FlightAware Discussions

What do you make of this at 1100mhz

Thought I’d treat my self to a FA dongle + Blue FA filter for the 1090mhz frequency.

Things started turning bad when i got my new antenna and realised that I was not getting anywhere near the range as I was on the old little hand made one I had. So anyway after further testing it would seem that there is something nasty at 1100mhz.

What you make of that?

Gutted as the antenna was going out side on the chimney but with interference like that it’s hardly worth it…


(top scan is the home made antenna, check further down, the bottom picture is the new one that I bought that I’ve had 2 of so far!)

The frequency range from 940 MHz to 1215 MHz is assigned to aeronautical radio navigation in the US as well as internationally. Do you have an aerodrome nearby? A good filter will block that signal.

Thanks, that’s what I’m saying, I went for this… I’m here in the U.K by the way, I’m not to far from a cell tower that’s just been upgraded. a few antenna etc. dishes on a tower about half a mile from me…

30-06-2020 07-05-33 30-06-2020 07-05-16

That filter has a pass band frequency range of 1080-1100 MHz. If you suspect interference right at 1100 MHz it might not be the best for your application.

There are numerous plans online for 1090 cavity filters you can make at home (I’m sure kits are available too) with a tighter range of 1086 - 1094 MHz.

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Rather than build a bandpass cavity filter in this case it may be easier to build a simple notch at the troublesome frequency.



Thanks, So is it worth sending that “Flight Aware” filter back and then maybe picking up something like a “RTL-SDR.com ADS-B Triple Filtered LNA - Bias Tee Powered - 1090MHz” + “Bias Tee”

This is a high performance filter and LNA combination for 1090 MHz ADS-B reception with 27dB of gain, a noise figure of around 1dB and over 60dB out of band attenuation. Designed to be used with bias tee power from our RTL-SDR Blog V3 dongles with the LNA mounted as close to the antenna as possible. It is triple filtered with a low loss high pass filter on the front end, and two 1090 MHz SAW filters placed in between and after the high performance low noise figure two stage MGA-13116 LNA. The triple filter design should help avoid dongle or LNA overload in noisy/strong signal environments.

  • Genuine RTL-SDR.com product

  • Aluminium case

  • SMA connectors

  • 3 filters at 1090MHz

  • 60dB out of band attenuation

  • NF ~1dB

  • SMA coupler included

  • Bias tee powered

That’s a really good performer, but unfortunately the chipset is end of life and no longer for sale.

Thanks, I can still buy one here in the UK, so, send the FA one back or keep that and run it all inline, it’s going to be a lot of MCX connections!

What ya think?

I can’t say for sure mate. Can’t make head’s or tail’s from your scan. Typically the FA dark blue filter in front of the FA Plus stick would be overkill since there is already a filter built-in to the stick.

Where was your antenna and exact setup when performing that scan? It wasn’t clear from your initial post. if you were indeed using the FA Blue dongle and Dark Blue FA Filter, then what you are seeing is probably waaaay too much gain since your entire passband is lit up like a Christmas tree. Kick the gain down some and get as many filters out of the mix as possible so you can get a true scan of your environment. It would be better if you could run a scan with an unfiltered/un-amp’d radio to get a better idea - if you don’t have one, don’t sweat it.

Kick the gain back down to maybe 33.8 (I’m assuming you’re pegged or AGC right now based on that gnarly scan) and take another peek before buying a bunch of stuff you may not need. I don’t know if I’d recommend the rtl-sdr triple filtered LNA in front of an FA Blue radio - thats a dump-load of amplification that probably wont be needed.

I’d recommend doing a wider band scan with whatever you currently have to see what else may be going on before plunking more money down on your system. Also, you shouldn’t need to be using MCX connections with your gear?

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Thanks, the antenna is mounted in the loft for testing, yes that’s correct, there’s only the FA blue dongle and also the FA blue filter attached to the pi.

This is the command that I’ve been running.

sudo rtl_power -f 800M:1200M:100k -i 30 -c 50% -e 30m -g 30 -F 9 >scan.csv

sorry didn’t mean MCX meant SMA

Is that an active antenna as well? With gain set at 30 according to your cmdline, I wouldn’t expect to see that much noise in your passband. Maybe see what it looks like at like 16.6 gain?

Mmmm, criss-cross fries! Thanks, now I’m hungry. :yum:

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haha! yeah this is the antenna.

I can run the command again, so using this…

sudo rtl_power -f 800M:1200M:100k -i 30 -c 50% -e 30m -g 16.6 -F 9 >scan.csv

I haven’t seen that particular antenna before, but seems interesting. It does not appear to be active (built-in LNA), so yeah… curious how the scan looks with less gain and if using less gain yields better results for you on the map. I’d also try with and without the FA filter inline to see if you can get a feel for which is giving better results. Those spectrum scan will only tell ya so much in the end - nothing beats real-world testing.

Running the scans now, the very first picture is the hand made one which was getting super duper range, how ever this is when all the problems started as I have an old scanner antenna up on the chimney I thought I’d treat my self to some new professional kit, so that’s why I ended up buying that “antenna” and the FA gear

After wiring it up for testing I realised that the range that I was getting was pants, this is when the scans started coming into play.

So as you can see from the 1st picture I posted the picture below shows the little hand made one and it’s scan results.

how ever that guy went out of his way to help me, he sent me a 2nd replacement which is in there now getting tested, it seemed as though it had more gain.

madness this little one got about 250 mile range.!

Have you tried your new antenna with the blue FA dongle but without the separate filter?

If not, can you give that a try?

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Here we are…(maybe it’s me but it looks worse with the filter attached?)

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Here is the scan with a rtl-sdr lna in use.

That’s a good sign then no? all them “blips” at 1090, not suffering any bleed over from other channels (like me and 1100mhz!)

I’m running 2 tests, 24 hours long as of 1.00pm today, one with the filter on and one with the filter off.

Yeah, super strange. Both scans using the same gain and nothing else changed between the filter and no filter tests? The top scan looks horrible - you still have an interesting spur at 1100Mhz (hence the name of the thread) that’s unknown, but not as worried about that as the overall noise on the top scan. Something’s going on with that filter according to those results if everything else was equal. Ideally run with as few components as possible so long as the scans looks clean and the bottom sure looks better to me than the top.

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I even got to the point where a guy told me to try powering off in between changing the filter over. Just to discharge everything. (Thanks @wiedehopf) I’m running 2 tests now, 24 hours with and without the filter. Turned the gain down…

So I wasn’t going mad I done 2 tests backs to back.

What do you think new filter? After all, support did point me in the direction of this forum?


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