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Lightweight Vertical Antennas


#21

An inverted-V dipole is surely more fit to use here in the UK, where the higher takeoff angle is actually beneficial because there are alot of chasers nearby and the relatively low summits provide enough room to spread your guy wires / dipole arms.

However, Western Europe is a special case, activators in other parts of the world might prefer a low-takeoff antenna that provides much better coverage to medium distances (and even long distances, if QRP makes it across) so they can reach enough chasers. Most of my activations were done in Romania, and in a 1500km radius you can barely find 1-2 chasers on the air at one point … of course you want as low takeoff as possible.

Then there is also the matter of transporting and installing the antenna. Tall summits tend to be rocky and narrow and the winds are no joke up there. A vertical requires just one point in the ground to drive a stake in (worst-case, you hold it with one hand), has a smaller wind surface, can be thinner because it doesn’t need to support extra weight and requires less coax because its fed at the bottom. All these things add up to a lighter backpack as well, wich gets significant if you have to hike 20km with 1500m+ level difference in one day.

I guess what I’m saying is there is no “best” solution, just stuff that fits better to a given situation.

Cheers,
Razvan


#22

Razvan,

Dipoles will give low angles of radiation, especially on summits, sometimes too low!

A vertical is likely to be difficult to feed properly. Angle of radiation is also likely to not be as low as you might think.

I agree that different situations require different solutions. I’m not an antenna experimenter, its an area that doesn’t interest me so much. I use what works for me.

Still sticking with dipoles! Agree that a low 40m dipole works well for close in work in UK. A 20m or 17m dipole at reasonable height above summit ground on the other hand works very well for DX.

The dipole - a Swiss army knife of antennas!

73, Colin


#23

Are you sure?


#24

I am by no means the expert here, but I started SOTA with a very lightweight 20 meter dipole, #24 wire stranded wire, that is deployed with a 16’ carbon center pole, always just on the ground, no stake base for pole, etc. and has at least 20’ extra string on each end. Wound up on typical plastic winder form. It is most often an inverted vee but in some cases high enough tie off lets it approximate dipole. Third leg of the tripod is my RG174 feed line (no balun). I successfully tune it on 40 and 30 when needed with a teeny tuner. 130 summits and a Goat on in time now, still the very same dipole I started with. Same winder even. The few times I used my 40 meter dipole I decided it was too long and too much effort on a summit. RG174 has served me well and always is strong enough in wind to keep the pole up. Rocky summits I just wrap the string on a rock. Wrap the RG174 on a rock too. Sometimes the antenna is miserably saggy and not pretty, but it always works. I know the eyes roll at the mention of RG174 but the initial RG58 just way too bulky. Station with batteries and antenna very close to a kilo. I am KISS guy.


#25

Yes :smile:


#26

“Dipoles will give low angles of radiation, especially on summits, sometimes too low!”

As far as I know and read (Rothammel Antennabook) a dipol at low height above ground produces a very high angle of radiation (almost 90 degrees above ideal ground).

73, Peter
OE5AUL


#27

Vertical (top at 7m, 2 sloping radials, 1mm copper wire, poor/rocky ground):

Inverted V (top at 6.5m, angle around 110 deg, 1mm copper wire, poor/rocky ground):

Both antennas offering SWR below 1.2:1 at 14.285MHz. On 40m at 6.5m Inv-V height the takeoff is 90deg with very little energy at medium/low angles.


#28

Yeah, fine, but the model shows a flat ground plane.

Note that I said that dipoles ‘will’ give a low angle of radiation. It all depends upon how the antenna is deployed.

It comes down to skill in portable operating, selecting the correct gear for the intended purpose.

Not all summits are flat - what happens when you model a peak where the ground falls away steeply? The angle of radiation will be lower or even very low.

Ground is the key!


#29

Indeed, software that maybe could simulate irregular ground is probably too expensive for us amateurs. The thing is, however you change the ground or other factors, the vertical antenna will always concentrate the energy at a lower angle. That’s why basically all broadcast stations use verticals, they need the best low-angle radiation they could get - even if they want that for a better straight-line coverage and not longest skip distance.

I do agree, ground is important and it impacts antenna performance, but low horizontal antennas will always send most of their energy straight up. Basically, a horizontal antenna that is not at least 0.5 wavelengths above the ground is generally more suited for short skip distances, while verticals provide the low takeoff angle necesssary for long-distance even when ground-mounted.

Cheers,
Razvan.


