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Thread: best antenna

  1. #2621
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    I don't think I've seen this mentioned, so, let me point it out ...

    For folks building antennas and looking for a quick comparison - start dump1090 in interactive mode, look for the "signal" column in the table, this displays what is known as RSSI or Received Signal Strength Indication - consider it an uncalibrated signal strength meter - you can use it to compare the strength of two signals received by the same hardware, very useful for quick comparisons, or tweaking/tuning/trimming antennas.

  2. #2622
    Passenger majo's Avatar
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    Hi fordem!

    Could you please explain where and how to enter that "dump 1090 interactive mode"?

    Thanks, majo

  3. #2623
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    Find the instructions you used to install dump1090 - they should tell you how to start it in interactive mode, and which directory you should be in.

    Typically it will be something like

    Code:
    ./dump1090 --interactive
    dump1090 has many options available, and these options are executed by including the "switch" when calling the program, if calling it from a command line prompt, or, if calling it from a script, the script can be edited to include the "switch" - at the command line type dump1090 --help to see the available options, it can be run with multiple options by entering the options on the same line, for example, if you wanted both interactive mode and the integrated web server at the same time.

    Code:
    ./dump1090 --net --interactive

  4. #2624
    Captain abcd567's Avatar
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    Test Results for Cantenna, Using Antenna Analyzer N1201SA.


    Test Setup




    R, X, VSWR, S11




    VSWR vs Frequency Sweep Plot. Marker at 1090 Mhz

  5. #2625
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    You kept the dielectric on the center conductor. What correction coefficient did you use?

    Sent from my Pixel using Tapatalk

  6. #2626
    Captain abcd567's Avatar
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    Quote Originally Posted by joni1101 View Post
    You kept the dielectric on the center conductor. What correction coefficient did you use?
    I applied no correction factor.

    The electromagnetic field of coax is totally enclosed inside the space between core & shield, and this space is totally filled with insulation. The speed of propagation along coax is therefore determined solely by elocity factor of the dielectric material in the coax.

    The antenna wire's electromagnetic field is un-enclosed, and is in a space of which the wire insulation constitutes negligible part (thickness wise). Its Velocity Factor is therefore:

    VFeff = (VF1 x t1 + VF2 x t2) / (t1+t2)
    where
    VF1 is velocity fctor of insulation, say 0.66
    t1 is thickness of insulation say, 2 mm
    VF2 is velocity fctor of air = 1
    t2 is thickness of air say 10 km **

    **The thickness of air in which electromagnetic field of antenna wire exists is the distance between transmitting antenna and the receiving antenna, hence it is in tens or hundreds of kilometers.

    Hence VFeff = (0.66 x 0.000002 km + 1 x 10 km)/(0.000002 km+10 km) = 10.00000132 / 10.000002 = 1

    Electromagnetic field of Antenna
    Occupies space between transmitting and receiving antennas





    Electromagnetic field of a Coax cable
    Totally confined in the space between core and shield i.e. totally inside the core insulation


  7. #2627
    Captain abcd567's Avatar
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    No correction factor required for insulation on Whip
    To verify above statement, I ran analyzer with insulated and bare whips, both 67 mm.

    The test proved that correction factor for insulation is not required.
    Both gave same VSWR (1.4) and both were resonant at same frequency (1090 Mhz).
    Please see photos below:

    Whips
    67mm bare, 67mm insulated, 72mm insulated




    Insulated Whip 67 mm
    VSWR, R, X, Z, S11 at 1090 MHz





    Bare Whip 67 mm
    VSWR, R, X, Z, S11 at 1090 MHz




    Bare Whip 67 mm
    VSWR vs. Frequency sweep, marker at 1090 MHz


  8. #2628
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    Thank you. Brilliant explanation and great tool you got to analyze antennas. Remember in the stackexhange forum the question on how long to make the sides of the can, whether you subtract the radius of the ground plane from the length of the cab to equal quarter wavelength. BTW in the ham stackexhange forum they wanted reputation score of 15 before you could post because they want to prevent that question from being spammed.

    Sent from my Pixel using Tapatalk

  9. #2629
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    Do you have some cans with bigger ground plane? Could you try cutting slots into the side of the can to electrically insulate the vertical shield? It's great you have this tool!!

    Sent from my Pixel using Tapatalk

  10. #2630
    Captain abcd567's Avatar
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    This type of tools are priced several hundred to several thousand dollars. I found this model for around $180 to $220 on ebay, and then found one seller for $140 on Banggod.com on special offer, so I purchased it from Banggood special offer seller.
    Last edited by abcd567; 2017-01-25 at 17:38.

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