Do I Need A Filter?

FlightAware ADS-B Flight Tracking
901

Well I just produced my first scan thanks to the clear instruction from abcd567 in post 2 so thanks very much for that! :+1:

scan_800_1200
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A cursory glance sees massive activity from at least 800MHz → 822MHz (based in the UK and wondering if that might be Mobile and/or DTV?) and also from 925MHz → 961MHz (Mobile?) but the 1090MHz signal looks weak by comparison.

I’m guessing this looks to be a good candidate for the dark blue FA 1090 Filter or would I be better served by a cavity/3-pole filter or similar?

I’m going to give the system a day or two to settle because it was only after I rebooted I realised I had previously edited the dump1090-fa to enable Adaptive Dynamic Range so not exactly a like-for-like comparison.

Prior to the edit sudo systemctl status dump1090-fa reported;

sudo systemctl status dump1090-fa
● dump1090-fa.service - dump1090 ADS-B receiver (FlightAware customization)
   Loaded: loaded (/lib/systemd/system/dump1090-fa.service; enabled; vendor preset: enabled)
   Active: active (running) since Sat 2022-01-29 08:17:07 GMT; 1 weeks 5 days ago
     Docs: https://flightaware.com/adsb/piaware/
 Main PID: 570 (dump1090-fa)
    Tasks: 3 (limit: 4915)
   CGroup: /system.slice/dump1090-fa.service
           └─570 /usr/bin/dump1090-fa --quiet --device-type rtlsdr --gain 60 --fix --lat xx.xxxxx --lon x.xxxxx --max-range 360 --net-ro-port 30002 --net-sbs-port 30003 --net-bi-port 30004,30104 --net-bo-port 30005 --json-location-accuracy 1 --lat xx.xxxxxx --lon xx.xxxxxx --write-json /run/dump1090-fa

Warning: Journal has been rotated since unit was started. Log output is incomplete or unavailable.

And following the first reboot since the edit it now looks like this;

dump1090-fa.service - dump1090 ADS-B receiver (FlightAware customization)
   Loaded: loaded (/lib/systemd/system/dump1090-fa.service; enabled; vendor preset: enabled)
   Active: active (running) since Mon 2022-02-14 00:35:20 GMT; 25min ago
     Docs: https://flightaware.com/adsb/piaware/
 Main PID: 535 (dump1090-fa)
    Tasks: 3 (limit: 4915)
   CGroup: /system.slice/dump1090-fa.service
           └─535 /usr/bin/dump1090-fa --quiet --device-type rtlsdr --gain 60 --adaptive-range --fix --lat xx.xxxxx --lon xx.xxxxx --max-range 360 --net-ro-port 30002 --net-sbs-port 30003 --net-bi-port 30004,30104 --net-bo-port 30005 --json-location-accuracy 1 --lat xx.xxxxxx --lon xx.xxxxxx --write-json /run/dump1090-fa

Feb 14 00:35:22 RaspberryPi-air dump1090-fa[535]: Found Rafael Micro R820T tuner
Feb 14 00:35:22 RaspberryPi-air dump1090-fa[535]: rtlsdr: tuner gain set to about 58.6 dB (gain step 29) (tuner AGC enabled)
Feb 14 00:35:22 RaspberryPi-air dump1090-fa[535]: adaptive: using 50% duty cycle
Feb 14 00:35:22 RaspberryPi-air dump1090-fa[535]: adaptive: enabled adaptive gain control with gain limits 0.0dB (step 0) .. 58.6dB (step 29)
Feb 14 00:35:22 RaspberryPi-air dump1090-fa[535]: adaptive: enabled dynamic range control, target dynamic range 30.0dB
Feb 14 00:35:22 RaspberryPi-air dump1090-fa[535]: Allocating 4 zero-copy buffers
Feb 14 00:35:32 RaspberryPi-air dump1090-fa[535]: adaptive: available dynamic range (29.1dB) < required dynamic range (30.0dB), switching to downward scan
Feb 14 00:35:32 RaspberryPi-air dump1090-fa[535]: adaptive: changing gain from 58.6dB (step 29) to 49.6dB (step 28) because: probing dynamic range gain lower 
Feb 14 00:35:32 RaspberryPi-air dump1090-fa[535]: rtlsdr: tuner gain set to 49.6 dB (gain step 28)
Feb 14 00:35:42 RaspberryPi-air dump1090-fa[535]: adaptive: available dynamic range (38.6dB) >= required dynamic range (30.0dB), stopping downwards scan here

So it looks to me like Adaptive Dynamic Range has reduced the Gain one step from 60 → 49.6 in the 30 minutes or so following the reboot which might go some way towards the 1090MHz signal looking a little weak? Or maybe because the graph was generated just after midnight with only 15 aircraft being received rather than the usual 200+?

Anyway it looks to me like it’s time to put the 1090 filter inline and run the heatmap waterfall graph again to see if that will reduce the out of band signals and check what effect that might have had on the 1090MHz signal read in conjunction with wiedehopf’s Graphs package.

This stuff is great…thanks guys! :+1:

Just want to make sure I’m treading the right path here…

Thanks & kind regards,
-=Glyn=-

902

Bear in mind though that the heatmap script will produce a scan that is auto scaled. Which makes comparison with later scans difficult.
The range used is shown in the output from the heatmap command as the z parameter
It finds the highest and lowest figures in the csv and uses them.
eg from a scan I did:
./heatmap.py scan.csv scan.png
loading
x: 4576, y: 60, z: (-37.070000, 4.400000)

You can force as fixed scale to make future comparison easier.
I suggest using something like -40 to 10 as a fixed scale so:
./heatmap.py --db -40 10 scan.csv scan.png

903

Ah I didn’t realise that.

