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Lightweight Vertical Antennas


#83

Well it was being videoed but there was no information given out at the time as to what would be done with the video.

And yes it was highly informative. The observation that an inverted dipole would be as effective as a horizontal dipole set at two thirds of the height of the apex of the inverted dipole was very intriguing. It almost makes me want to learn EZNEC!

Dave M0NDT


#84

Yes, it just raises more questions! From experience, and in agreement with comments made by more knowledgeable contributors than me, keeping the ends of the V well clear of the ground eg 1 metre or so, has a significant effect on performance. The statement above makes no mention of that…
As Jonathan observes, in practice, on a summit, there are likely to be compromises whatever you choose as an antenna.

It provides a nice mix of fun and learning :smile:

Adrian
G4AZS


#85

Most antennas work best on a warm sunny day with no wind and good band conditions.


#86

I find the buttock / ground interface is a critical factor too.


#87

Can lead to piles of contacts in some conditions


#88

I’ve temporarily “lost the use of my legs” after a couple of long activations. Amusing trying to stand up when you can’t feel anything in your feet!


#89

A cold ground can often trigger a bad back, I find. Not sure why !


#90

Especially if you arrive at the summit and discover that you left your pole in the car (note: only once in over 500 SOTA summits and 50 HuMPs).

Model that with EZNEC… the results -

Who needs a pole? Well actually, I am considering trying a vertical off centre dipole with the short length closest to the ground. No radials / counterpoises to worry about. The downside would be the additional weight of a 10m or longer pole over a 7m pole.


#91

I thought it was Paul’s job to hold up the antennas?


#92

Interesting stuff Gerald. I very rarely carry anything longer than my 5m pole, which packs down to 600mm and fits neatly on the side of the rucksack without snagging trees etc.

With that restriction, I have operated on 30m cw with a 1/4 wave wire draped from the top, and fed against a short random counterpoise - typically in foul conditions where anything more ambitious would be a challenge. On one occasion I couldn’t get it vertical, just poked it out of the stone summit shelter downwind and almost horizontal :smile:

Usually, this 5m pole supports my inverted V doublet for 60m / 40m / 30m

Optimising antennas is an interesting exercise, but I wouldn’t want to put any aspiring activators off. If your main aim is to qualify the summit (minimum four contacts), then it is surprising how simple the setup can be.
Working buckets of DX is another matter…

Adrian
G4AZS


#93

I don’t think there’s room for ridiculing in our hobby, it would be a shame if there is.
It would be really interesting to see or hear Roy’s presentation, as there is a lot of room for interpretation. While a dipole/inverted V at the right height and on the right direction certainly will perform better than a vertical, with SOTA the height is wrong, the orientation is random and the ground is bad. Which means usually you’re not “in almost every case”.
It is essential to understand that in the real world an antenna interacts heavily with the environment. Resonance, impedance, radiation diagram, all are extremely dependant on any objects in the antenna’s proximity. As the antenna radiates RF energy, the waves meet the nearby objects, where part of the energy is dissipated and the rest is reflected at various angles, depending on the shape and position of that nearby object. Usually the ground is the most significant object near your antenna: good grounds reflect most of the energy back towards the ionosphere, while bad grounds (like what we can find on most summits) eat up most of the energy and reflect very little. The reflected wave combines back with the rest of the energy radiated by the antenna, but because it has travelled a different path it has different phase, which means it will cancel the antenna’s energy at some angles and it will add up to it at other angles.
In our practical situation, a low-height horizontal antenna (inv-V, dipole, etc) cancels most of the radiation at low angles and adds up to it at high angles, which makes most of your effective energy go towards the sky. If that would be your wanted direction then yes, it would greatly outperform a vertical, but the HF RF waves that go straight up are either dissipated in the ionosphere or (if they are low enough in frequency and the propagation is optimal) return back to the Earth surface very close to where they originated. If you want contacts over 500-1000km, your best bet is to send more energy at lower angles, which you can do by either using a vertical or increasing the antenna height.
As a practical note, on a decent ground for the 20m band you would need to put a dipole about 12m high to have the optimal low-angle radiation; if it’s an inverted-V and the arms are sloping, the center need to be much higher than that. 40m needs double the height.
Luckily there are enough chasers in the UK to allow you to get away with high-angle radiating antennas. Most of my activations were done in Eastern Europe where you can count the active chasers in a 1000km radius on one hand, there we had to use verticals to reach most chasers.

