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Lightweight Vertical Antennas


#103

Hi Andrew

Just worked EU from Mt Stromlo using a EFHW J-Pole on 20m fitted to a 10m telescopic pole and JA using a 15m 1/2 wave inverted V dipole for my 2nd JA S2S.

73, Andrew VK1AD


#104

vim - no exceptions. :smiling_imp:


#105

I could agree with you but then both of us would be wrong instead of just yourself. :angel:


#106

Maybe someone has already mentioned the published work of KK4OBI, which finds an advantage of using only one radial with a 1/4 wave vertical. I have used this in a limited space on my roof for 40 meters. Dick found high radiation efficiency and about 4 db gain and F/B in the direction of the radial. http://www.qsl.net/kk4obi/Elevated%20Radials.html
I set this up so I can switch quickly between radials disposed at 180 degrees and it seems to bear this out. Seems too good to be true? Show me why not.


#107

It’s an appealing idea, to get gain by removing wires. But I wonder whether it is real gain over the full antenna or just directivity? Ie, maybe the only direction it hears and is heard in is the direction of the one “radial”, but is it as good as the original full vertical with ground plane?

In a conventional vertical with at least two radials the net radiation is from the vertical element only as the net radiation from the radials is close to zero as their fields are 180 degrees out of phase. But with only one radial, you have what is really a dipole, with one half vertical and the other half low and possibly parallel to the ground or even very close to the ground on the outside end. It would be very important to keep the end insulated and well away from the ground. It is more like a Skelton corner reflector dipole than a vertical antenna with a single ground wire, pretending to be a radial but without any other wire to counteract its field. Just because you stick a label on a wire saying it is a ground radial does not force the current to obey the label.

Your mileage will definitely vary with this one as there are many factors affecting its operation, tuning and impedance. Putting RF current in a wire close to the ground has to raise questions about losses from ground resistance.

Andrew VK1DA/VK2UH


#108

Rudy N6LF approaches this topic: http://rudys.typepad.com/files/qex-ground-systems-part-7.pdf both theoretically and also on an antenna range.

This is the last part of a series of articles which are well worth reading. He has plenty of interesting material on his site, though as he says, he prefers that it is not taken as gospel.

But, as Fred KT5X says who knows what the ground is really like on a summit, especially ones dropping dramatically either side. There is definitely a gap in the literature here.

One good suggestion I heard, at one of our vk3 dinners I think, was to use WSPR to measure performance in the field. Any one willing to step outside to settle this? Put a number of stations on with similar power and a choice of antennas and use the WSPR network to measure the pattern. With close timing on Tx propagation variations should be removed.

Ideally should be done somewhere with a good spread of receiving stations which is probably either continental Europe or the US.

Differences would obviously remain due to every summit and setup being different but at least we could establish some guidelines based on actual testing.

It would be a good article for a magazine I would think, if it hasn’t already been done.

Antennas at 10 paces.

Andrew


#109

Hi Andrew,

You need to minimise the variables. Same station, same QTH, antennas in same position, swap, A to B to A on several days. Takes into account varying propagation. Then change B for C and so on. A few have done this sort of test.

Or you could use a computer program to plot field patterns and strengths - EZNEC is free and this version is good enough to rate different antennas according to what you want.

73
Ron
VK3AFW


#110

Yes, in the article I cited he describes it as an “L” or “bent vertical”. I haven’t tried this in SOTA conditions, only on my 3-story roof. Quite possible it would be subject to ground losses in field conditions. The north-running radial is about 2 meters above and parallel to the flat roof (the south-running one slants down over the other side of the roof with the end about 4 meters AGL.)

The background is that it was originally a drooping (horizontal) dipole oriented E-W that worked sort OK for DX on 40. I wanted to try a vertical for lower takeoff angle DX performance and also on the off chance it would cut my very high noise on 40 (local-ish noise from 5-10 MHz - it did not) help). So I found some poles and “flipped” the dipole. After a few tries trimming the vertical and the radial(s), I got the SWR minimum where I want it.

I haven’t tried WSPR, and of course I can’t do A/B comparisons now but the RBN reports I get and the stateside QSOs are better than I ever got with the dipole, although I can’t factor out changed band conditions. North America, Europe, all of JA and most Chinese stations are to my north, but I have worked VKs that I never heard with the horizontal dipole. I was able to do an A/B check of south radial directivity with a DU stations. (microswitch and piece of string!)

Steve in OKinawa


#111

_Yes, in the article I cited he describes it as an “L” or “bent vertical”… Here are the firs few sentences:
What happens if…
we start with a standard vertical monopole
and systematically add 1, 2, 3, 4, 6 and 8 radials.

The standard conditions are: #14 wire for the antenna and a feed-point at 1/2 wavelength over ground.

