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Inverted V vs a Flat-top dipole?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by N3TD, Mar 25, 2009.

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  1. N3TD

    N3TD Ham Member QRZ Page

    Inverted V vs Dipole??????

    My primary interests are in DX and contesting.

    Land is not an issue for wire antennas (almost 2 acres to play with). My property in the back is surrounded by pine trees 40-50ft tall. So 1/2 wave lengths and longer are an option.

    Right now I have a off-center fed dipole at 28ft. I am looking at changing it from a flat top to an inverted V.

    I also want to get something up on 160m while I am considering a tower and beams.
     
  2. KA4DPO

    KA4DPO Ham Member QRZ Page

    The only big differenc between an inverted Vee and a flat top is that the inverted Vee is virtually omni-directional while the flat top will be somewhat directional to it's broadside and low signal off the ends.
     
  3. K5RCD

    K5RCD XML Subscriber QRZ Page

    Eric:

    With the real estate you have to work with, a horizontal loop, full wave, for 160 meters would be ideal.

    Get some ladder line, a good roller inductor tuner, a roll of 12 gauge insulated wire (THHN) from Home Depot and go for it.

    Most hams would KILL for such a setup.

    Let me know if I can help.

    You might find This helpful.
     
  4. KA4DPO

    KA4DPO Ham Member QRZ Page

    I forgot one thing Eric. The ends of an inverted Vee are usually mounted close to the ground so the takeoff angle is high. A dipole mounted 50 or 60 feet high will have a lower radiation angle and would probably be a better DX antenna. I say probably because it would be in most but not all casses. Propagation is a funny thing.
     
  5. NA0AA

    NA0AA Ham Member QRZ Page

    IIRC, there's a formula for the comparison - I believe the center of an inverted V has to be higher than the center of a flattop diple for equal effectiveness.

    As the dipole is raised higher above the ground, the radiation become more and more 'ideal' that is to say, nulls off the ends of the wires begin to become increasingly obvious and the classic 'pinched balloon' shape starts to evolve.

    And yes, that also means lower angles of radiation also result.

    IIRC, you have to get more than 1/2 WL above ground for this to happen.
     
  6. K4SAV

    K4SAV Ham Member QRZ Page

    If you compare a flat top 80 meter dipole at 50 feet with an inverted vee with top at 50 ft and ends at 10 feet, the flat top dipole will be 2 to 3 dB better at all elevation angles, broadside to the antennas. Close proximity to ground causes significant loss. However off the ends of the antennas and at very low elevation angles, the inverted vee will have more gain than the flat top.

    So I would recommend the flat top dipole unless your favorite DX direction happens to be off the ends of the antenna.

    For 160 it will be difficult to beat an inverted L, maybe 50 ft vertical to one of those pine trees and a horizontal wire to another tree. If you want to build a 160 inverted L, then it is very little extra effort to include another vertical element for 80 using the same radial system. For DX, the inverted L for 80 should be as good, or maybe a little better, than either the dipole at 50 ft or the inverted vee.

    Jerry, K4SAV
     
  7. G0GQK

    G0GQK Ham Member QRZ Page

    High and flat every time

    G0GQK
     
  8. K8JD

    K8JD Ham Member QRZ Page

    I work as far or even farther off the ends of my 160 and 80 M dipoles, than the broadside directions.. :eek:! Not much null off the ends unless the dipole is close to a wavelength up in the air.
    The inverted V dipoles have a lower resonant freq for a given length of wire ! Not much else.
    Getting the feedpoint of a dipole (the maximum radiation here) to the highest possible place is one advantage I can think of when you go inv V.
     
  9. KB5URQ

    KB5URQ Ham Member QRZ Page

    Would it not also be easier to implement a flat-dipole at height (say, 50 feet) than to use a loop?

    For a flat-dipole you'd need 2 structures to tie off to; whereas, for a loop, you'd probably need 3 or 4 structures to maintain the circular-type shape?

    Jason
    KB5URQ
     
  10. W4HAY

    W4HAY Subscriber QRZ Page

    I've used both the horizontal dipole and the inverted V. So many other variables come into play that I haven't been able to tell any difference.

