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Dipole Orientation.

Discussion in 'General Technical Questions and Answers' started by G7GPL, Nov 18, 2009.

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  1. G7GPL

    G7GPL Ham Member QRZ Page

    Hi all.

    I am about to erect a new antenna. Its a dipole for 20mts. Whats the best orientation do members consider for 'general use' for someone who lives in the north west of England. (Between Manchester and Liverpool.)

    I shall call the 2 ends of the dipole 'Nose' and 'Tail' ....... Yes I know a dipole has neither as its balanced, but it saves confusion. (imagine its a snake :) )

    So what do you all think is best for me for the 'nose-N-tail' to point. I have 3 options available to me. (due to available supports to string ends to.)

    North - South (nose-tail)

    NNW - SSE (nt)

    WWN - EES (nt)

    Many thanks, Nick
  2. AC0FP

    AC0FP Ham Member QRZ Page

    Just off hand I would chose your first or second directions listed, to give access to the maximum number of stations. With that said, what is the height of the 20 meter dipole? If the antenna is not at least 1/2 wavelength high then the overall antenna pattern will tend to be more "omnidirectional" with the maximum radiation lobe straight up! :eek:


    fp :)
  3. K7MHI

    K7MHI XML Subscriber QRZ Page

    i think your going to have problems with neighbors with a snake in the air! :)

    use all of them! start off in one, then after 6 months move to the next to see how you find new stations etc. or your signal strength working the old
  4. WA4ILH

    WA4ILH Ham Member QRZ Page

    Nick, Unless you elevate your dipole at least 1/4 wavelength above ground, it will exhibit little (or at least multiple lobe) directivity. A dipole is directive broadside to the array. If you want to talk to North America for example, (NW) the wires should run roughly southwest to north east, giving you a NW broadside pattern.
    (I see that I "doubled with AC0FP, who said about the same thing concerning height)
    Tom WA4ILH
    Last edited: Nov 18, 2009
  5. G7GPL

    G7GPL Ham Member QRZ Page

    :eek: ........... Eeeeeeeeeeeeeeeeek.! ........... Do they have 20mts on the space station. :rolleyes:;);)

    Antenna height will be about 12 mts.

  6. G7GPL

    G7GPL Ham Member QRZ Page

    Its ok.! .............. I live on a nudist colony. ;);):eek::D
  7. W5DXP

    W5DXP Ham Member QRZ Page

    To whom/where do you want to make contacts?
  8. G7GPL

    G7GPL Ham Member QRZ Page

    Well you 'Good ole' American boys seem a friendly bunch of 'renegades' ;) ...... Invariably polite and willing to chat about almost anything. Plus there are thousands of you. :)

    Good enough place to start eh.??

  9. G0GQK

    G0GQK Ham Member QRZ Page

    The wire is, or will be, approximately just under forty feet above ground so that will be sufficient to have some direction on 20 metres. The height to avoid is 3/4 of a wavelength, so the books tell us, I don't know never had an antenna above 25 feet. but you will find you will have more contacts with European stations anyway, because there are more of them, and they're closer.

    All this WWN busines has me confused, the best position, assuming you live in Warrington, is to have the tail pointing towards Frodsham and the head towards Bolton. You can then chat with Alberto and Klaus most of the day and Bob in New York when he pops in, and then hope for a goodly supply of sunspots.

  10. KJ6CNS

    KJ6CNS Ham Member QRZ Page

    Just wanted to ask for some clarification. When discussing height, is that height above land or height to any surface? Meaning if on a roof, do you count the feet above ground or the feet above the roof?
  11. G3TXQ

    G3TXQ Ham Member QRZ Page

    Even at a height of 15ft above average ground a 20m half-wave dipole has over 10dB eccentricity at DX take-off angles; so if you have a choice it's certainly worth pointing it in your preferred direction.

