Optimal EFHW Configuration for Low Angle DX?

[ultravista]

Looking for configuration recommendations for running an end-fed half wave, or non-resonant wire, for best low angle radiation. My current configuration for a MyAntenna's 80-10 is top fed @ 30 feet sloping to 20 feet.

My primary interest if HF DX on 10-40 meters.

[RobRich]

Check the antenna's FAQ section regarding radiation patterns.

https://myantennas.com/wp/f-a-q/efhw-antennas-f-a-q/

Ideally it should be horizontal and as high as possible. If that is not possible, the inverted-L config with 30'-40' vertical and the rest horizontal shows to be a decent compromise for upper-HF, low-angle propagation.

One of the usual issues is the pattern breaking into lobes as frequency increases. Are those lobes in directions you want? Is that even a concern? Another issue is gain versus radiation angles in the plots. If gets "real fun, real fast" trying to optimize performance across multiple HF bands regardless of polarization, especially if not using traps, multiple wire elements, and similar. A wideband design might get a decent match across multiple bands according to a SWR plot, but that often does little to indicate actual antenna performance.

Do you have room for another horizontal or inverted-L antenna? If you like your current end-fed antenna design, you can do a similar 40m-10m EFHW with a 49:1 unun and ~63-68' of wire potentially "better" optimized for upper-HF performance. Length depends upon the type of wire. A small cap might be needed if wanting to improve matching on the upper HF bands, MyAntennas sells such an antenna, though it could be homebrewed for (much) less, especially if just for receiving. The above linked EFHW 80-10 radiation patterns are also listed in harmonics, so use the plotted harmonics to determine how a 40-10 compares to your 80-10 at upper HF. YMMV.

[ultravista]

RobRich - a horizonal positioned EFHW will have a lower radiation angle than a sloper, L, or V?

[RobRich]

It can be with sufficient height depending upon frequency. Low angle lobes tend to develop as a horizontal wire approaches 1/2 wavelength height over ground.

From the FAQ links:

https://www.qsl.net/kk4obi/EFHW%20Straight.html
https://www.qsl.net/kk4obi/EFHW%20Inverted%20V.html
https://www.qsl.net/kk4obi/EFHW%20inverted%20L.html
https://www.qsl.net/kk4obi/EFHW%20Sloping.html

Compare the blue plot lines and gain numbers.

Your 130' as a horizontal at 40' height for 30m-10m has decent to good low-angle lobes and appreciable gain numbers. For example, 10m is 10.2dBi at 9.5 degrees.

Compare to a sloper with the high end at 40'. 10m is 4.62dBi at 19.5 degrees; a considerable difference.

There is the potential for some increased directivity with the other layouts versus a horizontal. The concern is you might optimize directivity for a specific band or two with a given layout, but otherwise it tends to shfit "all over the place" as frequency substantially changes.


Curious, can you deploy a vertical? Even just a wire run up to a tree limb or up an inexpensive crappie fishing rod. An approximately 18' to 20' vertical wire over a few on-ground radials should have decent low-angle receive performance for 30m-10m. You will want several to lots of radials if transmitting. Going longer will help with 40m, but you will start developing more high angle lobes on 10m, so it is a balancing act.

The "balancing act" is why I tend to favor my 31' vertical for general HF coverage. 31'-33' is a popular vertical length range to favor mid-HF performance. Others are 43' for improving performance dropping towards 80m, and 18' for improving performance increasing towards 10m. The downside is feedpoint impedance varies greatly across so many bands, from potentially a few ohms up to 1000s of ohms before even factoring complex impedance. Thankfully if just receiving, it is not that big a deal due to typical receiver gain*.

*IIRC, an older Navy study suggested even a 6' vertical wire should suffice for most general-purpose HF reception with an even then modern high-gain receiver.

[Josh]

Crucial to a efhw is orientation as it is a dipole, as a vertical it would be an omni, horizontal and it is bidirectional for all but nvis sigs. If it's a wavelength or longer on some bands of interest you can aim it towards a target like a beverage, but it has to be a few wl long to pull it off.

[Charlie_Dont_Surf]

All good points.

One more factor (though you have no control over it) is soil conductivity. In Florida and I guess maybe place like the Mississippi River Valley, the Texas Gulf Coast, perhaps the Rhine Valley and Finland (with many lakes and rivers) in Europe, the soil is much more conductive than it is here in the southern half of California and this affects all antennas.

Any HF antenna needs to be higher here (where the soil is poor) to distance itself from the lossy soil. In the case of any sort of unbalanced antenna like simple monopoles ("verticals" in ham speak), EFHW, inverted L, inverted F, etc., the worse the coil conductivity, the more extensive and longer the radial system needs to be for similar reasons: mask the close proximity of the very lossy ground to the antenna.

The difference between good and bad soil is modeled to be as much as 3-5 dB gain, depending upon many things, of course. Lossy soil can alter the directivity and pattern of an antenna to some degree, by altering how the radiation works with the soil (reflections, etc.)

So get that thing up in the air as high as you can.

[Josh]

Yep ground conductivity plays a major role in reception of hf and lower sigs.
Just note the z of the small loops as detailed in this link;
https://practicalantennas.com/theory/loop/full-wave/
Pay particular attention to Table II, where the Z is shown in relation to the mounting height of the loop, see how drastically it changes. This is why people think their low mounted antenna has a nice swr, well, it's only nice because of ground losses.
This treatise on loop antennae is one of the best I've found so far.