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Lightweight Vertical Antennas


#123

And before you arrive at a better simulation of the environment you need a more accurate idea of what the environment actually is. This is my point. I’m not against simulations, despite what Ron seems to think, all I am pointing out is that the real world grounds on summits can be a lot more variable and confusing than the few heavily smoothed parameters offered by programs. If recognising that there are reasons that simulations might be inadequate is a “tangent”, then it is a valuable tangent!


#124

Hi Andy,
They pay you in Whisky? Wow.

There are of course a limited number of default ground types but you can put in your own parameters, if you really need to.

Contrary to Brian’s proposal that you need a detailed electrogeological survey of every peak, you only need to use representative values in the simulation to see what happens.

Really it is whether a particular activation might be better with say a vertical and one radial or a low dipole or a similar choice. It is not to get a 0.1 dB perfect simulation of every antenna on every summit.

I know some folk get agitated over a few fractions of percent error so I wonder how they coped with 20% tolerance resistors and +100% -0% on electros?

If in doubt get out - and activate. So what if you only get 4 contacts instead of 40? A bad day on a summit beats a good week in the armchair.

73
Ron
VK3AFW
Time for morning coffee, the bands are almost totally dead.


#125

Hi All,

Update on the quarter wave vertical(17 ft) with one radial, 20 ft 3 inch 3 ft off the ground.

Assumption: I put in the right geometry.

EZNEC shows that on a flat site with “average” ground parameters ( loss 0.005 S/m, DC 13) the front to back at 16 degrees is about 6 dB. At higher elevation, 45 degrees, the front to back approaches 12 dB. So if you have some choice of alignment, run the radial in a direction that is away from your least desired direction. That’s where the null will be. Places at +/- 90 degrees will be almost the same as the most favoured direction. So in VK3 the radial should run N-S for good results to VK6 round thru VK4 to ZL. VK7 is not much worked on 20 m so a moderate null in that direction matters less.

Having a highly conductive ground makes the pattern become more like a hemisphere and going to free space makes the pattern more spherical. Higher conductivity, lower loss and a sharp ridge all improve the pattern.

It’s a viable antenna, which we knew.

73
Ron
VK3AFW


#126

Well you don’t need a hypr accurate model of the actual location. i.e. where every tree is etc. You can do very accurate modelling, it’s done to work out the currents in the skin of military targets when illuminated by RADAR etc. When you know those you can minimise the reflected energy or make it not go back to the illuminating source.

For most cases, it would be useful to express the ground in the near field, the ground in far field, the slope and whether you were in dense trees or open country etc. But in reality you don’t need to know chapter and verse unless you are building a 2MW long wave station.


#127

Further information about Owen’s test results.

The frequency was 7 MHz.

The tests consisted of multiple repeats of the following 5 minute cycle:

1 minute of callsigns to identify the test
1 minute of constant carrier on antenna A
1 minute of nothing
1 minute of constant carrier on antenna B
1 minute of nothing

The graphical results reflect this cycle. A rubbish minute followed by what is clearly a carrier with a varying S:N ratio. Then a minute of rubbish, then carrier for another minute. So the two antennas are compared by examining the S:N ratios in minutes 2 and 4.

So, disregard the question of which antennas were being compared here. (Clearly there was a reason for comparing those two antennas and I think you have to accept that the mobile whip was being measured in comparison with the G5RV as a reference antenna, thereby answering the question: How much worse is my mobile whip compared with my home G5RV dipole?).

Just consider the testing methodology.

  1. Same receiver, untouched, throughout the test. Not Jim and Fred being asked to read out their S meter readings from different locations and different brands of radio.

  2. signal to noise ratio used as a measure of actual signal level.

  3. Many measurements made. Not just one signal report from Fred or Andrew. Many measurements improves the reliability of conclusions drawn.

Antenna comparisons, like learning morse or which unix editor is best, can produce more heat and noise than people activating summits and making contacts.

73 Andrew VK1DA VK2UH


#128

Thanks for the further information Andrew.

Is Owen interested in investigating the question that underpins this thread I wonder?

73 Richard G3CWI


#129

Where did I say that?:grinning: This, I repeat, is what I am saying:

There is nothing wrong with suggesting a bit of due caution when applying the modelling of an antenna. A summit is a world away from the planar model earth, a nice pointy knob of solid rock or a long narrow inclined ridge with the ground falling away steeply on both sides is not going to be modelled simply, and I am not suggesting that anyone tries.


#130

Thanks Ron and thanks Andrew for the reading. I’ll add that to the list. the problem is they never compare the antennas that I’m interested in :angry:

In terms of verticals, the ARRL Low Band DXing book is also a useful read. I just checked my ARRL antenna handbook and it’s dated from 1988! Possibly time to update, never mind the ARRL handbook.

