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[KD0VE]

I have begun experimenting with elevated verticals.  I have found them to be easy to construct and surprisingly effective even with only 2 radials so I am working on an easy to deploy option for POTA and camping.  I know sloping elevated radials lowers the angle.  Wondering what the tradeoffs are for height vs. performance.  I'm thinking I can make a set up that will work on 10,15,and 20M with a relatively quick changeover.

thx in advance to anyone taking the time to offer advice.

[AK5B]

No, sloping the radials lowers the impedance---radiation angle stays the same.  N6LF found that 4 feet agl and two opposing radials at that height is a basic minimum---but even a few inches or 1 foot helps lower ground loss.  I do mine at 7 feet or more for less foreground clutter/stucco walls and hazard mitigation for humans and deer antlers.

I'm currently reworking my 5-band elevated fan vertical that came down in a storm and will post some details once it's back up soon (in the QRZ Antennas Forum).  Enjoy operating portable with your vertical, too!  Elevated verticals rock (especially over or close to saltwater)!

73,

Jeff, AK5B

[WB6BYU]

Here's one option, if you are using aluminum tubing rather
than wire.

Here is more data on ground planes, including the
effect of sloping the radials which slightly improves
the gain, but mostly gives a better match.   Unfortunately
I didn't include feedpoint height in that analysis.


The feedpoint height does depend on the frequency range
you are planning to use it on.  At VHF/UHF, where you are
using a direct path, height becomes much more critical.
At HF where you are planning to make use of ionospheric
paths, lower heights can work well.  As the antenna height
is raised, it can put more power into high angle lobes.  There
is still some improvement with height, but it is much less:
for a 10m vertical, there is about 1 dB improvement at the
lowest lobe (10 - 12 degrees) when the height is raised from
10'  to 30'.

Lower heights will still work, and may be more practical for
a portable antenna.  As it gets closer to the ground, you may
need to slope the radials less to keep them off the ground, but
even 3' off the ground doesn't drop performance by much, as
long as the ends are kept far enough off the ground (which
affects the tuning).

Of course, if you want to lay the radials on the ground, you
can put the feedpoint at ground level, but you may need
more radials for efficiency, and differences in how the
radials are installed (particularly how high off the dirt they
are, laying on grass, bushes, etc.)  will affect the tuning
and efficiency.

I have an old 10m Ringo vertical that I got with a broken
tuning ring.  It makes a simple telescoping quarter wave
vertical for 20m through 10m, used with two radial wires
for each band.  I generally put the feedpoint at 4' to 6'
off the ground using an old roof tripod for a TV antenna.
At that height I can't slope the radials much.

My guess would be around 3' as a reasonable minimum
height for the radials to be relatively independent of the
ground.  But the differences in that range are relatively
small, so mechanical issues may take precedence.

[N4UFO]

I used to have up a 160/80m loaded vertical with the feedpoint at ~3 feet with four aluminum fence wire radials on electric fence posts going out from it. (until I could lay out radials on the ground the following year) And currently I have a set of vertical wires up with the feedpoint ~5-6 feet on my beck fence with a pair of radials for each band going down the back side of the fence about 5 inches apart (same as the vertical wires, 5 inches apart). It works fine and I am making contacts all over the world. You can see pics and a details explanation on my QRZ page: https://www.qrz.com/db/n4ufo

So yes, as long as you keep the radials symmetrical and are well tuned, 3-4-5 feet is fine. Also, keep in mind when tuning them that best SWR at resonance will mean that the vertical or the radials will be slightly longer than the other. This puts the feedpoint of your 'bent dipole' slightly 'off center' and brings the standard 37 ohm feedpoint impedance of a ground plane up to 50 ohms and changes your minimum SWR from 1.4:1 closer to 1:1. This does the same as lowering the angle of the radials to 45 degrees down... that too, changes the feedpoint impedance to 50 ohms. You might want to leave extra wire that you can 'let out' or 'shorten up' in each installation to better tune the antenna. No two locations are the same, ground is different, surrounding objects are different, etc.

You could also make one set of radials with insulators and alligator clip jumpers at each band endpoint. Use where you clip the jumper back to the 'hot' wire to tune if needed. Honestly, I may be suggesting overkill for a portable setup, but want to mention it. Bottom line, I am saying, don't treat the radials like a 'snip & forget - close enough' piece of wire.  - Me, mine stays put and since I leave all the radials up, they interact so I took several days to get them all tuned. After tuning I got less than 2:1 across the bands.

As always, your mileage may vary...    but good luck with the antenna plan, it should do well for you. And the fiberglass electric fence posts for holding up radials wires are a few bucks apiece at about any farm supply store. Might want to check it out. For radials 20-10m might just need 1-2 per radial and no need to tie off to trees and upset park rangers.    I can visualize a collapsible tripod and some electric fence posts all fitting in a long bag and holding the entire thing up without attaching rope one.

73 & GL! Kevin N4UFO

[KD6VXI]

.1 wavelength.


N6LF has written on this.

--Shane
WP2ASS / ex KD6VXI

[KB1GMX]

WB6VYU, addressed most of the issues...

As you go lower in frequency you need to be higher to get the needed
ground clearance or the radials detune.  at 40M and lower you can't be
high enough as .1wave as one suggested is 4M.

Now the other issue is POTA, a vertical for 20M is 16.5ft (+-) but you
eat 33ft of horizontal space for two radials and you need to keep them
a few feet up.  Actually you might need to keep them far higher to keep
people from touching them, running into them, or pulling them down. 

