Most tuner losses occur in the same way as feed line losses - resistive losses in the conductors. In a tuner, that is usually in the inductance. The higher the current, the greater the resistive losses.
That's why high impedance feed lines such as open wire line have typically much less loss than 50 ohm coaxial line. Higher impedance means higher voltages and less current for a given power. (Excepting the use of some "ladder line" that has very small gauge conductors which offset at least some of its advantage). Tuners that must feed very low impedance loads often suffer losses in the inductors due to the high currents required. Some tuners such as the popular T-network type may have more than one combination of settings that will provide a match. One setting can produce much more current and so greater loss than the other. W9CF wrote a Java simulator that lets you see the predicted losses for various conditions. Just twirl the knobs and watch the SWR or let it "auto-tune" for a given load and frequency: http://fermi.la.asu.edu/w9cf/tuner/tuner.html 73, Ron AC7AC -----Original Message----- From: elecraft-boun...@mailman.qth.net [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Matt Murphy Sent: Thursday, April 05, 2012 12:53 PM To: d...@w3fpr.com Cc: Vic K2VCO; elecraft@mailman.qth.net Subject: Re: [Elecraft] K3 power reduction due to high SWR One related question, when speaking of the efficiency of a balanced feedline + balun and tuner, what would be a best/worst case scenario for the loss introduced by the balun+tuner? Would loss vary significantly by frequency for a nonresonant antenna? I'm trying to develop an intuition about the lossiness of the tuner+balun compared to, say, 50' of RG213. I've opted to use a 1:1 balun at the end of 450 ohm ladder line, then a short length of coax into a TenTec 229 tuner. In the informal test that I performed, the homebrew 1:1 balun + coax jumper improved the performance of the antenna compared with connecting it directly to the balanced line connectors on the back of the tuner. 73, Matt NQ6N On Thu, Apr 5, 2012 at 12:23 PM, Don Wilhelm <w3...@embarqmail.com> wrote: > Vic, > > Where was the frequency of the GDO with respect to the band the tuner > was set to? If it was below the band of interest, I would expect > something like that - the T-Network is a high pass filter. > > 73, > Don W3FPR > > > On 4/5/2012 12:28 PM, Vic K2VCO wrote: > > Speaking of balanced lines and tuners, I recently did an experiment > > that > surprised me. > > > > I have a dipole fed with 600-ohm open-wire line (and some window > > line > indoors). I usually > > tune it with a Johnson Matchbox, a fully balanced link-coupled tuner. > > > > I was lucky enough to get my hands on a massive, high-quality > > edge-wound > rotary inductor > > in a well-made aluminum enclosure. So I built a high-power T-network > tuner with it. I > > purchased a good (and expensive) 1:1 balun designed for use after a > tuner from DX > > Engineering, and compared the T-net + balun to the Matchbox. I > > didn't > notice any > > difference in the strength of received signals between the tuners. > > > > But here is the surprising part: I expected that the Matchbox would > provide better > > balance, which would reduce radiation and pickup from the feedline. > > To > test this, I > > coupled a grid-dip oscillator to the feedline about 20 feet from the > tuner. > > > > To my great surprise, the signal from the oscillator was much weaker > with the T-network + > > balun than with the Matchbox! > > > > Signals the same, 'noise' weaker. So much for the need for 'truly > balanced' tuners! > > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net Please help support this email > list: http://www.qsl.net/donate.html > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
