FlightAware Discussions

How to get ads-b signals from aircrafts on ground/runway

How far up are you? I know you are somewhat blocked to the West but have a great view South and East. Still haven’t gotten my antenna up on the roof and may not get it up as the Doc has me on NO LADDERS, EVER. :disappointed: So I have it on my back porch about 20 feet up. So obstructed view to South (well at least through a roof). Trying to hire someone to put it up for me and IF I ever find someone I will be scrambling to get 978 up as well.

Bob

Me, my antenna, and my Pi are all at the same level - 60 feet above road.

I live in an apartment in a high rise building. Everything is indoors, as the building managment does not allow anything projecting out of window or fixed on outer wall or on building’s roof. Me and my antenna both have identical view of outside world through a large window. :slight_smile:

60 feet is goood. Even if I put up a tower it would only be half that high. You also have Pearson in your backyard also (the busiest airport in Canada) Can you hear ground vehicles at the airport?

Bob

There is a 200 feet tall building across the street, which blocks the view of Pearson. However I still see some planes on ground by signals reflected by surrounding buildings.

Ever think of using a SDR dongle to listen at ATC or other public airport traffic? Probably would really kick up your ADS-B enjoyment. 1/4 wave antennas for air traffic are “window size”.

BD

I sometime listen to ATC VHF 118~135 Mhz, and HF ssb (120m to 10 m / 3 Mhz to 30 Mhz) on this one (Grundig Satellit 750)

Wow, sure beats the crap on my little windup model. Got to get one of those. Got a 2 meter icom ham that covers air (receive only in air band) with an Arrow Antenna J-Pole. Just as soon as I get on the roof. The old man’s lament.

Bob

I ran the 30 mins heatmap and this is what I get.
Below is the 30mins scan at 30db gain set on SDR. Preamp voltage is at 6V and I happen to see ground signals if the gain is set between 30-42db and Preamp volt is set at 6V in this location.

I move the antenna to the pole which has comparatively clearer view towards the Airport. This is what it shows for same 6V and 30 DB gain.

If I increase the height of the antenna then 1080 mhz gets stronger and I rarely get anything decoded on dump1090. Unless I reduce the preamp gain which allows only strong ADSB signals to reach the SDR.

Reducing the SDR gain does not help?
Try a gain of 20 or 25 when the antenna is up higher, but leave the preamp at 6V.

Looks like you get clear view of a mobile tower when increasing the height of the antenna.
That is likely overloading your preamp because it’s not really fit for purpose.

You could try without the preamp, the antenna has high gain after all.

Best solution remains the rtl-sdr LNA.

You could try a filter before the preamp i suppose:
https://www.ebay.com/itm/132406298935

But that’s money that can’t be used for the proper already filtered rtl-sdr LNA.
If you try a filter, i’d only try a really cheap one, if you can find one :wink:

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You are correct. If Antenna sees 270degs (as airport is there), then it has clear view of towers at 300 degs, then two more around 330-350 degs. Also it gets nice view of towers at 210 & 240 degs. Most of them are situated around 100-200 mtrs.

The place I get some Ground messages are from places which doesn’t have direct sight at those towers.

Only few messages gets decoded if the gain is reduced below 30. And they come at RSSI -20s when they are just some 14NM like that. Other than that nothing comes.

But if we reduce Voltage to preamp from 6 to 3V then more messages are decoded but only strong ADSB comes and no GND messages.

SDR is located two floors down. So cable length is atleast 30 ft. Without preamp this is what I am getting when the antenna is on the pole.

More or less I get only few messages and it is so bad that even small whip antenna inside the house will catch few more planes.

The preamp page link is giving error. Item not found. RTL-SDR LNA I will have a look. But any DIY solutions for this?

It was a link to a filter, not a preamp, but i wouldn’t recommend it anyway.

This is the rtl-sdr LNA: https://rtl-sdr.com/new-product-rtl-sdr-blog-1090-mhz-ads-b-lna/

You could try a cavity filter and place it between antenna and preamp.
https://www.changpuak.ch/electronics/interdigital_bandpass_filter_designer.php
https://keptenkurk.wordpress.com/2014/11/05/a-homebrew-1090mhz-ads-b-filter/

There are some threads on this forum as well, but i didn’t find them.

