If it’s ignored by most SOTA activators it’s not out of ignorance but because chasers are located typically at many compass bearings, which favours an antenna with an omnidirectional radiation pattern.
If I’m doing, for example, the transatlantic S2S weekend event I’ll choose a summit where I can align my dipole lobes with the great circular route for that region but otherwise the antenna orientation doesn’t matter much for general SOTA activations, especially when I’m working lower HF bands for country & regional contacts followed by higher HF bands for intercontinental Dx.
Furthermore, although some of the SOTA summits have nice, uncluttered, grassy [even flat] tops where I can position the antenna how I like, the majority are very rocky, lumpy summits often with several false summits which limits how I can orientate the wire antenna near my operating position in a sheltered spot out of the wind & rain. I’m sure many others have this problem.
At the risk of repeating what I said above, given the many confounding variables when operating from mountain tops, some of the discussion about optimizing the antenna design seems to me to be diminishing return on effort or indeed running contrary to practical considerations ‘in the field’.
Strictly speaking, this drawing does not correspond exactly to my antenna. The length specifications are slightly different (my antenna is approx. 1m longer) and my deployement was even more like an inv-V - so to be correct, the label on this drawing shouldn’t read “HB9BCB Design”, but maybe “based on HB9BCB design”
If I remember correctly, you made this drawing for your contribution to QRP ARCI some time ago?
What I mainly meant was not so much directionality in compass bearings but variations in take-off angle, resp. the distribution of radiation by angle, because this will influence the first hop distance (or better: the distribution of signal strength along that axis), so it is really hard to tell which one of two antennas will be better just by their overall efficiency. As long as potential chasers are available in all directions and within a wide range of distances, as typical for summits in the Alps, it may not matter much in practice.
After all, we essentially want enough QSOs with random fellows from the SOTA community. We do not need to establish a communications channel with a predefined target station.
We are in agreement, by the way: Any reasonable antenna will work for SOTA, at least in central Europe. Other regions might require a more careful choice so that your call for a contact falls within habitated land .
Dear Heinz,
you are right, it should read ‚based on a design by HB9BCB‘. Back then, I simply wanted to give proper credit (and if I remember correctly, the additional links and the tuning for inverted-L deployment were at least inspired by our discussions back then). Hope this is fine with you.
73 de Martin, DK3IT
For me it would be interesting to compare how the efficiency of the power fed in and the power delivered behaves in relation to the HF transformation. so from the losses.
Linked DIpol with Inverted Vee with approx. 15m cable
Dear Michael:
With this information alone, nobody can tell. There are just too many variables.
If you are speaking of the losses just of the feeding mechanism of two otherwise identical half-wave dipoles:
a) for a center-fed dipole, it is mainly the feedline loss, which depends on the length and type of feedline (in dB/100m from the datasheet), e.g. RG174 vs. RG58.
b) for the end-fed, it depends on the design of the matching circuit. A well-designed autotransformer can reach ca. 85+% efficiency, poor designs or poor builds less than 25%.
Both will also have additional losses if there is an impedance mismatch.
If built properly and deployed in identical set-ups, an end-fed vs. a center-fed dipole will behave so similarly in practice that no receiving station will be able to distinguish.
If you are talking of completely different antennas, it is just impossible to make a valid statement because of too many variables.
The differences between most popular SOTA antenna designs are less than ca. 6 dB (typically much less, if we leave out flawed designs or very short ones). Even this is hardly relevant in S-levels, although 6 dB (= one S-level) less means a 75% weaker signal (10^(-0.6) = ca. 0.25).
HB9SOTA did a substantial comparison of SOTA antennas in a field test back in 2017:
For most antennas tested, the difference was less than 0.5 S-levels.
That is all one can say at this level of abstraction. You can built and try - and this is what many hams consider an essential part of the fun. But since the outcome will depend on multiple variables (see above), such a single comparison will also be just of anecdotal value.
I may be wrong, but 6 dB less means minus 6dB, which is 1/4=25%of the baseline, and in terms of signal-to-noise ratio under otherwise identical conditions a loss of 75% (relative to 100%).
It is indeed as Martin briefly summarized above.
It’s understandable that one is primarily concerned with something that one can see and hold in one’s hands and not with all that is hidden.
With the mechanically as short as possible antenna you are aiming for limited space (in your case typically for densely overgrown/wooded hills), one would have to worry above all about the influence of the antenna properties by objects that are all around at a distance of less than lambda/2.
A very hidden and therefore often overlooked, not exactly complex, but for various reasons very difficult to record influencing factor also has an effect in the above cases from the following facts:
In the bark of shrubs and trees, water flows only in the summer months, not in the winter months. The attenuation of radio waves is therefore greater in the summer months
Dead trees do not attenuate radio waves to the same extent as healthy ones. In the case of infested trees that are not yet dead but diseased by bark beetle larvae, their sex, age, number and distribution per meter must be taken into account
Experience has shown that this influencing factor is particularly noticeable on April 1st.
Free tip
Simply realize a few hundred SOTA activations with a few tens of thousands of QSOs and don’t think that when particularly special events occur, you can/must explain quickly the cause of them, because there are usually too many unknown factors for that.
