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My sota antennas

What are you using for an earth to tune the antenna against?

Ed.

just the counterpoise wire that came with the end fed half wave antennas, no earth

OK, that’s fine Iain, as long as you’re not relying on the outer of the caox to tune against. The fact that getting near to the ATU causes it to go off tune, suggests to me that you’re getting RF back into it. Perhaps add an “ugly balun”?

Ed.

VHi all,
regarding the ‚high losses‘ argument against both end-fed antennas and their impedance matching devices and traps, do you have data? From my practical experience, it sounds like a myth. A properly built and tuned EFHW, even with traps (@HB9BCB design) shows no significant difference in performance to a linked dipole other parameters being equal.

Martin, DK3IT

Edit: With significant I mean more than 1-2 dB, which is typically small as compared to other variables in SOTA deployments.

ok i have a current balun i can try on next activation, dont have an ugly balun,

iain

martin

is 1-2db = 1-2 watts?

A dB (decibel) is a ratio of one value to another value on a logarithmic scale.

A change in power by a factor of 10 corresponds to a 10 dB change in level.

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While this statement is absolutely true, it has potential of making our good friend Iain confused. So, Iain, a change in power by a factor of 5 does not correspond to a 5 dB change in level but rather a 7 dB change in level, while a change in power by a factor of, say, 20 does not correspond to a 20 dB change in level but rather a 13 dB change in level, Ah, the beauty of the logarithmic scale!

Hi,

A 1dB loss means that ca 79 % of the input signal pass through (= ca. 21 % loss).

Computation: 10^-0.1 = 0.79 (0.1 instead of 1 because a dB is a decibel, an not a Bel.)

A 2dB loss means that ca 63 % of the input signal pass through (= ca. 37 % loss).

With QRP power (5W), I am usually heard reasonably well in all of Europe (in CW), except in the worst conditions, reports are mostly 559 +/-. So even 1 or 2 dB in loss will at worst mean a reduction of 1 in the RST (e.g. 549 instead of 559).

What I am trying to say: There are so many variables in a SOTA set-up that have a much higher influence, and the actual losses in a carefully built EFHW or carefully built traps will be quite limited.

Martin

But a tuned circuit has very good out of band rejection, which is useful if your radio has a very wide front end as it prevents the receiver from overloading when on summits crowded with other transmitting antennas.

So DB is a fraction of my power, but still a substantial loss from my portable station, My reports from Saturday were disappointing to say the least, but I was heard

Is it the mountain tuner? Or the Un-un which is a tuned circuit

Many thanx for all the help

Hi Iain,

The unun is not tuned, it will do the same job over a range of frequencies. The tuner will involve a tuned circuit on the frequency in use - which is why you have to adjust it.

I agree with Martin’s comments above, that the difference between an end fed halfwave (with unun or tuner), a centre fed dipole, or a trapped version of either antenna, will not be significant in terms of making lots of contacts versus only a few.

A difference of one or two dB might affect the sort of contact where one station can hear the other, but just can’t understand everything they are saying, and the qso fails after a long attempt. In that case, it might just help - but how many of those do you have?
One S point change is generally taken to be a 6dB change in signal level, a 3dB change would be half an S point…

It is interesting and fun to experiment with antennas, and certainly, a poorly designed or built matching unit (tuner or unun) can have a big effect. But I would choose from the options you mention on the basis of what is convenient for you.

You mentioned keeping the ends of the antenna wire clear of the ground by about a metre, and that is good practice, as you can lose quite a lot through ground loss if the ends are close to earth.

73
Adrian

Thanx Adrian
I understand what u have written, thanx for taking the time to simplify it for me. It has reassured me about my antenna choice.
Iain👍

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I think it can be helpful and educational (and dare I say fun) to sit and have discussions about antennas and the math behind them. However, In some cases like this, I think it is a little like arguing about what sports car is better based on the published specifications when, in fact, the best thing to do is get out and drive.

I would suggest just picking something “good,” get out there, and dont look back for a while. With experience and/or a desire to tinker at a later point, you may try different things, but just picking something and going with it will pay far more educational dividends than constantly changing. In this hobby and many others I have been in, people look for the perfect killer antenna or recipe or whatever. The truth is, it doesnt exist.

I currently use a resonant EFHW with a home built 64:1 unun. In just getting out and using it, I have learned a lot about it and have been doing well with it. Is there something better out there? Maybe. Is there something better out there for me? No, not currenty.

2 cents from someone who is also on the journey.

-Steve
W2SWA

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Excellent advice :+1:

Couldn’t agree more! Any antenna that’s in the air and connected to a radio is infinitely more effective than the best of super-antennas you’re thinking of building :wink:

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Yes!

I would like to stress that for a SOTA antenna, theoretical efficiency is only one of the many variables for its actual usefulness and performance. In my SOTA antenna projects, I now tend to start with what is doable from the perspective of handling and then test whether it works sufficiently well. For instance, my two SOTA vertical designs:

are mainly inspired by an optimized handing on small or crowded summits. They are less performant than a full-size dipole (center-fed or endfed), but in practice, I can manage more QSOs on a challenging summit because I am QRV within 1 - 2 minutes. Still, I can work @SP9AMH with QRP2QRP regularly.

A dipole / EFHW with traps might be a little less efficient than a linked dipole. But when in a hurry on a summit, the antenna with traps allows me trying for a nice DX catch on 20m at the end of an activation in winter in a few more minutes, while I would not have the time to take down the antenna for a band-change.

As for the “any antenna design works” argument, I think we should add that this is true as long as you do not make any mistake building and tuning it: If you just look for a low SWR, you may never notice very bad construction mistakes that cause a lot of losses, for instance

  • long coax for sections with a very different impedance from 50 ohms,
  • shorts or cold solder joints,
  • core losses,
  • capacitative coupling into nearby metal or otherwise conductive objects,

etc.

So a WSPR performance comparison against a reference design is always useful. Low SWR just assures an impedance match to the transceiver, so that the finals do not get blown away. 80 % of your antenna can be actually a dummy load, while you can still achieve a 1:1 SWR, as any full dummy loads proves.

73 de Martin, DK3IT

Thanx for replies
I am in the process of building a pico trapped version
For more convenience and faster set up

Many thanxx
Iain

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I am using center feed dipoles for each band for many years. It requires to carry and install 3 antennas, but it does not require tuner.

If you add two pairs of the SOTAbeams Pico Traps to your 40m center-fed dipole, you will be able to turn it into a very convenient 3-band antenna that does not require an ATU either.

See here:

You will only have to observe that

  • you have to tune it starting with the highest frequency and the traps and following wire segments already installed and
  • the resonant lengths will be a bit shorter than for a linked dipole because the inductances of the traps extend the respective segment electrically.

73 de Martin, DK3IT

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