ADS-B very poor reception - Why ?

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Patrick73
Posts: 76
Joined: Thu May 31, 2018 9:39 am

ADS-B very poor reception - Why ?

Post by Patrick73 » Tue Jul 23, 2019 10:09 pm

Hi there !

This afternoon, with a friend, we made our first ADS-B attempt, in a favourable environment.
We went to the top of a mountain (1400 masl) that offers a beautiful panorama. The surrounding reliefs were quite distant and not very high (about 5° maximum). A quick test on FM / DAB / air band, allowed us to notice that the reception towards the North (Geneva, Switzerland, 100 km) and West (Lyon, 100 Km) was excellent, as expected.

But it proved catastrophic in ADS-B : only about 30 planes visualized on the map in 4 hours, the most distant being at ... 30 km, south ! Yes, 30 km while we were clear almost at 360°, using 3 differents aerials (see out setup below).
Of course, we checked again the coax, the connectors, everything was fine. We can't believe the 3 antennas were faulty. We can't believe the RSPduo is deaf neither at 1.090 GHz.

The only explanation we found was that we were using the 4G of a mobile phone, connected to the laptop, to view Virtual Radar map. Could this interfere with reception on 1090 and explain such poor results despite a very good location and suitable equipment ???
Or maybe a nearby transmitter could be responsible ?

Advice highly appreciated.

Our set-up :
RSPduo / dump1090 (latest versions)
Log periodic (130-1300 MHz, new) + Colinear + 5/8 ADS-B antennas (both new), 5m above the ground.
Only 8m of quality / low loss coaxial cable (50 ohms)
No LNA.
2 laptops (same trouble with both)

Thanks !
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Patrick73
Posts: 76
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Re: ADS-B very poor reception - Why ?

Post by Patrick73 » Wed Jul 24, 2019 6:53 am

Another strange thing : as the minutes went by, it seemed that we were receiving fewer and fewer planes.
Note : I make the same observation at home this morning (a few planes visible during the first 20-30 minutes and then almost nothing afterwards). OK, my home location is very poor for ADS-B, in a valley with mountains all around but I see as many planes as yesterday on the top of the mountain ! Same antennas (i.e ADS-B colinear and 5/8), desktop PC. Of course, VRS shows my RSPduo as "connected" but not a single aircraft has been reported in the last half hour (about 10 reported the 10 first minutes after I started Dump1090). I closed the app, and lauched it again several times, no effect. Any idea ?

As an attachment, here is a capture of what I see on 1090 (from home). FM and DAB notch are engaged.
Does it look OK ? Are these 'traces" ADS-B signals or any interference whatsoever ?

Thanks for your precious help.

EDIT : I forgot to mention that the capture was made using the ADS-B colinear antenna, at home, about 6m above the ground. FM / DAB notches On, gain set to almost max.
Attachments
1090.JPG
1090.JPG (264.18 KiB) Viewed 3223 times
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VK3MHZ
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Joined: Sun Apr 30, 2017 7:24 am

Re: ADS-B very poor reception - Why ?

Post by VK3MHZ » Thu Jul 25, 2019 3:34 pm

I guess the first question that should be asked is if you were in a high traffic area for planes?
Secondly, of the antennas you were using, a log periodic would be directional.

The co-linear may not have been the best choice at such a high elevation either. As it would have a reasonably flat angle of radiation (and reception), you may have had greater success with a 1/4 wave.

I doubt if the mobile phone would have caused any problems, although I do not know (and you never stated) what frequency bands your phone uses for voice/data in your country - it may possibly have caused problems, but I would err on the side of saying no. I have successfully ran ADS-B portable whilst using a broadband (mobile) modem at the same time along with the phone running.

Another thing, from your image, your LO is on the same frequency - I am going to take a fair bet this is the root cause for your lack of reception. Change it LIF mode and offset the LO from the main frequency before you hit play.
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Patrick73
Posts: 76
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Re: ADS-B very poor reception - Why ?

Post by Patrick73 » Thu Jul 25, 2019 7:45 pm

Thanks for your reply.
I guess the first question that should be asked is if you were in a high traffic area for planes?
Yes, the traffic is very dense in this region. We could see dozens of planes above our heads. In addition, Geneva and Lyon airports (Switzerland capital city and french 2nd biggest town) are not very far away (about 100 km).
The co-linear may not have been the best choice at such a high elevation either
Indeed, the colinear antenna was probably not the most suitable, but the results were about the same when using the 5/8. As for the log periodic, we obviously turned it in all directions, without changing the number of received aircrafts.
Another thing, from your image, your LO is on the same frequency - I am going to take a fair bet this is the root cause for your lack of reception
The capture was made after our tests, just to show the signals (interferences ?) visible on 1090. Anyway, as you probably know, it is not possible to modify the LO during ADS-B reception since it's Dump1090 that drives the RSP (I mean SDRuno is closed).
I suppose Dump1090 handles this DC spike problem perfectly in ZIF mode :D
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MikeHarding
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Re: ADS-B very poor reception - Why ?

