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Thread: QUICK SPIDER - No Soldering, No Connector

  1. #11
    Flight attendant Wolli's Avatar
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    @abcd567:

    Yep. My intention is to try that one first as it is extremely easy to build - although your experiences with the Coax Antenna are not too promising as you posted here. In a second step I'll try your Cantenna (same posting also), which is much more promising as you state there (and also quite easy to set up).

    Trials will hopefully start in the next days/weeks, when I find some time. I'll let you know about the results of my attempts.

    Greetings from Germany to Canada, and have a nice weekend, -Wolli-

  2. #12
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    Did the quick spider outperform the Cantenna?

    Sent from my Pixel using Tapatalk

  3. #13
    Captain abcd567's Avatar
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    Quote Originally Posted by joni1101 View Post
    Did the quick spider outperform the Cantenna?

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    My Cantenna performs slightly better than Spider, but for some others Spider performs better than Cantenna.

    Actually it is not the antenna alone. It is (antenna+coax+location) which decides overall performance. Since Cantenna and Spider are very close in performance, any one of the two can perform better than other depending on location & coax length.

  4. #14
    Captain abcd567's Avatar
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    Testing of Quick Spider by Antenna Analyzer

    VSWR=1.2, R=59Ω, X=5Ω, and S11=-20 @1090 MHz




    Plot of VSWR vs Frequency 137.5 Mhz ~ 2700 MHz.
    Marker at 1090 MHz, minimum SWR at marker


  5. #15
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    Looks like this antenna has very slightly better specs than the Cantenna. Can you affect the impedance by the angle of the spider legs?

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  6. #16
    Captain abcd567's Avatar
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    Quote Originally Posted by joni1101 View Post
    Looks like this antenna has very slightly better specs than the Cantenna. Can you affect the impedance by the angle of the spider legs?

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    I did not measure the impedance with radials at different angles, only at 45 degree slanting down.
    Theoretically horizontal radials have 32 ohms, 45 degree slanting have about 50 ohms and vertical (i.e. a dipole) have 75 ohms.

    Practically for ADS-B, I compared message rate for horizontal and 45 degree slanting radials, and noticed only slight increase in adsb message rate with slanting radial. Please see this post:

    Why Antennas Have Ground Plane?

    Please note that the instrument I have used measures only VSWR/R/X/Reflection S11.

    It does NOT measure following important parameters:
    1) Antenna Gain
    2) Antenna Directivity/Radiation curve
    3) Common mode/unbalanced currents in feed coax

    The purpose of this instrument is to check:

    (1) At what frequency antenna is tuned. The tuned frequency is where the SWR-Frequency curve is at minimum. If it is tuned at lower than design frequency, trim the whip, if tuned at higher frequency, add a piece to whip.

    (2) How much is VSWR. If measured VSWR is greater than 1.5, than impedance matching devices should be used. Once the VSWR is below 1.5, its actual value does not matter, then it is the Gain and Directivity which really make difference.
    Last edited by abcd567; 2017-01-30 at 02:07.

  7. #17
    Captain abcd567's Avatar
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    Quote Originally Posted by joni1101 View Post
    Can you affect the impedance by the angle of the spider legs?
    Please see attached photos. Readings are:
    (1) Spider with horizontal radials, z=26, swr=1.9
    (2) Spider with slanting radials 45 degrees, z=67, swr=1.3
    (3) Spider with vertical radials, z=73, swr=2.2

    32501334462_b814ba037c_b.jpg . 32654383295_a06f14e4a4_b.jpg . 31811480314_35dc93800a_b.jpg

  8. #18
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    Very interesting. Amazing how these small changes in geometry affect performance. Best bet is 45 seems like?

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  9. #19
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    Well, I wanted to give it a try as my first ads-b antenna and this tiny GP gave me 500Km (i.e. 270nm) of coverage at the first attempt !!
    I have to admit that my balcony is at 330m above sea level and I only have the ocean in front of me and this helps a lot
    Nevertheless I have no coverage toward the West.
    Im really happy so far but Im already building a J-pole for more coverage before start feeding FR24 with my brand new Orange Pi PC Plus.

    Btw as you can see I kept the cable to the minimum :-)

    IMG_20170426_153009.jpg

    IMG_20170426_194854.jpg

    Thanks abcd567 ;-)

  10. #20
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    Do I understand it correctly that

    - the outer wires have no contact to the inner wire?
    - that this kind of antenna helps against doughnut-effect with very near planes during landing and starting?
    - that the blue plastic-thing helps reflect waves from nearby planes?
    - does the blue plastic-thing helps with nearby planes if I put it under the 68cm flight-aware-antenna I have bought?

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