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  • bimmerdriver
    replied
    Thank you for the suggestion about the ground plane. I set the antenna on the top of a small metal pail, placed upside down. I think it made a difference of perhaps a couple of dB.

    You can see a slight uptick at around 1900.

    dump1090-localhost-signal-8h.png

    dump1090-localhost-signal-24h.png
    There are relatively few flights between midnight and 6 AM.
    Attached Files

    Leave a comment:


  • abcd567
    replied
    Originally posted by bimmerdriver View Post

    Thank you for your reply. I should have been more clear in my post. The photo is not of my exact antenna. It's the closest that I could find on the internet. My antenna has a shorter cable. It's actually around 1 m in length, although it's probably not very good quality.
    As the total signal loss is product of loss per meter x length, even with a high loss cable like RG174, the total loss will be very small if coax length is short (1 meter).

    You can improve the range and number of aircraft with this tiny antenna by:

    (1) Placing it near a glass window or wooden outer wall. Both the glass and wood will pass rf signal with minimum loss.

    (2) This antenna's base is only 1 inch in dia and provides only a small ground plane. Place antenna over a metallic plate or food-can. This will enlarge it's ground plane substantially and improve range & plane count. If metallic plate or food-can is made of iron or steel, the magnetic base of antenna will cling to it, and prevent it from falling. Keeping the whip in vertical position gives the best reception as the ADSB signal is vertically polarized.

    Leave a comment:


  • bimmerdriver
    replied
    Originally posted by abcd567 View Post
    The coax cable of these antennas is generally low-cost RG174 which has high signal loss per meter.
    Signals from distant aircraft are already weak. If this coax has a length longer than say 3 meters (10 feet), the signal from aircraft farther than say 100 nm becomes so weak, it is below the level of signal which can be detected by the dongle. This limits the range to around 100 nm.

    If you want longer range, try to keep the coax as short as possible, preferably not more than a meter (3 feet).
    Thank you for your reply. I should have been more clear in my post. The photo is not of my exact antenna. It's the closest that I could find on the internet. My antenna has a shorter cable. It's actually around 1 m in length, although it's probably not very good quality.

    Leave a comment:


  • abcd567
    replied
    The coax cable of these antennas is generally low-cost RG174 which has high signal loss per meter.
    Signals from distant aircraft are already weak. If this coax has a length longer than say 3 meters (10 feet), the signal from aircraft farther than say 100 nm becomes so weak, it is below the level of signal which can be detected by the dongle. This limits the range to around 100 nm.

    If you want longer range, try to keep the coax as short as possible, preferably not more than a meter (3 feet).

    Leave a comment:


  • Questions about Antenna and Signal Strength

    I'm using an inexpensive antenna and it's not in a great location. It's on a window sill and has only about 90 degrees of unobstructed view all the way to the horizon. The longest detection range is around 150 nm but the average range is 37 nm. Over 95% of the detections are within 50 nm.

    Here is the antenna:
    CE08549-2.jpg
    Here is the range:

    dump1090-localhost-range-2h.png

    Here is the signal level:

    dump1090-localhost-signal-2h.png

    The screen captures are from this afternoon, which is relatively quiet, in terms of aircraft traffic.

    According to graphs1090, 2.2% of messages are greater than -3dB of signal strength.

    Would it make much difference if I improved the antenna or got an LNA without improving the location?

    I was thinking of trying to make a colinear coax antenna using some RG58.
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