Performance of baluns.
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Performance of baluns.
 
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Hello all,
Have noticed over the recent years that current baluns are used in places where the load/source Z is not purely resistive (OK will allow a little reactance) , example - an incoming transmission line that looks like R +j (quite a lot) goes to a balun then the to an ATU then to the TX. I was brought up to understand that in such a case, outgoing transmitter power would NOT result in equal and 180 degrees out of phase currents on the transmision line wires. i.e. the antenna would see an "unbalanced source" I was always told to put the balun between the Tx and the ATU, and to make sure that the ATU presented the balun with a R +/- j0 load , or simply put was "tuned up". (Loved those swinging links). I appreciate that there are a lot of "but ifs", but was Teacher right in the fundamentals? If so, it might go some way to explain why some antennas that are looking for a balanced feed are misbehaved. 73 Geoff GM4ESD _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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The current balun can be readily demonstrated to provide equal and opposite
currents to highly unbalanced loads. A simple test is to connect a balun to a load consisting of a 50 ohm resistor connected to a common or ground place and similarly a 100 ohm resistor. Measurement of the r-f voltage across the resistors will show that equal currents are being forced through each as the voltage across the 100 ohm resistor will be twice that of the 50 ohm resistor. Roy Lewallen W7EL and Walt Maxwell W2DU have both discussed this test and Roy described a test fixture for demonstration. I have built the fixture and carried out the test with a simple W2DU bead balun and found almost perfect balance with equal currents being delivered to unequal load resistances. Simple 1:1 current or choke baluns such as the bead baluns are relatively insensitive to load impedance. I use them to transition from ladderline feeding multiband balanced antenna loads to coax to enter the shack to the tuners. The load seen by the baluns varies widely with band as would be expected. The Elecraft 4:1 balun is unique in its design and is able to provide an approximate 4:1 transformation over a wide range of frequencies and load impedances. Thus there is little need to restrict its connection to the input of a tuning unit. Teacher wasn't wrong, Geoffrey - it has just been a long time! 73, George W5YR (58 years a ham the end of this month) Fairview, TX [hidden email] http://www.w5yr.com ----- Original Message ----- From: "Geoffrey Mackenzie-Kennedy" <[hidden email]> To: <[hidden email]> Cc: "Elecraft Discussion List" <[hidden email]> Sent: Friday, August 06, 2004 10:47 AM Subject: [Elecraft] Performance of baluns. Hello all, Have noticed over the recent years that current baluns are used in places where the load/source Z is not purely resistive (OK will allow a little reactance) , example - an incoming transmission line that looks like R +j (quite a lot) goes to a balun then the to an ATU then to the TX. I was brought up to understand that in such a case, outgoing transmitter power would NOT result in equal and 180 degrees out of phase currents on the transmision line wires. i.e. the antenna would see an "unbalanced source" I was always told to put the balun between the Tx and the ATU, and to make sure that the ATU presented the balun with a R +/- j0 load , or simply put was "tuned up". (Loved those swinging links). I appreciate that there are a lot of "but ifs", but was Teacher right in the fundamentals? If so, it might go some way to explain why some antennas that are looking for a balanced feed are misbehaved. 73 Geoff GM4ESD _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Geoffrey Mackenzie-Kennedy-2
On Fri, 6 Aug 2004 16:47:57 +0100, Geoffrey Mackenzie-Kennedy wrote:
>Have noticed over the recent years that current baluns are used in places > where the load/source Z is not purely resistive (OK will allow a little reactance) , >example - an incoming transmission line that looks like R +j (quite a lot) goes >to a balun then the to an ATU then to the TX. There are some detailed discussions about baluns and their use on W8JI's website. Do a google search. Tom makes the point that it is the common mode impedance of the transmission line that must form a voltage divider with the choke balun, and that if that impedance is too high (as it would be when it is close to an odd multiple of quarter wavelengths), the balun must be a very high impedance to be effective. DX Engineering sells a nice selection of W8JI-designed baluns. I have several models and have opened some of them up to look at them (the ones that I can take apart with screws). These are the best commercial baluns I have seen, and nothing else is close. One of their characteristics is that the ferrites they use are "beefy" enough to provide that higher impedance (and to provide a higher power rating without saturation or overheating). Jim Brown K9YC _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Re: Performance of baluns.