AFAIK the free versions of NEC don’t allow for modelling of cliff’s, or similarly steep terrain. Hopefully I’m about to be proven wrong about that. Not every SOTA summit is like this, but many of the ones I’m interested in seem to be. I would love to to find the time to stuff about in the tool, but after a day spent on computers in the office, it seems I’d prefer to just melt solder or be outdoors :smile: I have a mountain of photographs awaiting editing that prove this.

As for sucking eggs, well where I am is what you say, elevated vertical with a few radials (with backup antennas, feedlines) but unfortunately that means a longer and heavier pole than I might wish to carry, especially something involving steep or vertical terrain. The base MTR kit is getting very light however.

Andrew


#131

Hi Andrew,

Well the 1988 ARRL Antenna Handbook info is still 100% OK. Antenna development since then has been mainly for hand held radios and cellular phones and GPS navigation devices.

Yes the free programs have limits. But that isn’t a reason to not use them.

The dipole is the parent of almost all the antennas you will need for SOTA. In it’s vertical format the question you have to answer is half wave or quarter wave? Half waves can be end matched by a tuned circuit or a nominal quarter wave of transmission line with a stub. A quarter wave is best with two to four radials but works with a moderate null with only one.

Compromises, eg 1 radial, come with performance cost. A vertical can be shortened as can the radials with some inductance. Efficiency falls as does the 2:1 SWR bandwidth. You might accept these costs for the convenience of a smaller antenna.

MF and LF vertical antennas are often much less than 0.1 wave length in height so the efficiency drops away unless elaborate ground mats and top loading are used. The bandwidth gets very narrow.

Any antenna that works acceptably well on a flattish mountain top will work better near a cliff or on a steep narrow ridge. However personal safety is more important than an extra S unit.

The closer to the ground any part of an antenna is the more it will be detuned and the greater the influence of the ground on the vertical pattern. You are better off using a tuner to get the SWR down and working the stations than examining the rocks and soil to divine the conductivity and dielectric constant.

Concentrate on what you can control.

If you were setting up a home station then you have the opportunity to select a site on a cliff or in a swamp or whatever will give you an advantage. You can only choose to activate a peak or not activate it.

There are some good suggestions in this thread regarding light weight verticals. A link dipole works well even when not very high. DX performance would be enhanced by running the 20 m section as an L with one leg vertical and the other horizontal near the ground. For 30 and 40 m the centre bit can still be vertical improving the DX signals.

73
Ron,
VK3AFW


#132

I am surprised that thus far no mention has been made of the HF Terrain Analysis software HFTA. This used to be bundled with the ARRL Antenna Book.


#133

In the case of the “single radial vertical” I doubt it. But interesting problems intrigue him, especially where there are mistaken beliefs afoot. You will see from his many articles that he frequently challenges the many myths and Rules of Thumb (ROT) commonly found in amateur circles. :slight_smile:

73 Andrew VK1DA vk2uh


#134

Hi Andrew,

Pick two antennas that interest you. Build and take both on your activation and try them.

Or email me the details of these two and I’ll run comparative simulations and send you the results.

73
Ron
VK3AFW


#135

For the sake of testing, I have constructed a 20m inverted V and a 20m single wire 1/2 wave J-Pole which for the latter I have used to successfully complete DX and DX S2S QSOs. What’s the problem with a single element antenna that is proven to work?

How about Andrew 1DA and I set up his 1/4 wave GP and my antennas on Mt Taylor for a real environment test?

At the conclusion of that test you can put this thread to bed :slight_smile:


#136

Hi Andrew,

I think Andrew is hoping that there is a small antenna like the Miracle Whip that he can use to get results comparable with proven designs like the two you mention.

The absence of a list of tiny self supporting verticals that work well is significant.

Maybe a loop antenna would suit Andrew, The typical loop is not much good on 40 but passable on higher bands, IMO and IME.

By all means compare your antennas but will it tell us anything we don’t already know? It won’t close down this thread, I suspect.

73
Ron
VK3AFW


#137

N6LF’s article does reveal that the radiation from a vertical with a subset of the standard radial pattern does favour the direction in which there are radials.

However in the fine print he notes that the efficiency of the entire thing goes down when you do that, including lower radiation in the direction of the radials.

This makes sense when you consider that the rf current induced in the ground by the field around the antenna is flowing in lossy ground and that is apparently where the power is being lost.

The conclusion of this is that when you compare a vertical that has an asymmetric arrangement of radials with a standard configuration of equally spread radials, you find that the asymmetric radial configuration works worse in all directions and even worse in the direction of the missing radials. That may well represent directivity but it will not be helpful in making contacts.

73 Andrew VK1DA VK2UH


#138

Hi Andrew,

Interesting. I need to read that article but two points need comment.

There’s no refuting that any HF antenna over lossy ground will have a lower radiated signal compared to operation over ground that is not lossy. Ground level radials must be more affected than an end fed vertical because the coupling is higher. (I think). Will you lose more than 3 dB? My initial thought is no but I’ll do a simulation later today and report back.