#30

Yes indeed Razvan. My ground mounted SteppIR vertical 40-6m is relatively deaf short distance (nearby EU) but works extremely well long distance. There is quite a large radial system which helps and I have no idea about the ‘quality’ of the ground beneath it and do not really care as I cannot do anything about it anyway!

Night night.
Mike


#31

A comparison of models of the antennas I use for SOTA using 4nec2.

All low mounted inverted-V dipoles will show a pattern with the greatest gain perpendicular to the ground. It does not matter if the ground is absorbing or imperfect there will be an image of the antenna which will reflect the rf. This is perfect for NVIS on the lower bands where the F-layer will reflect it back down at high (elevation) angle.

A vertical is ideal for DX but ideally it needs to be elevated above the ground (so does a dipole if it is not to be affected by the ground). In that case the highest gain is horizontal. If it is near the ground then it will be lossy and the maximum gain will be at a higher (elevation) angle.

You can see the above in the figure below. A 40 metre dipole has highest gain upwards but the quarter-wave vertical will out-perform it at lower angles even though it is inefficient with a gain of -4.5 dBd (i.e. 4.5 dB less than a dipole in free-space). Note, it is hard to raise this 40 metre antenna for SOTA use so that the feed is appreciably above the ground.



A 40 metre inverted-V dipole with top at 5 metres (blue) and a quarter-wave 40 metre ground mounted vertical with three resonant radials (red), both over a finite ground (13+i0.002)

For 17 metres I use a 5/8 wave vertical because I can load a 40 metre vertical to work on that band without having to dismantle everything (I just add a stub). As before, in the figure below a low slung dipole shows lots of gain vertically but it is not so clear cut that the 5/8 wave is any better; it is more about what is suitable for the location. An elevated quarter-wave ground-plane is more efficient at low angles and it is possible to raise it high enough using a 10 metre pole.



A 17 metre inverted-V dipole with top at 5 metres (blue), a stub-matched 5/8-wave 17 metre ground mounted vertical with three radials (red) and a 17 metre quarter-wave ground-plane with the feed point at 5 metres (green), all a over a finite ground (13+i0.002)

While the ground is flat in the model it should not change the overall pattern to any great extent other than to tilt the lobe relative to the average ground tilt.

The difference between portable verticals and dipoles is the order of a few dB for DX; the patterns for other HF bands will be similar. It comes down to preference and convenience but all the antennas I have described can be made easily (without the need for a tuner) and I have built and used them.

I did a write about a set of fan dipoles that I built a long time ago which I have used since:
www.moosedata.com/g6wrw/hfdipole.pdf

Carolyn


#33

A common error is to assume that your RF ground coincides with the surface of the soil. This is not so. If you measure the RF current between the earth side of the feed to a vertical and its buried radials, you will find that the current diminishes during a drought and increases during wet weather. The efficiency of a buried radial or earth mat type of RF earth is related to the moisture content of the soil. I have heard that buried radials and earth mats are pretty inefficient in arid climates!

The moisture content of the soil controls its conductivity. You could bury your radials in powdered salt but until that salt is wetted the radials would be very inefficient! I suggest that the true location of your RF earth is not the surface of the ground but the depth where soil is saturated to the point where any further addition of water would make the soil drip. At that point every soil particle is surrounded with water and the traces of soluble salts dissolved in the water from the soil (those same salts that constitute plant nutrients) make the water conductive - pure water has very low conductivity. What this amounts to is that the RF earth plane is more or less coincident with the water table.

How does this impact on SOTA operating? Basically there are two types of summit, summits clothed in organic soil and vegetation, and summits that are essentially bare rock. Summits clothed in organic soil and vegetation will have the water table at some point above the surface of the underlying rock, bare rock summits will have a rapid surface run-off, some will enter the joint system opened up in the rock by relief of pressure during erosion - the water contained within the joint system flows down until the overburden of rock is such that the joint system is closed - the rock itself will normally be a fairly good insulator, the water perched in the joints will offer much greater conductivity. Since the joint system will also allow a fairly free radial flow of water out and down to the point where it issues forth in springs, you can expect that either the water table as such will be well below the surface or that you will have a pretty poor ground. Lying radials on a rocky ground should normally be equivalent to a vertical with elevated radials over organic soil. I say “normally” because a few types of rock are conductive, but in practice we can ignore that.

What this boils down to is that for SOTA and possibly for all locations all radials are actually elevated!

Brian


#34

And so it comes full circle again :smile:

Dipoles work well on hills because the RF ground is either very poor or sloping, lowering the angle of radiation.

