Which SDR do you use?

6 years 6 months ago #11 by achan011
Hey guys,

actually I'm using a normal software defined radio usb stick (RTL2832) from adafruit (www.adafruit.com/products/1497) in combination with an self-built groundplate antenna to receive signals on my raspberry pi.

Do you think that I can improve the signal strength with the FlightAware Pro Stick (flightaware.com/adsb/prostick/).
Specs: Amplifier: 19dB with 0.4dB noise figure and OIP3 +39dB

Which SDR do you use with your raspi?

Best,

Andy

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6 years 6 months ago #12 by achan011
Replied by achan011 on topic Which SDR do you use?
Big improvement with the dongle as you can see here:



I had to play with the gain settings in dump1090, so I tried 40db instead of max gain to get this result.

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6 years 6 months ago #13 by schaefer
Replied by schaefer on topic Which SDR do you use?
Nice! That's a considerable improvement!!

It is quite common for SDRs that setting the gain to the max value results in clipping or other kinds of signal distortions. I've got this RTL SDR dongle:


I'll do some tests as well.

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6 years 2 months ago #36 by weddy
Replied by weddy on topic Which SDR do you use?
Hello im using the R820T2 as well
Im using a 19db preamp a homemade filter and a 8 elements coco antenna on the roof.

Edwin

90086

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6 years 2 months ago #37 by schaefer
Replied by schaefer on topic Which SDR do you use?
Have you ever tested how much improvement in terms of message rate or range the preamp brings?

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6 years 2 months ago #39 by weddy
Replied by weddy on topic Which SDR do you use?
Hello
No never test it what the message rate is when i dont use a preamp .
i always aimed to get a high as possible rate around the 1400/1500 msg
But i can do a test if you want to see what it does foor a hour or so.

Edwin

90086

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6 years 2 months ago - 6 years 2 months ago #40 by schaefer
Replied by schaefer on topic Which SDR do you use?
Would definitely be interesting to know! If you want you could share a screenshot of the rate graph during your experiment.

What I can tell from our sensors is that dump1090 can achieve rates up to 2k Mode S/ADS-B messages per second. But this does not only depend on your setup. It also depends on your location (close to a major airport, no mountains, SSR radar nearby, ...). The best sensor in terms of message rate at the moment is a Radarcape with an average rate of 2200 messages per second at daytime. But it's located like 2km away from Frankfurt airport which is probably optimal for such a metric.

Another limiting factor is the bandwidth of the 1090MHz datalink of about 1 MBit/s. A long Mode S transmission lasts 120µs (including preamble), a short one 64µs. Assuming that there are no overlapping transmissions (e.g. FRUIT), there is a theoretical maximum of 8333 long msgs/s and 15625 short msgs/s. OpenSky's dataset consists of about 40% long messages and 60% short message. Assuming that this is also the fraction that is transmitted by aircraft, we have a theoretical maximum rate of 12708 messages per second.

Of course this is totally utopic since aircraft do not send their messages in a synchronized fashion and the transmissions will arrive at your receiver at the same time and many of them will "destroy" each other. We found that if there are, say, 100 aircraft in the reception range of your receiver, about 90% of the transmissions are expected to overlap. So if your receiver is implemented well (and dump1090 and Radarcape are pretty good) and it can recover one of the colliding transmissions in 20%, you'll end up with a maximum rate of 2414 messages per second for that particular scenario.

If you want to beat that you have to either come up with a revolutionary receiver implementation or with stuff like multiple receivers with directional antennas. The latter is what "professional" companies like Thales or Rockwell usually do.
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6 years 2 months ago #41 by weddy
Replied by weddy on topic Which SDR do you use?
i will do a test and remove the preamp and let you know what the results are.
For my location and antenna setup its the max i can get out of the dump1090.
The antenna height is only 14 meter, i live near amsterdam and there are a lot of tall buildings that block my way.
As you can see i got a good range but you always want more.
But the antenna i use is a homemade 8 elements coco antenna that performs well.
but indeed the pro directional antenna will be much better but its a hobby hahahaha.

Edwin

90086
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6 years 2 months ago - 6 years 2 months ago #42 by weddy
Replied by weddy on topic Which SDR do you use?
ok I did the test
Whit preamp i got a msg rate of 1400
Then only the sdr dongle got a msg rate of 1100 +/-

Edwin

90086
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6 years 2 months ago - 6 years 2 months ago #46 by boab
Replied by boab on topic Which SDR do you use?
I use the FlightAware RTL stick and noted considerable improvement over my previous blue R820T2 stick. I have tried several receivers airspy/beast/planefinder and the FA comes out as best (just). I have a jetvision.de active antenna, approx 20db gain, and the dump1090 gain is set to 22.9.
Typically during day I get continuously 1700/1800 messages/sec peaking at 2000.
I regularly experiment with my setup but suspect may have reached my locations limit.
I am in a good location in a busy area 10km from London Heathrow so lots of local traffic but still regularly get 200+nm.

Boab
90047
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6 years 2 months ago #47 by weddy
Replied by weddy on topic Which SDR do you use?
Whow nice results boab.
I also have a flightaware stick here but it doesnt make a difrnce whit the rtl-sdr stick.
I have the preamp close to the stick so what the flightaware stick have is a sort of lna4all preamp built in.
It should help me if i place the lna direct under the antenna .

Edwin
90086

90086

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6 years 2 months ago #48 by schaefer
Replied by schaefer on topic Which SDR do you use?
Yes nice boab, that's pretty good for such a cheap SDR!

I think you're right weddy! Placing it close to the antenna helps a lot since most antenna cables absorb a lot of noise from the environment and the longer they are, the noisier the signal gets that arrives at the receiver. Amplifying a noisy signal results in a noisy signal :-) So if you place the amplifier close to the antenna, the "clean" signals become amplified which helps a lot. Problem is the power supply for the amplifier I guess.

This is btw also what the active antenna boab mentioned does. It's got an amplifier (and filters) right next to the antenna which is powered over the antenna cable.

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4 years 9 months ago - 4 years 9 months ago #354 by alzaman
Replied by alzaman on topic Which SDR do you use?
Apologies for regurgiating an old thread . . but i'll contribute seeing as i'm new here, but not to ADS-B!!

I currently use NooElec NESDR Smart with 2 home made 16 element CoCO Antennas split into the RPi 3. I also have the FlightAware SDR receiver (The orange one) - originally used for the 2nd RPi 3 which fed from the rear.

My location is good, high and no ostructions to the front - so i'm receiving 680 KM as a maximum directional range.

Hopefully i can feed FR24 again and Opensky again - at present i can't :blink:
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4 years 8 months ago #407 by schaefer
Replied by schaefer on topic Which SDR do you use?
This thread never gets old :-)

Did you ever compare the two dongles by using the exact same setup and just replacing the dongles?

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4 years 8 months ago #409 by boab
Replied by boab on topic Which SDR do you use?
All my tests were done using antenna splitter, That long ago!, as day to day or hour to hour were not compatable with the relatively small differences i was seeing.
Since then system been running on auto pilot ;-)

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