We begin with 1-Radial at 90° A 50-50 ratio, bent dipole commonly called an “L-Antenna”.

The resonant length is 2.54% longer but the impedance is only around 42 ohms or 1.2 SWR at best
The radiation pattern has 4.3 dBi gain on the side with the radial and -4.5 dBi quieting on the back
% radiation efficiency is the highest of any radial configuration: 58.6%
_Compare this with 36% and 1.33 dBi gain for a vertical dipole_

#112

The point is if you setup the stations simultaneously one can eliminate much of the variability propagation, not entirely but largely. Of course now one has slightly different situated antennas but in the real world we still have an enormous variation in summit conditions. I think this is a reasonable compromise to speed things up and eliminate the highly variable propagation. Of course if buildings, fire towers etc are present then this is problematic, and you need a long enough area to avoid interaction.

As for models, they have their place, but the point is you can’t model something properly if you don’t have reasonable inputs. We can’t even seem to agree where the ground actually starts, let alone how good it might or might not be. That’s the point of this - does it really matter on a summit if the dipole is not as high as it should be over a flat and good ground?

But of course in every test involving countless variables there will always be those that will question choices after the fact. I suspect the personal bias you mention (wait until you see this with camera equipment! :laughing:) will prevent any actual attempts to resolve this, or prove reasonable expectations such as Andy’s are still correct for our situation.

I’d just be interested to know for my remote activations which horrible compromise might work better, or well enough.

Andrew


#113

Owen vk1od/vk2omd built a switchbox to do that comparison. Want some reading? here you go:

http://owenduffy.net/module/smbk/AB.htm

Compared a G5RV dipole with a mobile whip here:

Also, a “number of radials” comparison, which also has some comments on buried v. elevated radials.

http://owenduffy.net/grabber/cs07/index.htm

In summary, if elevated by even just one metre, 3 radials provide close to the same performance as an antenna with a 16 or more buried radials.

That’s my reason for using 3 elevated radials.

73 Andrew VK1DA/VK2UH


#114

I must be a bit dim but I can’t interpret Owen’s whip vs G5RV results.


#115

Rest assured it isn’t just you, Richard, it baffled me, too!

The script doesn’t even say what band the tests were performed on. This is significant because the G5RV polar diagram exhibits lobes giving peaks and nulls, on the higher bands there are multiple lobes which have some gain, so the band and orientation relative to the remote station becomes important in an A/B comparison- we don’t know if the path was in a null or peak of the G5RV if we don’t know the band.

Brian


#116

Hi Brian

He does state in the preamble that the tests were carried out on 40m. But I too find the rest impenetrable :frowning:

73 de Paul G4MD

Edit: There is a link to a “statistical analysis” at the end of the article - seems to demonstrate that ridiculously short verticals are the next best thing to a dummy load, which we knew already :-s


#117

Ahh. Yes, the statistical link is more helpful. He concludes that a G5RV is a better antenna than a 40m mobile whip. Whoever would have thought it?

It does not do anything to illuminate the vertical vs horizontal hilltop antenna debate though.


#118

Hi Andrew,

CAUTION. This email contains instructions on sucking eggs.

The fact that each summit is likely to be a quite different RF location, environment, subject to different propagation, etc is a red herring.

The fact that some models have poorly thought out assumptions, relationships and inputs has nothing to do with antenna simulations using properly engineered programs.

By 1970 the US DoD was selling copies of its Numeric Electromagnetic Code - NEC for $100 for Yankees and $200 for aliens like me. I would offer you a copy but the CIA would see that both of us met with unfortunate accidents. It’s also in FORTRAN and you need to write your own GUI.

EZNEC is based on the NEC engine and is user friendly and is available for free and nothing off the webby thingy. It’s designed for amateurs so you can use it without reading the instructions. It’s not quite perfect but it’s damn sight better than guessing what might happen. If you pay for the next up version is will meet most amateur needs quite accurately. It is still possible to do dumb things with the inputs and get crap out. The results of dumb behaviors are less expensive and traumatic than doing the same thing on the summit. When computer programs are able to see, understand and fix our errors we need to reach for “The Hitchhikers Guide tho The Galaxy”. IIRC in such a circumstance it says “RUN”.

A computer simulation can be run for any antenna and the effects of ground proximity, antenna configuration, ground conductivity, conductor size, etc etc all included as variables which you can adjust for a range of simulations.

For a wire SOTA antenna I prefer to start with an inverted vee configuration with centre at 8 or 10 m and ends at 1 to 3 m above an average ground. This is my most commonly achieved set-up for a horizontal wire.

For a vertical a 10 m mast is assumed and I adjust the shape and radials as I might or have used in the field.

