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Say I have a shortened HF dipole (with significant inductive loading and/or capacitive hats), and can only mount it very close to ground level (but not touching), over lossy ground, and with no radials or counterposes. (situation is temporary portable operation in an extremely constrained area).

To minimize ground losses and/or maximize radiation efficiency (what little is possible given the constraints), would it be better to orient the low short dipole horizontally or vertically?

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    $\begingroup$ I believe that mounting it vertically would be better. A low horizontal dipole loses a lot of power to the ground, plus the takeoff angle is very high, if I remember correctly. Not posting a full answer since I don't have sources, though. $\endgroup$ – Nat Mote Feb 21 at 18:53
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    $\begingroup$ @NatMote I don't have references either, but I fully agree with you. It's better if our answers include sources, but it is not mandatory. If you post that as an answer, I'm confident that it will receive upvotes in addition to my own. :-) $\endgroup$ – Mike Waters Feb 21 at 19:46
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    $\begingroup$ Fair enough, done! $\endgroup$ – Nat Mote Feb 21 at 22:23
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Generally, a low horizontal dipole doesn't do a good job of radiating power to where you want it. I found an interesting analysis of horizontal dipole height, which ran a number of simulations and found that at low heights (less than 1 wavelength, roughly) the dipole's radiation pattern has a significant vertical lobe. At heights of 0.2 wavelengths or less off the ground, the direction of maximum gain is straight up.

I have read elsewhere that low dipoles also tend to radiate a lot of power into the ground. So, you would be spending a lot of your power heating the ground and space.

I believe polarization is important for groundwave propagation, but for skywave propagation it is minimally important unless you have a specific QRM issue that you need to work around. So, for the purposes of this answer, I will assume that polarization is not an important consideration.

With that in mind, a vertical dipole is likely to be more effective. In practice it's likely to be similar to a monopole with radials, which is an antenna configuration that is widely used with positive results.

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  • $\begingroup$ A dipole antenna is usually assumed to have the feed line running perpendicularly to the antenna, which is more difficult to arrange for a vertical dipole. If the feed line doesn't run perpendicularly, then it interacts with the antenna, which is another way of saying it becomes part of the antenna. The usual wisdom is that a balun, such as a common-mode choke, is needed to mitigate the undesirable interaction from the feed line. $\endgroup$ – rclocher3 Feb 25 at 20:47
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Below is an analysis that may be useful in answering this question. It shows the complete radiated fields from the horizontal dipole and the vertical monopole defined there, for elevation angles from zero (the horizontal plane) to 5.7° above it.

The space wave and groundwave of the h-pol radiator are out of phase near the surface of the earth, and tend to cancel each other.

That does not occur for vertical polarization.

enter image description here

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    $\begingroup$ Note this graph is "sideways" - field strength is on the horizontal axis, and the vertical axis is distance. $\endgroup$ – hobbs - KC2G Feb 22 at 16:20
  • $\begingroup$ Yes, the graphic shows the field intensity (labels on the horizontal axis) at elevations above the horizontal plane (labels on left vertical axis) at a fixed distance of 0.162 km (~1/10 mile) from the radiator. $\endgroup$ – Richard Fry Feb 22 at 16:47
  • $\begingroup$ I'm confused. So the graph shows the electric field strength in the near field, right? Why do you say 0.162 km distance, but then the vertical axis is 0 m to 50 m? Why show the field strength for radiation only from 0° to 5.7° from the horizontal? What does this plot show that the usual polar far-field plot doesn't? $\endgroup$ – rclocher3 Feb 25 at 20:36
  • $\begingroup$ The plots lie in the far field of those radiators.The vertical axis shows height above Earth at that 0.162km range. The 5.7 deg vertical span compares their low-angle radiation, which is the purpose of the study. $\endgroup$ – Richard Fry Feb 25 at 22:47

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