Tropospheric ducting or scatter vertically polarized?

Discussion in 'VHF/UHF - 50Mhz and Beyond' started by KJ4RZZ, May 8, 2017.

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  1. KA9JLM

    KA9JLM Ham Member QRZ Page

    My guess is that is the problem.

    I am a bit surprised a licensed operator does not know better. :( A attic TV antenna picking up a TV transmitter is a bit different.

    My indoor cookie sheet antenna works fine for repeaters. I would never expect it to work on simplex, Unless it is a mile or so.
     
  2. KJ4RZZ

    KJ4RZZ Ham Member QRZ Page

    I think you're on to something here. Thanks.
     
  3. KJ4RZZ

    KJ4RZZ Ham Member QRZ Page

    Possibly. When he gets a better antenna outside we'll find out.
     
  4. KM3F

    KM3F Ham Member QRZ Page

    On a long path its not just the tx power that is important but over the horizon scatter that takes place.
    The receiver end is in the micro volt range detecting a very small portion of the scattered signal amplitude.
    The rest of the power is just wasted.
    The use of gain antennas only has the low scatter signal to work with at each end.
    The uses of gain antennas for TX only increases the scatter level at each end.
    We all waist power to provide micro volt level of signal to hear with down near the noise level of the systems.
    Looking at the propagation drawings doesn't address these facts.
    They make it look like 40 watts TX is 40 watts received at the other end.
    Not so.
    Look at it like a bucket of water has considerable weight = Tx power but when vaporized can cover a very large area.
    It only takes a little of the vapor condensing on a smooth surface to detect its presence = Rx to see it has arrived at a distance point.
    Good luck.
     
  5. KM3F

    KM3F Ham Member QRZ Page

    A J pole and Slim Jim are virtually the same antenna just a different construction.
    Ask what determines the pattern angle of any antenna!
    It is the phase and Vector summing along the pattern of the reflections between the antenna and ground in the antenna near field.
    If Radials are used at the antenna they take the place of the ground effects '''for the most part''', but the pattern still remains the same as long as the radiating element length is not changed to any great degree.
    This is why a dipole pattern changes from low to high elevation within one wave length height changes.
    At low elevations under a quarter wave length the pattern is virtually a bubble looking straight up.
    As the height get greater the pattern begins to split in its center with lobes emerging at lower angles and center of lobe reducing .
    Its nothing to do with the fact it is a Dipole.
     
  6. K0PJS

    K0PJS Ham Member QRZ Page

  7. KE4VNC

    KE4VNC Ham Member QRZ Page

    This should be your coverage to ground level:

    tmp_14028-Screenshot_2017-05-11-17-59-401979691006.png
     
  8. AI3V

    AI3V Ham Member QRZ Page

    Unless you can visually see, with your own eyes the other antenna, you do not have a line of sight path.

    Under ordinary land conditions, you do not have a line of sight path.

    That leaves troposcatter.

    This form of propagation relies on power.

    The more power, the more scatter.

    In SW Pennsylvania, two stations running 100 watts and 4 wavelength boom yagi-uda antennas can easily talk a hundred miles in any direction.

    Put both stations on top of a hill, and it's more like 300 miles.

    You need more power, and more antenna gain.

    And you need to get those antennas on the sky side of the roof.

    Rege
     
    AD5KO likes this.
  9. W6KCS

    W6KCS Ham Member QRZ Page

    That was really informative, Rege, I didn't realize my HT was working troposcatter through the walls of the house and the trees outside. Likewise I didn't realize knife-edge diffraction and ducting was really troposcatter propagation. Is it also responsible for the 4/3 K factor used in a microwave path analysis? Thanks for the education.
     
  10. AI3V

    AI3V Ham Member QRZ Page

    You are not using "knife edge" on 2m. This is a optical lab bench gimmick.

    4/3 propagation is troposcatter, and based on wideband FM and lousy sensitivity old school receivers. It is not used for any serious microwave work. "Public safety" radio salesmen love to sucker unknowing police Chiefs into paying for "site surveys" based on it....

    Ducting is simply a particularly good form of troposcatter.

    It really is as simple as you either have a true optical path, or you don't.

    Good day sir.

    Rege

    Edit: I will design, quote, install and GUARANTEE a true Los path. Non Los and it's " let's try"
     
    Last edited: May 15, 2017

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