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Optimal height for inverted V

Discussion in 'CB Antennas' started by codeman, May 22, 2016.

  1. codeman

    codeman Recovering Crackerhead

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    I have used my dipole hung horizontally or in a sloper configuration from about 8 to about 12 foot high but I'm thinking about running it as a inverted V on a painter's pole front about 20 foot tall. I am looking for mostly dx contacts but would like to be able to talk to base stations on sideband that I talk with from time to time with the furthest being about 50 miles from me. I am able to talk with them from my pickup with a Uniden 980 with a RM Italy 203 and a Wilson 1000 mag mount. Should I be able to make local contact up to 50 miles or so with the inverted V at 20 feet?


     

  2. Needle Bender

    Needle Bender ...he thinks it's funny that I stepped in it

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    An inverted V is about as close as you're gonna get to an Isotropic, that being a point in space which radiates out spherically exactly the same in all directions and angles.

    - Pic from http://w4neq.com/htm/doublet.htm - but keep in mind, that's only 80 feet high on a band where a 1/4 wave is 60' long! This pattern would be equal to an Inverted V for 11m at approx only a 12' high apex! - Try to get it up to 36'-45' if possible.

    [​IMG]

    The higher you get it the better, as in just about ANY antenna installation, but keep in mind when going from a flat-top dipole to a 90° Inverted V, you're losing 3dB in the broadside direction to pick up performance in the perpendicular directions.

    PS: At 120° or a 60° angle per side, you'll have the flattest SWR when cut to R=52, X=0.

    If you're trying to make an omni out of it, then get it as close to a 90° as possible (a 45° angle for both sides) and yes, HIGH AS YOU CAN!!

    Remember, the higher you get it, the longer it will need to be to tune a flat SWR.

    *EDIT* - avoid using non-insulator-broken metal guy wire, use dacron covered kevlar if you can.
     
    #2 Needle Bender, May 22, 2016
    Last edited: May 22, 2016
    codeman and Sonar like this.
  3. wavrider

    wavrider W9WDX Amateur Radio Club Member

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    http://www.hamuniverse.com/wb4yjtdipolepatterns.html

    Good reading, gives radiation patterns for dipoles and the best height for vswr match.

    Depending on what you are wanting to do, height is a big factor, higher is not always better, look at the radiation patterns of the dipoles at different heights and you will notice deep nulls, that is what you want to avoid is the nulls.
    Believe it or not 1/2 wl agl works awesome.
     
    codeman and Needle Bender like this.
  4. Needle Bender

    Needle Bender ...he thinks it's funny that I stepped in it

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    Hey there's John, one of the nicest guys I ever knew via HAMateur radio!

    Only issue I see with that page is he's referring to flat top dipoles, not INV Vs, unless I read it wrong.
     
  5. Beetle

    Beetle Sr. Member

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    There's not really much difference between the two. A half wavelength in the clear (measured at the feedpoint) is probably the most convenient height - as in lowest for decent operation. You might find that higher is better for your location. HOW MUCH higher is something for you to determine by experimentation.
     
    222DBFL and Road Squawker like this.
  6. wavrider

    wavrider W9WDX Amateur Radio Club Member

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    I have tried flat tops and inverted V's, from top band to 10 meters, multi band fan dipoles and the old ladderline fed multiband doublets.

    End results the inverted V for ease of construction and impedance matching, coax fed, easy to install, one support required, few hundred feet of Dacron rope some 1:1 current baluns and you have an impressive start on an antenna farm.
     
  7. Robb

    Robb Yup

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    Minimum of 18 ft above the ground at its lowest points.
    Otherwise, some transmitted RF energy will be absorbed by the Earth.
     
    #7 Robb, May 24, 2016
    Last edited: May 24, 2016
  8. tba02

    tba02 WOOF

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    222DBFL and codeman like this.
  9. Beetle

    Beetle Sr. Member

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    "Above ground" doesn't necessarily mean measured from the lawn or soil directly below the feedpoint. It means above the actual RF-conducting depth, which depends on several things, including just where you are.

    If you're in the Navy, out on a ship, then "above ground" can be measured from the surface of the ocean, OR from the deck on a larger ship such as an aircraft carrier. If you're out in the southwest desert, the water table is really deep in places, and that makes for a really deep ground. Places in central-to-east Texas have some of the best soil conditions for antenna work.
     
  10. 2RT307

    2RT307 Sr. Member

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    Interesting!

    73,
    Brett
     
  11. codeman

    codeman Recovering Crackerhead

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    Just want to say thanks for all the information you guys gave. I will mount the inverted V at about 20 for now and see how that goes. Whenever I get a permanent house situation I will try mounting it on a longer push up pole.
    Oh...and thanks for the links. I may even learn something.
     
    #11 codeman, May 26, 2016
    Last edited: May 26, 2016
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  12. 222DBFL

    222DBFL Sr. Member

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    I will say this. Both horizontal dipoles I had up worked well at 18ft, but when I placed them at 35-40ft high off the ground, they worked much better. Less obstructions to deal with and also I was able to get the feed line to stay straight for a long ways. This helps a lot as well as having a good 1:1 matching balun or some good snap on ferrite chokes that fit snugly on coax. Also using a Low Pass Filter helps. Also make sure to use good weather proofing and to do it properly. Take your time here. It will save you a lot of headache later on!!
    I preferred my horz dipoles versus the inverted V, but that is just a matter of opinion. Both types of dipoles work very well and are an easy way to make contacts around the world.
    Also just FYI, both my dipoles were hung in 3 trees total. Almost an L type setup but, with some space between antennas. One pointed N/S and the other E/W. They do work well as they will cut a lot of background noise and also reject a lot of stations you might not want to talk to depending on the conditions. At any rate, just my experience with the 2 I had up. They have since come down as 11m DX has died, but will be repurposed for other bands! Be safe and have fun! Good day.
     
  13. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    Indeed. We are talking about RF ground in this case and depending on soil type it may be a few feet below the surface of the ground or many feet.
     
    Mudfoot likes this.
  14. 2RT307

    2RT307 Sr. Member

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    I used to string one up between the house and the kid's swingset. All of about 6 feet off the ground. Worked stateside dx with it, too. The most important thing is just to get on the air!

    73,
    Brett
     

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