Help making a ugly Balun for c b radio

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original45
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Help making a ugly Balun for c b radio

Post by original45 » 30 May 2016, 15:13

Been looking at swr again on my next inverted v centre fed wire diapole. Still not where IDE like to be.
So IDE like ideas for a Balun please and coax length ,coil length best suited to 11 mtr.

I have had a little look on net , I believe around 20 ft coax is best , and a 4" coil of coax with 5 windings if this is correct.

If I reduce size of coil to 2 or 3 inch would this cause issues ?
Would I then need to increase amount of coils ?
IDE like to have the Balun as small dia as possible as its for back pack and 4-5" isn't preferable unless it's going to effect its ability so I need to confirm this please with you guys who know.
Advice appreciated .

I'm trying to keep it compact ,lightweight but effective so if smaller is a no go I will follow best advice .
Cheers

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Re: Help making a ugly Balun for c b radio

Post by Tigersaw » 30 May 2016, 16:15

I take it you are talking about a common mode choke, in this guise often referred as a balun or ugly balun. It wont improve your SWR at the antenna feed point, but will eliminate common mode feeder current that can give all sorts of strange results and indications.
If you want something that actually works and is small, look here http://gwhip.co.uk/baluns/current/
However, if its just for portable operation why bother? (unless you are using huge power and suffer RF shocks from the mic or other strange effects.)

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Re: Help making a ugly Balun for c b radio

Post by original45 » 30 May 2016, 16:36

Thank you .
Re swr that was my mistake sorry .
I'm not 100% clued up on this .
I think I read somewhere that the inverted v wire can cause feeder radiation I think it said and can be improved by adding a 1-1 balun .

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Re: Help making a ugly Balun for c b radio

Post by Tigersaw » 30 May 2016, 16:44

An inverted V is an excellent antenna, simpler to erect than the dipole and more omni-directional coverage with just a little loss compared.
Trouble is they are both balanced antenna, and you are feeding with unbalanced feeder. Due to mismatching and the fact that the antenna will never be perfectly balanced due to the environment and construction, you end up with the shield of the coax also becoming part of the whole antenna system. Sometimes this can be to your advantage though, so don't get hung up on it all.
I do use chokes (ones in the link), but thats more because without one some RF can get back into the shack, and wierd things happen like the PC mouse freezing or the TV turning itself on.

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Re: Help making a ugly Balun for c b radio

Post by original45 » 30 May 2016, 17:38

I think I will just put 5 x4" coils of RG around a plastic former right bellow feed and see how it goes. .
I shall do this very temp style in case I don't need it .

It seems a decent antenna and maybe I'm looking into it too much and it's decent as is.
It's my second attempt , was just looking to improve it if possible .

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Re: Help making a ugly Balun for c b radio

Post by rogerbeep » 31 May 2016, 08:54

Instead for making a rather big airwound coil you can also use 12-15 clip-on ferrites in a row immediately beside each other.
In the same way as the ugly balun this will also eliminate common mode currents outside the coax cable.
Whatever you use to eliminate common mode currents, make sure that you are not pulling the coax out from the plug. Some people tend to think that the soldered connection and cable friction can take up any load.

Suitable clip-on ferrites which matches the diameter of your feedline is found at ebay for just a small amount of money.

Personally my opinion is that this solution looks much better than the ugly balun (literally speaking) - which I used before.
You can make it look even better if you use a length of heat shrink tubing outside the ferrites, this will also prevent them to open and/or fall off.
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Re: Help making a ugly Balun for c b radio

Post by original45 » 31 May 2016, 10:59

Thank you I will check these out they sound great.
Had another go today.
I tried 2 coax cables to see how either if effected swr.
Rg58 20 ft swr on 40 was 1.3 channel 1 was 1.5
Rg8 mini 30foot Swr on 40 was 1.6 channel 1 was 1.2

I'm guessing coax length may be critical?


The other thing was I had more static noise with 58 .
Thanks again
Enjoying this but it is complicated if your not knowledgeable on such. Very interesting .

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Re: Help making a ugly Balun for c b radio

Post by kr0ne » 31 May 2016, 13:23

I'd say that your 20' of RG58 has more loss than your 30' of RG8, based on that...

I'm assuming that you are measuring the SWR betwedn the radio and the co-ax, rather than between the co-ax an the antenna here. If so, your reflected signal is subjected to 2 x the loss caused by the co-ax (once as it travels to the antenna and once more as it is reflected back towards your meter) whereas your forward signal is not subjected to this at all.

End result is the more lossy the co-ax, the lower the SWR as measured between the rig and the feeder.

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Re: Help making a ugly Balun for c b radio

Post by original45 » 31 May 2016, 14:05

Got ya. Yes I'm measuring swr between radio and coax.
I noticed swr went to red when feeder coax wasn't ganging central from v but more too one leg.
Yes the rg58 is old stuff not sure of quality but has to be 30 years old from memory.

Any benefit to measuring between coax and feed .
I found it strange that with one higher channels were lower swr but swapping over it was reverse.
Gonna stick to rg58 I guess ,
And going to make a third with the outer protector on just the inner black rubber jacket see how that works.
Thank you for explaining the loss to swr result

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Re: Help making a ugly Balun for c b radio

Post by kr0ne » 31 May 2016, 18:31

The correct way to measure antenna SWR is with the meter between the antenna and the co-ax... it's not really practical for most of us though, so we stick the meter between the co-ax and the radio instead and measure the SWR of the entire antenna/co-ax system.

It's not perfect but it's close enough. Best not to get too focussed on the "perfect" SWR I reckon. ;)

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Re: Help making a ugly Balun for c b radio

Post by original45 » 31 May 2016, 19:18

Excellent ,thank you.
Will make another and test swr from between antenna and coax next time .
Appreciate the tips and advices all that have given it.

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Re: Help making a ugly Balun for c b radio

Post by wa10 » 31 May 2016, 21:46

when coax length effects vswr readings like that its usually common mode current causing it, there should be little change in vswr due to the small difference in cable loss at those lengths,
putting a functioning choke at the feedpoint would prove if its cmc causing the vswr readings to reverse,

or maybe your old rg58 is damaged.

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Re: Help making a ugly Balun for c b radio

Post by original45 » 01 Jun 2016, 08:37

Wa10 thank you ,I will put a temp Balun in and re check.
Has anyone an idea of how many feet apart between the bottom of legs they should be to ensure the correct degree of inverted v for 11 mtrs ?

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Re: Help making a ugly Balun for c b radio

Post by original45 » 08 Jun 2016, 13:57

Little further help please.
Looking at a chart I found re turns of coax to mghz it states 5 turns of rg58 on a 4.25" former.
I only have 4" former so do I still only use 5 turns or use 6 to make up for the lesser dia.

Thanks

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