Posted: 12/31/2011 9:03:28 AM EDT
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Is a balun made to "balance" coax? How does one know which balun to use for what antenna type? I see many different baluns such as 4:1, 9:1? and others. I was looking at building something like this: Thanks VRMN |
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A balun is a transformer used to connect balanced lines to unbalanced lines. Those ratios (4:1, 9:1, etc.) of impedance are used to bring known loads up or down to whatever impedance you're after. Typically 50 ohms or much closer to 50 ohms so you can use a tuner.
If you're looking to build a doublet, you'll be a lot better off using balanced line. There is no one balun that's going to be the correct ratio for using a doublet on all bands, so you'll just have to compromise. Using a tuner with a built-in balun and balanced line all the way to the shack will give you a lot less loss. The next best thing is running just enough coax to get the feed line outside the shack and putting a balun on it and then go balanced line from there. A 1:1 balun will give you a better balance and you'll have a little less loss. A 4:1 balun will give you a little more, but you can get away with running a cheaper tuner with less power handling capacity and less range. If it sounds like I'm a bit anal about getting every watt out of my station as I can, it's because I am.  But then I can't count how many times I've been told, "I can't believe you're only running 100 watts!" and I think that has a lot to do with it.
If you're more concerned with multiple bands on one wire and the loss doesn't bother you (and there's nothing wrong with that really) then I'd forget the doublet and go this route: Balun Designs 9:1 Unun Prune the wire and counterpoise and you can use all bands on one wire with no tuner. Sure you'll have some loss but it would really convenient and you only have one antenna to dick with. I'm considering doing it just so I can easily get on the air on 160 and 6 meters, the two bands I can't cover with the loop antenna I'm using now. Sure it won't be an optimal antenna for those bands, but it's better than no antenna at all. 
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Quoted:
Is a balun made to "balance" coax? How does one know which balun to use for what antenna type? I see many different baluns such as 4:1, 9:1? and others. I was looking at building something like this: Thanks VRMN Did you see that picture of Piccolo on that site? 
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Some reading from naval warfare novelist and ham, Don Keith:
http://www.donkeith.com/n4kc/article.php?p=13 Feed the Beast (all about feedlines) http://www.donkeith.com/n4kc/article.php?p=12 Skywire Horizontal Loop Antenna http://www.donkeith.com/n4kc/article.php?p=22 To Five Get-On-the-Air-Quickly Ham Antennas. http://www.donkeith.com/n4kc/article.php?p=32 Resonance Schmesonance http://www.donkeith.com/n4kc/article.php?p=15 Having more than one antenna These are short, you can read all in 20 minutes. You may not get the full grasp, but they are short reads. Read them over again. Again in a year. |
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Quoted: Thanks A_F_M!Some reading from naval warfare novelist and ham, Don Keith: http://www.donkeith.com/n4kc/article.php?p=13 Feed the Beast (all about feedlines) http://www.donkeith.com/n4kc/article.php?p=12 Skywire Horizontal Loop Antenna http://www.donkeith.com/n4kc/article.php?p=22 To Five Get-On-the-Air-Quickly Ham Antennas. http://www.donkeith.com/n4kc/article.php?p=32 Resonance Schmesonance http://www.donkeith.com/n4kc/article.php?p=15 Having more than one antenna These are short, you can read all in 20 minutes. You may not get the full grasp, but they are short reads. Read them over again. Again in a year. |
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Any time, guy!
Also, go to www.hamuniverse.com and on the left side click "Antenna Design". Lots and lots of excellent HF and VHF/UHF antennas, practical, easy-to-build, sound designs. Also, right click and Save As this pdf link, it is an excellent antenna book that will keep you busy. http://www.hamuniverse.com/n4jaantennabook.pdf As I said to another Arfcommer today, these books, a 4:1 current balun, a 1:1 current balun, a roll of 14 ga stranded THHN wire (500' spool), and some end insulators, and you have all you need for a few years of antenna experiments. (Edit: Plus a spool of 550 paracord.) http://www.universal-radio.com/catalog/antsup/4818.html These are excellent, and for my portable antennas, don't chip like porcelain. You can also get these at farm supply / feed & seed stores sold as electric fence insulators. Have fun and see you on the bands! AFM |
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Quoted: I use some derlin rod that I have for my insulators for now until I run out.Any time, guy! Also, go to www.hamuniverse.com and on the left side click "Antenna Design". Lots and lots of excellent HF and VHF/UHF antennas, practical, easy-to-build, sound designs. Also, right click and Save As this pdf link, it is an excellent antenna book that will keep you busy. http://www.hamuniverse.com/n4jaantennabook.pdf As I said to another Arfcommer today, these books, a 4:1 current balun, a 1:1 current balun, a roll of 14 ga stranded THHN wire (500' spool), and some end insulators, and you have all you need for a few years of antenna experiments. (Edit: Plus a spool of 550 paracord.) http://www.universal-radio.com/catalog/antsup/4818.html These are excellent, and for my portable antennas, don't chip like porcelain. You can also get these at farm supply / feed & seed stores sold as electric fence insulators. Have fun and see you on the bands! AFM I forgot about the hamuniverse website. I see a "familiar" call sign there.  I just had a contact in AL with my homebrew Yo-yo antenna strung up in my hallway and bedroom. 59 signal too himthrough my unfinished EMCOMM box on battery power.
