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Full wave antennas for CB

Discussion in 'CB Antennas' started by linearone, Feb 19, 2009.

  1. linearone

    linearone King of NY

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    Has anyone other than myself tried this?

    YEARS ans YEARS ago I made a full wave wave dipole for 11m. I had it horizontal about 12 ft. off the ground and just about stretched across the yard suspended from pcv insulators from tree branches made of solid #10awg. it had a high swr with no matching device. well... high by cb standards for hamsters it was perfectly acceptable, over 2:1 maybe, I really cant remember... anyway I didnt care becasue I didnt have a tuner and apparently if you read the manual Galaxy says its saturn base can run into a 2:1 swr indefinetely with no ill effects (read the manual, Im not lying).

    I had mixed results, it was way more narrow than I expected, perhaps because it was so low to the ground. it made my signal lose all its carrier and on the recieving end it was all swingy. but loud. perhaps since it had the appearance of no carrier it sounded all crappy and wooshy and swingy to the reciever. I dunno. I never played with it much after this. I still have it somewhere in the closet. I would like to build a small tuner for it just to see how it would compare to a half wave dipole in the yard...

    anyone else done this?



    Does it have any benefit?
    :confused:
     

  2. Beetle

    Beetle Sr. Member

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    A "full-wave" dipole, center fed, will have a very high impedance - hundreds or even thousands of ohms.

    That's why a dipole, by definition, is a half-wavelength, and center fed. Its feedpoint impedance is a good match to 50/75 ohm coax, and it's pretty much the de facto standard by which all other antennas are measured.

    A center-fed wire antenna which isn't cut for a specific band or frequency is more correctly called a doublet.
     
    rabbiporkchop and DainBramage like this.
  3. linearone

    linearone King of NY

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    back to my question ... is there any benefit from a full wave antenna?
     
  4. DX-DIGGER

    DX-DIGGER Member

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  5. W5LZ

    W5LZ Crotchety Old Bastard

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    There's no benefit in a center fed full wave doublet.
    - 'Doc
     
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  6. C2

    C2 Sr. Member

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    Well, there I thought I'd be able to use an 80 meter dipole on 40 meters as well as 20 and 10, perhaps all the HF bands, with a so-so tuner...?
     
  7. HiDef

    HiDef Active Member

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    You can if it is fed with balanced line.

    A full wave dipole shows some broadside gain over a halfwave if it isn't too low to the ground.
     
  8. W5LZ

    W5LZ Crotchety Old Bastard

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    C-2,
    A full wave doublet is certainly usable! But on the band it's designed for it isn't really going to be worth the trouble. A typical 1/2 wave doublet would out perform it in almost every instance.
    Now, if you were to bend that full wave doublet into a loop...
    - 'Doc
     
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  9. Beetle

    Beetle Sr. Member

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    Back to my answer ... no. At least not at antenna heights typical for CB and ham installations. Besides, if you're feeding the antenna with coax (you didn't specify), your loss will be atrocious at the fundamental frequency, even if you use a good "tuner" (which, as you know, doesn't change a thing with conditions downstream from it).

    However, why not get a few good antenna books and study up a bit, and then experiment?
     
  10. Beetle

    Beetle Sr. Member

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    I liked the one comment about how much time it would take and how much trouble it would be if he put up an antenna only to find that it didn't work. This guy probably wants somebody to design it, build it, install it and adjust it at his place. Then probably operate his station for him, so HE won't have to waste time and effort.
     
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  11. Wire Weasel

    Wire Weasel Senior Moment

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    Hey linearone,

    Although to the untrained ear, the idea of a full wave antenna sounds great. You know, a 1/2 wave is better than a 1/4 wave. A 5/8 is better than a half. So why isn't a full wave the way to go. Well there is ONE full wave antenna for any frequency, but it's not a vertical type or a dipole configuration. As stated above, the electrical math isn't right for a full wave dipole. They don't work electrically. That's why they aren't used.

    The full wave antenna that does work is the Loop, sometimes called a Loop Skywire. Very famous antenna that's been around for a long time. Great antennas too. Many hams use them and I use them. Almost all of my HF work is on a horizontal loop cut for 80 meters. It also serves as my "flatside" antenna for 10-11 meters.