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I will try the cavity but I heard it is not easy to tune properly without proper equipment. RF cable cut to the desired frequency length and shorted will be effective filter? Suppose using a T joint, an RG 6 cable cut to length for 1080 mhz or 960 mhz and shorted will reduce the those signals?

I removed the connector. Plugged the Nooelc Mini SDR directly to the pi and still I am getting some signals from 880mhz and 960 mhz. No wire not even adaptor. Gain was set to 49.6.

Nothing you do will be easy to tune without a RF analyzer of some sort.

I suppose you could turn up the LNA you have to full voltage so it produces noise.

Then you can use the filter directly in front of the dongle and do power scans?
That should you give a rough idea of the center frequency of the filter.

A noise generator would be better but it could work just with the gear you have.

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I will try the idea.

I tried the idea and I had LNB (used in satellite dishes) which outputs from 950-2160 mhz and also satellite receiver with loop out (power block). Hence I used it as signal source for the making Coaxial cable filter. Comparatively strong signals were on 940 Mhz and at 950 Mhz. So idea is to block it. Initially I tried band pass for 1090 but not able to succeed.

This is the noise source and it is not perfect but something better than nothing. Some what giving signal enough to make a filter.

Cut two coaxial cable for the lengths 940 and 950. Used two T joint adapters.

Putting this near antenna before the preamp worsens the reception as 1090 Mhz gets 2-3 db weaker and per amp fails to amplify it!

Hence I put it after preamp and reception seems to be better than earlier but hard to confirm exactly. Seeing more ground traffic.

Earlier if preamp voltage is increased above 6V then there won’t be any ADSB reception (may be 950mhz saturates). Now after the filter at 12V ADSB comes properly but at 6V no ADSB(may be preamp doesn’t send high DBs in the coaxial line and due to line loss with the filter it is affecting)!

AGC is constantly giving one ground message at -3.1 dBFS and some times even lower. Some aircrafts on the ground are coming around -7 to -10 and some at even -31 dBFS. But they are not consistent they just like that come suddenly and then vanish.

Will it be worth trying SAW filter and adding it near/after preamp to see whether it helps?

The present arrangement has around 3 db loss which will be same with SAW but quality of filter will be higher than now.

Planes on the ground: O’Hare, Chicago, USA

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Put SAW filter near the RTL dongle. Gain is set to full 49.6. Mobile signals still manage to enter. But atleast now I am able to see 1090 Mhz better. Decoding wise not able to see any big change. May be there but without able to compare realtime it is just guess work.

I need to try different amp or RTLSDR 1090mhz amp (not at all cheap and more over I also need rtl sdr dongle) or need to try with better antenna if I still wish to get ground signals. Any advice or suggestions how to go from now on? Is GSM band still overloading the dongle?

You can just inject 3.5 V for the rtl-sdr LNA, don’t necessarily need the v3 dongle.

Turn down gain for the scan, otherwise you can’t compare signal strenght very well.
But it doesn’t look too bad, should work fine.

Once you are really limited by terrain, there is just nothing you can do beyond a certain limit.
(not sure you already reached that limit, but you might have)

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I will reduce gain and will do another scan. Without SAW when aircraft goes to 275 or 250ft there wont be any updates after some time it will show GND and aircraft will jump positions 1 or 2 times and will vanish. Again it will come back moving into taxiway for some time before vanishing.

With SAW filter it is showing aircrafts till 150 to 100ft then 2 or 3 seconds later showing GND and shows aircrafts scrolling on the runway for some time before vanishing and again during taxiway.

Taxiway C is shown without filter but with a filter it is not shown. Taxiway M is shown with filter which isn’t without a filter. Totally confusing.

You know where to put the gain in the scan command?
This would be with a gain of 15:

sudo rtl_power -f 800M:1200M:100k -i 30 -c 50% -e 30m -g 15 -F 9 >scan.csv

The gain for the scan is independent of dump1090 gain.

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