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In reply to this post by George, W5YR
Hello George,
Many thanks for your comments which I shall have to read later - Daughter + Dog arrived about 30 minutes ago. First licence late 1946 - a hunted DX morsel - but manners were better then !! 73 Geoff GM4ESD ----- Original Message ----- From: "George, W5YR" <[hidden email]> To: "Geoffrey Mackenzie-Kennedy" <[hidden email]> Cc: "Elecraft Discussion List" <[hidden email]> Sent: Friday, August 06, 2004 5:19 PM Subject: Re: [Elecraft] Performance of baluns. > The current balun can be readily demonstrated to provide equal and opposite > currents to highly unbalanced loads. A simple test is to connect a balun to > a load consisting of a 50 ohm resistor connected to a common or ground place > and similarly a 100 ohm resistor. Measurement of the r-f voltage across the > resistors will show that equal currents are being forced through each as the > voltage across the 100 ohm resistor will be twice that of the 50 ohm > resistor. > > Roy Lewallen W7EL and Walt Maxwell W2DU have both discussed this test and > Roy described a test fixture for demonstration. I have built the fixture and > carried out the test with a simple W2DU bead balun and found almost perfect > balance with equal currents being delivered to unequal load resistances. > > Simple 1:1 current or choke baluns such as the bead baluns are relatively > insensitive to load impedance. I use them to transition from ladderline > feeding multiband balanced antenna loads to coax to enter the shack to the > tuners. The load seen by the baluns varies widely with band as would be > expected. > > The Elecraft 4:1 balun is unique in its design and is able to provide an > approximate 4:1 transformation over a wide range of frequencies and load > impedances. Thus there is little need to restrict its connection to the > input of a tuning unit. > > Teacher wasn't wrong, Geoffrey - it has just been a long time! > > 73, George W5YR (58 years a ham the end of this month) > Fairview, TX > [hidden email] > http://www.w5yr.com > > > > ----- Original Message ----- > From: "Geoffrey Mackenzie-Kennedy" <[hidden email]> > To: <[hidden email]> > Cc: "Elecraft Discussion List" <[hidden email]> > Sent: Friday, August 06, 2004 10:47 AM > Subject: [Elecraft] Performance of baluns. _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Re: Performance of baluns.
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In reply to this post by Jim Brown-10
Hello Jim,
Many thanks for your comments and the information about W8JI. Will take a look at his website. Sorry that this is brief, but will study your comments when the local QRM abates. 73, Geoff GM4ESD ----- Original Message ----- From: "Jim Brown" <[hidden email]> To: "Geoff Mackenzie-Kennedy GM4ESD" <[hidden email]> Cc: "Elecraft Discussion List" <[hidden email]> Sent: Friday, August 06, 2004 5:28 PM Subject: Re: [Elecraft] Performance of baluns. > On Fri, 6 Aug 2004 16:47:57 +0100, Geoffrey Mackenzie-Kennedy wrote: > > >Have noticed over the recent years that current baluns are used in places > > where the load/source Z is not purely resistive (OK will allow a little reactance) , > >example - an incoming transmission line that looks like R +j (quite a lot) goes > >to a balun then the to an ATU then to the TX. > > There are some detailed discussions about baluns and their use on W8JI's > website. _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Re: Performance of baluns.
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In reply to this post by Geoffrey Mackenzie-Kennedy-2
Hi Bob,
Many thanks for comments - much appreciated. When I got my first licence in 1946, not in the UK, ATUs were usually big beasts with hefty plug-in coils, widespaced air variables, swinging links and lots of big insulators. Usually the ATU was at some distance from the Tx and its pi network output ' tank ', and both Tx and ATU homebrewed (also the antenna of course). If you were very lucky, you used coax between the ATU and Tx, but to most of us in the southern hemisphere at that time, coax was a word only and never seen. The swinging (or fixed) link of the ATU presented a balanced load to the Tx - not like a link at the grounded end of a L-C tank. And that's where the balun came in, if you were fussy. It is the ' old habit ' problem I am afraid Bob. I hope that your K2 is behaving. My K2/100 worked right off, thanks to the good engineering at Elecraft. First ' commercial ' rig ever owned here. All the best, Geoff GM4ESD ----- Original Message ----- From: [hidden email] To: [hidden email] Sent: Friday, August 06, 2004 8:01 PM Subject: Re: [Elecraft] Performance of baluns. Hi Geoff, Not really sure how you could put a balun or indeed what it's use may be between a TX and ATU as all of these devices that have been produced for quite a long time now are for unbalaced coaxial lines. You would have to go back long before you got your licence and myself for that matter to the 1940's to 1950's to see otherwise for amateur equipment. Military equipment may be a different story for which I have no experience. _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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