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glenn north lincs
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PostSubject: advice on coax connection   advice on coax  connection Icon_minitimeThu Nov 04, 2021 12:56 am

can anyone advise. having read and watched many videos on building a dipole.

 when watching videos all show 50 omh coax connected at center point, however when reading some books they recommend using a 1-1 balun and 75 omh coax

question?
a   which is better
b   can anyone give a youtube link showing results when using a balun and 75 0mh coax

thank you
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Victor
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PostSubject: Re: advice on coax connection   advice on coax  connection Icon_minitimeThu Nov 04, 2021 10:32 am

If the following helps anyone in any way then I'm happy....


You won't see a difference in SWR usually, whether you have a BALUN on a dipole or not.
(Doesn't matter how expensive the SWR meter is either.)

You also won't see a difference if you check with an antenna analyser.
(I don't on a MFJ-259B or NanoVNA.)

You WILL however see a difference if you use an RF current meter :-



Nice visual example there. advice on coax  connection 1f44d 


I never used BALUN's, chokes or anything to start with on any dipole or Yagi-Uda beam, (it also utilises a dipole). They all seemed to work fine so why bother?

It was only seeing examples such as in the video above did I construct an RF current meter and saw it for myself that I did something about it. It didn't make any difference perceived or otherwise to my transmissions probably due to low power use, but it made a huge difference to my reception noise floor which reduced dramatically.


If it helps anyone in any way again.....
(All of my antennas are home made)

I have a 'Maxwell' choke on my vertical 'Double Extended Zepp' dipole for 2m

An air wound or coaxial 'Ugly Choke' on my 2m Horizontal Halo

A 'Sleeve' or 'Bazooka Choke' on my VHF and UHF Yagi-Uda beam antennas

A '1:1 Common Mode Choke' on my HF Fan Array Dipole, (All working from 160m through to 10m)

The last example reduced my HF noise floor by some 2 to 3 S-points(!!)


Don't let it bother you if you don't have a BALUN or Choke, a dipole will work regardless....Any antenna is better than NO antenna. Wink


For examples of such various chokes here's a good website :-

https://www.dj0ip.de/rf-cmc-chokes/different-kinds-of-chokes/



Regards coax impedance, you pays your money and takes your choice...

A dipole is widely regarded as having a 75 ohm impedance, (usually specified as 72 ohms)....but all of that depends on where and how the dipole is mounted, closer to the ground or higher up, within the vicinity of other objects etc. Just check the impedance on a Yagi-Uda beam and that impedance can be very low or quite high depending on the design. The '75 ohm' dipole thing may be why it's recommended but also in old books 75 ohm was the common coax to use even with Ham Radio.


I use 75 ohm coax throughout all my setups for the following reasons :-

It's cheap, (even the quality stuff), not only that but you can get it from anywhere.

It's 100% screened.

It works from HF to VHF through UHF.

All my coax routes are short runs.


So it does the job for my purposes. advice on coax  connection 1f44d 

Some complain you can't solder the braid? I use compression fittings for everything so never face that problem. Wink
The theoretical 1.5:1 SWR from the 75 to 50 ohm mismatch never seems to materialise in the real world either.
I also don't run hundreds of Watts.


Anyway, all of the above is a cumulation of the experiences I've come across and someone else may see things completely differently. I've no issue with 50 vs 75 ohm, RG213 vs whatever, BAL-UN's, UN-UN's etc. etc......debates are one thing, pointless arguments are quite another.

My best 'advice'?

Do whatever makes you happy. Most of all just simply enjoy your 'radio', life's too short for anything else.


If any of that 'waffle' didn't help then so be it - but it might be of benefit to someone.


All the best,
Victor

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glenn north lincs
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PostSubject: Re: advice on coax connection   advice on coax  connection Icon_minitimeFri Nov 05, 2021 1:36 pm

thank you victor
after reading your last comment to me from earlier post, like you said so much to learn.
i was wrong and thank you for the correction.
i was so wrong on so many things bull in a china shop.
with no help coming from the local ham club, i have set myself a learning program
currently reading up on loading coils and chokes.
i may have many more questions to ask so i am sorry in advance.
one last thing, was in a shop yesterday and saw a by-cycle stand £20. big tripod and extended pole 2 meters plus, and a swivel clamp to turn  bike either vertical or horizonal. now i am not suggesting  anything. but think antenna mount and not bike.

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PostSubject: Re: advice on coax connection   advice on coax  connection Icon_minitimeFri Nov 05, 2021 3:05 pm

Hi Glenn,

No need to apologise my friend, sometimes things can be a bit frustrating and overwhelm us.


There is so very much to learn with 'radio' and it's quite the daunting task especially if we feel we have been mislead with false information, pet theories, sales spiel or even the atypical 'snake-oil'! Wink

I certainly enjoy the aspect of continuous self learning and radio seems to have a limitless path of knowledge to follow. As I mentioned in this posting I never used to 'choke' anything and learned otherwise, but I didn't kick myself in the butt for it, instead I was rather pleased to have learned something new and put it into practice.


I really do wish you well with your radio interests especially as you have chosen to learn and understand rather than simply be a radio consumer. Not that I have anything against 'consumers' of radio either before someone jumps up. Wink

I'm liking your thinking with the bicycle stand too....You know when 'radio' has taken over when you can immediately see how something can be utilised for such rather than it's original intention or design.
(I'll bet that'd make one hell of a beam rotator! Very Happy )



Enjoy your radio Glenn, enjoy the forum too, there's a lot more helpful people out there than you think.

Look forward to more postings from you.


All the very best,
Victor

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Ivy Mike
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PostSubject: Re: advice on coax connection   advice on coax  connection Icon_minitimeSun Nov 07, 2021 6:29 am

A CMC at the feed point is a good thing.
Not only does it stop RF in the shack it helps to stop pick up of interference.
A simple choke made from a large ferrite ring wound with coax, 9>12 turns on a Mix 31
should do it, put one at the entry to the shack as well.

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PostSubject: Dipole    advice on coax  connection Icon_minitimeSun Nov 07, 2021 9:08 am

Me personally I've always used 50hm if you want to use a ballum then that's ok but if it's just for 11m then just make sure the coax is slightly longer both ends so when doing the trimming for the swr but good luck.
Don't forget 9ft either side 👍
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PostSubject: Re: advice on coax connection   advice on coax  connection Icon_minitimeMon Nov 08, 2021 8:39 pm

Howard wrote:
Me personally I've always used 50hm if you want to use a ballum then that's ok but if it's just for 11m then just make sure the coax is slightly longer both ends so when doing the trimming for the swr but good luck.
Don't forget 9ft either side 👍

You don't trim the coax to alter the SWR. If altering the length of the coax alters the SWR that suggests you've a big problem, that your coax is forming part of the antenna. I'm guessing that you don't use a BALUN or put in a RF choke because if you did then it wouldn't matter how long the coax was, it wouldn't affect the SWR.

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