+++++++++++++++++++ Reply-To: From: "Ron D' Eau Claire" To: Subject: RE: [Elecraft] EC! competition: Balanced auto ATU Date: Fri, 8 Feb 2002 10:01:50 -0800 > An auto ATU for balanced line would be a great project. > Paul M0CDP I'd second that, but there's more at stake for most of us than getting a balanced output. The main interest in balanced feedlines for me and most ops I know is to be able to run very high SWR's on the feedline with multiband doublets, G5RV's, etc., and not suffer excessive losses. That means very high SWR's on the feedline. High SWR's mean that the ATU has to deal with very large impedance transformations efficiently, and it has to be able to handle very high voltages when it sees a high impedance at the feeder or very high currents when it sees a low impedance at the feeders. Ron AC7AC K2 # 1289 ++++++++++++++++++ Date: Fri, 08 Feb 2002 10:17:29 -0800 From: Vic Rosenthal Organization: Transparent Software To: Elecraft Subject: Re: [Elecraft] EC! competition: Balanced auto ATU Ron D' Eau Claire wrote: > > The main interest in balanced feedlines for me and most ops I know is to be -- snip -- Absolutely right. Which means that a tuner with a built-in balun on the output side won't cut it! 73, Vic, K2VCO Fresno CA ++++++++++++++ Reply-To: "Don Wilhelm" From: "Don Wilhelm" To: "Jonathan Taylor, K1RFD" , "Elecraft" Subject: Re: [Elecraft] EC! competition: Balanced auto ATU Date: Fri, 8 Feb 2002 19:05:16 -0500 Gang, Putting the balun ahead of the tuner and floating the tuner will not result in a balanced output!!! The result will be a balanced input to the tuner (due to the balun), but because the inherently unbalanced tuner design will not present the same impedance for each leg of the transmission line that follows it, the balance will be upset right at the output of the tuner. Sorry folks, we just can't fool mother nature. I realize that there have been several tuner designs that use this principle, and some report good balance, but I often wonder what the test conditions where when the balance measurements were made. 73, Don Wilhelm - Wake Forest, NC W3FPR home page: http://www.qsl.net/w3fpr/ QRP-L # 485 K2 SN 0020 mailto: w3fpr@arrl.net ----- Original Message ----- > One technique is to put the balun *ahead* of the ATU, and "float" the ATU. > That way, the balun always sees the same impedance, yet the output is > balanced. +++++++++++++++++++++ From: "Jerry T Dowell" To: "Don Wilhelm" , "Jonathan Taylor, K1RFD" , "Elecraft" Subject: Re: [Elecraft] EC! competition: Balanced auto ATU Date: Fri, 8 Feb 2002 17:02:13 -0800 Kirchoff's Laws say you are wrong, Don. See Al Roehm's article "Some Additional Aspects of the Balun Problem" , on page 172 of "The ARRL Antenna Compendium", Vol. 2, or the corresponding QST article. A single-ended LC network will do just fine feeding a balanced line if the network itself is fed with a good current balun. The currents on the balanced line will be equal and opposite, thanks to Kirchoff (and Mother Nature). Jerry, AI6L ----- Original Message ----- From: Don Wilhelm To: Jonathan Taylor, K1RFD ; Elecraft Sent: Friday, February 08, 2002 4:05 PM Subject: Re: [Elecraft] EC! competition: Balanced auto ATU > Gang, > > Putting the balun ahead of the tuner and floating the tuner will not result > in a balanced output!!! ++++++++++++++++++++ Date: Sat, 09 Feb 2002 08:31:42 -0800 From: Vic Rosenthal Organization: Transparent Software To: Elecraft Subject: Re: [Elecraft] EC! competition: Balanced auto ATU Don Wilhelm wrote: > > Putting the balun ahead of the tuner and floating the tuner will not result > in a balanced output!!! > The result will be a balanced input to the tuner (due to the balun), but > because the inherently unbalanced tuner design will not present the same > impedance for each leg of the transmission line that follows it, the balance > will be upset right at the output of the tuner. The tuner circuit does not have to be balanced, but it needs to be symetrical with respect to ground. For example, a simple PI or T circuit can be used as long as the components are not close to a metal chassis. 73, Vic, K2VCO Fresno CA ++++++++++++++++++