Cheers,
Razvan YO9IRF / M0HZH


#94

Lossy traps? that’s an old wives tale. Traps may lose as little as .3 DB each. I use tinsy traps all the time. In an end-fed arrangement, there is only one trap for two band operation and mine weighs about three grams :wink: - fred kt5x (WS0TA )


#95

So much knowledge being expressed, but what actually applies? On a rocky summit, where I am looking down hundreds, sometimes thousands of feet, is there a ground? Or does the antenna most closely resemble a pattern generated in free space? I really, really don’t know. What I DO know is that using an EFHW made with #28 teflon wire deployed on a six ounce 4 meter fishing rod in what is referred to as an inverted-L and while running five watts, I have sometimes worked DX fully halfway around the world. I don’t know what the predominant take-off angle is, but it isn’t straight up! - Fred KT5X ( WS0TA )


#96

There is a lot of experience and old wives tales and misunderstood and misremembered facts Fred.

I think it’s reasonable to assume traps are lossy untill you have measured them and proved yours are not lossy.
I think it’s reasonable to assume antenna tuners are lossy you have measured them and proved yours are not lossy.

Likewise it’s reasonable to assume a simple vertical is a better DX antenna than a dipole until you have measured them.
I know from my experience that most of the summits I work from have enough soil/vegetation/bog/water and heather that they are similar to the ground in my garden. I know that in a few weeks in EA8 the summits will be lava and my antennas will work very differently to back home.

The wonderful thing about SOTA and hammery activities is you can make antennas for buttons and play with them. You can find an antenna buddy who is interested in what you are doing and you can arrange skeds to check out the same antennas in different situations and confirm that Roy is correct. Or not. (I don’t think it’s the latter!)

So our old wives tales will have a massive element of truth to them. The hard bit is knowing when the old wife is right and when she is wrong.


#97

For 20/17/15 meters I made a parallel vertical groundplane using a 5-meter telescoping fishing pole. The vertical elements are 3 insulated wires spaced about 3 cms apart, adjusted to 1/4-wavelength on each band. Yes, they interact a bit but can definitely be tuned. You can figure out how to do this and still let the pole collapse without tangling the wires. The bottom 30 cms of the fiberglass pole slides into the top section of 40-mm PVC pipe through a hole cut in a PVC top cap, and the bottom section (total 200 cms) is cut at an angle to slide into soft ground, or alternately fastens to a steel stake for hard ground. The radials are cut to 1/4 wavelength, 2 per band, attached to the top of the PVC with a ring of solid copper wire. They act as guys, staked near the ground with aluminum tentstakes. With the feedpoint at 2 meters height it becomes very secure in the wind. Alligator clips at the end of 10 meters of 75-ohm TV coax make connections at the feedpoint. The whole deal fits in a homemade carry bag 1bout 120 cms long and weighs 2.5 kgs with coax and stakes. It cost me almost nothing to make except time!

I’ve only given a sketch here, and it took me a few tries to get it right, but if you’re motivated you can easily replicate it. I tuned it to SWRs about 1.6:1 across the whole bands, and it is a great DX antenna.


#98

I did not realize that my post was #95 in this topic! I’m a newcomer to SOTA and things are very different out here in Okinawa than in the US and EU, and even mainland Japan, especially band conditions and lack of high summits. I built the triband vertical I described above as a beach antenna where it is impossible to hoist my parallel dipole or longwire/ATU combo, but I have used it on several SOTA activations and like how it performs. A little trick for the ends of the six radials (which incidentally when stored are wound on pegs on one of the PVC support sections). I use a length of shock cord between the radial end and the tent stake, which puts the radial end about 30 cms off the ground and has prevented any of the thin wire radials from snapping in wind gusts.

