Here I go again. I found a wire dipole that has a 1:1 Balun ( had it stuck away for several years). I have put it up instead of trying the 102" whip I wrote about earlier. I tried it in an inverted "V" at a 55' angle and 45' angle, tried it horizontal too! I cut it the right length, aprx 8'5" on each side... the swr was over 3 at Channel 40 and around 2.5 at channel 1. I cut off 1 inch, no change, cut off another inch, no change, total cut 3" off with no change. I checked the continuity from side to side on the Balun and it has continuity! On a regular wire I've never seen continuity between the 2 sides (Braid and center conductor) unless there is a short between the sides. Now get this...AT the radio the braid side has no continuity to the center conductor. What the ...is happening here. First can't adjust SWR and now this?? Is this the way a Balun is supposed to work? Before I do another one I have to figure this out...Never used a Balun before (Never knew they existed until I found this. I've forgotten it I suppose). Any help will be appreciated. Thanks, TD
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Help...wire dipole and Balun high swr
- Thread starter TD126
- Start date
A dipole for 11m/CB band needs to be 17' 4" overall length and does not need a balun.
Perhaps you should start over . . .
Perhaps you should start over . . .
Yep
I had never used a Balun before when I built wire antennas...don't know why they included one with this...I bought several years ago...I probably will shelve it and when this cold spell breaks start over with plain wire or try the 102" whip configuration...I tinker too much for my own good LOL. Thanks for the input more is welcome...as for the length I was going by what the antenna had for the 11 meter band...It was for a mullti-band and "Cut it to length),
I had never used a Balun before when I built wire antennas...don't know why they included one with this...I bought several years ago...I probably will shelve it and when this cold spell breaks start over with plain wire or try the 102" whip configuration...I tinker too much for my own good LOL. Thanks for the input more is welcome...as for the length I was going by what the antenna had for the 11 meter band...It was for a mullti-band and "Cut it to length),
Because you're using a BALanced antenna on an UNbalance feeder.
The balun acts to block RF common mode coming down the outside of the braid of the coax due to imbalance in the dipole. This in turn prevents your rig from becoming RF hot and as well as reducing RFI also increases antenna performance.
RF chokes should be installed with all antennas fed by coax.
are you saying you cut 3" off one side,..... or, 1 1/2" off both sides for a total of 3"
either way,............. it's too short
Until the balun goes wonky like mine did this weekend and you have RF all over the shack.:w00t:
HMMM???
No balun needed at the feed point of a dipole??
Sure there is.
Use a 1:1 current balun at the feed point, it will connect an unbalanced transmission line (coax) to a balanced antenna (dipole). I,E. BALanced to UNbalanced. BALUN.
The Current balun will force equal but opposite amounts of current onto the radiator ( the wires ).
3:1 VSWR on ch 40, 2.5:1 VSWR on ch 1, the antenna is TO LONG, not to short.
If you are using a current balun at the fed point, and it is a 1:1 type and you have no continuity on the braid to any side of the dipole then it is a bad balun.
If you are using a 4:1 or other type then I would suggest removing the balun for testing purposes. If the balun is faulty then replace it with a 1:1 current balun.
As mentioned earlier a balun does help prevent eliminate CMC.
The dipole can and will be effected by what is around the antenna. Metal structures buildings towers etc. etc.
468/frequency is the formula for a 1/2 wl dipole.
Hope you get it fixed and up in the air.
I put a simple 1/2 wl dipole up for a friend of mine, at 1.2 wl height above ground. He laughed and joked about how a simple wire would perform.
First contact on 11 meter SSB was in to England. He stopped making jokes about a simple wire.
No balun needed at the feed point of a dipole??
Sure there is.
Use a 1:1 current balun at the feed point, it will connect an unbalanced transmission line (coax) to a balanced antenna (dipole). I,E. BALanced to UNbalanced. BALUN.
The Current balun will force equal but opposite amounts of current onto the radiator ( the wires ).
3:1 VSWR on ch 40, 2.5:1 VSWR on ch 1, the antenna is TO LONG, not to short.
If you are using a current balun at the fed point, and it is a 1:1 type and you have no continuity on the braid to any side of the dipole then it is a bad balun.
If you are using a 4:1 or other type then I would suggest removing the balun for testing purposes. If the balun is faulty then replace it with a 1:1 current balun.
As mentioned earlier a balun does help prevent eliminate CMC.
The dipole can and will be effected by what is around the antenna. Metal structures buildings towers etc. etc.
468/frequency is the formula for a 1/2 wl dipole.
Hope you get it fixed and up in the air.
I put a simple 1/2 wl dipole up for a friend of mine, at 1.2 wl height above ground. He laughed and joked about how a simple wire would perform.
First contact on 11 meter SSB was in to England. He stopped making jokes about a simple wire.
If you are concerned about 'imbalance' then a balun is a good idea. Over the years I've had no problem with not using a balun. If that 'imbalance' caused a problem I couldn't tell it. So, whatever depending, a balun isn't strictly necessary for any balanced antenna and unbalanced feed line.
