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#1
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tech. Q. about balun
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I have a rookie question related to baluns. In what sense is said that a coax. cable is an unbalance line an antenna is a balanced system a twin cable is a balanced line ? Of course a second question would be how does the balun interface a balanced and an unbalanced system? Cordially, Nic. http://www.csd.uwo.ca/~nic -----= Posted via Newsfeed.Com, Uncensored Usenet News =----- http://www.newsfeed.com - The #1 Newsgroup Service in the World! -----== 100,000 Groups! - 19 Servers! - Unlimited Download! =----- |
#2
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In article ,
"Nicolae Santean" wrote: I have a rookie question related to baluns. In what sense is said that a coax cable is an unbalance line The outer shield is ground and the inner carries the signal asymmetrically. an antenna is a balanced system a twin cable is a balanced line ? If you have a balanced antenna like a dipole then yes. Of course a second question would be how does the balun interface a balanced and an unbalanced system? By shifting the ground reference, splitting and phasing the signal to be differential going from unbalanced to balanced and performing the reverse actions to go the other way. -- Telamon Ventura, California |
#3
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NS,
FEEDLINES: A Coax Cable is an Unbalanced Line (Single Wire and Ground Shield). Balanced Lines are like Ladder Line and TV type Twin Lead (Dual Wires). ANTENNAS: Balance 'type' Antennas: Dipoles, Loops, Rhombic, Inverted "V", etc. Unbalanced 'type' Antennas: Long Wire, Zep, Random Wire, Inverted "L", Sloper, etc. MATCHING TRANSFORMERS / BALUNS / MLBs: * Balun Reading List ( Long ) http://groups.yahoo.com/group/Shortw...na/message/337 A Matching Transformer can be used to 'connect' an Antenna Element to a Feed Line. A "Balun" is specific type of 'matching transformer' that is used to 'connect' a Balanced Antenna to an Unbalanced Feed-Line. Another specific type of 'matching transformer' that is used to 'connect' an Unbalanced Antenna to an Unbalanced Feed-Line is called a "Magnetic Long Wire Balun" (MLB). The MLB is often used with the common Random Wire Antennas and Coax Cable Feed-Lines used by most Shortwave Listeners (SWLs). * Magnetic Longwire Balun (MLB) - Build Your Own "DIY" http://groups.yahoo.com/group/Shortw...na/message/177 http://groups.yahoo.com/group/Shortw...na/message/466 http://groups.yahoo.com/group/Shortw...na/message/467 READ these three Links 'presented' by John Doty: [ Hosted by The Association of North American Radio Clubs "ANARC".] * Longwire Impedance Matching. {Check-Out the Graphs} http://www.anarc.org/naswa/badx/ante..._longwire.html Actually, a fixed Matching Transformer can dramatically reduce the wild swings in Antenna Efficiency that a Coax Fed Wire Antenna exhibits. * Grounding is the KEY to Good Reception http://www.anarc.org/naswa/badx/antennas/grounding.html * Low Noise Antenna Connection http://www.anarc.org/naswa/badx/ante...e_antenna.html iane ~ RHF .. Some Say: On A Clear Day You Can See Forever. http://groups.yahoo.com/group/SWL-AM...na/message/502 I BELIEVE: On A Clear Night... You Can Hear Forever and Beyond, The Beyond ! .. .. = = = "Nicolae Santean" wrote in message = = = ... *** post for FREE via your newsreader at post.newsfeed.com *** I have a rookie question related to baluns. In what sense is said that a coax. cable is an unbalance line an antenna is a balanced system a twin cable is a balanced line ? Of course a second question would be how does the balun interface a balanced and an unbalanced system? Cordially, Nic. http://www.csd.uwo.ca/~nic -----= Posted via Newsfeed.Com, Uncensored Usenet News =----- http://www.newsfeed.com - The #1 Newsgroup Service in the World! -----== 100,000 Groups! - 19 Servers! - Unlimited Download! =----- .. |
#4
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Okay, I think we should take it slowly (probably I have less knowledge than you think). Assume we talk about a receiver's antenna. A dipole antenna is said to be a "balanced" system. To what apply the qualifier "balanced"? What is "balanced" in the dipole? RF current distribution (should be along this line)? Then, about the feed lines. If an arbitrary cable is impedance-matched to the antenna and is not grounded, it seems that the current distribution mimics that of the antenna. Is grounding which makes a difference ? What can be "unbalanced" in a feed line? I am interested in understanding the concept, really. Intuitively, when something is qualified as "unbalanced", it refers to some sort of asymmetry in characteristics. What specifically are these characteristics and why/where are they asymmetric? So really, the question stands up. Please be more elementary in explanation. Thanks a lot. Cordially, Nic. http://www.csd.uwo.ca/~nic "Nicolae Santean" wrote in message ... In what sense is said that a coax. cable is an unbalance line an antenna is a balanced system a twin cable is a balanced line ? Of course a second question would be how does the balun interface a balanced and an unbalanced system? -----= Posted via Newsfeed.Com, Uncensored Usenet News =----- http://www.newsfeed.com - The #1 Newsgroup Service in the World! -----== 100,000 Groups! - 19 Servers! - Unlimited Download! =----- |
