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Thread: Short Range Performance

  1. #1
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    Short Range Performance

    Hi All,

    I hope this is the right place. Please feel free to point me towards others that might have faced similar issues.

    Setup:
    Windows 10
    dump1090 v1.10.3010.14
    monitoring traffic with PlanePlotter

    Variation A:
    FA 1090Mhz aerial + 5m cable
    FA filter
    FA Pro Stick

    Variation B:
    dvb-t RTL dongle
    standard dvb-t aerial

    I was at Luton today to get some ADS-B data. As I am not really interested in long range, but more interested in runway and ground coverage, I thought it would be great to place my kit near the tower.
    Interestingly when I used Variation A, I had great long distance coverage, all the way to the north of France. Flights dropped out at about 500ft above ground and I had rarely any AC on ground.

    When I used Variation B, however, I lost most of my long distance range and picked up more AC on ground.

    Do you have any idea why this would happen?
    Is it a hardware issue with the dongle/aerial/ filter?
    Is it a setting in dump1090/planeplotter?

    My initial idea was that dump1090 might have been overwhelmed by the amount of flights it had picked up and then prefereably only reports the flights further away. Another thought was that the signal of AC so close might be too strong for the aerial, so the cheaper areal, due to its loss actually performs better in that environment.

    However, when I did something similar at Bristol I did not face those issues and had sufficient ground coverage.

    Hope someone has an idea and can help.
    Thank you.
    baschtl

  2. #2
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    Yep. Radial pattern of high gain antennas is to reach as far as they can, while sacrificing close contacts (or units are overrun with data strength and cut it off)

    Sometimes referred to as the 'donut' effect
    Posts not to be taken as official support representation - Just a helpful uploader who tinkers

  3. #3
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    Thank you for the quick answer.
    Make totally sense.

    Do you know of any setup that would support short range performance in a more reliable way than the dvb-t dongle/aerial?

    Would it be possible to artificially reduce the gain or to avoid the overrun?

  4. #4
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    Sticking it in a metal box (car boot) or similar to drop the signal rate, or even putting on an angle. But when you do that it will shorten the long distance range in the opposite directions.

    Making sure the tv antenna is trimmed to right length and putting it on a can lid or car roof will also help with near radiating as it will give more guidance to the signal as it were.

    Also try removing the preamp/filter which in itself will allow a bit more leak and possibly lower the input
    Posts not to be taken as official support representation - Just a helpful uploader who tinkers

  5. #5
    Captain Anmer's Avatar
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    Have you trued adjusting the gain of your Pro Stick?
    Mike


    www.radarspotting.com

    Radarspotting since 2005

  6. #6
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    Hi Anmer,

    yes I played around a little bit with the gain. However, haven't seen any significant improvement.
    Please corret me if I am wrong, but usually dump1090 tries to run with the maximum available gain. Which is in my case 46-49 db I think.
    I tried to reduce it down to 20 or even 15, but I have to admit I didn't really know what I was doing as I have never faced that kind of issue.
    Also most of the ideas above crossed my mind when I was traveling back home, so I couldn't really test it further.

    The setup is currently running inside a building to shield it from "too" strong signals. Unfortunatly, I don't have direct access until Friday, but I will keep you posted whether the coverage has improved.

    If you have any other ideas I'll try to test them and keep you updated.

    Regards
    Last edited by baschtl; 2018-03-06 at 21:46. Reason: spelling

  7. #7
    Captain Anmer's Avatar
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    I've been told that a gain of 30 should help with traffic between 0.5 and 150 miles. 50 is good for 5 to 300 miles range.

    But I haven't tried this myself.
    Mike


    www.radarspotting.com

    Radarspotting since 2005

  8. #8
    Captain abcd567's Avatar
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    I use FA Pro Stick + FA Filter + mag mount whip (which came with a generic DVB-T).

    I have cut the removeable part of mag mount's whip to 52 mm length (there is 15mm length hidden inside the plastic base), so total length is 52+15=67mm= 1/4 wavelength.

    The mag mount is placed over lid of a cookie can to provide ground plane. I have tried many values of gain and found that for my setup and location, best reception is at gain =35.


  9. #9
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    We have retried it with different gain settings and it turns out that
    --gain 16.6
    is giving a sufficient ground coverage.
    We loose quite a lot of long range coverage but for our needs that isn't important.
    I was considering running two instances of dump1090 with two antennas and different gain settings to cover both.
    I have seen that the dongle can be defined in dump1090. Is it then as simple as that, that you select for the short range one dongle/aerial with reduced gain and the other dongle/aerial with the maximum gain settings.

    I just need to teach my recording script how to merge the two different data sources into one.

    Regards
    baschtl

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