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

[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).

[ABi69]

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

IMG_20201029_101404.jpg

[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.

[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

[ABi69]

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

[wiedehopf]

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

[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...

[ABi69]

Thanks to all, i've ordered FA dark blue filter and will report.

[wiedehopf]

Just because you see something in the scan doesn't necessarily mean you need extra filtering.

If you have good range, no need to try extra filtering.
But with a mobile transmitter that close it could be benficial but it's basically impossible to tell without trying.

[abcd567]

In this case adding another filter (FA dark blue) may or may not help. Only by installing it you will know. As Spider is a low gain antenna (2 dBi), the insertion loss of the additional filter may reduce performance. However these are possibilities, and you can know if it improves, remains same, or decreases performance only after installing FA dark blue filter.

[ABi69]

Very sure...
I hope that this is not a fake device, but i bought it directly from their ebay-shop.

https://www.ebay.de/itm/RTL-SDR-Blog-ADS-B-Triple-Filtered-LNA-Bias-Tee-Powered/283992357982

IMG_20201020_010647.jpg

[abcd567]

I'm using a Raspberry Pi equipped with RTL-SDR RTL2832U DVB-T Tuner Dongle, RTL-SDR BLOG 1090 MHZ ADS-B LNA

The RTL-SDR BLOG 1090 MHZ ADS-B LNA has a triple filter built in,

RTL-SDR BLOG LNA comes in two versions, one without filter, other with triple filter. Both look very similar.

Are you sure you have the triple-filter one? If you had tripls filter one, it is unlikely you will still get 960 Mhz interference.


TRIPLE-FILTERED 1090 MHZ LNA

RTL-SDR-Triple-Filtered-1090LNA.jpg




WIDE-BAND LNA

RTL-SDR-WideBand-LNA.jpg

[ABi69]

Thank you very much!

[abcd567]

ABi69

You have interference from GSM950. Purchase Flightaware Dark Blue Filter.

Do NOT purchase the Light Blue one, it wont help in
your situation.


FA-Filter-Dark-Blue.png . . FA-Filter-Light-Blue.jpg

[ABi69]

Hi,

I'm using a Raspberry Pi equipped with RTL-SDR RTL2832U DVB-T Tuner Dongle, RTL-SDR BLOG 1090 MHZ ADS-B LNA and a selfmade spider-antenna.

The RTL-SDR BLOG 1090 MHZ ADS-B LNA has a triple filter built in, but there seem to be lots of signals in the range between 930 and 960 Mhz caused by a GSM-antenna 60 meters away from my ADS-B-antenna...

Could you give me an advice for a suitable filter for my setup?

Thanks!


scan.png

scan.jpg