Post by MikeHarding » Fri Jul 26, 2019 12:06 am

I played with ADS-B for the first time a couple of weeks ago:
W10 notebook
RSP1A
Antenna = 68mm galvanised wire wrapped around screw on mag. mount and mounted on a saucepan at 1m height

I am in a low RF noise, low plane numbers area of Australia but received aircraft up to 120km distant despite my terrible antenna, nothing wrong with the RSP1A.

I'd say it's possible but unlikely your phone was desensing the RSP1A - turn the phone off?
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VK3MHZ
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Re: ADS-B very poor reception - Why ?

Post by VK3MHZ » Fri Jul 26, 2019 6:20 am

Patrick;

I have never used SDRuno in conjuntions with Dump1090. Just merely monitored the squitter's with SDRuno.
For ADS-B I run dedicated RPI's and Dump1090.

As like Mike, I have also done tests with very average antennas.
My first ADS-B antenna was a SO-239 chassis socket, with a 1/4 wave-length of thick enameled copper wire in the center socket, and the same copper wire x4 as ground planes soldered to the chassis of the SO-239. The height was only 10-12 foot AGL, using RG-58 coax of about 15 foot length and I was getting 70-90nm average depending of direction. Towards the West I was getting 110nm.
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Patrick73
Posts: 76
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Re: ADS-B very poor reception - Why ?

Post by Patrick73 » Fri Jul 26, 2019 7:53 am

Hello buddies !

I just performed a rather improbable test : I simply replaced the RSPduo by a poor RTL dongle (the cheapest one can find on the internet).
Same cable, same antenna, same connectors (with an additional adapter because this dongle has a MCX plug).

Believe me or not, the screen is full of planes, up to 240 km. I can't believe my eyes.
Back to my RSPduo : almost nothing, farthest plane : 15 km.

I don't know what can be wrong ...
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sdrplay
Posts: 978
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Re: ADS-B very poor reception - Why ?

Post by sdrplay » Fri Jul 26, 2019 8:25 am

Hello Patrick,

You shouldn't be seeing poor performance with the RSPduo and I suspect it's a settings issue. Some reminders....

1. for the RSPduo you should be using windows version of dump1090 and the latest version (currently 1.45) for best performance (remember this will require the 3.04 API installed from the downloads page on our website)
2. by default the dump1090 will use tuner 2 as the input - you can use the command line option of --rspduo-tuner1 to use the other tuner
3. also by default the RSPduo will be used in master/slave mode - it may be worth trying single tuner mode, by using the command line option of --rspduo-single

Hope that helps,

Best regards,

SDRplay Support

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Patrick73
Posts: 76
Joined: Thu May 31, 2018 9:39 am

Re: ADS-B very poor reception - Why ?

Post by Patrick73 » Fri Jul 26, 2019 9:09 am

Thanks a lot for the prompt reply.

I'm indeed using Windows version of dump1090 and both - the RSPduo and ADS-B installer - latest versions, i.e 1.32 / 1.45.
by default the dump1090 will use tuner 2 as the input
I think you found the problem. I was using port 1 and at no time did I think I would try port 2. Shame on me !
also by default the RSPduo will be used in master/slave mode - it may be worth trying single tuner mode, by using the command line option of --rspduo-single
Sorry, I'm not familiar with these command lines.
How and where do I have to type this "--rspduo-single" text ?

With all my thanks for your precious help.
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sdrplay
Posts: 978
Joined: Wed Jan 07, 2015 7:58 am

Re: ADS-B very poor reception - Why ?

Post by sdrplay » Fri Jul 26, 2019 9:40 am

Hi Patrick,

When you run the dump1090 options from the start menu, that is running batch scripts. If you open a command prompt and navigate to...

C:\Program Files (x86)\SDRplay\dump1090

(assuming you are on x64 machine and use the default installation directory, otherwise change directory to where you installed dump1090)

then you will see a number of .cmd files...

start2.cmd
start2I.cmd
start8.cmd
start8I.cmd

the 2 and 8 refer to 2 and 8 MHz demodulator modes - the 8 MHz mode, will require more CPU but in theory should show you more planes.

the I refers to interactive mode, so use the I version if you want to see the plane list in the command prompt or without the I if you don't want the interactive mode.

Look at the contents of the file (we'll use start8I.cmd as an example...)

Here is the important line...
.\sdrplay_dump1090.exe --dev-sdrplay --interactive --net --oversample

to add a command line option, just add it to the end and hit return, so for example to switch to RSPduo single tuner mode you would run...

.\sdrplay_dump1090.exe --dev-sdrplay --interactive --net --oversample --rspduo-single

Once you've found a good set of options that works best for you, you could also create a batch file and maybe create a link to it on the desktop for example. I wouldn't change the above cmd files directly as they will overwrite when you install a later release and you'll lose your modifications.

Hope that helps,

Best regards,

SDRplay Support

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