I read the W8JI comments presented in that link on the Elecraft website. I was familiar with Tom's work and comments from emailing with him on this particular subject many years ago.
The one thing that struck me in W8JI's paper is at the end and embodied in Tom's comment that -- "The irony is, moving the balun to the input mostly works only when the balun is not needed!" For those who want a really high efficiency balanced tuner, go to ARRL publications back several years to find a link coupled tuner. With switching between series and parallel tuning, it can handle impedances from very low to very high. The input is DC isolated from the output, and the input can be either unbalanced or balanced. The output can be either balanced or unbalanced depending on where you connect the output tuned circuit. The venerable Johnson Matchbox is an example of a link coupled tuner. The taps onto the output tank circuit were created by the differential capacitor in the output tank circuit - that allowed it to be boxed up into a bandswitchable box without need for connecting the antenna feeders to taps on the tuner coil. That works quite well , but it restricts the range of matching impedances to significantly less than would be obtained by the basic tuner with taps on the inductor. Yes, I do use these tuners, and they are configured for single band use at the antenna - 3 coax feeds for HF and 3 for VHF/UHF give me access to all my antennas The nearest antenna is 200 feet of coax away from the hamshack, and that is why I use tower mounted preamps for VHF/UHF. I will never give up my Matchbox until it is pried from my cold dead hands - I use mine mostly as a test instrument - as bandpass filter as well as an impedance transformation device. After experimentation asnd development, the permanent tuners are designed and installed in the antenna field - I have tuned coax fed antennas for each band from 160 meters through the 432 MHz bands. I use the Matchbox tuner only for experimental antennas until I can develop a permanent and dedicated tuner for any one antenna. OK, those are the advantages - the drawbacks are that that the link coupled tuner arrangement does not lend itself well to bandswitching, but i would suggest it be the tuner of choice for situations where the antenna is used for only a single band - put the tuner on the antenna feedline and tune it to resonance (and minimum SWR) once and be done with the settings. 73, Don W3FPR On 12/8/2011 6:28 PM, Eric Swartz - WA6HHQ, Elecraft wrote: > Hi Ignacy, > > This is a common misconception. (One which I held until recently. :-) It > turns out there is no advantage to placing the balun at the input of the > L-Network tuner. Since one end of the balun is grounded by the input to > the tuner, it is still presented with the same stresses under high SWR > situations. Baluns at the input and output both drive balanced loads > equally well. > > We've now put together a web page describing the impact of placing the > balun at the input or at the output of a L-Network tuner. See: > > http://www.elecraft.com/KAT500/input_versus_output_balun.htm > > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