(I probably should finish it one day.) |
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Quoted:
Is a balun made to "balance" coax? Sorta. It converts BALanced to UNbalanced, hence the name. Coax is unbalanced, it has signal on the center conductor and an outer shield. How does one know which balun to use for what antenna type?[/div][div]I see many different baluns such as 4:1, 9:1? and others.[/div][div]I was looking at building something like this:[/div][div]http://rogertango.com/articleread.aspx?idnumber=34232411 Thanks VRMN Anything other than 1:1 is also going to act as a transformer, to change the impedance. Almost always this is to adapt a higher impedance balanced side to a lower impedance unbalanced side, in order to feed certain antenna designs from typical 50 ohm coax. An easy example would be a folded dipole in the 200 to 300 ohm range, using a 4:1 balun to feed from 50 ohm coax. Selecting a transformer to change impedance is going to depend on what kind of antenna you are feeding with it and what the characteristic impedance of that antenna is. |
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Quoted: Thanks Gamma.Quoted: Is a balun made to "balance" coax? Sorta. It converts BALanced to UNbalanced, hence the name. Coax is unbalanced, it has signal on the center conductor and an outer shield. How does one know which balun to use for what antenna type?[/div][div]I see many different baluns such as 4:1, 9:1? and others.[/div][div]I was looking at building something like this:[/div][div]http://rogertango.com/articleread.aspx?idnumber=34232411 Thanks VRMN Anything other than 1:1 is also going to act as a transformer, to change the impedance. Almost always this is to adapt a higher impedance balanced side to a lower impedance unbalanced side, in order to feed certain antenna designs from typical 50 ohm coax. An easy example would be a folded dipole in the 200 to 300 ohm range, using a 4:1 balun to feed from 50 ohm coax. Selecting a transformer to change impedance is going to depend on what kind of antenna you are feeding with it and what the characteristic impedance of that antenna is. [div] [/div] [div]I noticed that on Big Daddy's EMCOMM box thread, he had an Un-un? installed to his yo yo?[/div] [div]Is this correct?[/div] [div] [/div] [div]Maybe Im just complicating things too much. I had pretty good luck with my multi band dipole but I just couldnt get anything past the east or west coasts.[/div] [div]I could hit Canada and South America but, that was about it. I was however limited to height so that Im sure was a factor.[/div] [div] [/div] [div]Im trying to get the spark back with some new knowledge. [/div] |
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Quoted:
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Thanks Gamma. I noticed that on Big Daddy's EMCOMM box thread, he had an Un-un? installed to his yo yo? Is this correct? Maybe Im just complicating things too much. I had pretty good luck with my multi band dipole but I just couldnt get anything past the east or west coasts. I could hit Canada and South America but, that was about it. I was however limited to height so that Im sure was a factor. Im trying to get the spark back with some new knowledge. An "Unun" is a line isolator... to stop RF from flowing down the outside of the shield on coax. This is useful for example for a ground mounted HF vertical, where the outer shield of the coax becomes part of the ground plane and will have a lot of RF on it. At some point away from the antenna (preferably more than 1/4 wavelength) you put the unun on there to prevent that RF from coming all the way back to the transmitter. If you're looking for DX a low height dipole is a poor choice as they have very little low angle radiation. A vertical with a decent ground plane would do much better. |
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Quoted: A vertical really isnt doable due to my setup.Quoted: Quoted: Thanks Gamma. I noticed that on Big Daddy's EMCOMM box thread, he had an Un-un? installed to his yo yo? Is this correct? Maybe Im just complicating things too much. I had pretty good luck with my multi band dipole but I just couldnt get anything past the east or west coasts. I could hit Canada and South America but, that was about it. I was however limited to height so that Im sure was a factor. Im trying to get the spark back with some new knowledge. An "Unun" is a line isolator... to stop RF from flowing down the outside of the shield on coax. This is useful for example for a ground mounted HF vertical, where the outer shield of the coax becomes part of the ground plane and will have a lot of RF on it. At some point away from the antenna (preferably more than 1/4 wavelength) you put the unun on there to prevent that RF from coming all the way back to the transmitter. If you're looking for DX a low height dipole is a poor choice as they have very little low angle radiation. A vertical with a decent ground plane would do much better. |
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Quoted:
Quoted:
Is a balun made to "balance" coax? How does one know which balun to use for what antenna type? I see many different baluns such as 4:1, 9:1? and others. I was looking at building something like this: Thanks VRMN Did you see that picture of Piccolo on that site? http://logo.cafepress.com/nocache/7/2752247.jpg I believe you are mistaken. I am the man on the right. 
Your mistake flatters me but I am not quite that young.
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When you buy a balun, try to get a CURRENT balun, not a voltage balun. A current balun will help keep RF off the shield. Your antenna will behave much better.
But one place you want a voltage balun is with a "Carolina Windom" that utilizes part of the shield as a "vertical radiator". This antenna uses a "line isolator" 10' down from the balun. This is nothing more than a choke. You can make such a device by using snap on ferrites. For a 66' overall (40 meters on up) Carolina Windom, use 8-10 beads snapped on the coax 10' down from the balun. For an 80 meter version, use 12-15 beads located 20' down from the balun. These beads snapped on immediately below a dipole center insulator would be a "choke balun". Like the Carolina Windom, this will keep RF off the shield... and out of your shack where it can cause all kinds of mischief. |