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Author Topic: Optimal EFHW Configuration for Low Angle DX?  (Read 2775 times)

Offline ultravista

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Optimal EFHW Configuration for Low Angle DX?
« on: June 14, 2023, 1305 UTC »
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.

Offline RobRich

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Re: Optimal EFHW Configuration for Low Angle DX?
« Reply #1 on: June 15, 2023, 0420 UTC »
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.
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Offline ultravista

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Re: Optimal EFHW Configuration for Low Angle DX?
« Reply #2 on: June 15, 2023, 1520 UTC »
RobRich - a horizonal positioned EFHW will have a lower radiation angle than a sloper, L, or V?

Offline RobRich

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Re: Optimal EFHW Configuration for Low Angle DX?
« Reply #3 on: June 16, 2023, 1809 UTC »
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.
« Last Edit: June 16, 2023, 1817 UTC by RobRich »
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Offline Josh

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Re: Optimal EFHW Configuration for Low Angle DX?
« Reply #4 on: July 15, 2023, 0110 UTC »
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.
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Offline Charlie_Dont_Surf

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Re: Optimal EFHW Configuration for Low Angle DX?
« Reply #5 on: July 16, 2023, 0805 UTC »
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.
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Offline Josh

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Re: Optimal EFHW Configuration for Low Angle DX?
« Reply #6 on: July 18, 2023, 1853 UTC »
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.
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Offline jonesypeter

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Re: Optimal EFHW Configuration for Low Angle DX?
« Reply #7 on: June 12, 2024, 1911 UTC »

https://www.qsl.net/kk4obi/EFHW%20Sloping.html

Where the author says 'The general rule is to position an antenna is "as high as wide". ', do they mean at 45 degrees?  Thanks

Offline RobRich

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Re: Optimal EFHW Configuration for Low Angle DX?
« Reply #8 on: June 13, 2024, 1245 UTC »
It means a typical horizontal half-wavelength dipole antenna should be (if possible) mounted as high as it is long. To be more technical it is the half wavelength of the tuned frequency instead of the antenna's physical length.

For example a typical 40m dipole at ~66' total length would offer good overall performance when mounted horizontally at ~66' height versus a lower height.

That said and factoring the "more technical" aspect, ~66' height would still be applicable even if using loading coils to shorten the antenna to say 33' total length.

Actually there can be lots of other considerations like NVIS at lower frequencies, but anyway, it is a good basic guideline for typical HF half-wave dipoles.

Even a multi-band "EFHW" is still a dipole; just a extremely offset fed one. Getting an 80-10 EFHW up ~133' for 80m is probably not happening for most, thus like most things radio, actual height will be a compromise for your particular deployment situation.

Even if just a few feet off the ground, any antenna tends be better than no antenna. At the extreme, people have worked HF contacts with wires on the ground.... and even on dummy loads. ;)
« Last Edit: June 13, 2024, 1343 UTC by RobRich »
Tampa, FL USA | US Map Grid EL88
Airspy HF+ Discovery | KiwiSDR 2 | 2x Msi2500 Msi001 | 2x RTL-SDR V3 + NE602 | 2x RTL-SDR V4
148' + 60' Loops-on-Ground | 31' Vertical | 18' End-Fed Vertical | PA0NHC MiniWhip

Offline jonesypeter

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Re: Optimal EFHW Configuration for Low Angle DX?
« Reply #9 on: June 14, 2024, 1736 UTC »
It means a typical horizontal half-wavelength dipole antenna should be (if possible) mounted as high as it is long. To be more technical it is the half wavelength of the tuned frequency instead of the antenna's physical length.

Thanks so much for answering my dumb questions!  While I have you can I ask some more?

With the charts on the following page:

https://www.qsl.net/kk4obi/EFHW%20Sloping.html

Am I right in thinking that the red line is looking down from above at the radiation pattern, and the blue is showing from the side the area with the best gain?

I understand for long distance DX that a low take-off is good so you get longer distance via the F layer.

