it can’t read the signals from many other aircraft.
So you should set gain at something in the middle (around 25 or 30) and then test increasing and decreasing the gain once per day to see if your performance improves.
thanks actually the adaptive gain was turned on so it was getting set by dump1090-fa to 46.9 that’s where I got the setting from
Ive tried today setting different gains around 35 or so I don’t see as many aircraft as I do when I set it to adaptive gain and it sets it back to 46.9
I was looking at another older post by wiedehopf saying you should set the gain to when you only get about 5% strong messages. I did get it to about 6 or 6 with a gain of 32.8 and when I set to adaptive gain I get about 14%
I don’t understand why he says around 5% is optimal I would have thought the more percentage of strong messages the better
but also this guide was made before dump1090-fa version 6 was released with the adaptive gain feature
A strong message is a signal that is close to your location ( within 5-10 NM) and the higher that percentage the more you are reducing the ability to recieve weak signals that come from a greater distance.
So a high number of strong signals has a negative impact on your range and receiving aircraft from a greater distance.
Regarding the use of filters, the RTL-SDR triple filtered LNA was nice. (Unfortunately it’s no longer available). It had a high-pass filter at the input to filter out possibly strong broadcast FM stations, followed by an amplification stage, followed by a bandpass 1090 MHz filter, followed by another amplification stage, followed by another bandpass 1090 MHz filter. That’s kind of how you have to do it to provide sufficient amplification without overloading.
Hopefully, someone will produce a similar filtered LNA to replace the RTL-SDR device. However it appears from this thread and the antenna thread, that vendors are getting out of the ADS-B components business. Not sure why, except that maybe the total market for these devices is just not big enough to justify producing a product.
thanks a lot again so I completely misunderstood it lol
I thought a higher gain gave you less messages from nearby aircraft but increased your range but its the other way around.
In fact, its a lower gain that gives you less messages from nearby aircraft but increases your range…
So I am going back and starting to try with 29.7 now. but I wonder then if so many people report that the adaptive gain works so well for them why is it setting it so high at 49.6 to get more strong messages because that contradicts wiedehopf 's post about setting it lower to get around 5% strong messages
and then… at 29.7 i get around 0.08% of strong messages even after running it for a while but when I bump up to the next gain 32.8 I get about 7% so I cant find that 5% goal
because I can still find it some places to buy
If thats the case should I get this rather than the flightaware band pass filter?
Also since my mate wants to get into this filtering too but he still has the noelec dongle which doesnt have filtering or lna
If he was to get one of these triple filtered lnas does that mean he doesnt need to get the prostick plus anymore since this triple one will do the same thing?
I am still trying to get my head around the requirements for bias tee power if I do get one of these. I dont think the prostick plus has bias tee power? So I need an external bias tee power?
Also it says make sure the antenna is grouned if the LNA is close to the antenna but what is ‘close’ the LNA for me would be 2-3 metres away from the antenna if I got one.
EDIT: So it seems the RTL V4 dongle has bias tee power. So am I at the understanding that if I got this dongle + the triple pass filter I dont need external power and I can then do the setup:
Antenna → Triple Filter → RLT V4 → Pi
and then I just have to enable the bias tee power setting via software?
The less than 5% rule is good if you are very close to an airport with lot of nearby aircraft taking off or landing.
The less than 5% rule is also good if you are directly under a flight path.
For conditions other than above two, higher gain is better, as is my case, and that is why adaptive gain setting of 49.6 gives me the best result in terms of max range, messae rate, and plane count.
Yes, that’s the setup I have, but I have V3 of the RTL-SDR dongle.
Try to get the V3 version of the RTL-SDR dongle. (The V4 has parts that are end-of-life as I understand it).
No. you had it right.
Gain = Amplification. So a strong signal and lots of gain results in overload and no received message.
A weak signal and low gain gives you nothing.
Here comes the personal interest part. Some people are only interested in local traffic (maybe at a local strip), so set the gain low so as to not have the receiver overloaded. Other sites are interested in long distance at the price of gaps in the local paths.
Setting the gain somewhere in the middle is a good start point - and work from there.
So as I understand it I will no longer get the Flightaware Pro stick plus + flightaware band pass filter
I will get the RTL V3/V4 dongle + RTL triple pass filter and enable the bias tee power in software and thats all I need? Dont need any external bias power etc?
And that setup would be better than using the flightaware dongle and band pass filter?
Looks like I need coax between the Dongle and the Filter though? Any recommendations?
I read this about enabling the bias tee power
***WARNING:** Before using the bias tee please ensure that you understand that you should not use this option when the dongle is connected directly to a DC short circuited antenna unless you are using an LNA. Although the bias tee circuit is dual protected against accidental shorts with a thermal self-resetting fuse and overcurrent protection on the LDO, short circuiting the bias tee for an extended period of time (days) could damage the LDO or fuse permanently. Only use it while connected to an actual powered device, like an LNA, active antenna or the SpyVerter.*
But this should be because I am putting an LNA between the dongle and the antenna which is the triple filter?
So you recommend getting the rtl v3 dongle as opposed to the v4 because V4 contains end of life parts but just wondering how it affects? Is it because the drivers wont kept updated for end of life parts or if it is faulty and needs to be repaired it cant be? Just curious thanks
That’s all you need. Whether it works better than flightaware dongle and bandpass filter I can’t say.
As far as coax, use LMR240. You don’t need LMR400.
I don’t use any coax. Just an N-SMA adapter from the antenna to the LNA and SMA-SMA adapter between LNA and dongle. Then about 15 ft of USB cable from the dongle to the RPi.
The wideband LNA link you referenced in your last post isn’t a filtered LNA. You probably don’t want that. Possibly the filtered LNA is no longer available.