So the practical problems are more concerning than the electrical
for POTA.  Obviously 15 and 10 m make those issues easier to
manage with the antenna being smaller.  For that a field assembled
vertical using aluminum tubing on a 6-10ft tripod is very doable
but do watch for eyes meeting the ends if not high enough.

Also as you go higher in frequency especially 10M antenna height is
a factor due to ground clutter like buildings and trees.  The feed
point and radials are not much an issue but general height over
close by obstacles.

There is no magic numbers as its frequency dependant.  There
may be minimum numbers oft repeated as others have used them.
The problem that persists is you site may not be the same (likely)
as their site for ground conductivity and overall terrain height.

Allison

[W1VT]

I had a 40M ground plane with the radials just 2ft above the ground.
It was up only briefly as 2ft is a tripping hazard.

But, I used it to work Japan and India, VU2TS!  I ran the 500W amp and used a flag antenna to hear him on 40 CW.
As I recall it was just 15 minutes before his local noon in India.  He lives way out in the sticks on a nature preserve.

My ground conductivity is excellent, as I live on heavy clay soil with poor drainage.
I've dried out my basement by planting a long bed of roses 15 feet away from the house to soak up the water.

Zak W1VT

[RFRY]

I have begun experimenting with elevated verticals.  I have found them to be easy to construct and surprisingly effective even with only 2 radials so I am working on an easy to deploy option for POTA and camping.  I know sloping elevated radials lowers the angle. ...  I'm thinking I can make a set up that will work on 10,15,and 20M with a relatively quick changeover.

Below is a description of a portable, 3-band, HF vertical antenna that needs/uses no radials. It might be worth building, experimenting with, and some real-world testing.

Its calculated performance is quite good, and it would be fairly easy to transport and set it up at an outdoor site.

73, W9XMT

[WA3SKN]

Before investing too much in this, I have been advised that many of the parks forbid driving any stakes in the ground or any guying.  Please check with the park you plan to visit for any restrictions.
It will help with the planned activation.

-Mike.

[VR2AX]

There is a technical article in the September 2022 RadCom which looks at this and related topics. It is titled 'All we need to know about ground plane antennas' (or similar), by G3LNP.

One interesting point the author makes: 'when we elevate the antenna [ie above ground] we do not take the ground with us'. So, actual base height will have different effects on radiation angle.

[N2TO]

For POTA activations I was using inverted-vees but park rangers asked that I do not use trees. I went to Plan B for a stand-alone antenna to work 20M and 15M.

I made 1/4-wave vertical elements with two 1/4-wave raised radials for each band. Purchased two masts from the Mast Company (tnx AE0Q!), using 19' mast for 1/4-wave verticals. Twenty ga stranded wire. Davis RF RG-58 C/U coax, 1:1 CMC 12 turns on Fair-Rite 2.4" Mix 31 at feed point and 1:1 CMC 12 turns on Fair-Rite 2.4" Mix 43 at rig. Flagpole-To-Go tire mount (drive-over). Running IC-703 at 10 watts on CW and SSB I've worked a lot of QSOs. Thanks hunters! Lately I am running my FT-857D at 20 watts out. I have worked with the radials at an open angle of about 100 degrees and 180 degrees. It depends on location, people and other cars in the area. Nylon twine to hold element to top of the mast.

I keep the radial ends elevated to 2' using two 1 gallon water bottles with square wooden dowels taped to the bottles. I cut off 1' to make them manageable.

I wanted the most efficient stand-alone antenna and to fly under the radar. I want to avoid WHAT THE HELL IS THAT!? from folks. The second 22' heavy duty mast will be used in the Spring to support a home-brewed 44' doublet with home-brew ladder line. Kitchen garbage bags and small plastic bags keep schmutz off the tire mount and bottles. I have read papers listing 5% and 1/16-wave above ground to minimize losses and this is less at 20M. However it works really well and gets me on the air. Rangers have stopped by to say hello, and all is well. Next antennas to make will be for 17M and 6M, thinking about a multi-band as well.

GL

73 Kevin N2TO

[N2TO]

Mast Co 19' and 22' masts:

https://www.tmastco.com/main/page_products_telescopic_poles.html

Flagpole-To-Go standard tire mount:

https://flagpoletogo.com/products/tire-mount

I saw the prices of some drive-over mounts and had sticker shock. I was prepared to make one but then saw this. Parts would have been more at Home Depot or Lowes.

GL

73 Kevin N2TO

[KK4OBI]

I have often wondered about your question so I ran a model with the minimum two radials at various heights just to see.  You will find a summary what I found at this link:

https://www.qsl.net/kk4obi/Elevated%20Radials.html

Read the section "What happens when elevated radials become close to ground?" and Figure 2.

I used to think that one of the features of a vertical antenna was how little it was effected elevation from ground.  Now I see that this applies only if the antenna is higher than 0.1 wavelength... like 6 feet on 20 meters.  You can see how radically the frequency and lengths of the vertical and radials are effected below this height.

 

[AC6LA]

I have often wondered about your question so I ran a model with the minimum two radials at various heights just to see.  You will find a summary what I found at this link:

https://www.qsl.net/kk4obi/Elevated%20Radials.html

What a great overview!  Hats off to KK4OBI.

Dan, AC6LA

[N1UR]

Given that you are talking POTA application and the high bands, I would use the 0.1 wavelength guidance and 4 radials (non sloping).  Put clips on the radials to swap with bands and a way of changing the radiator length.  Should work well. 

The other question is ground losses.  Depending on what you are over, the performance could vary by up to 5 - 6 dB.

Ed  N1UR