Can I also confirm that an EFHW at its lowest frequency acts like a dipole.  The reason I ask is that, if you read the following from the RSGB.  Actual page 7 of 32, but page number in book is 55.

https://www.rsgbshop.org/acatalog/PDF/Successful_Wire%20Ant_sample.pdf

It says that a sloping dipole can be good for long distance work. This seems to go against other stuff I've read in those links above.

Finally, do you know if the author of those QSL.net articles is still around?  The resolution of the graphics is hard to read, and there seem to be random non-ascii characters that pop into the text?

Best wishes

Peter

« Last Edit: June 14, 2024, 1739 UTC by jonesypeter »

Offline RobRich

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Re: Optimal EFHW Configuration for Low Angle DX?
« Reply #10 on: June 16, 2024, 1453 UTC »
Correct for those diagrams as published. Red is looking from above. Blue is looking from the side. Also correct on the angle of radiation. Lower towards the horizon tends to improve DX performance.

Note sloping tends to shift the radiation pattern and angle of radiation. Usually you can add or subtract a dB or few towards (or away from) a particular direction if desired. However dropping the lowest end far enough down towards the ground might also start incurring additional ground losses, especially at lower frequencies. YMMV.

Unless looking for NVIS for local to regional work at lower frequencies, a horizontal dipole at approximately 1/2' wavelength above moderate to decent ground can return up to ~8.5dBi of gain. That said I am inclined to say "whatever" to a couple or even possibly a few dB on HF as propagation does much of the heavy lifting anyway. ;)

Looks like KK4OBI did the QSL article:

https://www.qrz.com/db/KK4OBI

If interested enough in the models, EZNEC is not too hard to learn for basic wire antennas.

https://www.arrl.org/antenna-modeling-for-beginners
https://www.eznec.com/

Also correct that an EFHW is a half-wave dipole typically at its lowest frequency. "Typically" as there are ways to add lower frequencies with coils and similar. If just a basic wire, you are end-feeding the half-wave dipole at a voltage node. At higher frequencies, AFAIK, it starts looking more like a collinear dipole array or probably even a longwire as frequency increases.

Since we are on the topic of end feeding, note even an "end-fed" antenna is subject to Kirchhoff's first law, meaning there are still some currents on the transformer side opposite the primary antenna wire. Those currents tend to common-mode couple to the feedline if no other RF ground or counterpoise is available, thus why many recommend placing a simple RF choke a few feet down the feedline from the antenna.

Anyway, do not overthink the antenna modelling for a simple wire HF antenna. Get the wire as high as possible for your deployment situation, and do not be concerned if there is a slight to even moderate slope towards whatever direction. Barring some type of antenna failure, you should be making lots of contacts as an amateur op.... or likewise receiving lots of stations if a SWL.

BTW, if ya' are really wanting those extra dBs of directional gain on a low band like 80m, you might later look into a wire yagi or similar.
« Last Edit: June 16, 2024, 1507 UTC by RobRich »
Tampa, FL USA | US Map Grid EL88
Airspy HF+ Discovery | KiwiSDR 2 | 2x Msi2500 Msi001 | 2x RTL-SDR V3 + NE602 | 2x RTL-SDR V4
148' + 60' Loops-on-Ground | 31' Vertical | 18' End-Fed Vertical | PA0NHC MiniWhip

Offline jonesypeter

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Re: Optimal EFHW Configuration for Low Angle DX?
« Reply #11 on: June 16, 2024, 1630 UTC »
Anyway, do not overthink the antenna modelling for a simple wire HF antenna. Get the wire as high as possible for your deployment situation, and do not be concerned if there is a slight to even moderate slope towards whatever direction. Barring some type of antenna failure, you should be making lots of contacts as an amateur op.... or likewise receiving lots of stations if a SWL.

Thanks very much for the answers.  Much appreciated.  I got my full licence last year (M0LMG) although I have been an SWL since childhood, but it's not until you get on the air that you start thinking more about these things. 

I'm currently using an EFHW from UK Antennas.  It's arranged as a sloper, as we have a good size garden (by UK Standards), and there is a large tree at the end of the garden so I was able to set-up a pulley system.

https://www.ukantennas.co.uk/product/multi-band-with-bracket-40-20-15-10m/

Thanks again.

Peter M0LMG

 

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