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I have been trying for ages to find a way to mount a 10 m vertical Yagi properly, so that the mounting pole doesn't stuff up the impedance and radiation pattern, and have had no luck so far. Apart from using a non-metallic pole or using 2 phased vertical Yagis on a cross boom just so that they can be mounted so the mounting pole is not in line with the elements, there doesn't seem to be a practical method.

If I mount two Yagis on the same boom each with a polarization of 45 degrees or half way between vertical and horizontal and each antenna rotated around the boom 90 degrees from the other so that the antenna looks like a set of X's or a quad with no wires around the outside, then if I phase the driven elements of the two antennas together using coaxial matching stubs or similar, then can I adjust the feed point phase so that I can get either horizontal (or more importantly vertical) polarization and therefore minimize the effect of a metal mounting pole because it's not in the same plane as the antenna elements ?

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  • $\begingroup$ Is there a reason why you haven't considered a non-metallic mast, such as fiberglass or plastic pipe? Wouldn't that be much simpler and cheaper? $\endgroup$ – Mike Waters May 25 at 1:54
  • $\begingroup$ @MikeWaters I have looked at this and have been unable to find anything suitable. Plastic and fiberglass has too much flex and will wave around in the wind too much in my opinion. $\endgroup$ – Andrew May 25 at 1:58
  • $\begingroup$ You just haven't found the right material yet. Schedule 80 plastic pipe is quite stiff, as is fiberglass. $\endgroup$ – Mike Waters May 25 at 2:02
  • $\begingroup$ And kindly clarify exactly what you mean by "stuff up". $\endgroup$ – Mike Waters May 25 at 14:17
  • $\begingroup$ an old (mid 1980s) one-piece fiberglass windsurf mast, they're usually ~ 15ft, can be cut and drilled, stiff yet flexible...can be found very cheap or even free. $\endgroup$ – Tyler Stone May 25 at 17:53
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Yes, it is possible given two antennas at orthogonal angles to adjust the relative amplitude and phase between them and create vertical, horizontal, or anything between polarization. You can even create circular polarization of either chirality, or elliptical polarization.

However, this does not solve the problem of the antenna interacting with the mast. The coupling between the mast and the antenna is proportional to the cosine of the angle between them. When the mast and antenna are aligned, coupling is at a maximum. When the mast and antenna are at right angles, the coupling is theoretically zero.

Your described arrangement places the mast at 45 degrees relative to each antenna, meaning there will be less than maximal, but still significant coupling with the mast. Unless of course the antennas are phased to provide horizontal polarization when the mast is vertical, but this is no different than could be achieved with a single antenna.

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  • $\begingroup$ Thanks very much for that Phil, lets say that i was prepared to put up with the less amount of coupling 45 deg would give compared to in line with a metal mast, could you point me in the right direction for setting up the variable phasing ? Is it just the simple matter of a T piece and then different lengths of coax sections connecting to the feed point which will then determine the resultant phase ? And Also, running two driven elements will give better capture area for receive right ? $\endgroup$ – Andrew May 24 at 23:14
  • $\begingroup$ Phil one more comment, your answer suggests the idea that the resultant polarization from two phased antennas is the parameter if you like that should not be inline with a metal mast, whereas i believe it's the physical polarity that's important in this case and not the resultant polarity of the two antennas ... any comments on that ? $\endgroup$ – Andrew May 25 at 1:17
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    $\begingroup$ @Andrew It's the electric field, not the pieces of aluminum, that interact with the mast. Whatever phasing arrangement you come up with, it's not going to interact with the mast any more or less than if you just mounted a single antenna that way, and did away with this complicated arrangement. $\endgroup$ – Phil Frost - W8II May 25 at 3:46
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    $\begingroup$ @Andrew and no, you don't get any additional capture area. That there are two antennas is precisely offset by the fact that each is sub-optimally oriented. If you want to increase capture area (meaning, increase gain) then you have to mount the antennas such that they are not orthogonal. People do that, search "stacked yagis". $\endgroup$ – Phil Frost - W8II May 25 at 3:49
  • $\begingroup$ @Andrew Per Phil's suggestion, here is a search for questions about stacked Yagis. Looks like you'll find some useful info there. $\endgroup$ – Mike Waters May 25 at 14:06
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You should be able to use a traditional offset mount:

enter image description here

The counterweight balances the weight and the wind-generated torque of the yagi. If you want to use a different offset for either side, use simple proportions to create the same gravity- and wind-driven torques. Given the relatively small offset required, this doesn't seem too onerous.

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    $\begingroup$ Protip: using an identical Yagi for the counterweight works well and yields more gain :D $\endgroup$ – Phil Frost - W8II May 25 at 21:31
  • $\begingroup$ @PhilFrost-W8II Yes, as long as the offset is correct to produce gain. It is surprising how much difference there is in optimum spacing for different antenna types; it is definitely not a "one size fits all" situation. $\endgroup$ – Brian K1LI May 26 at 12:23
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Treated as an issue for a practical solution, probably a v-pol yagi with a good F/B ratio in free space could be mounted so that it is sufficiently decoupled from a conducting/re-radiating, vertical support mast adjacent to it so as not to seriously affect the far-field radiation pattern of that yagi+mounting environment.

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    $\begingroup$ Hi Richard thanks for the reply, you didn't answer my question, but can you tell me how to mount so it's sufficiently decoupled from an adjacent vertical support ? $\endgroup$ – Andrew May 25 at 1:14
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    $\begingroup$ The usual solution is to mount it a wavelength or two horizontally away from the mast, or from the back, a quarter wave from the reflector. Neither of these are so practical at HF. $\endgroup$ – tomnexus May 25 at 3:12
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I think you are giving too much credence to the vertical support interfering. I have been designing and installing similar antennas since the 1960's. I have installed hundreds of vertical beams with an omni directional on top I have done this from 20 meters up through 450MHz including lots on 6 10 and 2 meters oh yeah and untold amounts of CB antennas. Yes the vertical tube makes a little difference but it is so infinitesimal it is not worth worrying about. Remember antennas in the real world are all about compromise. If it works use it! There are hundreds of things that affect antenna functionality some in good ways some in bad. Theory is great but it is just that THEORY! Theory is our way of explaining why and how things work, BUT in the real world grounds are not consistent neither are other obstructions, so build it the best you can then using the instrumentation at your disposal tweak it to the best you can, then quit worrying about it and enjoy using it. Conditions are going to be in flux so deal with it! We do not live in a perfect world enjoy the ride quit worrying about the color of the fenders it doesn't change the trip or the destination! Laurin WB4IVG

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