    My present trap dipole is kind of in between. It's not flat, but the included angle is too large to be classified as a V. 50-100 Watts give me access to the world when Ol' Sol cooperates.
     
  11. AD5ND

    AD5ND Ham Member QRZ Page

    A dipole normally radiates a stronger signal than an inverted V. The ends are up higher so there is less ground lose. It needs at least two supports.

    An inverted V only needs one support. This one of reason for it being so popular. It has been called omni directional "radiates poorly in all directions"

    A large loop must have at least 3 supports. If more than one of them is a tree then it will eventually fall down. A loops biggest claim to fame is that its radiation resistance doesn't very as widely as most other antennas. That makes it easier to load on its even harmonics.

    If i had your property I'd put up a large loop for 160 and use it on 80 also. On 40 I'd use two dipoles orientated 90' to each other and as high as I could get them. Verticals for 20 and up.
     
    Last edited: Mar 26, 2009
  12. K3STX

    K3STX Ham Member QRZ Page

    I don't think the reason a flat-top dipole has more gain than than inverted vee has to do with ground losses, I think it is that the effective height of the point of maximum radiation (the center of each dipole leg) is LOWER in the inverted vee and a horizontal dipole.

    The properties of two dipoles whose center of each leg is 50 feet off the ground will be similar (not identical, but similar). It is just that you would need to get the inverted vee 75 feet up in the air to get the center of each element to be at the 50 foot level.

    Inverted vees are not omni-directional; at a given height they are are more omni-directional than a flat-top, but if high enough they work fine. People all over the world make multi-element inverted vee-beams, why would they do this if the antenna was omni-directional?

    Generally, for wire antennas (and DX) higher is better. THAT is why a flat-top is preferred. This is all described in the ARRL Antenna Book.

    paul
     
  13. K1LLR

    K1LLR Subscriber QRZ Page

    K1LLR idea
     
  14. W0BTU

    W0BTU Ham Member QRZ Page

    Hello Eric,

    160 is the only band I currently operate, using CW around 1825. It's a great band, and it's not called the "Gentleman's Band" for nothing. You will find that a vertical with a good radial system will work well for DXing while using a separate RX antenna such as a Beverage or a K9AY loop.

    I should warn you about something, though. ;-) If you operate 160 meters much, you may get the Topband Disease.

    Perhaps I should now explain the symptoms of the disease. They are as follows:

    * Desire to be on the radio at sunrise.
    * Desire to be on the radio at sunset.
    * Desire to be on the radio at all times in between Sunset and Sunrise.
    * Desire to struggle for months to work a single station in a new country. In extreme cases, this might go on for more than a year. A good example is Riki, 4X4NJ in Israel who tried for two years to finish off working all the states in USA.
    * Never being satisfied with the antenna system and constantly trying new ones.
    * Only comes down to see the family after working a new country (to gloat). During the rare fantastic opening, will come down after each new country and hold up fingers indicating how many new countries were worked so far. ...
    * Drinks lots of water before going to bed with the sole purpose of waking up in the wee hours of the morning to see if a new country can be found.
    * Has problems getting to work on time during the winter months.
    * Sends equipment and wire to people in unworked countries, hoping that the end result will be their QSL card on the wall.
    * Spends thousand of dollars going to rare countries just so other people can work it. This is a problem, as they don't get credit for the country themselves!!

    If these symptoms persist for more than one sunspot cycle (every 11 years), then you should strongly suspect TopBand disease.
    More info at http://n6tr.jzap.com/tbdisease.html
     
  15. KA4DPO

    KA4DPO Ham Member QRZ Page

    So if the ends of an inverted vee are like, oh, 3feet off the ground and the angle between the legs is 90 degrees or less they aren't really omni directional. Oh, OK. I'll go along with that just so we don't have to hurl cowpies at each other.:D
     
  16. N0AZZ

    N0AZZ Ham Member QRZ Page

    I have 3 160m antennas up at this time a Hy Tower with a top mounted 160m kit on it with 18 120' ground wires for that band, a 270' OCFD with 6/1 balun and coax fed @ 60' with 20' at ea end, last a full wave loop @35' coax fed.

