FlightAware Discussions

Do I Need A Filter?

I’ve got the: “elevated feed”, but without the tuning notches.
I ordered mine naked, and built my own raydome.

I like these, not because they are a great antenna, but because they are repeatable (and very cheap)


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That would be the 170mm board then correct? Probably could use a dedicated thread for these things. I also find them fantastic for testing as they are easy to work with.


I did it : https://discussions.flightaware.com/t/ads-b-antennas-cheap-chinese-pcbs-and-the-others

(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.

(2) The scan 1 shows RF noise picked by antenna, and scans 2 & 3 show how filters remove this noise.

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



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



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



Yes, two different versions;

cf1090-kt30-wide 1090 MHz cavity filter for Mode-S / ADS-B - wideband
cf1090-kt30 1090 MHz cavity filter for Mode-S / ADS-B

Both work excellent esp the outer band behaviour.
I still have to hook them up to a NanoVNA that I ordered, but it seems to take like forever to arrive here. I’d like to experiment with the effect of a low and high temperature environment (put 'em in the freezer/oven for a while).
Another advantage is that they are DC shorted so no static build-up.

I want to place it in a box with a Triple Filter LNA (the MGA-13116 has better Noise and Linearity figures than the PSA4-5043+)

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Hi, sharing my scan, first time looking at a signal, not a lot of planes today due to covid restrictions. What do you think? I’m using a Nooelec 820T NESDR Mini with factory antenna.

And can you explain please the sort of “complementary” colors between 870-880 and 880-890?
I was sure that the GSM band was 850-900, not seeing anything there, but some in the middle.
Will love to know too what is “pulsating” at 939mhz.

This is what I found in Amazon that delivers here, both cost more than my entire setup xD


Anyone tried this filter?

I have not personally, but for those interested, here is more information about the design and specs:

Hi all
just checked my airspy mini with Spectrum Spy, 3 pics
could some one decode these for me, i cant really see 1090 signal
mid range gain
1 without tri/lna
2 with triple filter lna,
3 full gain with tri/lna
with my lower secondary antenna

Hi all, I’d like to ask for your opinions. Currently, my feeder setup is an OrangePi Zero LTS with Piaware 4 on Armbian, RadarBox Outdoor ADS-B Antenna, and ADS-B RTL-SDR Discounted Bundle (got it last month from RTL-SDR Blog), and a FlightAware Dual UAT/ADS-B filter. I wasn’t able to acquire the FlightAware ADS-B only filter due to lack of stock and I thought it’d do just as well (stupid decision). Also apparently I live within 200m of a cell tower (this fact was just recently known to me).

When I went to finish the setup this morning, I was greeted with an awful message rate (avg at 8msg/s, maxing out at 20) with unreliable tracking, even though I live within 20km of a major international airport (CGK/WIII). Then, I went ahead and did a spectrum scan and got these results:

scan w/ FlightAware Dual UAT/ADS-B

So it seems to me that the ~900MHz GSM signal is overwhelming the 1090MHz signal. And I’d have to get a better filter/dongle. In your opinion, would something like this Aliexpress filter work?

EDIT: Removed a sentence which didn’t fit my current circumstance

I have not tried this filter, just now looked at its Aliexpress page and found a scan which is copied below. If this scan is realistic, seems it can get rid of GSM950. However only the one who has used it in location having GSM950 can tell about it’s performance

As given on the graph:
Center frequency =1090 MHz
Span = 500 MHz

Hence scan’s:
start frequency = 1090 - 500/2 = 840 MHz
stop frequency = 1090 + 500/2 = 1340 MHz


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

There will be a SAW filter in that housing. It’s the same type as used in the dongles with integrated filters. They are not the highest performing filters, but an excellent starting place.
If you have the RTL-SDR blog V3, I’d normally recommend the matching filter/amp, but being close to a busy airport may cause a lot of overload. It is definitely a good choice if you are after long range.

I found a different chart for what seems to be the exact same filter from a different seller

This chart shows what seems to be a different filter profile (please correct me if I’m wrong; i’m a total newbie who’s eager to learn). Do you think this filter will do an okay job filtering the strong 900MHz GSM signal?

Has anyone tried this filter?
US $3.54 + Shipping US $1.53
Estimated Delivery: 30-50 days

ADS-B active receiving antenna 1090 MHz Hot ADS-B+ Lna Filter ADS-B 1090mhz Bandpass Filter For Software Radio Sdr


1 Technical indicators
They posted Antenna Specs for Filter :wink:

DIMENSIONS (this image is from another supplier)

Yes, I did, along with a classic R820T TCXO dongle. From the top of my mind, it was more an amplifier than a filter, or said another way, I felt more the amp effect than the filter effect. However, I could take it for another test run during the day and post the results here.
Spoiler alert: I don’t have any real test instruments, I’ll run scans using raspi tools like rtl_test or rtlpan.exe

Quick & dirty output from rtlpan, graph from LibreOffice :

On those tests, amplifier gain is set at 40dB for both runs.

It’s all about presentation. I don’t think it will, especially if the 950MHz signal is too strong. In the graph the starting frequency is 40 MHz so each horizontal division is approx. 300MHz. Each vertical division is 10dB (blue line).
So @ 900MHz the attenuation is approx. -17dB. @ 950 (Europe) approx -8dB.


Plot the graph using “Spektrum”. It is quick & easy. Click here to see How-to.



…or when you use an Airspy, SpectrumSpy. Less options than spektrum/pavels, therefore easier to operate, plus it has a waterfall.

EDIT: added SpectrumSpy image + typo’s

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