It shouldn't have made any difference in SWR when using a 1:1 balun, but an inverted 'V', depending on the angle of the dangle between the legs will drop the input impedance from something close to 75 ohms to something closer to 50 ohms. No impedance transformation necessary.
If you could number the people who use baluns with dipoles against those that don't, the people who don't use them greatly outnumber the ones who do. In general, it won't make a hill of beans worth of difference. And considering some of the conditions of their use, a balun is just another point of failure. Suit yourself...
- 'Doc
It shouldn't have made any difference in SWR when using a 1:1 balun, but an inverted 'V', depending on the angle of the dangle between the legs will drop the input impedance from something close to 75 ohms to something closer to 50 ohms. No impedance transformation necessary.
If you could number the people who use baluns with dipoles against those that don't, the people who don't use them greatly outnumber the ones who do. In general, it won't make a hill of beans worth of difference. And considering some of the conditions of their use, a balun is just another point of failure. Suit yourself...
- 'Doc
err, his antenna is too short, it needs to be in the 17.2 to 17.4 feet range.
once he gets it fairly close to resonance, .,.. ..if there is a 3:1 VSWR on ch 40, 2.5:1 VSWR on ch 1, the antenna will be too LONG.
after I had done everything else...changing height, location, angle, shortened it by folding back, lengthened it adding wire...everything I could think of from past experience... THEN I followed the 'struction and cut 1.5 inch off each side in equal parts from side to side. The BALUN was what I could not figure out ...that is what had the effect on SWR. SO, my next question is, will it damage and cut performance if the SWR is not make right (and then HOW would one adjust SWR with the BALUN...use a tuner?)
Try removing the balun completely. Then check the antenna out and get it the best length overall - equal length on each side. That should get you below about 1.5:1 SWR - assuming you're using 50 ohm coax.
The 1:1 balun isn't going to do anything significant to the operation of the antenna unless there are metal structures near the antenna. I've used probably 30 dipoles for various bands in the last 50+ years and NEVER had to use a balun.
The 1:1 balun isn't going to do anything significant to the operation of the antenna unless there are metal structures near the antenna. I've used probably 30 dipoles for various bands in the last 50+ years and NEVER had to use a balun.
A dipole is a balanced antenna, which means both 'sides' of it should be the same length (as close as possible, no need for a micrometer though).
One means of adjusting SWR is by how much 'dangle' an inverted 'V' antenna has, the angle between it's legs. The less angle between those legs the lower the input impedance gets. That angle ranges from 'flat', 180 degrees to something like 100 - 110 degrees. Any narrower than that and you really aren't doing any good. There's quite a bit of adjustment there, and it can get fairly 'small', 'exact', sort of.
A 1:1 balun is more of a balance equalizer than an impedance matching thingy. It certainly will convert an unbalances feed line (coax) to a balanced one for connection to a balanced antenna, but isn't magical, won't 'make everything better'. If the impedance on one side of it is 50 ohms then the impedance presented to the other side of it is 50 ohms. If 62 ohms, then it presents 62 ohms to the other side. It doesn't 'cure' SWR problems at all.
And just for grins, if shortening the thing doesn't make for any improvements, why not try lengthening the thing? You may have gone past the 'sweet spot', so go back and find it.
Only do one type of change at a time! Length, or height, or angle of the dangle, don't do it all at once or you don't know what the devil 'fixed' anything. "Any moron knows that!", right? Well, sometimes us morons have to be reminded, you know?
And don't get caught up in the numbers game! A 1.5:1 is just as good as a 1:1. There's a lot of 'skootch' (technical term) in it, don't insist on perfection, it never happens.
Have fun. Even if it seems like it, it really ain't impossible...
- 'Doc
One means of adjusting SWR is by how much 'dangle' an inverted 'V' antenna has, the angle between it's legs. The less angle between those legs the lower the input impedance gets. That angle ranges from 'flat', 180 degrees to something like 100 - 110 degrees. Any narrower than that and you really aren't doing any good. There's quite a bit of adjustment there, and it can get fairly 'small', 'exact', sort of.
A 1:1 balun is more of a balance equalizer than an impedance matching thingy. It certainly will convert an unbalances feed line (coax) to a balanced one for connection to a balanced antenna, but isn't magical, won't 'make everything better'. If the impedance on one side of it is 50 ohms then the impedance presented to the other side of it is 50 ohms. If 62 ohms, then it presents 62 ohms to the other side. It doesn't 'cure' SWR problems at all.
And just for grins, if shortening the thing doesn't make for any improvements, why not try lengthening the thing? You may have gone past the 'sweet spot', so go back and find it.
Only do one type of change at a time! Length, or height, or angle of the dangle, don't do it all at once or you don't know what the devil 'fixed' anything. "Any moron knows that!", right? Well, sometimes us morons have to be reminded, you know?
And don't get caught up in the numbers game! A 1.5:1 is just as good as a 1:1. There's a lot of 'skootch' (technical term) in it, don't insist on perfection, it never happens.
Have fun. Even if it seems like it, it really ain't impossible...
- 'Doc