How to make a Balun

[LeeCavanagh]

I know the concept, but not all antennas need a balance do they? I have a feeling my manufacturer said it’s a tuned antenna and doesn’t need a Balun (but I may have dreamt that)

What’s the difference between 1:1, 4:1, 6:1 , is 1:1 a filter that is specific to your freq? And are the others blocking harmonics? More like a choke?

I’m sure some of you can help answer this.

I’m unclear on the difference between, current 1:1 ratio balun (which I’m considering making) VS a voltage balun (which I’m guessing will still self radiate to a degree?)

But I’m learning

What’s better, a ferrite rod or ferrite ring or tordroid, or just using co-ax turns?

I found this site, and considering the co-ax current balun
https://www.m0kwr.com/Downloads/Baluns/ ... Baluns.pdf

Rg6 would be 27” markers on coax rg6, 3 turns
Rg58 would be 26” markers on coax rg59, 3 turns

Thoughts?

[radium98]

thanks for sharing the great and valuable infos , can you help to make 50 to 75 ohms

[Albert H]

There are various kinds of transformers for feedlines. The ratios you've seen are impedance ratios - a 1 : 1 transformer doesn't change impedance, but a 1 : 2 does (typically 50Ω input will be transformed to 100Ω output in that example). Some aerials have impedances (NOT "resistances" - RF is AC) that are not conducive to direct connection to your 50Ω feeder. The folded dipole (for example) shows a feedpoint impedance of around 300Ω, so you'd need a 1 : 6 transformation ratio to get the aerial to match the transmitter feed.

The other issue is that many aerials require a balanced feed: The simple dipole - for example - is about 72Ω and needs a balanced feed. This is where a "balun" gets involved. The clue is in the name - balun is Balanced to Un-balanced.

You'll also discover that aerial configuration changes impedance, necessitating different matching transformers (or other kinds of network - see the old NRG Half-wave Vertical for example).

If you start with a folded dipole (300Ω balanced), and add a reflector behind it to save wasting power in directions away from your target area, you'll discover that the impedance of this simplest "Yagi" aerial is lowered - typically to around 150Ω - this needs a 3 : 1 impedance conversion, but still needs the balun function to make it match accurately to your feeder....

If you look up some of the papers on antenna design, you'll quickly realise that the mathematics involved is pretty hairy!

[Albert H]

Incidentally - the best balun I've found for simple dipoles is the "Pawsey Stub". It simply uses a length of your feeder. It's well worth looking it up on line to see how it connects.

[radium98]

Thank you , in simple words.

[LeeCavanagh]

Thanks Albert, really good stuff.

[LeeCavanagh]

Incidentally - the best balun I've found for simple dipoles is the "Pawsey Stub". It simply uses a length of your feeder. It's well worth looking it up on line to see how it connects.

Ok, so the example I put in the 1st post was a 1:1 current (dirty balance) choke ? I think I have that right)
And the Pawsey stub (folded balun) would be
300 / 100 x 0.66 x 0.25. (For my RG8 coax, although not sure this is the best coax for the job - but I shit loads of it, is it really bad to leave a coil of the extra coax from the antenna line right next to your rf amplifier - lol - something tells me it is )

I’m going to try making one, thanks Albert

[yellowbeard]

Incidentally - the best balun I've found for simple dipoles is the "Pawsey Stub". It simply uses a length of your feeder. It's well worth looking it up on line to see how it connects.

Ok, so the example I put in the 1st post was a 1:1 current (dirty balance) choke ? I think I have that right)
And the Pawsey stub (folded balun) would be
300 / 100 x 0.66 x 0.25. (For my RG8 coax, although not sure this is the best coax for the job - but I shit loads of it, is it really bad to leave a coil of the extra coax from the antenna line right next to your rf amplifier - lol - something tells me it is )

I’m going to try making one, thanks Albert

That type of coiled coax choke should be mounted up the mast as close as possible to the antenna. It won't do any impedance or balanced to unbalanced conversion but it will stop RF coming back down the braid of the coax into your gaff.

[LeeCavanagh]

Great, that’s what I need.

[Albert H]

Actually - no. A coil like that might

[Albert H]

Actually - no. A coil like that might help a bit, but won't eliminate RF coming down the outside of the coax entirely.

[LeeCavanagh]

Actually - no. A coil like that might help a bit, but won't eliminate RF coming down the outside of the coax entirely.

Thread got a bit mixed, I’m going to make the one you suggested , it’s because I put the name of the 1st one in my reply.