Don’t get me wrong, verticals have their place and it’s fun to try different ways of doing things.

My position is - verticals work and dipoles work, use whichever is most convenient. For me, a dipole is most convenient and not to be discounted for effectiveness.

73, Colin


#35

This is what I suspected when I ran the EFHW over the rocks, and before I went I spoke to others and that was the general opinion. The rocks would absorb some RF, but I did manage a contact over 1700km on a band that was essentially dead at the time.

My original question asked about lightweight vertical antennas, with the a suggestion of using the MFJ-1979, and I got a few answers; I may still get myself the MFJ and some mounting gear for it, as long as I can keep the weight down. My goal here is to keep the weight of all radiogear under about 1.5kg, that means antenna weight of less than about 700g; for a dipole that needs to include antenna, ropes, coax and mast.


#36

Fine business.

I got pretty close -

This is my lightweight setup which uses a dipole (surprise!)

Proven to work well, many local and >3000 mile QSOs under its belt.

Try a wire vertical, see if it works for you.

Colin

Edit - I read 700g as entire station weight :smile:


#37

Don’t you just love forums. So often some not actually replying to the original question.

I come across this reluctance to acknowledge that verticals (except EFHW which I personally don’t like) actually work to provide consistent contacts and have a smaller footprint easy to erect and can be extremely light weight.

What I tend to do when someone claims this or that antenna is the bee knees is I look at their logs, see how many activations they have done, how many contacts on which bands and what modes they use.

If they are doing a lot better than me I will copy their antenna!

Carolyn


#38

Hello,

my experience with lightweight vertical ants is the one I used for years when I started on SOTA.
I used a 7m long light wire plus 4 ground radials 4 meter long, a 5 meter fishpole and an ATU for band tuning.
I think I would rather prefer such wire and pole than the MFJ telescopic you suggests because of potential weight saving and because I fear if that collapsible stainless will withstand for years the strong winds that we usually face on summits.

Your proposal is not bad but if you look for simplicity I’d say go with wire. If you add links on it you can get rid of the ATU and that’s it.

Personally, I must admit that since I started using multiband End fed Half wave (and I was reluctant at first) I found them as very good performers so I don’t use verticals anymore, although I always collect similar results on summits no matter which antenna I carried.

Carolyn, concerning comparison of results with antennas we shouldn’t forget to include Output power and activation time & bands as a factor of reference. Anyway an A/B test is the only way to do proper comparisons.

Good luck with your setup, probably the MFJ will do the deal if it meets your weight target. Could you add the actual weight of that model, just for reference? I don’t find it on Internet…
VY 73 de Ignacio


#39

I’ve tried verticals (both single-band and loaded), end-fed random wire, and dipoles.

The MP-1B loaded vertical has always been the hardest work for making contacts, but that’s no surprise; too much gets lost in that coil, especially on lower bands. It’s useful only where set-up area is severely restricted, particularly where there’s no way to support a standard telescopic pole. The end-fed wire has worked not too badly (typically about 2 S-points down on the diplole), and can sometimes be deployed where there’s not room for an evenly-guyed pole. The single-band verticals (with elevated ground-planes) are pretty good (especially on the higher HF bands) if the surface allows them to be put up, provided they’re not in among the trees. The dipole, however, has been the best all-rounder, so it’s my first choice if the surface conditions allow, but obviously it needs enough space to spread out left and right…

Go to the middle of nowhere in tree-less flatland (say in KJ80ih), and the single-band verticals (assuming you pick the right band) are a better bet than the dipole, at least on the bands I’ve tried to make contacts on from there…

73, Rick M0LEP


#40

I’ve not found anywhere like this in Scotland, Wales, England, France, Germany, Luxembourg, Netherlands, Austria, USA (CA), Canary Islands, Madeira or Ireland. I’m sure they do exist. They must do, people keep writing about them.


#41

I’ve supported roach poles with bungees or duct tape to fence posts, trig points, trees, wooden seats and even on one occasion to a neolithic standing stone in Cornwall. I’ve jammed poles into clefts in rocks, snow drifts, peat hags (I regretted that one, it took ages to clean the muck off!) rotten wood in a stump, and a sand dune on Shell Island. I do carry a set of guys and tent pegs but I hate using them as I am always in too much of a hurry to descend and get warm to make a neat job of packing them, and it takes ages to untangle the blighters! So yes, I have to agree with Andy, it might take a bit of ingenuity but it should always be possible to erect a roach pole. Keeping it up might occasionally be a problem…!

Brian