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Affect of TV Receive Antenna Height on Signal Strength It Receives

Discussion in 'VHF/UHF - 50Mhz and Beyond' started by W9XMT, Jul 22, 2019.

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  1. KL7AJ

    KL7AJ Ham Member QRZ Page

    The ground reflections can either reinforce or cancel out the desired signal. Look up FRESNEL ZONE references.
     
  2. KD0CAC

    KD0CAC Ham Member QRZ Page

    Eric , looked it up when it was mentioned earlier , and could not come up with a picture of one .
    Now if we could make a tool that would let us see electromagnetic waves - and then aim the antenna at them , with all this line of sight & reflecting ;)
     
  3. KL7AJ

    KL7AJ Ham Member QRZ Page

    Here ya go!
    https://www.everythingrf.com/rf-calculators/fresnel-zone-calculator
     
    KD0CAC likes this.
  4. KD0CAC

    KD0CAC Ham Member QRZ Page

    Put that link in my bookmarks .
    So my take is there is no fresnel antenna , maybe a vague analogy , there is no such thing as a digital antenna ;)
     
  5. W9XMT

    W9XMT Ham Member QRZ Page

    Below are two slides from a PPT presentation I made a long time ago that give an overview of the importance of Fresnel zone clearance for terrestrial, point-point space-wave paths.

    [​IMG]

    [​IMG]
     
    KD0CAC likes this.
  6. W2WDX

    W2WDX Subscriber QRZ Page

    @W9XMT Does the fresnel zone vertical height vary with frequency? Would it be correct that that dimension would be narrower as frequency increases or is it dependent solely on distances? At what frequency or band does this phenomenon present itself in significant practical ways? In the formula what is "n"?
     
  7. W9XMT

    W9XMT Ham Member QRZ Page

    The widest vertical dimensions of the Fresnel zones are directly proportional to the frequency, the path length, and order (number) of the Fresnel zone (1,2,3 etc).
    In general, probably for all frequencies greater than 30 MHz.
    "n" is the order of the Fresnel zone. Clearance for the 0.6 Fresnel zone for the entire length of the LOS path has zero affect on the 1/r loss for that end-end path length and frequency.
     
  8. KA9JLM

    KA9JLM Ham Member QRZ Page

    Poof...
     
    Last edited: Jul 23, 2019
  9. KL7AJ

    KL7AJ Ham Member QRZ Page

    There's no magical line of demarcation between UHF and VHF....or lower. It's all a matter of degree. Fresnel zones could apply to VLF....though not too practically. :)
     
  10. N9RMA

    N9RMA Ham Member QRZ Page

    So my rabbit ears rapped in foil are not good!!!! Bob N9RMA
     

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