FlightAware Discussions

Diagnosing interference

I’m running PiAware, latest build, never logged in via SSH. I’m near a few cell towers and there is high voltage power lines near me too. So I’m wondering about interference. I’m told that the cell towers will also be upgraded soon with new 4g and 5g antennas. So who knows what will happen.

I’m running the blue pro stick plus. I have also ordered the 1090 bandpass SMA filter just to double up (waiting for it to arrive).

My question is… I’ve seen people with all those graphs looking at the spectrum and what’s going on. Is there a beginners guide or a “how to” anywhere? I’ve had a look around the forum, but cant find anything. Thanks for your help.

 

Do I Need A Filter?

 

Mobile / Cell Phone Frequencies close to ADS-B Frequencies ES 1090 MHz and UAT 978 MHz.
Regional Deployment Designated by the ITU (International Telecommunication Union) for the operation of GSM mobile phones and other mobile devices.

Mobile Cell Phone Frequencies Close to 1090 and 978 MHz

Thanks. Yes I saw that, which is why I ordered the bandpass SMA. I just wanted to know if there were instructions anywhere so I could get some nice pretty graphs showing what’s being transmitted.

(1) Download Spektrum for Windows

Direct Download Link for Current Latest release for Windows: spektrum-win64.zip

Check Download page for Latest Release:
https://github.com/pavels/spektrum/releases

(2) Unzip the file, and inside you will find a file named spectrum.exe.

image

 

(3) Plug the dongle in your Windows Computer. If you have a dongle without integral filter, it will show all the signal existing in your area.

(4) Connet the antenna directly to yor dongle (No Filter)

(5) Double click the file spektrum.exe and the program will start

(6) When the program starts, it will detect and list the dongle as shown below. Click on the dongle name, and wait few seconds for scan to start.

image

 

(7) Click on the “Measure” button
image

 

(8) On “Measure” window, “Gain” will be by default 50 (it is actually 5 dB). Adjust gain by bringing mouse pointer above 50 and turning mouse’s scroll wheel. Set it to maximum 496 (it is actually 49.6 dB).

image

(9) Leave her to run for 5 minutes so that it repeats scan several times.

(10) Repeat scan with a filter inserted between Antenna and Dongle.

Here are 3 scans I have done recently:

NOTE-1:
The scans below were done in an urban area with strong Cell/Mobile, TV, FM, Fire, Ambulance, Taxi, and other communication signals at VHF, UHF and Microwave frequencies. Other locations may not have such severe RF interference.

NOTE-2:
The scan 1 shows RF noise picked by antenna and processed without any filter, The scans 2 & 3 were done with filters, and show how filters remove this noise.

Scan 1 of 3 - FA Antenna + Generic DVB-T (no internal or external filter)

Thumb-Generic DVB-T
CLICK ON IMAGE TO SEE LARGER SIZE

 

Scan 2 of 3 - FA Antenna + ProStick Plus (Only Internal filter of ProStick Plus. No External filter)

image
CLICK ON IMAGE TO SEE LARGER SIZE

 

Scan 3 of 3 - FA Antenna + ProStick Plus (with internal filter) + External Filter (FA Light Blue)

imageimage
CLICK ON IMAGE TO SEE LARGER SIZE

 

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Spektrum is also my go-to for these tests (when possible). Although, I personally handle gain a bit differently which I feel provides better results:

Let it run for a couple seconds using the default “50” to show the floor, scroll the mouse wheel up until you see an approximate 5dB increase (watch the left side of the screen and note the output increase as you increase gain). Once set, click the “auto scale” button and you’re off the the races.

Here are two examples of the identical setup using both methods as a quick comparison - I guess it boils down to personal preference in the end as I don’t think there is a wrong or right way:

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The problem with changing the scale is that it makes it more difficult to compare the actual signal levels.
Take your two examples : looks like picture 2 has a better signal as it’s sharper and peaks higher on the screen with less other signal interference, yet it’s actually 10dB weaker. That’s 10x less of the signal you are trying to receive.
The dB per division is also different between the two pictures, 4dB per in first, and varies between 2 and 3 dB per in the second.
Will that make a difference? Maybe.
If you stay sharp and confirm what you’re looking at, it’s fine.

As always, depends on what you’re doing and what you want to measure.

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Yeah, there are a bunch of different toys to play with in the latest Spektrum. Reference graphs are fun as well. Same setup before and after cavity filter:

Doesn’t matter in the end, so long as the user understands what he/she is seeing.

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Spektrum Guide here:

https://github.com/pavels/spektrum/blob/master/README.md

 

 

Is there anything that can run on a Mac or on the PI itself ?

I wanted to see how much interference there is. I have a Flightaware antenna, very small, high quality cable and are getting maybe 20 NM coverage. I’m near two cell towers and some power lines, so I think its related to that.

 

(1) GQRX
For Mac, Raspberry Pi, Linux 64-bit:
https://GQRX.dk/

(2) CubicSDR
For Mac & Win:
https://cubicSDR.com

NOTE: I have NOT tried the above noted software ( I dont have Mac).

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Thanks sooo much for this. I’ll have a look at both.

You’ve got a good receiver, a good antenna and you are running good quality coax - you should be doing much better.
I suspect a fault in the coax as the most likely cause.
It’d be worth getting/making an alternative cable for elimination.

Yes I’ve done that. It’s my second cable. No difference. The additional filter will arrive soon, so I’ll see if that helps.