One of the questions I normally get from students in the RTO Course once we move into HF is all about Baluns- what are they, what do they do, why are they needed and which one is the right one for my needs? The answer, like a lot of things in radio, can get pretty technical and go over people’s heads. The concept behind a balun is that its a type of transformer. BALanced to UNbalanced line. Dipole antennas are electrically balanced, and when they are fed with coax, they need a transformer because coax is electrically unbalanced. Without that transformer, residual current will cause your feedline to radiate as well- which causes a significant amount of loss and an unreliable radiation pattern.
The other reason you need a transformer is that the impedance (resistance) value, measured in Ohms, is usually never exactly 50. Your radio needs 50 ohms- too much resistance, and you’re not only inefficient but you’re generating heat. For that reason Baluns are measured in ratios- the most common ones are 1:1 (50 ohms:50 ohms, also known as a current choke). 4:1 (200:50), and 9:1 (450:50).
Anyway, that’s the quick and dirty from my end, here’s the rest: All About Baluns
And if you want hands on with these concepts, come on out to class- I’ve got two on the schedule for this Spring. Don’t miss an opportunity to expand your skillset.
10 thoughts on “A Good Site on Understanding Baluns”
GREAT link NCScout! I just ordered a 1:1 balun from BalunDesigns.com for an upand coming project. I really like working with those guys. I have done some interesting antenna set-ups and I always run by them my next best antenna creation or rework. They are quick to write back and offer suggestions on what balun would work for my application. Thanks!
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After lengthy discussions with some extremely knowledgeable folks, I won’t touch a commercial balun with a 10′ pole. I have a pretty badass choke balun plan some may want to try out. Prior to using this design, I was using 8 ring toroids arranged in a circle with a gap between the ferrites for air-cooling. Then coax was wound through the toroids, effectively isolating the feed line.
The above choke performed well, but I was looking for advice from the original designer of the binocular choke design I ripped off, so I reached out to him concerning my modifications.
Based on his recommendations, the current balun/choke is comprised of slightly less than 12 inches of RG-303 coax, strung with nine inches of concentric ferrite beads. RG-303 coax has solid Teflon(R) dielectric; it is rated for high power up to 30 MHz; and its outside diameter is about 0.19”.Onto this RG-303 coax I strung nine solid beads of mix-31 ferrite, Fair-Rite part number 2631480002. Each of these beads is 1.0” long. Then, over (i.e., around, surrounding) the p/n 2631480002 beads, I strung eight solid beads of mix-31 ferrite (Fair-Rite part number 2631102002). Each of these beads is 1.125” long; so the length of these eight beads is nine inches, the same as the length of the nine thinner beads inside.
This concentric bead design significantly enhances choking impedance across the entire HF spectrum; at it’s lowest it’s in excess of 1000 ohms, and impedance increases concurrently with an increase in frequency.
The ring balun is significantly easier to build than the concentric bead balun, but isn’t quite as high-performance. The finished version is shown above. It’s since been revised with right-angle connectors at the box.
The recipe is easy: three turns of coax through 8 rings of Mix 43 ferrite, evenly spaced using zip ties, and stuffed into an electrical enclosure. Two SO-239 to SO-239 bulkhead connectors at the box.
my very first dipole antenna was a home-brew Standford research institute with an ugly balun. Worked awesome for me. I didnt have the knowledge to have the fancy graphs, but it sure had good reports. Barefoot from Salt lake city to the cook islands and australia. I know, i know, propagation.
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Since craigslist and fakebook have been blocking our underground church movement we had to resort to our comms guy and his pirate station to announce meetings,groups,services and speakers . I forwarded this article to him and he is working on it for us to implement . His rig is mobile and he keeps us all informed despite the blackout attempts of tptb . He will be playing with Mike’s idea also from the comments section . He loves playing with his radio and it has become our only truly dependable source of info . Got comms ? You will need them .
I just made one yesterday. I used a 240-31 toroid and 17 turns of rg316 coax. I’m licensed upto 400 across the pond but in the absence of a linear amp I can only make it to 100 watts. This combo is good for that with some headroom. The 31 mix is good from 1.8 mhz to about 14mhz. For 3.5 to 28 mhz you could use a 43 mix toroid.
Discovered your website a while ago…longtime lurker. Keep it up. Solid info.
I made a 1:1.
This site also has good info. http://www.ifwtech.co.uk/g3sek/in-prac/
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