Or, scientifically: If you want to understand causal effects, you have to
a) control, in a randomized fashion, a single variable that we assume causes some effect,
b) keep all other variables as equal as possible (“ceteris paribus”);
c) measure and repeat the measurement often and trying to avoid any pattern in the timing of the measurements/experiments (otherwise, if you always go to the pub on Saturday nights, and your friend Joe does the same, you might assume that Joe is spending all of his life in the pub).
While we sometimes have to accept a compromise, the above is a good and practical guideline - e.g., it is better to run two WSPR beacons in parallel than to do sequential antenna tests.
Also, the better you can isolate aspects of your model, the more you will be able to discover.
For instance, measuring the efficiency of a broadband transformer with the setup described by Owen Duffy (and explained very well by Heinz in this forum) is better than using two transformers back-to-back, which in turn is still better than assessing a complete antenna system by the number of QSOs.
In these sad times of alternative “facts”, esoterics, and clickbait journalism, we as radio amateurs could and should evangelize the ideas and keep alive the torch gifted to us by the heroes from the age of enlightenment; of which some paid their insights with their lives…
Simultaneously testing two antennas using synchronised WSPR transmissions, when done carefully, can give excellent results. It’s important to get lots of data though. Hundreds of data points are needed for anything useful to be concluded when the potential differences are small.
Spot On!
With bands going up and down a lot at the moment, lots of data points are needed and the best would be as you say to have two synchronised (and identical output) WSPR transmitters connected to the two antennas under test at the same time testing the antennas on the same bands at the same time.
These analyses are all well and good, and interesting in their own right, but at the end of the day a successful activation of a summit comes down to so many factors that it would take an army of geniuses to figure them all out.
For me, the issue is simple - can I get some contacts - any contacts - from a summit, after I’ve set up my limited gear the best way I could, given the circumstances? As far as antennas go, I personally have two choices - a linked dipole or a vertical. Depending on the circumstances, I’d take one or the other: lots of trees on the summit => take the dipole only; very little space on an open summit => take the vertical. If it’s a long walk-in, take the lightest and hope to fate.
Here’s one snapshot from my activation last year of the Brandkopf DL/BE-028, where I set up the linked dipole for 20/40 meters in far from ideal circumstances, with the 7-meter pole leaning against a tree, and the antenna strung out between the trees where it could fit - I’ve sketched roughly where the wire was strung heading away into the distance (the small pile of stones just beside the left-most tree is the summit cairn ):
With this complete pig’s ear of an antenna I made 25 QSOs, on 20m and 40m, with the furthest 40m contact OH3GZ 1500km to the north, and the furthest south EA7GV on 20m at 1700km, all with excellent signal reports using 15W on SSB. I’ve deployed this antenna in several similar circumstances on SOTA summits and have regularly got a decent number of contacts before they dry up.
If I were to listen to people tell me that this antenna has no chance of getting a signal out, with all those trees around, I’d have stayed in bed until 9 and had an early liquid lunch.
No amount of modelling in EZNEC, nor optimization of antenna type, height, build or materials, etc. is going to be able to beat just putting the antenna up, switching on the radio and … the rest is up to you.
[quote=“DM1CM, post:73, topic:26749”]
Here’s one snapshot from my activation last year of the Brandkopf [DL/BE-028][/quote]
That could just as easily have been a photo of any of my many activations of DL/AM-180 Berndorfer Buchet - Like yours, my linked dipole on a 6-metre squid-pole there works despite being surrounded by trees, in fact, it has delivered S2S SSB QRP contacts into VK on more than one occasion.
I did once try a vertical there - never again! It was impossible to get any contacts. the vertical trees and vertical antenna simply do not go together well.
This echoes your point of having two dissimilar antenna systems and choosing the best one for the site as required.
It’s not about the answers. It’s about the questions.
It doesn’t matter where you feed a halfwave wire, it radiates the same. It’s about how. If you deploy the halfwave wire as an inverted-vee, then feed it on the end… it will radiate exactly the same as if it was fed in the center.
By feeding it on the end, you can eliminate the weight and loss and the time to uncoil and coil the coax. You also eliminate the connectors which when often manipulated may have a broken connection so multiple points of failure are gone. without the weight of the coax, you can use a much lighter pole, and lighter wire.
I use #28 teflon wire. My antenna weighs about 40 grams including traps for multi-band operation. My pole weighs 209 grams and extends to about 6 meters while collapsing to about a half meter. Makes for a very easy carry.
The end of the wire plugs directly into an adjustable unun which plugs directly into the radio. The unun is built in a dental floss case and weighs 18 grams. It tunes the antenna to 1.1:1 and has a measured loss of about a half DB.
With such a light weight wire and the pole leaned away from the wind, it has never broken, nor has the thin wire which presents essentially no wind resistance. The far end of the wire is supported with braided (non-stretch) fishing line that is extremely strong. There is no end insulator. It isn’t needed if the supporting material is non-conducting and at QRP power levels. I tie the thread to the wire using a “nail-knot.” Or a button would do fine.
Had no trouble working multiple European stations from a mountain peak in New Mexico this morning while running five watts.
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