The azmuth radiation pattern from a single radial system may be affected but I doubt that for say a 4 radial system the pattern is affected unless the radials have different losses. (The far field has no nett component from the radials if symmetry applies.)

Tthe elevation pattern is greatly affected by ground conductivity and losses and height above the ground.

In practice a half wave vertical should be less ground dependent than a quarter wave with ground level radials but both can be effective dx antennas for the activator. A single radial quarter wave vertical is still a viable antenna albeit with a moderate null in the direction away from the radial. That directive may be modified by ground losses. Again I’ll report back after doing some simulations.

73
Ron
VK3AFW


#139

Hi,
Simulations using EZNEC V6 confirm that the azimuth radiation pattern for a quarter wave vertical with 2 radials is little affected (0.5 dB max) by the ground going from perfect conductor to very lossy. The deviation from a perfect omnidirectional pattern is less than 0.5 dB for 2 radials cf 4 radials.

Going to three or four radials is fine philosophically but in practice on a summit is a time waster and hard to do in well vegetated summits. I have often operated on the side of a track and having a radial crossing the track is a concern.

The elevation pattern changes of course as losses rise with the low angle radiation falling away as the ground losses rise. Lifting the radials reduces the losses a bit but does not restore the pattern. (3 m max assumed, ground still lossy).

DX signals (16 degree elevation) are 6 dB down for lossy ground typically. ERP is down about 6 dB fof a lossy ground compared to a lossless one.

Interestingly for a 1 radial quarter wave radiator the best compromise seems to be to run the radial along the ground. The front to back is about 6 dB but raising it to 9 feet agl increases the F/B ratio to 11 dB and increases the amount of signal going vertically up. Comparing the radial on the ground with radial 9 ft up, the signal at 16 degrees varies by about 1 dB. For a radial on the ground/grass the set-up time is reduced and no need to find supports or have long cord extensions in order to keep it above head height. A shorter mast can be used.

Should you be struggling to work a station in the null direction I’m sure you could grab a radial with an alligator clip and have it deployed in 45 seconds and then have a 6 dB or more lift.

The length of the radials for resonance varies by almost 2 m when different elevations and different ground conditions apply.

Therefore having an ATU is recommended due to the wide range of ground conditions likely to be encountered especially in the SE VK Alps.

Adding a loading inductor shortens the antenna and can be used on the radial(s) as well of course but bandwidth shrinks and losses are higher. Whether it is worthwhile is a matter of individual choice. getting a wire 17 ft up on any summit should be possible.

For the same lossy ground my 6.7 m/side doublet (7 m at the centre inv vee) is comparable to the vertical broadside on and about 6 dB down off the ends so compares surprisingly well with the one radial vertical with the advantage of being multiband.

It is a bit harder to erect in the forest. I could of course run one leg vertically and the other just on the bushes if it was a tricky QRH. The simulation shows this is not a bad option for 20 m with just the one null off the back, away from the horizontal wire as expected. It is viable for stations no closer than 150 km on 40 m.

I think my work is done now.

73
Ron
VK3AFW


#140

Hi Ron

Many thanks for your analysis of what we call an “upper and outer” in these parts. It was what I used for my one and only foray into intercontinental SOTA DX, when I managed four VK’s on 20m, obviously more by luck than judgement! Feedpoint was about 1m off the ground with the radial (aka other leg of the dipole) run out horizontally along a (wooden) fence towards the West.

If work permits hope to be out on the EU-NA s2s event with an “optimised” antenna…

73 de Paul G4MD


#141

Loaded vertical element 23’ long and one elevated (6’ above a fairly conductive ferroconcrete roof) loaded radial 24’ long on 40 meters: Directional, with about 1/2S in favor of the radial direction compared to another opposite radial. Bandwidth is narrow to be sure but I only work the bottom 50 of the band. SWR is below 2:1 from 6950 to 7075. Signal reports from DX stations are better than the same antenna erected as a drooping dipole at the same elevation. OK, not very scientific, but it is getting QSOs on the US west coast that were a real struggle last spring when the band was decent.


#142

I think I’m the Andrew being referred to here. It’s so hard to tell :smile:

I was just trying to propose how people might be able to quantitatively resolve this in the presence of so many questions around the environment. I do have more than a passing interest in the answers however as it potentially affects the weight on my back, and I am intellectually curious about the actual ground situation in certain cases. These cases most certainly do not apply to 90+% of the summits in SE Australia however.

So no, I’m not after a miracle whip, not when it would violate my antenna rule that the more metal in the air the better the antenna (generally). Lightweight wire is also rather cheap.

I am personally interested in a comparison between the GP with 3/4 radials and the elsewhere mentioned mono band j-pole. I have the components now to construct the latter so I may well perform this comparison in the field.

Perhaps the easiest thing is to drop a dit and do the other scheme which involves a flat body of salt water all around. :laughing: Certainly easier to reason about and sell to the wife.

Andrew VK3JBL