    I'd opt for North-South for the wire direction to favour the "ex-colonials over the pond" :)

    Steve G3TXQ
  12. G3TXQ

    G3TXQ Ham Member QRZ Page

    It depends on how big the roof is. What matters is the antenna's height above wherever the ground reflections are taking place for a particular path. That might be the "real ground" for low take-off angles, and the roof at high take-off angles (assuming the roof is conductive).

    Steve G3TXQ
  13. G3TXQ

    G3TXQ Ham Member QRZ Page

    With respect, this a "part truth" :)

    Take a 20m dipole and stick it at a height of 15ft. The maximum Gain is at an elevation of 90 degrees and there it's omnidirectional. However, at a take-off angle of 20 degrees in the broadside direction it's only 5dB worse, so there is still plenty of DX to be worked; but end on it's 15dB below maximum, so orientation does matter even at such a low height.

    Steve G3TXQ
  14. AG3Y

    AG3Y Ham Member QRZ Page

    One-half wavelength on the 10 meter band is certainly a short enough length that you should be able to rotate a dipole using a standard TV rotor ! Just how limited is the area ( "garden" ) you plan on mounting this dipole in ? I would make some sort of bracket and put up a dipole made of aluminum ( aluminimun ) tubing and experiment to your heart's content! The nulls off the ends might be more advantageous than the lobes to the sides, for elminating interference from some nearby source!

    73, and good luck! Jim
    Last edited: Nov 18, 2009
  15. W5DXP

    W5DXP Ham Member QRZ Page

    I point my 20m rotatable dipole broadside in the direction to which I desire to communicate. If the 20m dipole is not rotatable, it should be pointed in your favorite direction - hence my original question. The combination of the free demo version of EZNEC and PIZZA will tell you everything you need to know.
  16. K6OK

    K6OK Ham Member QRZ Page

    Technically your dipole should be pointed at right angles to the Great Circle path to your target area. Here's a Great Circle mapper:

    You can see the optimum dipole orientation to target the U.S. would be NE-SW. The map says 300 degrees bearing, so your dipole should be pointed 300 - 90 = 210 degrees. The other end of the wire would be at 210 - 180 = 30 degrees.
  17. G7GPL

    G7GPL Ham Member QRZ Page

    The height that I give is height above the ground and will be about 2 mts above the apex of the roof. (roof is tiles with timber supports so non conductive)

    I have some confusion here. Some are saying the critical height is at least 1/4 wavelength and some are saying its a 1/2 wavelength above the ground.?

    Thanks for all the help and advice so far.

  18. K3STX

    K3STX Ham Member QRZ Page

    The critical height is the height of your antenna above ground!

    Seriously though, get it as high up as possible. Yeah, 1 full wavelength might not be ideal, but you are talking about 40 feet. This is a little over 1/2 wavelength, that would be great. I have a 20 meter dipole up about 40 feet and it is broadside to Europe and it is a great antenna. And I can still make QSOs to South America with it; it might FAVOR NE/SW, but that does not mean it is deaf everywhere else, just not optimal.

    Don't overthink this, it is just wire.

  19. AI3V

    AI3V Ham Member QRZ Page

    Don't forget that having a "G" prefix is good for at least 8.25 db of signal over somebody with a "AI" prefix!:D

  20. K6OK

    K6OK Ham Member QRZ Page

    The optimum (not critical) height above ground is at 0.6 wavelength, not 0.5 wavelength. There's another optimum height at 1.1 wavelengths.

    At 0.5 wave, the main lobe peaks at about 7 dbi at 26 degrees.
    At 0.6 wave, the main lobe peaks at about 7.4 dbi at a lower angle, about 22 degrees. More gain at a lower takeoff angle is better.

    0.6 wave height is about 39 feet for 20 meters, so your 40 feet actual height is nearly perfect. It will work very well.

    Here's the NEC pattern at 0.6 wavelength. This is looking straight down the wire.


    Good luck and 73
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