#5
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Nicolae Santean wrote:
So really, the question stands up. Please be more elementary in explanation. Thanks a lot. An electrical generator is most efficient when the load impedance(1) is the same as the generator impedance. That is when it can deliver the most power. In a receiver setup, the antenna is the generator(2) and the leadin cable + radio is the load. When the two impedances are matched, as above, the maximum amount of energy can be transfered from the antenna to the radio. The leadin coax + radio has a set impedance, as does the antenna(3). The 'balun' or 'unun' is the means used to match these two items via a ratio of windings. Sometimes the balun is used directly between a tuner circuit and antenna..usually in a transmitter setup. The rules for receiving and transmitting antennas are very very similar but as a rough rule of thumb, receiving antennas are more forgiving of design errors. Lots of good sites out there. a quick search will get you some more results. http://www.qsl.net/aa5tb/balun.html http://home.att.net/~DickWD8CEB/Balun.html (1) Impedance is opposition to current flow, not necessarily of the resistive kind only. (2) A wire being crossed by radio waves generates a small electrical signal. (3) A normal, fixed length of wire as opposed to the multi tapped varieties used by those with large antenna farms.. mike mike |
#6
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Thank you for the detailed answer. Below are my comments. An electrical generator is most efficient when the load impedance(1) is the same as the generator impedance. That is when it can deliver the most power. ...... However, I was not talking about impedance matching - which is the job of a transmatch(tuner) - but rather about coupling a balanced and an unbalanced segment. Some people - like myself till recently - confuse the impedance matching with the balun coupling. I agree that a balun can sometime do both, but its main purpose is to couple balanced and unbalanced segments. The leadin coax + radio has a set impedance, as does the antenna(3). The 'balun' or 'unun' is the means used to match these two items via a ratio of windings. Nope. There are baluns (1:1) which are not designed for impedance matching. So, I made some research and I got at least a partial understanding : In a dipole, the electrical potential swings symmetrically above(+) and below(-) the "ground level"( 0 ) - that's why is called a "balanced" system. Both poles of a dipole are "hot", in the sense that they generate/receive useful RF signal - of course out of phase. By contrary, a coax has the shield set to 0 potential (grounded) and only the inner wire is "hot" (carries signal). That is why is called an "unbalanced" line. If a coax is used to feed the antenna then the coax has only one "hot" wire (the inner one). The outer shield is "grounded", hence is "set to 0". If a balun is not used to couple the antenna with the coax, then one pole becomes RF inert, since is grounded by the coax. In this case, the dipole antenna becomes a poor inverted L antenna, since only one pole acts as an antenna. In case that the coax is not grounded, then it is equally bad : the feed line becomes part of the antenna and it degrades its performance. The purpose of a balun is to change the phase of the currents delivered by the dipole such that it creates an additive effect and feed the inner wire of the coax with added signal from both poles. So basically, the balun "collects" the signal from both poles, adds them up and pump them through the inner wire of the coax. It does so through a transformer coupler. For example, if the dipole is polarized (+x volts, -x volts) , then the balun feeds the coax with (0 volts, +2x volts). As a side effect, the balun isolates the antenna and the line such that the line does not influence the operation of the antenna. Please keep me honest - tell me whether I got it right. Yours cordially, Nic. http://www.csd.uwo.ca/~nic -----= Posted via Newsfeed.Com, Uncensored Usenet News =----- http://www.newsfeed.com - The #1 Newsgroup Service in the World! -----== 100,000 Groups! - 19 Servers! - Unlimited Download! =----- |
#7
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This was a good explanation actually. It just took me time to understand it. Thanks, Nic. By shifting the ground reference, splitting and phasing the signal to be differential going from unbalanced to balanced and performing the reverse actions to go the other way. -- Telamon Ventura, California -----= Posted via Newsfeed.Com, Uncensored Usenet News =----- http://www.newsfeed.com - The #1 Newsgroup Service in the World! -----== 100,000 Groups! - 19 Servers! - Unlimited Download! =----- |
#8
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NS,
