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

[ABi69]

First try with the filter was not successful. I found out that the filter blocks the power-supply from RTL-SDR-Dongle to the RTL-SDR-LNA.
For the second try i mounted the filter between LNA and antenna. Result was a bit lower range, roundabout 20 nm...
And it seems that the GSM-signals aren't bothered by the filter mounted directly at antenna...

scan.png

scan.png

I think i have to buy a separate bias-tee with power-supply so that i can mount the filter directly at the RTL-SDR-Dongle...

[wiedehopf]

I'm not sure you need anything in addition to the rtl-sdr LNA ....

[ABi69]

It's only a try because 60 meters away from my receiver there is a large GSM-antenna on a roof.

[abcd567]

image_11148.jpg


https://www.ebay.com/itm/154092554595

10-6000MHz Bias Tee DC Blocker RF Microwave DC Feed 50V SMA-K For Active Antenna

[wiedehopf]

Either the filter is too wide band (FA light blue instead of dark blue) or the signal couples in after the LNA, this could happen due to coax shielding or something, i don't know.

[ABi69]

It's definitely the dark blue one so you might be right with a shielding problem.

IMG_20201029_101404.jpg

[ionut-florian]

Hello, all,

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. I made four tests, two with the JetVision Dongle, with and without the FA dark blue filter, and two with the FlightAware ProStick Plus dongle, with and without the FA dark blue filter.

In the case when the FA dark blue filter isn't attached, there is little improvement in the 930-960 MHz band filtering when switching from JetVision Dongle to FlightAware ProStick Plus as it can be seen in the first two images. However, when switching in the RPi receivers I have from JetVision to FA ProStick Plus, the FA ProStick Plus works better, as expected.

As for the last two pictures, 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).

[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)"

[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!

[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/

[Siphon]

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

[ABi69]

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

[iDjul]

Hi All,

Here my results, what do you think?

Regards,

scan2.jpg

scan.png

[abcd567]

Hi All,

Here my results, what do you think?

Regards,

Yes, a filter will most likely improve reception

[Duccio]

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