Steve


#99

Hi Andy,

How about an old husband’s tale? Would that be better?

Two OH rules:

1 There ain’t a perfect SOTA antenna.

2 Simple and lightweight.
Gain and both dx and NVI major lobes.
Pick one.

Personal bias rends to override actual experimental evidence and select what suits, hence “proof” my antenna is better than yours.

Supplementary OH Rule #1.
The antenna you have on the summit for an activation is at least 40 dB better than the one you are thinking about in your armchair.

I also have never been to a summit where I could not set up my squid pole. I do take a steel spike (and small hammer) designed to support the pole and when the ground is too rocky to drive it in then the available rocks make a mini-cairn around the base. Some builders line makes good guys and rocks or pegs fix the ends or those. Usually a crack in the rocks can be found that will accept the peg. The pole doesn’t have to be perfectly vertical.

Supplementary OH Rule #2:
Being prepared to adapt is better than whinging about imperfection.

Heading for air raid bunker now.

73
Ron
VK3AFW


#100

I think you are spot on Ron.

It’s easy to become complacent and just accept things the way they are. So I think it’s good that Colin brought this up again. If it prompts people to go and play about with different designs and experiment then it’s a good thing.


#101

This is VK3ARR’s ham radio equivalent of Rule 34: “If you can think of it, there’s a page on Hamuniverse claiming it’ll give you a 3 S-point improvement on receive - no exceptions”


#102

Gee, fortunately no one asked which unix editor was better…

To address the original question. My practical experiences:

Homemade 1/4 loaded vertical than just fits on a lightweight telescoping pole: Found that it took too much time to layout the radials due to the scrub on our summits in VK. Was able to use it on 20/30/40M with different taps, but NVIS performance seemed a bit down, medium - long performance seem great. NVIS barely works on 40M now so that’s a problem that’s solved itself :smile:

Dual band 20/40M (+10M maybe) EFHW (loading coil on 40m): This is much easier to setup and the loading means that the horizontal distance required is quite small if used with a 7m pole. It also works fine with the shorter travel pole. It’s either setup as a inverted L (mostly vertical) or inverted V. The most used antenna now -very flexible and allowing for situations where the pole has to be at one end of a small summit.

20M 1/4 with 3 elevated radials (which are probably more like a 20 or 30 degree angle) built for DX: Really easy to setup on the 7m pole and I have no complaints with DX performance. The elevated radials do require a bit of space. This sometimes requires some thought about setup and trip hazards, not to mention potential public exposure to high voltages and RF fields, more so than with a dipole in my mind. Will be rebuilt with traps to allow for 15m and maybe one other band for DX optimised activations.

Linked dipole for 20/17/15: The linked nature is a bit of pain, but I’ve not yet been unable to set it up somehow. It’s usually in my travel kit along with the EFHW, now been extended to 30m.

There are most definitely some summits where particular antennas will be difficult to setup.

VK6/SW-004 (Toolbrunup Peak): large boulders form the small top. It would be challenging to properly layout radials or maybe (it’s been a while since I was up there) put a full size 40m dipole up without potentially interfering with other members of the public. Weight is also a concern with the final ascent near vertical in places, at least the route we took.

Te Kou E5/RA-002 is another interesting one. Movement on the top was seriously challenging (tropical jungle, drop-offs) and the best spot was occupied by the commerical comms gear. The dipole was used - fortunately only 20 up was needed. Laying out substantial radials would have been near impossible with the jungle. On a not so hypothetical return, I’d be looking at half wave verticals.

Having a few options you can choose amongst seems the best bet, especially depending on whether you just need local or really need good dx performance. The dual band loaded EFHW does give me a number of options in constrained spaces and is fairly simple and quick to setup, hence it’s been my preferred antenna. I am building a second trapped EFHW for 20/30/40 to utilise space when I have it and to better suit the MTR.

After some of my recent summits, I am looking forward to a nice rolling hill with nothing but grass on top. And sunshine too please.

Andrew