"Please keep me honest - tell me whether I got it right." Yes - You Got it Right. For a Dipole (Balanced) and a Coax Cable (unbalanced) set-up with a Matching Transformer (Balun) between them. Your basic description of a Coax Cable would also apply to a Single Wire Antenna like a Longwire or Random Wire which is an Unbalance Antenna. So then the Matching Transformer becomes a "Un-Un". Keep-Oon Your Quest for Knowledge ~ RHF .. .. = = = "Nicolae Santean" wrote in message = = = ... *** post for FREE via your newsreader at post.newsfeed.com *** Thank you for the detailed answer. Below are my comments. An electrical generator is most efficient when the load impedance(1) is the same as the generator impedance. That is when it can deliver the most power. ...... However, I was not talking about impedance matching - which is the job of a transmatch(tuner) - but rather about coupling a balanced and an unbalanced segment. Some people - like myself till recently - confuse the impedance matching with the balun coupling. I agree that a balun can sometime do both, but its main purpose is to couple balanced and unbalanced segments. The leadin coax + radio has a set impedance, as does the antenna(3). The 'balun' or 'unun' is the means used to match these two items via a ratio of windings. Nope. There are baluns (1:1) which are not designed for impedance matching. So, I made some research and I got at least a partial understanding : In a dipole, the electrical potential swings symmetrically above(+) and below(-) the "ground level"( 0 ) - that's why is called a "balanced" system. Both poles of a dipole are "hot", in the sense that they generate/receive useful RF signal - of course out of phase. By contrary, a coax has the shield set to 0 potential (grounded) and only the inner wire is "hot" (carries signal). That is why is called an "unbalanced" line. If a coax is used to feed the antenna then the coax has only one "hot" wire (the inner one). The outer shield is "grounded", hence is "set to 0". If a balun is not used to couple the antenna with the coax, then one pole becomes RF inert, since is grounded by the coax. In this case, the dipole antenna becomes a poor inverted L antenna, since only one pole acts as an antenna. In case that the coax is not grounded, then it is equally bad : the feed line becomes part of the antenna and it degrades its performance. The purpose of a balun is to change the phase of the currents delivered by the dipole such that it creates an additive effect and feed the inner wire of the coax with added signal from both poles. So basically, the balun "collects" the signal from both poles, adds them up and pump them through the inner wire of the coax. It does so through a transformer coupler. For example, if the dipole is polarized (+x volts, -x volts) , then the balun feeds the coax with (0 volts, +2x volts). As a side effect, the balun isolates the antenna and the line such that the line does not influence the operation of the antenna. Please keep me honest - tell me whether I got it right. Yours cordially, Nic. http://www.csd.uwo.ca/~nic -----= Posted via Newsfeed.Com, Uncensored Usenet News =----- http://www.newsfeed.com - The #1 Newsgroup Service in the World! -----== 100,000 Groups! - 19 Servers! - Unlimited Download! =----- |
#9
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In article ,
"Nicolae Santean" wrote: *** post for FREE via your newsreader at post.newsfeed.com *** Thank you for the detailed answer. Below are my comments. An electrical generator is most efficient when the load impedance(1) is the same as the generator impedance. That is when it can deliver the most power. ...... However, I was not talking about impedance matching - which is the job of a transmatch(tuner) - but rather about coupling a balanced and an unbalanced segment. Some people - like myself till recently - confuse the impedance matching with the balun coupling. I agree that a balun can sometime do both, but its main purpose is to couple balanced and unbalanced segments. The leadin coax + radio has a set impedance, as does the antenna(3). The 'balun' or 'unun' is the means used to match these two items via a ratio of windings. Nope. There are baluns (1:1) which are not designed for impedance matching. So, I made some research and I got at least a partial understanding : In a dipole, the electrical potential swings symmetrically above(+) and below(-) the "ground level"( 0 ) - that's why is called a "balanced" system. Both poles of a dipole are "hot", in the sense that they generate/receive useful RF signal - of course out of phase. By contrary, a coax has the shield set to 0 potential (grounded) and only the inner wire is "hot" (carries signal). That is why is called an "unbalanced" line. If a coax is used to feed the antenna then the coax has only one "hot" wire (the inner one). The outer shield is "grounded", hence is "set to 0". If a balun is not used to couple the antenna with the coax, then one pole becomes RF inert, since is grounded by the coax. In this case, the dipole antenna becomes a poor inverted L antenna, since only one pole acts as an antenna. In case that the coax is not grounded, then it is equally bad : the feed line becomes part of the antenna and it degrades its performance. The purpose of a balun is to change the phase of the currents delivered by the dipole such that it creates an additive effect and feed the inner wire of the coax with added signal from both poles. So basically, the balun "collects" the signal from both poles, adds them up and pump them through the inner wire of the coax. It does so through a transformer coupler. For example, if the dipole is polarized (+x volts, -x volts) , then the balun feeds the coax with (0 volts, +2x volts). As a side effect, the balun isolates the antenna and the line such that the line does not influence the operation of the antenna. Please keep me honest - tell me whether I got it right. Yes I would say you got it right. -- Telamon Ventura, California |
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