Yes, and even simple estimations can help you pick where to setup and what to use…
Hmmm, you can. If you repeatedly activate the same summit among the other summits you activate, then you can review the operating positions and antennas used and pick the antenna and position according to what you want to do. My contesting mob have been operating from the same site for 20 years. We have done work to find the best heights and where on the site to operate from to get the “best” results with large Yagis for VHF, i.e. the location on the slopes and height AGL for the antenna. We do low-effort versions of what professionals do when re-engineering their big systems.
Absolutely! If I look at my SOTA logs, there are not that many summits that get repeated activations. Most are activated by me just once in my quest for more uniques. Often the operating positing is dictated by the weather and the need to get out of wind etc. But when the WX is OK I will try to operate from a position that suits what DX may be available. I nearly always look at the 3d view of the summit on Google Earth etc. to see if there are some good slopes facing in “useful-for-DX” directions.
So yes, the antennas models over real or ideal ground show what happens and experience using those antennas on varied summits means you can learn how they get affected and try to work with those effects. And there’s lots of outliers “why did it work so well on this summit and not that one when the conditions seemed similar” . Or the ground in EA8 or CT3 really doesn’t seem to have much effect compared to the UK.
We could go back and forth forever on this. The key phases are “in advance” and “exactly”. This would only ever be true if the antenna were in free space (a vacuum) a big distance from any other object. For instance, to name just one input parameter: you usually don’t know exactly how the composition of soil, rock, dampness, etc of the ground varies over the entire near field. For many rocky, uneven summits, that precision of measurement becomes impossible. So, the calculation of the antenna’s predicted characteristics & performance in that specific deployment cannot be known exactly in advance.
Yes, indeed. But that’s different from what Johannes wrote about and that you challenged. And by your description you come to the conclusion [about which antenna to pick] heuristically [using the antenna(s) repeatedly] and not by prediction.
One man, one test, one summit, lead me to conclude that my rucksack mounted flowerpot, when standing, was no better than a Diamond RH-770 telescopic whip.
In the Lake District the Wainwrights on the Air often requires activation of multiple summits in relatively quick succession - this is where the rucksack mounted flowerpot can come into it’s own as there is zero setup time required. The RH-770 is probably a better bet in all other cases if you aren’t going to lift the flowpot antenna in the air. Of course a rucksack mounted flowerpot catches on everything and anything that happens to be dangling above your head (I struggled to get it out of the door when I did the test without taking out several decorations).
Sometimes other factors - weight, convenience, adaptability, can also weigh in on the decision.
I do also have a mil whip style antenna that I used on the SOTA LD weekend connected to a shoulder mounted ft1xd. The antenna isn’t perfectly resonant on 2m fm but when using /PM it allowed me to catch as many LD activators as possible between summits.
I mean you look a bit of a tool. No worries for the most part catching stuff however as most LD summits are tree less - even Grayrigg Forest
If you look at manpack antennas they normally have a spring joint to allow the antenna to bend. Or they are some kind of blade with construction remarkably similar to a steel tape measure. That makes them rigid enough to support their own length but able to deform and bend when they hit something and then return back.
There are plenty of such antennas for sale on the world’s favourite tat bazaar but exactly what the specs are and actual performance figures are remain firmly in the minds of entrepreneurs from the Middle Kingdom.
I used to use a flowerpot for SOTA activations on VHF, and wile they are a great antenna, i found slimjims have a slight performance edge over the “pot”… as for an ideal height, I always found they worked well atop a 6M fishing pole very effectively!
I read somewhere that foot soldiers can get away with inefficient VHF manpack antennas and low-power radios because the base stations have very efficient antennas and high-power radios. I would imagine a /PM amateur would have a harder time making A.R. contacts especially in hilly areas.
From my limited tests [e.g. 2m SSB QRP with FT817 in rucksack and RH-770 ½-wave whip sticking up from the rig] I got nowt but white noise in my earphones between my CQ calls whilst walking up G/LD-056 until almost at the summit where contacts became possible.
Personally, I don’t want to have /PM QSOs before I reach the activation zone (each is potentially a chaser lost) or even until I’ve set-up at the summit (I don’t want to hold a radio and log calls whilst I’m walking). I don’t want to risk damaging the radio kit (including from rain) or making a navigational error by being distracted. But I can see the pleasure of chatting with your mates while you walk.
I think 60m SSB NVIS would work better when trying to communicate between the valleys but an HF vertical whip manpack antenna isn’t going to help. A 60m horizontal EFHW would work but whilst /PM I would need 2 or 3 attendants walking in a line behind me and holding my antenna wire above their heads. Any volunteers?
Probably true. My actual point was using blade style antennas that fold and recover makes a pack mounted vertical a lot more convenient when walking. It wont get snagged on overhanging branches and snaps back into shape once past the obstructions.
No, but there lots of photos of infantry with a flexible HF whip that’s pulled over so it’s shooting up for NVIS. But of course I can’t find a suitable photo now !
Yes the inter-turn capacitance resonates with the coil inductance to create a series resonant tuned circuit. This effectively isolates the aerial from the feed line.
The maths that sits behind this arrangement is very complex. However from a practical perspective, the coil diameter / length ratio is important. Too small a diameter can create a coil that will not resonate as expected.
Hope that helps.
Thanks for reply. SRC had to be self reasonant choke, but wanted to make sure. Am interested in the lighter weight RG174 type used with very little lead in.
I couldn’t find photos of manpack bent-over HP whips (for NVIS) for foot-based radio operators, but only for vehicles.
They are large which makes me wonder if they are impractical for individual use when on the move, and that foot patrols would setup a NVIS antenna only when stationary. But if anyone knows otherwise, or better still has a photo …