Thanks for the heads-up Lawrence.

Kind regards,
-=Glyn=-

904

Hi,
I just started with tracking air planes.
I’m currently using a Generic DVB-T USB-stick with an antenna (cut a bit short at 50 mm, with the internal 15 mm somebody mentioned in this thread, I should get 65 mm instead of 67 mm) powered by an USB hub connected to my Raspberry 2B.
Unfortunately I can’t place my antenna outside and my windows are quite thick and my line of sight is quite limited (I’m living on the first upper floor and there are many high buildings and trees around the building). I can track some air planes but want to improve the results.

To create the scan picture on Bullseye, I had to switch to Python3, therefore sudo apt-get install python-pil became sudo apt-get install python3-pil
and I had to replace the first line in heatmap.py
by #! /usr/bin/env python3
Maybe this is helpful for others.

Here is my scan

scan
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As expected there is a strong signal at 960 MHz (Europe GSM) and I think I need a filter. Do you agree and which one do you recommend

Do you think It is worth to change to an “official” FlightAware stick or a different antenna?

Thanks for your replies. In the meantime I’ll look into the threads regarding the gain optimisation.

905

A very easy, zero-cost, but noticeable improvement in reception can be obtained by placing mag-mount Whip Antenna over a metal food-can or metal plate.

NOTE: An additional advantage of using a plate or can made of iron/steel helps in keeping the mag-mount whip from falling, as mag-mount base clings to the iron/steel.

Optimized-Whip-on-Plate-1
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Optimized whip on a food can
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Additional advantage of using cookie can lid :slightly_smiling_face: :wink:

Cookie_Monster

1 Like
906

Sure this is going to help others. Thank you for posting. :+1: :+1: :+1:

I would like to edit the first post of this thread to incorporate these changes, but unfortunately forum does not let members edit posts older than a month or two.

Only Flightaware staff has the authority to edit old posts.

907

Filter or better antenna doesn’t really help with obstacles.

You can likely get a bit more by upgrading the antenna / SDR but the gain will likely be minimal if you’re so obstacle limited.

908

I liked the idea of buying cookies and got a box similar to the one of @abcd567

cookies
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I “installed” it at noon, but I didn’t get visible changes:

dump1090-localhost-local_trailing_rate-24h
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Filter or better antenna doesn’t really help with obstacles.

My naive hope was, that an antenna/filter helps to receive week signals partially blocked by obstacles?
Is there an easy explanation, why the 1090 MHz signal is in your explanation more or less line of sight but e.g. GSM seems to go through buildings? Is it just signal strength?
Do you expect that the 1090 MHz signal is also blocked by 3 layer of window glass, a wooden outer wall or window shutters (in the picture above I closed them, but don’t know if the reduced signal is due to less flights in the evening or weaker signal)?

909

It could also be due to the GSM frequency used, which can be as low as 380MHz:

Also GSM transmissions come from the cellular telephone network and there are multiple cell sites. If your phone has a weak signal when connected to one site it’s automatically switched to another with a stronger connection, probably due to the cell tower’s location. ADS-B doesn’t work that way, the aircraft is where it is and if you can’t receive its ADS-B messages through being blocked by obstructions then that’s just the way it is. You’ll just have to wait and see if the airplane moves into an area that’s within your antenna’s actual range. Also your cell towers are going to be a lot closer to your location than an airplane that’s 200 nautical miles away.

910

No harm (except a lighter wallet :wink:) in trying a better antenna and a better dongle. My situation is almost like yours, and when I used Flightaware antenna, Flightaware prostick and Flightaware Filter, my performance visibly improved over mag-mount whip and generic DVB-T dongle.

911

It is on floor now. Raise it by placing it over a small table, tripod or chair.

912

GSM towers are high up for a reason.
Aircraft 150 nmi far away are basically on the horizon, so there will be many more buildings / hills in the way.

And yes the signal strength is lower for aircraft that are far away.

If the window shutters are metal they’ll block everything.
Otherwise the materials shouldn’t be too terrible.

1 Like
913

Some self experiments identified that it will get better by eating up all cookies… :rofl:

2 Likes
914

scan
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what about my scan?

915

Seems like some GSM towers are close by?

916

Finally got around to doing a test with my new RTL-SDR blog stick and LNA.

Prostick Plus:

scan
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RTL-SDR Blog V3 + Triple Filter LNA:

scanwithamp
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Pretty significant difference with the extra filtering. Haven’t seen too much of a difference performance wise(I was hoping for a significantly higher message rate), but I’m still messing around with the gain.

Also I had to place the LNA right in front of the stick, don’t think it’ll survive the brutal summers over here if placed outside.

Max messages I’ve seen is around 500/s.

Capture
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2 Likes
917

I placed mine inside of a small upside-down plastic bottle with the neck sawed off and painted flat black inside and white outside. So far no problems, but it doesn’t get nearly as hot here in SE Asia as it does where you live.

918

I was thinking of doing something similar, but using aluminum foil on the outside to reflect sunlight.

I haven’t seen any operating temperature specifications for the LNA, don’t think it’ll be able to survive 50C+direct sunlight. There isn’t really any shade on our roof either.

919

Has anyone used this low-cost SAW filter?

https://www.aliexpress.com/item/1005001923773712.html

 

Graphs & Picture From Customer Reviews

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Before & After

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920

image

 

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