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 Best SWR adjustment method?

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karelgol
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karelgol


Call Sign : 19-CT-024
Posts : 103
Times Thanked : 4
Join date : 2020-05-21
QTH or Location : Steenwijk, JO32bs
Equipment Used : Dynascan AT5555,President Lincoln I, President Bill Asc, KL-200P, T2LT, 5/8 Gainmaster, Emperor LA-50
Age : 64

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PostSubject: Best SWR adjustment method?   Best SWR adjustment method? Icon_minitimeTue Mar 16, 2021 8:36 pm

As you might have read i've build a bent dipole with telescopic arms. I'm just wondering how i could get the best SWR setting. I started out with the width given by the design program (MMANA). Now i suppose i fiddle with the left or right leg length adjustment(just one leg) to get the lowest SWR. Am i correct that at that time i have my dipole electrically balanced? Then i'll adjust both legs with the same amount to get the SWR at my wanted frequency. Is this the correct order for getting the best result or am i overdoing things, as for a vertical you only adjust one length? Your thoughts please.

73
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Alan Pilot
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Alan Pilot


Call Sign : 163-CT-220...MW7TTA
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Join date : 2019-11-19
QTH or Location : Anglesey North Wales
Equipment Used : Yaesu FT-991A,,Yaesu FTDX-10,,Icom ic-7300,,Anytone AT-D878UV PLUS",,LINCOLN II+.
Age : 149

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PostSubject: Re: Best SWR adjustment method?   Best SWR adjustment method? Icon_minitimeWed Mar 17, 2021 7:08 am

Would think you just move one side only.
The side that is connected to the center of the coax not the braid.
Well that's what i would do anyway but could be wrong.
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Victor
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Victor


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PostSubject: Re: Best SWR adjustment method?   Best SWR adjustment method? Icon_minitimeWed Mar 17, 2021 8:20 am

Hi Karel,

Nice to see and hear your continued experiments with antennas.

I've always adjusted my dipole antennas so that they are physically 'mirrored' and then hopefully electrically balanced too. Wink

You can land up backwards and forwards though and completely botch it up(!)


The following link might help a bit with some described practices for tuning dipoles :-

https://www.hamuniverse.com/easydipole.html


As for the lowest SWR reading, I always tell people not to get too wrapped up with it. A SWR of 1.9 or lower will do the job and I'm always happy if I manage 1.3 to 1.7.

Anyway, you've done well with your construction so far so I wish you the best with tuning it and finally using it.


All the best,
Victor
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karelgol
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karelgol


Call Sign : 19-CT-024
Posts : 103
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Join date : 2020-05-21
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Equipment Used : Dynascan AT5555,President Lincoln I, President Bill Asc, KL-200P, T2LT, 5/8 Gainmaster, Emperor LA-50
Age : 64

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PostSubject: Re: Best SWR adjustment method?   Best SWR adjustment method? Icon_minitimeWed Mar 17, 2021 8:54 am

I found an excel sheet https://www.m0mcx.co.uk/quick-swr-calculator-for-vertical-and-dipole-ham-radio-antennas/ which does the calculating described in your link.
Thanks for your response, have learned a lot from building this antenna. Think for the next one i use some bigger tubing, this one looks a bit flimsy (10 and 8mm alu tubing).

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SangueG
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PostSubject: Re: Best SWR adjustment method?   Best SWR adjustment method? Icon_minitimeWed Mar 17, 2021 7:07 pm

I think you said you managed a best SWR of 1.3:1 on 27MHz? I would be very happy with that figure.

Personally, if you do try to adjust, I would adjust both legs equally. I have always done this with flat dipoles, Vs and inverted Vs. I have never built a bent dipole though, so there may be some differences.

I don't how hard it would be for you to adjust the bend angle? I found this web page which shows how to tune by angle of bend. That makes sense to me as I have adjusted angle between legs of inverted V for best tuning...

https://www.qsl.net/kk4obi/Center-fed%20Laterally%20Bent-end%20dipoles.html
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karelgol
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karelgol


Call Sign : 19-CT-024
Posts : 103
Times Thanked : 4
Join date : 2020-05-21
QTH or Location : Steenwijk, JO32bs
Equipment Used : Dynascan AT5555,President Lincoln I, President Bill Asc, KL-200P, T2LT, 5/8 Gainmaster, Emperor LA-50
Age : 64

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PostSubject: Re: Best SWR adjustment method?   Best SWR adjustment method? Icon_minitimeWed Mar 17, 2021 9:50 pm

The left and right leg are the same(or should be) and i was just wondering if adjusting just one leg would get the swr down to an optimum and from that point on i'd have to adjust both legs equally to get the lowest swr on the center frequency. I'm quite happy with the results so far, but wondered if the above described method would get a better result.
Changing the bent angle isn't really an option as i took the length of the bends the same as for a 27MHz Moxxon. Still have to ask my neighbour if he would object to having part of my moxxon above his garden. If he's OK i'll add a reflector to this antenna and use it as a moxxon. Have to figure out if building a DIY rotator mechanism is an option.

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Northern Crusader
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Call Sign : M0GVZ / 26CT1760
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Join date : 2019-11-13
QTH or Location : IO94SA
Equipment Used : Icom 7300, TS480, President McKinley, Albrecht AE6110, CRT Mike
Age : 52

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PostSubject: Re: Best SWR adjustment method?   Best SWR adjustment method? Icon_minitimeFri Mar 19, 2021 7:26 pm

No, you adjust both legs equally. Whilst you can get a low SWR altering just one leg you'll end up with a massive imbalance in the antenna with more current flowing in one leg than the other which will both affect efficiency and increase the risk of RF current flowing on the outside of the coax, aka common mode RFI, and all the grief that comes with that.
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karelgol
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karelgol


Call Sign : 19-CT-024
Posts : 103
Times Thanked : 4
Join date : 2020-05-21
QTH or Location : Steenwijk, JO32bs
Equipment Used : Dynascan AT5555,President Lincoln I, President Bill Asc, KL-200P, T2LT, 5/8 Gainmaster, Emperor LA-50
Age : 64

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PostSubject: Re: Best SWR adjustment method?   Best SWR adjustment method? Icon_minitimeFri Mar 19, 2021 8:00 pm

So, no possibility to get the antenna electrically balanced through SWR measurements, just measure with a ruler?

73
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