If I find that a particular antenna has very little radiation below 30 degrees elevation then is is not included in my list of good DX antennas.

The ARRL Antenna Handbook has most of the important antenna basics in easy to understand form so it’s worth setting aside the screen and keyboard and reading a copy. It won’t solve every problem you have but you will have a good platform from which to start thinking and exploring.

In an afternoon with EZNEC I can look objectively at more antennas than I could in a year of going to the local park and playing all day on the bands.

My preferred antenna is a centre fed doublet, 6.7 m per side fed with 300 ohm ribbon to a 4:1 balun and an ATU. Covers 7 to 54 MHz with rapid QSY. Not quite as good as a link dipole but I’m prepared to wear the penalty. Others may have different acceptance criteria.

For a versatile high performance but simple monobander, a 5/8 vertical with 3 or 4 radials can’t be beaten IMO. It has both low angle and high angle lobes and even a little gain. Again others may not like it’s lack of azimuth directionality or the need for a decent roost on bands below 20 m.

If going to a remote location, study the site at the top for restrictions on antenna layout, decide what bands you need to use, then take two antenna, two feedlines and the biggest telescopic pole you can fit in plus a roll of duct tape and one of builders line. What else you need to duplicate is up to you.

I don’t expect many of the posters on this theme to agree with me. I do however suggest that they at least download a decent antenna simulation program and spend a day getting familiar with it and looking at the effect of ground types and antenna height on the elevation and azimuth radiation patterns of their favourite antenna.

73
Ron
VK3AFW


#119

The problem that I see is that in the field (as against in the computer) we are dealing with a hugely complex topic when we consider ground conductivity, particularly on a summit where geometry comes into play. Conductivity is dominated by water, where it is and how contaminated it is - except in the case of a few natural minerals that we might encounter on a summit, such as graphite, magnetite and sulphides. In general the rock that we encounter on a summit is of low to very low porosity, which might imply low conductivity in the absence of high conductivity minerals, but this is complicated by the fact that water will be concentrated in joint systems and sometimes bedding planes. Such water will have variable conductivity depending on what minerals will be dissolved in it and this will vary with the rate of flow, controlled by the availability of meteoric water (rain, snow melt etc.) Add to this the effect of orientation of the joints and you can arrive at a situation where the conductivity can be anisotropic, varying with the direction in which it is measured. Thus we have conductivity that can vary with time as the availability of meteoric water varies, and with direction under the influence of joint systems - and this is only dealing with the hard rock, the backbone of a summit. We also have to deal with the conductivity of the soils that may clothe a summit, and in this country that may vary from a scattering of sand and gravel or a spread of scree or clitter to a few metres of peat.

For these reasons it would almost be surprising if the performance of an antenna on a summit corresponded to the predictions of a computer, and it would be unsurprising if the performance varied from summit to summit or even from one location to another on the same summit!

Brian


#120

Hi Richard,

I agree, it is a bit obscure. Some of the 1 minute segments show remarkable changes in the noise level and that’s what puzzles me. Perhaps an AGC effect. I have asked him a few questions. Perhaps comparing the s:n levels is the best way to look at the plots.

Other test results seem to be clearer.

I think the controlled antenna switching is a great idea and that’s what I was mainly wanting to link to. The only drawback for suburban testing is interaction between the antennas, which could mean that it is the combination of the two that is really being tested.

The difference between his tests and what most amateurs do is the absence of “S meter” readings. I hear amateurs switching between antennas and asking the listeners to report the S meter readings using ssb signals. The variability between radios and operators make such results quite unreliable. Other tests are even conducted on different days for different antennas. Current propagation instability should have taught everyone the futility of expecting conditions to remain stable even from one hour to the next.

So despite some of the results being unclear, I think there is a lot of merit in Owen’s approach.

Andrew VK1DA VK2UH


#121

Hi Brian,

I did state that you can do simulations on the same antenna with different ground conditions. Therefore you can see which of two antennas will likely be the best field performer, regardless of the summit conditions. Try as many variants as you like.

I’m not interested in arguing about maybe if and which way did the water go. I wanted to point to a way whereby the argument/mystery as to which antenna might be better could be resolved.

Whether you accept it or not, simulation in science and engineering has been in use with unchallenged success for hundreds of years. When you use F=ma you are simulating the real world. Once it was long hand calculation now it is by computer. There was an earlier post on this thread where field patterns were shown. A different program name but the same basic physics at it’s core.

Try it before you bag it or drag the thread off on a tangent.

73
Ron
VK3AFW


#122

Damn right. Selling simulations of pre-silicon chip designs keeps me in whisky!

In the case of antenna simulations you normally get a few types of ground, perfect, poor, so-so etc. To make the simulation more accurate you just need to better simulate the environment.