Shortened antenna , loading coil vs tuner

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by IK3UMT, Jan 7, 2020.

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  1. IK3UMT

    IK3UMT Ham Member QRZ Page

    We have to shorten our radiator (a vertical, a dipole etc).
    What's the real difference between insert a loading coil along the element (and in different positions) and tune the bare metal whip by adding an external coil at its base , using the same element length in both cases ?
    Pros, cons , power handling, bandwidth etc ?

    Federico
    ik3umt
     
  2. WA7ARK

    WA7ARK Ham Member QRZ Page

    Placing the loading network(s) further out from feed-point increases the average current in the antenna region(s) between the feedpoint and the load(s) to maximize radiation.

    The best you can do to shorten a vertical or dipole is to place a capacitance hat(s) at the distal end(s) of the radiator, and then put inductive load(s) that are close to the cap hat(s).
     
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  3. WA7ARK

    WA7ARK Ham Member QRZ Page

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  4. AA7QQ

    AA7QQ Ham Member QRZ Page

    Linear loading can yield better results than coils.

    Ed
     
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  5. W9XMT

    W9XMT Ham Member QRZ Page

    Below is an analysis of a vertical monopole antenna using linear loading. The loading used produced a self-resonant antenna, requiring no loading coil or tuner.

    The entries marked by a red rectangle in the graphic show that, for the modeled conditions...
    • the 100m length of conductor used for this helical antenna has a radiation resistance of 0.23 Ω, and
    • the peak gain of this configuration is -11 dBi.
    However, if that 100m conductor was installed as a geometrically straight, vertical conductor, then for the same installation environment/conditions it could have a radiation resistance of about 100 Ω, a peak gain of about +7 dBi, and a radiation efficiency of 95% or better (compared to 2.2% efficiency for the helical version).

    Antenna theory (and this NEC analysis) show that the performance of a linearly-loaded vertical monopole is related to its overall end-end physical dimension, not the length of conductor used to form it.
    [​IMG]
     
  6. K0UO

    K0UO Platinum Subscriber Platinum Subscriber QRZ Page

    It's been years since I reviewed that excellent article, thank you for sharing it.
     
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  7. IK3UMT

    IK3UMT Ham Member QRZ Page

    Thank you all for sharing
     
  8. AC6LA

    AC6LA Ham Member QRZ Page

    In addition to the link that Mike provided for the "Verticals Without Vertigo" Cebik article, almost everything that LB ever wrote can be found on this page:

    http://on5au.be/Cebik documents.html

    Unfortunately there is no master index for the entire collection so what I usually do is a "site search" with Google, something such as this search string:
    Code:
    site:on5au.be verticals+vertigo
    The "site search" function is also available with DuckDuckGo and other search engines.

    Dan, AC6LA
     
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