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Trial Run Results for Four Sizes of Ground Planes

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  • Trial Run Results for Four Sizes of Ground Planes

    Please scroll down to see test result graphs.

    Ground Plane Sizes Tested:
    25 mm dia mag mount only
    73mm dia can
    100 mm dia can
    165mm dia can

    Antenna Used:
    1/4 wavelength mag mount whip

    Image 1 of 5: Test Setup

    Images 2 & 3 - First Round of Trial Run

    Images 4 & 5 - Second Round of Trial Run


  • #2
    how can the can help the antenna to get a better range?


    • #3
      Originally posted by dedicados View Post
      how can the can help the antenna to get a better range?
      The complete antenna has two limbs in opposite directions. This antenna is called a "Dipole". Core wire of coax is connected to one limb, and the shield/braid of coax is connected to the other limb.

      Another type of antenna is called "Monopole". It has one limb (whip) to which core wire of coax is connected. A ground plane acts as the second limb, and shield/braid of coax is connected to it.

      The mag mount has a small metal disc of 25 mm dia which acts as ground plane. However 25 mm dia is too small to provide sufficient ground plane effect. Placing mag mount base on a can enlarges the ground plane to the diameter of the can, and reception improves.

      dipole and monopole+groundplane.gif
      Last edited by abcd567; 2016-05-27, 18:59.


      • #4
        I lack the proper test equipment to tune, optimize, and evaluate antennas. Cost of these equipment (Spectrum Analyser, VNA, Signal Generator, etc) runs in several thousand dollars at minimum, so out of reach of a normal hobbyist.

        Due to lack of test equipment, I use trial runs and performance graphs, a practical way out for a hobbyist without fancy test equipment.

        Now I have run a simulation software 4nec2. The results of these software carries an eror of 5% to 10%, and is not suitable for constructing a high gain antenna. However these are good aproximation to general behaviour & trends.

        Below are screenshot of results of frequency sweep for 4 different sizes of ground plane disc. The whip in each case is 1/4 wavelength (69mm).

        The X-axis represents frequency in Mhz. Frequency Sweep from 500 Mhz to 1500 Mhz

        Screenshot 1 - 25 mm dia ground plane disc - Resonant at 1300 Mhz
        The 25mm (1 inch) dia disc is actually the built-in base plate of stock antenna.

        Screenshot 2 - 65 mm dia ground plane disc - Resonant at 1120 Mhz

        Screenshot 3 - 80 mm dia ground plane disc - resonant at 1090 Mhz

        Screenshot 4 - 100 mm dia ground plane disc - resonant at 1070 Mhz


        • #5
          If I could solder worth a crap I would try this myself.

          On a four or eight leg spider, are there benefits of putting the disk, to which the legs are attached, out to 68-69 mm? Or is the spider a whole different type of deal.

          In frustration, since I could never get the right stuff ordered, I went to Lowes, got a copper post top, cut it up, and crafted a round, copper disk, about the size of a large washer, say 30 mm. I then feebly soldered 8 legs to it, and upped my max range with cantenna from 65 to 90 miles with the mforphodite spider! To embarrassed to provide image!

          I am still in testing stage, with antenna on open front porch. Just wondering if instead of using the coax connector, one could make an even larger disk and get better results. Assuming one can solder!