Vertical vs dipole on 20m and up

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by N1BBR, Oct 7, 2010.

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  1. N1BBR

    N1BBR Ham Member QRZ Page

    I recently had the opportunity to add a 5/8w 20 meter vertical to my current setup. I currently have a 135' doublet, ladder-line fed up at a height of 55' which favors North-West/South-East. Secondly I have a 34' doublet, ladder-line fed up at a height of 40' which favors East/West.

    I've had the vertical in a number of setups now.
    Ground mounted with 24 1/4w radials set above a layer of chicken-wire mesh which lays on the ground 1/4w diameter.
    The vertical has L/C matching for low swr at 7.01mhz

    I've also had the vertical at a base height of 3 feet, and a base height of 10 feet. I feed the vertical with 30 feet of brand new RG8/X bury flex coax.

    I have an ABC switch which allows me to switch between antennas.

    I was surprised to find that the two doublets out-performed the vertical on 20 meters, almost all qso's I had with stations 3000miles and beyond. I would have thought that the vertical would outperform the dipoles for the more distant contacts, but this was not the case.

    As a matter of fact, I had the experience many times of having contacts with over-seas stations coming in on the small doublet with an S6 strength and when switching over to the vertical the signal absolutely disappeared!

    I have a VK contact that I have made a number of times who always indicates that the small doublet is stronger for him than the vertical on 20m.

    I'm starting to think the vertical would be put to better use on lower bands.

    I would appreciate any comments or suggestions from hams who have empirical rather than conjectural knowledge on this subject.

    Thanks
    N1BBR
     
  2. G0GQK

    G0GQK Ham Member QRZ Page

    There really aren't any rules, some days one antenna work may better than another, if you have more than one you can make your choice. Signals arrive and presumably depart a station at different angles at different times of the day and presumably vary with the season and time of day. You are lucky in being able to have dipoles at a good height above ground so if the dipoles work better you have your answer.

    G0GQK
     
  3. G3TXQ

    G3TXQ Ham Member QRZ Page

    I know you said you wanted an "empirical" response, but I'm surprised you are surprised ;)

    Simple antenna modelling shows that on 20m the 34ft doublet at 40ft would easily outperform a 5/8 wave vertical at low take-off angles - by as much as 6dB; and that assumes the vertical+ground system is 100% efficient.

    As a very broad generalisation, at the sort of heights Hams typically erect horizontal dipoles they will outperform verticals on 20m thru 10m; verticals come into their own on 160m and 80m. Somewhere around 40m it's "break even".

    Red trace is the doublet at 40ft, blue trace is the 5/8 wave. "Average" ground is assumed; poor ground would favour the doublet more, and good ground the vertical:

    [​IMG]

    73,
    Steve G3TXQ
     
    Last edited: Oct 7, 2010
  4. EI4GMB

    EI4GMB Ham Member QRZ Page

    I agree. I have used verticals in the past and didn't find them a vast improvement on my horizontal G5RV Jr. In some instances they were even worse.

    73

    Fred EI4GMB
     
    Last edited: Oct 7, 2010
  5. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Now put up a beam and you'll see another amazing difference.
     
  6. W5DXP

    W5DXP Ham Member QRZ Page

    There's an old saying in ham radio: "A vertical radiates equally poorly in all directions." Why would anyone think an antenna that radiates (and receives) in all directions would not have S/N problems compared to an antenna that radiates (and receives) broadly in two directions? Make your 34 foot ladder-line fed dipole rotatable (like mine is) and your vertical will hardly ever equal it for 20m-10m operation.
     
  7. W9PSK

    W9PSK Ham Member QRZ Page

    How did you make a dipole rotatable? I'd like to read about something like that. Maybe you could start a new thread on it?
     
  8. WA8UEG

    WA8UEG XML Subscriber QRZ Page

    Both W5DXP and WIK's comments are Sooooooooo true.
     
  9. KM1H

    KM1H Ham Member QRZ Page

    Rotating a single 33' element can be handled by even the smallest TV rotator.

    A simple Gamma match using the center conductor and dielectric of RG-213 works well plus a sleeve balun or do the old 40's classic of a split element using ceramic insulators over a short hunk of wood.

    Even a tribander DE can be made to work.

    Carl
    KM1H
     
  10. KL7AJ

    KL7AJ Ham Member QRZ Page

    You will have to read my December QST article, "Gimme an X, Gimme an O, What's that spell? Radio" wherein we demonstrate that Ionospherically refracted H.F. signals are always circularly polarized.


    Stay tuned!

    Eric
     
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