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My sota antennas


#1

i use 20 40 and 80m band, end fed half waves, all seperate, so i carry 3,

i use a 40-20 and 17m tuner for 20 and 40m, and a Homebrew 49-1 unun with an ft80a-43 toroid, for the 80m version, which will supposidly give me 80, 40, 20,10 without built in tuner, havent tried yet

was wondering which is more efficient. tuner or unun,

also
the unun doesnt mind if im near it,the tuner doesnt like me near it, swr jumps up after i tune for lowest swr, for some reason, tuner was a kit, i built,

i always try to keep the unun, and tuner about a metre from the ground, usually tied on my 10m travel mast,
all antennas also use counterpoise


#2

Is your tuner a tuned circuit? If so, then the stray capacitance inherent in such a device will have a much bigger effect on the SWR, hence the jump when you take your hand away. You just have to tune a bit lower and hope it goes bang on when you take your hand away; it gets easier with experience. I have read that tuned circuits are very low loss, but I can’t say I have any evidence to hand for that assertion.
de OE6FEG
Matt


#3

Matt, i dont know if its a tuned circuit, dont know what that is!, i try the tune somewhere else and see if it goes lower,
their is a jump when i move my hand away. but no jump with the unun. got me thinking maybe the unun is better, but i dont know
think ive read that toroids are very lossy though dont know if thats in a certain situation.

ive been thinking making a standard linked dipole, maybe using croc clips, or sotabeams pico traps which i already have, but would a standard dipole be more efficient than an end fed dipole???

just want as efficient an antenna as possible, same as all activaters


#4

Unless there are practical considerations that would absolutely require you to use an end fed half wave you might consider trying a linked dipole. You’ll find it quite resilient to things like feedpoint height, ground conductivity, and your proximity to the system. If you label both sides of the dipole you can even convert it into a hasty 1/4 wave vertical, if your mast is tall enough.

I only pull out the EFHW on skinny summits where walking around too much exposes me to major hazards, like cliffs or cornices.


#5

the only reason for the end fed halfwaves, is that, it was the first antenna i ever heard of. and just stuck with it as it just worked,
now though im getting on a bit with portable ops im thinking maybe i can improve . the performance of my antenna. get more qso,s and quicker

is a linked dipole, more efficient than an end fed linked dipole?. or am i just being stupid as their both half wave dipoles. only fed at different points


#6

There are a few other variables in play, but broadly speaking you’ll find a dipole more efficient than an EFHW, if only because the dipole doesn’t require a transformer that may be subject to higher losses. Adding traps instead of links may change that, as the traps will add some loss.

There was an excellent comparison of seven antennas antennas on four bands done last year by HB9SOTA.

You can find the report here: https://hb9sota.ch/wp-content/uploads/2017/07/wspr_gurten_hb9sota_20170702_en.pdf

And the reflector discussion here: Seven SOTA antennas compared using WSPR on a summit


#7

thanx, il go and read these now, thanx for info, and links


#8

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

Ed.


#9

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


#10

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.


#11

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.


#12

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

iain


#13

martin

is 1-2db = 1-2 watts?


#14

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.


#15

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!


#16

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


#17

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.


#18

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


#19

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


#20

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👍