    The loop is the best antenna for NA, CA and out to about 2000 mi and quiet but not a DX antenna in my book for my location. The vertical and the OCFD just depends on the station and what day it may be. Some days I work the same people "DX" and one antenna better than the other the next day the opposite. The OCFD will work 6-160m using the internal tuner on radio or amp if any is needed at all except for band to band edge on 160 then I use a manual.

    Put up what you can and enjoy I'm a gray line guy myself but sometimes do wake up a 4 am local time and work a few. A good way to get feet wet is to work the 160m contest i would not miss it but I'm not a contester :)
     
  17. N5KRC

    N5KRC Ham Member QRZ Page

    Sounds like an excellent time to install and learn how to use some antenna modeling software!

    I believe NEC comes with a simple dipole model as an example. Shouldn't take but a second to change a few values and compare and inverted-v and flat-top, and you'll visually get an idea of what your RF will do.
     
  18. W8JI

    W8JI Ham Member QRZ Page

    There are two reasons there are so many different answers:

    1.) The behavior of the inverted Vee dipole (an inverted V is a directional longwire, NOT a dipole) depends on V angle and height

    2.) People have antennas they just like and don't like

    If we cut through all the old wife's tales, here is what we really have.

    An inverted Vee dipole has a little bit less null of the ends, and a little bit less gain. Not much different than a dipole, just a little bit. How much different depends on the V angle, but it never is omni directional.

    At angles more than 120 degrees it is pretty much like a dipole. My 160 and 80 meter "inverted Vee dipoles" have 15-20 dB nulls off the ends. That is hardly omni-directional.

    The real effect of dropping the ends, unless the angle is too narrow, is the effective height is reduced. If the ends get near earth losses naturally will increase some amount, but at heights of .05 wavelength at the ends (13 feet on 80 meters, 6-7 feet on 40) losses are negligible.

    They essentially are like a dipole at lower height. My 160 inverted V dipole is at 315 feet apex height, and the ends are at 260 feet. It acts very much like a perfectly flat dipole at 290 feet would act. Like all dipoles the pattern is perfectly horizontal broadside, and the pattern tilts more and more vertical moving around toward the ends. All dipoles work this way, all inverted Vee dipoles work this way.

    A REAL Inverted V antenna is vertically polarized and radiates off the end. They take a very high apex height, and are a few wavelengths long. They don't work that well though, I've had them.

    A loop antenna is not magic either, except on harmonics the impedance is low. This makes it a good multiband antenna, but other than that the loop has no real advantage. Loops are simply "different" in where the lobes and nulls fall, and really have no other special characteristics like significant gain or noise reduction. They are easier to match on harmonics.

    For 160, since you have no height, you may want a vertically polarized antenna like an inverted L. You could also put up an 80 meter ladder line fed doublet, and bring the feeder straight down to earth. Then it could be fed as a T antenna on 160 against a radial system, and as a doublet on higher bands.

    A 60 foot high 80 meter ladder line fed doublet would work well from 160 through 10 meters fed that way.

    I'm of the opinion that the most simple basic systems are best if well planned, and that too much wire in a small area is a bad thing. With only 2 acres, we have to plan carefully. I've got maybe 10-12 acres dedicated to transmitting antennas and I plan what antenna aims through what other antenna, and what is close to each other.

    The last thing I would do is surround a beam antenna with a big long high wire antenna on every side. It is just asking for re-radiation and pattern distortion. Better to have one simple basic clean system that is planned to not put things in the way of directions you want to work.

    73 Tom
     
  19. K3STX

    K3STX Ham Member QRZ Page

    "ONLY" two acres.

    Good one!!:rolleyes:

    paul
     
  20. EI4GMB

    EI4GMB Ham Member QRZ Page

    Hi Eric,
    A dipole is most effective when configured as a horizontal or flat-top antenna.
    It would be more suited to Near Vertical Incidence Skywave (NVIS) when hung as an inverted vee.
    In this position the effective range of the antenna would be limited.
    Hope this helps.

    Kind Regards

    Fred EI4GMB
     
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