Do I need a Filter? - Find RF Signals In Area

[abcd567]

Are you using a LNA (RF Amplifier)?
Failure of LNA or lack of power supply to LNA results in the LNA instead of boosting the signal, attenuate (reduces) severely. This will result in sort of heatmap scan you got.

If you are not using a LNA, but the dongle you are using has built-in LNA, then failure of dongle's LNA chip, or lack of enough DC power to dongle can also result in the yype of heatmap you got.

[furkly]

Connected the dongle via a USB extension cable and got a super weird result:

Scan 3.png

Went back to directly connected:

Scan 4.png

Ran rtl_power with the -T command per that thread, same as the other results:

Scan 5.png

[abcd567]

Someone in Flightaware forum got similar scan and found that running the rtl_power turns OFF the bias-t of his dongle (RTL-SDR Blog V3). This makes his LNA to stop working, and the dongle stops getting 1090 MHz signal, and gets only noise which resulted in this sort of scan.

https://discussions.flightaware.com/...ter/27833/1004



.

[abcd567]

furkly

It is likely that this type of heatmap is caused by the noise generated by RPi and picked by the dongle.

Instead of plugging the dongle directly into RPi, use a usb extender cable to connect dongle to RPi. This will create some physical seperation between Pi and Dongle. Also the USB 3.0 ports are noisier than USB 2.0 ports. Try to plug your dongles in USB 2.0 ports. The Pi 4 has two USB 3.0 and two USB 2.0 ports.

[furkly]

I did a scan and it basically looks like the entire range has noise - but surely that's not correct?scan.png

Edit: I believe it's power supply related. I moved it further from the rPi and it's much better, but there is still noise:
scan.png

I'll grab a replacement genuine rPi power supply and retest.

[Kvisko]

The next day.

I was using a non-name non-RTL-SDR usb card to measure, with generic dipole antenna. That might make the measurement funny. So, today I took a 1090 MHz antenna and RTL-SDR v3 USB receiver.
This is the result:


Now I see that there is a considerable noise in 1090 MHz region.
Let'e try my second location:

That's more like it!

The moral of this is - use good equipment for measuements. Preferably the one that will be used for "production".
Now, I will have to use the filter to see if it resolves my problems.
Cheers!

[bocachica@duck.com]

One of the best filters i ever had: http://shop.sysmocom.de/products/cf1090-kt30
You can see the result on: https://wolvex.nl/Airplanes.html

[Duccio]

Hi everyone, can someone help me to read this graph? thanks

[abcd567]

Hi All,

Here my results, what do you think?

Regards,

Yes, a filter will most likely improve reception

[iDjul]

Hi All,

Here my results, what do you think?

Regards,

scan2.jpg

scan.png

[ABi69]

I would place amp near to antenna and filter near to receiver.

[Siphon]

What is the best place to put the FA dark blue filter?
After the antenna or after my RCA d903 amp ?

[ABi69]

Third try with this equipment:

RTL-SDR RTL2832U Dongle ---> FlightAware dark blue filter ---> 10-6000MHz Bias-Tee DC Blocker (powered via Raspberry USB-port) ---> Cable ---> RTL-SDR BLOG 1090 MHZ ADS-B LNA ---> 4-legged spider antenna


Scan without FlightAware dark blue filter:

a.png

b.jpg


Scan with FlightAware dark blue filter mounted between RTL-SDR RTL2832U Dongle and Bias-Tee:

1.jpg

2.png

3.png


There's only one permanent signal left at 958 MHz, all other signals where filtered out... It seems that the range is slightly reduced roundabout 10 nm. Will try to build a better antenna as next improvement.

Flightradar Wanne-Eickel, North Rhine Westphalia, Germany

http://flugradar-wanne-eickel.tk/tar1090/

[ionut-florian]

Thank you for the suggestions, abcd567, I will try also the Option 4.

Indeed, I am limited by the terrain, the maximum range from heywhatsthat.com is consisted with the limit for which I am tracking aircraft. Currently I can ensure visibility on the entire south side, the north is almost inexistent. I guess if I increase the antenna height, I might observe some increase in the overall range. (quite difficult as I am already at 4th floor out of 4 floors, I may consider to change the current home just for that, LOL )

Regarding the performance graphs, I already installed them couple of weeks ago, they are, indeed, a useful tool.

Below is the maximum range polar diagram from the AirNav RadarBox software, which in my opinion is great to check the visibility when you want to install such a receiver in a certain location.

Also, I guess it's better to move at some point to dump1090-fa (the bundle from wiedehopf) and run some scripts for automatic gain optimization. I am currently using pi24 image and I can only make manual adjustments to the gain values and it seems a very lengthy process, considering that the traffic varies quite a lot during the day, so I am not sure if comparing the results will be relevant for a certain gain value.

Anyway, cheers, thanks again for your help and keep up the good work!

[abcd567]

I also made some tests to see if I need a filter or not. Option 2 didn't work for me, so I went with Option 3 instead.

Try the newly added OPTION-4 which uses Windows software "Spektrum". I have added it today a short while ago.
It scans a wider range (24 Mhz to 1800 MHz) and is very fast.
It takes about 1 minute to complete one sweep from 24 MHz to 1800 MHz.
You need to leave it running only for say 5 minutes to repeat it say 5 times.

when the FA dark blue filter is attached, the filtering is dramatic, if I can say that. However, the actual changes, with filters attached to the RPi aren't so visible (maybe the number of received messages from aircraft improved, but there is no improvement for the range and it is still room for that).

Range may be limited by your terrain.
Determine what maximum range you can get at your location by method described in thread What is the Maximum Range I can Get?

If your range is less than what is shown by above method, then it is most likely due to antenna is not high enough, or placed at alocation to be clear of surrounding obstructions (buildings, trees etc) and cannot see horizon in all/most directions.

I also recommend you to install performance graphs It is a good tool to monitor your ADS-B system's performance.
The graphs can be installed by following command

sudo bash -c "$(wget -q -O - https://raw.githubusercontent.com/wiedehopf/graphs1090/master/install.sh)"