What kind of antenna would be used for 2-meters SSB mobile operation?

Discussion in 'VHF/UHF - 50Mhz and Beyond' started by KC0BUS, May 28, 2019.

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  1. AI3V

    AI3V Ham Member QRZ Page

    No real performance differences, it really depends on which construction method you prefer.

    And a car is plenty big enough hunk of metal to completly, utterly dominate any "ground effects" "out to 40 feet or so"

    Think about this, A Yagi-Uda uses a single half wavelength wire as a reflector, not a billboard.

    Rege
     
  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    That has absolutely nothing to do with ground effects. A "reflector" doesn't reflect anything, it enhances charge acceleration.

    The same Yagi uses the ground beneath it to reinforce its radiated wavefront and thus provide more "real gain" than the same Yagi in free space can. And where that ground reflection occurs depends how high above ground the Yagi is installed, but can be hundreds of feet away.
     
  3. KM3F

    KM3F Ham Member QRZ Page

    The term reflector is most often taken in the wrong context as if bouncing a signal off the rear element.
    Yes it does end up enhancing charge acceleration but the enhancement is the near final result.
    The action to get there are almost never explained on these boards so becomes used out of context.
    Examples:
    1. A two element beam does not have to have a ''''''reflector'''''' to form a pattern favoring a direction. A director will accomplish the same final result.
    2. Consider the driven element radiating it's energy both forward and to the rear.
    This energy excites the so called reflector that re-radiates back toward the driven element.
    That 'reradiated' energy causes phase additions, subtraction and cancellations across the excited field to form the beam effect to favor one direction or said another way shapes the power applied to favor one direction.
    The conversion process that go on in between and how the energy is radiated get complex.
    At the ham level we don't get into all this so it just stops at the antenna.
    Using the term reflector is like using the term antenna tuner improperly.
    Most know what is meant but many do not.
    A more proper use of the term reflector belongs in the light end of the spectrum where
    photo properties are more in direct effect such as the head lights in an automobile to direct the source forward.
    In the end it's all the same 'game' but at different levels of energy and time relationships.
     
  4. AI3V

    AI3V Ham Member QRZ Page

    So now explain how a single wire , slightly longer than 1/2 wavelength has the same effect on the redirection of energy from the driven 1/2 wavelength element as would a infinite, perfectly conducting plane surface.

    Rege

    Here is a hint: inverse square law
     
  5. AI3V

    AI3V Ham Member QRZ Page

    No Steve, once again you just don't understand whats going on.

    Consider the roof of a ordinary car is about a wavelength square on 2m.

    Thinking dirt 40 feet away has anywhere near the same effect on the redirection of energy is silly.

    Google yourself up a copy of

    Microflect's Passive Repeater Engineering handbook

    and lean a bit about the subject.

    Rege
     
  6. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Rege, I give up on you.

    Passive repeaters have zero to do with Yagis. The "reflector" element of a Yagi is tightly coupled to the driven element and just made inductive to create a phase delay in reradiation.

    Fun test which I'm certain you've never tried, but we did this at a few VHF-UHF conferences as a parking lot demo:

    Mount a 2m halo on a 10-15' mast above a car body (temporarily), park another vehicle a few hundred feet away at the other end of the lot or field, using a calibrated F/S meter connected to a horizonally polarized antenna. Transmit with the halo, record the F/S reading once the F/S antenna is peaked for max reading. Record reading.

    Drop the mast and mount the same halo 6" above the car roof and repeat the same test. Record reading.

    What's the difference?

    Results: Generally, no difference.

    Try it.

    This is what Cushcraft did in the mid-60s when they started selling their "Squalo" antenna for mobile work, using plexiglas spacers and suction cups. The car roof is much too close to create the phase shift required to enforce reradiation, so it kind of disappears from the model and becomes reasonably transparent. Far-field F/S measurements confirm this. The actual "ground" around the antenna is "earth," way outside the automobile structure.

    upload_2019-6-3_9-5-45.png
     
  7. AI3V

    AI3V Ham Member QRZ Page

    Steve, if you did one tenth the tests and installations you claim you would have to work 100 hours a day 38 days a week.

    When you read up on reflections, take a look at a antenna called a "turnstile over reflector"

    Mebby something like the 2x2 array of them on the wsc-3 satcomm antenna I played with on the aircraft carrier.

    Its almost like you make this stuff up as you go along, like a salesman selling to somebody who dosn't understand what he's buying.

    Rege
     
  8. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    What, exactly, have you done/built/tested?

    You might want to scan the "VHF" column articles 1984-1988 where I authored every one of them and included demo reports, photos, block diagrams, case studies, writeups (with lots of photos) of setting up antenna ranges for VHF-UHF antenna measurements, etc.

    I don't recall seeing any of this published by you.

    I may have missed it, though. Provide some links?
     
    WA3GWK likes this.
  9. KM3F

    KM3F Ham Member QRZ Page

    Yeh I think Rege needs to review some theory and update his thinking.
    Until then, no use in trying to explain anything he refuses to even consider from such a mind set.
    What you ask me to explain I already did in my post.
    How did you miss it?. Look again or are you refusing to consider it?
    Remember phase additions and subtractions forming the beam?
    If that does not happen, there would be no beam formation.
    The earth or ground plane does have an effect but not the only effect.
     
    Last edited: Jun 3, 2019
  10. W1VT

    W1VT Ham Member QRZ Page

    I used to drive a Saturn sedan with a roof rack that was sturdy enough to support a 4 element 2M Yagi mounted on an antenna rotator. I could drive around with the antenna mounted dead center on the roof. Alternately, I'd run two rotators side by side, one for 10GHz and another for 2M.
     

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