FlightAware Discussions

Bad reception / Cell tower interference?

Hi there, i recently moved into a place with roof terrace, and was looking forward to excellent ADS-B reception. I started test-installing my antenna to see how good it is. So far, i’m very underwhelmed.

I’m in São Paulo, Brasil.
I’m quite close to Congonhas airport (< 2 miles).
I’m very close to the flightpath of incoming airplanes (~0.5 miles?).
I’m also close to two (i think) cell sites, both on top of neighboring buildings.

My antenna is LOS to incoming aircraft, but my Pro Stick Plus does not pick up their messages. It does pick up some messages from aircraft further away (5 to about max 100 miles), although reception is spotty at best (i get like 10 messages/s on a good day)

Now i don’t know much about antennas, signals, frequencies (much of what i read here sounds like gibberish to me hahah), i’m quite the noob. Is there anything i’m doing wrong? I’ve read that cell towers might interfere with reception, and i have two close by. Can i do anything about that? I’ve read about band filters? Can this help? Is there anything else i’m missing?

Thankful for any tips! Thank you!

A band filter will help you to maybe see further than 100 miles but you have other issues besides the interference.

If you receive aircraft further away but not the close by ones, the receiver is overloaded by the planes themselfves, thus you need to reduce the gain:
Thoughts on optimizing gain
or
https://github.com/wiedehopf/adsb-scripts/wiki/Automatic-gain-optimization-for-readsb-and-dump1090-fa

The antenna isn’t mounted very well, it’s too close to the metal grid.

If that is mounted with tape … that is prone to fall down at some point.
At the very least use tape at the top and the bottom of the antenna … that at least should work until the tape is destroyed by the sun.
I suppose you could even use some plastic or wood between the antenna and metal and then wrap tape around it with a spacer at the top and the bottom.

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I live in an apartment and have Cell antennas on top of my building and other adjuscent buildings. I had same problem as you have. I solved it by adding a Flightaware Filter between antenna cable and the dongle.

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Thank you for the tips, i’m going to see if i can reduce the gain per your links.

The current mount is very temporary, i was just testing some positions. I’ll attach them with a proper mount yet :slight_smile:

What’s the difference between those two filters? One says dual 978+1090, the other only 1090?

I was looking into buying one of those to see if it improves things

If you can, attach a horizontal pipe to the current metal grille (if it is strong enough) and attach the antenna vertically, 1m or so from the building.
It looks like you are quite high up from the street, so use some proper clamps and locking nuts unless you know the local judge.
You can also add a safety cable to the heavy parts, in case all else fails.

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No worries about the current “mount”, that’s temporary for testing only… i have better positions to mount the antenna, where there are no metal parts nearby

Both are same. The label “1090” was on original few releaes. Later it was changed to “1090+978 dual band”.

There is another model of Flightaware filter which is for Europe. It is Dark Blue in color and removes GSM900 band which is in Europe. Since Brazil does not have GSM900, you will not need the Dark Blue one.

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This page seems to say GSM900 is in fact used in Brazil.

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I just tried your “Percentage of strong messages” command and got…
Percentage of strong messages: 145.351

I guess that’s a bit much? :sweat_smile:

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I set gain to 30 and omg, so much better! I actually pick up airplanes that fly by my building now. This is amazing, thanks so much! Will monitor this a bit and tweak further if needed.

Percentage of strong messages: 7.467

Before you go ahead with purchasing a filter, run following two scans to see what RF interference is received by your antenna:

(1) Wide band scan - 24 Mhz to 1800 Mhz:
Spektrum - How-to Speedily Scan RF Noise in band 24MHz ~ 1800MHz

(2) Narrow band scan - 800 Mhz to 1200 Mhz
Do I Need A Filter?

 

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Do i need one? :thinking:

I can’t run the wide band test right now, i’m on a Mac

At least it would not hurt.
I have a similar scan and was able to remove the noise outside 1090MHz by using the dark blue FA Filter.

At the end it did not give me a better reception, but that strongly depends on the environment

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Oh.
I’ve never seen that … would have thought that count is always less than the total count.
Might have to do with the number of CRC corrected messages maybe i’m not adding them to the total.

Yeah if you get aircraft further away but not close to you … it’s too much gain in 99% of cases.
Glad you’re getting the close by planes, those are often the most interesting to look at after all.

Actually looks like the light blue would be sufficient to reduce the strong interference at 900 MHz and below.
Anyhow … whichever is available to you.

Do you have HDMI devices in that room, that could also be limiting range as it’s picked up by the antenna.
Insufficiently shielded HDMI cables in active use are a regular culprit for having limited range.
The interference is especially bad as it includes the frequency you’re trying to receive so you can only receive strong signals.

The alternative location for the antenna sounds like it would remove that possible issue.

If you want some statistics or another webinterface have a look at the stuff here:
https://github.com/wiedehopf/adsb-wiki/wiki/Raspbian-Lite:-ADS-B-receiver

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I’ve written a post on how to improve ADS-B reception. It deals with everything from antennas, amplifiers, filters and the software-defined radio specifications as well. Feedback is welcome as I would like to improve it.

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Yeah i ordered one, let’s see how that goes.

Nope, the next HDMI device is far away

Nice entry.
What i am missing is the geographical aspect which limits the range and cannot be improved with any technical equipment.
You should mention the ability via heywhatsthat.com to identify the theoretical max range.

Small cut-outs of your scans make it easy to see extent of RF noise / interference.

Seems you will benefit from a filter.

  • The GSM800 band is strong
  • The GSM 900 also exists (RF at 960 Mhz), but not as strong as GSM800
  • The noise around 1090 is mostlikely from HDMI as already pointed out by @wiedehopf

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