When antenna tilt matters

Discussion in 'Mobile Radio Systems' started by KX4O, Jul 26, 2018.

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  1. KX4O

    KX4O Ham Member QRZ Page

    Addressing some concerns some of you reasonably raised of having an antenna with too much gain, I measured my dual bander antenna in the chamber in support of a work project and have some results to share with you.

    [​IMG]

    https://www.hamradio.me/antennas/when-antenna-tilt-matters.html

    The test antenna is a simple halfwave (or nearly so) at 2m, but a decent collinear at UHF. This gives us two patterns for the price of one session. The nulls at relatively low elevations in the image above are daunting, but I will leave it up to you all to ponder its effects on the mobile operator and his/her ever tilting vehicle.
     
  2. G3YRO

    G3YRO Ham Member QRZ Page

    I bet the actual radiation patterns are very different from his computer simulations !

    Roger G3YRO
     
  3. KX4O

    KX4O Ham Member QRZ Page

    These aren't simulations.
     
  4. K0BG

    K0BG Platinum Subscriber Platinum Subscriber QRZ Page

    They're not simulations. They sort of coincide with Danny's Richardson, K6MHE, article with respect to mounting positions: http://www.k0bg.com/images/pdf/mobile_vhf_ant.pdf

    If a 1/4 wave would have been used, there would still be some nulls, but not nearly as deep as those shown. Notice two things; the low angle radiation (near Ø°) which doesn't help much when using repeaters, and the nulls just above them (≈20°). So much for perfect patterns!
     
  5. KX4O

    KX4O Ham Member QRZ Page

    That would be more akin to this measurement from my previous article where the overall pattern shape of the halfwaveish NR770 tracks well with the 1/4 wave patterns from the <cough>mag mount</cough> differing primarily in amplitude...
    [​IMG]
    The green trace has those first nulls of the NR770 at a slightly lower elevation that the mag mount 1/4 wave attributable IMHO to the NR770's slightly higher center of radiation over vehicle metal and ground.
    One wonders what is optimal for most conditions. We flatlanders in Virginia have a repeater with antenna some 270 meters over terrain. At typical distances where signal strength begins to matter, the angle of elevation to the repeater's antenna is under one degree. Counter to that would be the notion of diffracting over local obstacles. That said, is terrain hugging low angle radiation really a bad thing?
     
  6. K0BG

    K0BG Platinum Subscriber Platinum Subscriber QRZ Page

    As you alluded to, it depends on the HAAT of the two communicators. That's a mobile working through a repeater typically. In the mountain west, it is not uncommon to see several thousands of feet difference in the HAAT between them. In these cases, a regular old 1/4 wave is usually the best bet. Unfortunately, it is difficult to understand that higher gain isn't the answer even in the flat lands of America. It is also the reason Pacific Rim antenna companies often leave off the designator (dBd vs. dBi).
     
  7. KE5PPH

    KE5PPH Ham Member QRZ Page

    So after looking at the fancy pictures, you're saying to get the most out of antenna you need to be moving fast enough to make it wave in the wind? there by closing the gaps/nulls in the pattern?
     
  8. K1ZJH

    K1ZJH Ham Member QRZ Page

    Besides, most hams won't accept the fact that it is very difficult to reach 6 dBd omni coverage on 2 meters using a 20 foot long antenna.
     
  9. K0BG

    K0BG Platinum Subscriber Platinum Subscriber QRZ Page

    No. What it really means is, that too many newcomers put too much emphasis on antenna gain and transmit power, and bulk at paying for quality and performance.
     
    KB0MNM likes this.
  10. KB0MNM

    KB0MNM Ham Member QRZ Page

    Balk ( most folks will 'get' that Alan meant balk, as in shy away from paying for quality and performance ). Some are willing to pay more for the height advantage of an electrically folded mount, yet that has it's own issues... Pobody's nerfect. ( They did crucify for that... ).
     

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