FlightAware Discussions

Do I Need A Filter?

Uputronics filter with usb supply to filter

That looks better, might be your bias-t is doing something strange.

How did you switch on the bias-t anyway?

I did use this guide: https://www.rtl-sdr.com/getting-the-v3-bias-tee-to-activate-on-piaware-ads-b-images/

Forgot to mention i’m using the Flightaware Prostick Plus instead of the rtl sdr V3 dongle

I’m confused now :stuck_out_tongue:

Does that combo work for you now?

To deactivate the builtin bias-t:

sudo systemctl stop dump1090-fa
sudo rm /etc/systemd/system/dump1090-fa.service.d/bias-t.conf
~/rtl_biast/rtl_biast -b 0
sudo systemctl restart dump1090-fa

Then you should be able to use the rtl-sdr v3 with the uputronics amp as well.

Looks like it does, but its getting the same results as the LNA,

Setup: PI -> Flightaware Pro stick plus -> Uputronics filtered preamp -> 15m coax -> antenna

Gain is 29.7, percentage of strong messages: 6,053


I will try this tomorrow, thanks for all your help!

Maybe the problem was only present for the scan.

If you want to do two more scans with the rtl-sdr v3 + LNA combo, then do one scan with the first command issued before the scan and then the second scan with the other command issued before the scan.

~/rtl_biast/rtl_biast -b 0
~/rtl_biast/rtl_biast -b 1

At least one of those scans should be completely black :wink:
And if the not black scan shows noise, then there is a problem that’s either with the LNA or with bias-t.

You said the scan with the v3 + uputronics driven by the v3 bias-t was bad as well, yes?

Yep thats right. Could i do something wrong with activating the bias tee? I did just copy-paste on the RTL-SDR guide for activating.

There are some cases where the activation just doesn’t work.
But i would expect a black spectrum and no planes in that case.

The two scans with manually activating and deactivating the bias-t before the scan should make it clear.

As my soldering iron has fried itself sometimes ago, I used soldering gun to solder the wires from 5V DC adapter to the Bias-T. It seems excessive heat from the powerful soldering gun damaged the delicate copper strip on the PCB, and a little pull on the adapter wire caused the wire to pull out along with the copper strip to which it was soldered :frowning_face:.

Have ordered these two. These do NOT require soldering, as screw terminals have been provided for DC supply wires.

The reason for ordering 2 is that these have different sma terminals. One has female/female, and other has male/female. This gives flexibility in different configurations.

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Thanks for these instructions. I have been trying to decide if the blue FA filter was helping or hurting. I have the blue FA pro stick and the FA antenna, and have been playing around with gain to try to find the highest airplane count with my current antenna location.

I finally got around to following these directions today, and it looks like I have some cell tower interference in my area. Put the filter back on, and the results look pretty good!

Before (no filter):

After (with filter):

I appreciate the tips! And the time that everyone puts into their contributions.

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Statistics are useful for that:


Use the filter for a week, then do another week without filter.
Check if the numbers change.
(might also want to check gain: Thoughts on optimizing gain)

Thanks. I have been using the graphs for a while, and tweaking the gain to get to that 5% strong messages goal, but I seem to have enough variability in the traffic in my area that it is difficult to see any obvious trends.

Since this scan shows that I definitely am seeing strong GSM interference, I will leave the filter in place and continue trying to find the ideal gain setting.

You are right.

Your Scan without filter shows GSM-850

This is 1090MHz part of your scan

Mobile / Cell Phone Frequencies Close to 1090 MHz ES and 978 MHz UAT

GSM-850 is used in most of North, South and Central America.
(ITU-Region 2).

Also used in Australia & New Zealand in addition to GSM-900/EGSM-900
850 MHz 824 - 849 MHz 869 – 894 MHz
GSM-900 / EGSM-900
GSM-900 is used in most parts of the world: Africa, Europe, Middle East, Asia (apart from Japan and South Korea where GSM has never been introduced) and Oceania.
(ITU-Regions 1 and3)
900 MHz 880 – 915 MHz 925 – 960 MHz

hmmmz… a late reply, but 15m of coax will give you a lot of attennuation (loss) at this frequency, no matter what low loss cable you are using. Get the LNA as close to the antenna as possible and your range will improve.

Will any of your install options work with and odroid / airpspy setup or point to the relevant install please, I haven’t done any recent tests with this equipment.