    You can make one cut just for CB, total length around 36 feet. However, loops have no gain at the cut frequency. It will radiate just fine with no SWR, but will be a no-gain antenna. An Antron 99 or a simple dipole would kick its ass. Loops do increase in gain as you increase in frequency, and they are great multiple-band antennas, so my loop for 80 meters has more gain and works well on 40, 20, 17, 15 meters ect.....as well as working very well on 80 meters too even without any gain. The propagation is basically straight up and down on 80 meters, and the loop is an awesome performer for me up close and out to however far the band is working, usually several hundred miles (several states out.)

    So good luck!
     
  12. COBRA148FGTLDX+

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    FULL WAVE LOOP

    Actually a Full Wave loop will have approx 2 db gain over a dipole antenna depending if its a circular , 4 sided quad or 3 sided diamond configuration .
    You should have added a 1/4 wave matching stub of rg 59 or rg 11 coax at the antenna and would have gotten a low swr .

    Connect the shield of a "Short Piece" of 75 ohm coax to one end of the loop antenna , Connect the center of the 75 ohm coax to the other end of the loop antenna. The length of the 75 ohm coax is most important. It will be used as a Q section.
    To determine the length to use, Use this formula "Length in feet = 246 x VF / Freq in Mhz" VF = the Velocity Factor of the coax. So multiply 246 by the Velocity Factor of the coax , Then divide by the frequency . 5 ft 11 1/2 inches is a 1/4 wave at 27.205 middle of cb channels
    so 6 ft will do it .


    If you use RG59 or RG11 with a Velocity Factor of 0.66 , For the 75 meter band the Piece of 75 ohm coax should be about 42 feet long , It doesn't need to be exact . RG59 and RG11 coax usually have a Velocity Factor of 0.66 , Foam dielectric coax such as RG6 might have a Velocity Factor of 0.81 or more.


    Put a PL259 coax connector on the unused end of the 75 ohm coax, Screw a PL258 double female coax connector onto this PL259 coax connector. Then connect 50 ohm coax to the other side of the PL258 double female coax connector, Use any length 50 ohm coax needed to reach your Transceiver.
     
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  13. niterider

    niterider Member

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    The Quad or "Loop" is a full wave, however it isn't a vertically linear full wave, but rather a "closed" circuit design, so it's a little different than having a full wave antenna that is straight vertical. Both sides of the coax are terminated into this antenna. Meaning, Half of the full wave's cycle is dedicated to the coax center conductor, and the 2nd out of phase half is connected to the sheid. There is also an "open" version of the loop as well, but the closed circuit is the most popular. The shape of the antenna elements curve to meet each other, so it doesn't act like a 36' full wave vertical antenna in that sense. A 36' vertical antenna technically has less gain than a smaller 22'6" 5/8 wave antenna. This is because, a halfwave is the longest you can keep an element's currents in phase, and once you exceed 5/8th wavelength, the out-of-phase currents start to cancel out enough to lose performance. Meaning even with a 5/8th wavelength antenna, 1/8th of the antenna is actually "out-of-phase". Once you get to a 3/4th wavelength, the out of phase portion starts to transition from being negligible to a degradation effect (loss) of antenna performance.

    The exception of vertically lengthening for more gain, would be electrically phasing two antennas, in a way to cancel out the out of phase portion. This is known as Collinear antennas. Big Hair Antennas are the only CB antennas that I seen, that have done this. To make this work, you need about a 45' to 50' vertical antenna overall. Rumor is, he no longer making antennas though.


    A quad on the other hand works a little more differently, and has a tad more gain than a dipole (2db theoretically). I am a big fan of Quads or full wave loops, because they also pick up less noise, and better matching solutions are available, than using the ol gamma match method (which has some loss).
     
    #13 niterider, Apr 6, 2009
    Last edited: Apr 6, 2009
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  14. bob85

    bob85 Supporting Member

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    big hair was slow out of the blocks,
    ham international did the 5/8 over 1/4wave big-mac and avanti phased elements with the sigma4 back in the early 80's, there has been a handfull of clones since, all are top performers;).
     
  15. if it was a full wave length its my understanding it would radiate up out the top much more than on the sides . if its used horozontal would it make it produce more signal out the hot end than off the sides like a 1/4wdp .

    im sure that its been tried befor and since its not popular that it doesnt work well that way .
    any idea what were/are the problems ?
     

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