KD0OTK
Member
What are the advantages of having the balun near the antenna feedpoint? Or could I just put it near the radio? Thanks
Baluns, feedpoint or radio?
- Thread starter KD0OTK
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It just depends on where you should be doing any impedance transforming, if required. Other than that, put the thing at the feed point of the antenna, unless you particularly want CMC's or a radiating feed line. Or, where does the unbalanced feed line connect to a balanced antenna? Put it there.
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KD0OTK
Member
Well. I'm putting up a dipole. And that's unbalanced (I think). So I suppose I should be putting the balun at the feedpoint. What is the advantage of doing that vs just putting in a few feet from the radio? It would serve the same purpose, right?
majoco
Stirrer
A dipole is balanced. It's the coaxial cable you're feeding it with that is unbalanced (BAL-UN, get it?)
But a dipole has a resonant frequency where the feedpoint impedance is about 72ohms, so you would have a 1:1 balun to feed into 75ohms coax cable to your rig. However as soon as you get away from the resonant frequency the feed impedance goes haywire from anything from a dead short to a high impedance so your matching is useless. Fine for a single frequency, crap for a all-frequencies receiver. A long wire or an offset dipole with an UN-UN would be btter -see thw Wiki on this site.
But a dipole has a resonant frequency where the feedpoint impedance is about 72ohms, so you would have a 1:1 balun to feed into 75ohms coax cable to your rig. However as soon as you get away from the resonant frequency the feed impedance goes haywire from anything from a dead short to a high impedance so your matching is useless. Fine for a single frequency, crap for a all-frequencies receiver. A long wire or an offset dipole with an UN-UN would be btter -see thw Wiki on this site.
prcguy
Member
A 1/2 wave dipole in free space might be around 72ohms but most people have their HF dipoles much less than 1/4 wavelength above ground and the impedance is probably closer to 50ohms or lower at resonance.
If the OP is making a dipole for a specific frequency a balun is not a bad idea but I've never noticed any difference adding or removing one.
If this antenna is for multiband use coax is a bad idea like magoco said and I would feed it with balanced line all the way to a tuner or if a SW receiver, all the way to the receiver with no tuner.
prcguy
If the OP is making a dipole for a specific frequency a balun is not a bad idea but I've never noticed any difference adding or removing one.
If this antenna is for multiband use coax is a bad idea like magoco said and I would feed it with balanced line all the way to a tuner or if a SW receiver, all the way to the receiver with no tuner.
prcguy
This is what I use, with balanced line and an SGC autotuner in place of a balun. I get outstanding results from 160-10 meters.
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