Hi Don, Thanks for your explanation. Yes, I can follow you in this reasoning, and totally agree. I was clearly not reading carefully enough earlier posts, and was jumping to conclusions.
Per-Tore / LA7NO On 1 August 2014 03:32, Don Wilhelm <[email protected]> wrote: > P-T, > > No, a conjugate match will assure 100% power transfer. > > Look at it this way - what the conjugate match says is that if you cut a > transmission line at any point, looking one way at that cut point, you will > have some impedance - example is 70 + j20. Now look the other way and the > impedance will be the conjugate match - 70 - j20. That is the condition > that exists. > It also happens to be the condition for maximum power transfer. > > Since that cut can be made at any and all points along the transmission > line - think what would happen if the efficiency at each of those points > (when connected together) were 50% - nothing would get to the antenna. So > we know that 50% is *not* the efficiency of any and all junctions of any > conjugate match. > > Mixing the conjugate match concept with the maximum power transfer theorem > is getting us into confusion - there are 'holes' in that combination. Yes, > they work together, but not seamlessly. > If a generator has an internal impedance of 50 ohms, the maximum power > transfer will be only if the load to that generator is also 50 ohms. That > says nothing about a conjugate match. > > Now to further complicate things, the internal impedance of a generator > has nothing to do with the efficiency of that generator - especially if we > are discussing a PA output stage. Bringing the conjugate match concept > into the internal design of a PA stage is in error - it just does not work > that way. The conjugate match only applies to the output of that amplifier > stage. > > In other words, if we send 10 watts into a feedline (or ATU), all 10 watts > will go to the load (antenna) except for losses in the feedline. > > I am not about to embark on the design and efficiency of a PA stage on > this reflector, so take the conjugate match and maximum power transfer > theorem only to the terminals at the PA stage and all will make sense. > They do not apply to the internals of that stage. > > 73, > Don W3FPR > > On 7/31/2014 7:32 PM, Per-Tore Aasestrand wrote: > >> Hi Don, >> >> On 1 August 2014 01:16, Don Wilhelm <[email protected]> wrote: >> >> If one uses the voltage divider example, yes the maximum efficiency is >> 50%, >> >>> But the output of a PA stage is not a resistor, and the collector load >>> "resistance" is set by the designer to produce the output power desired. >>> >>> I fully agree. >> >> But will not a conjugate match also imply a max efficiency of 50% >> >> P-T >> ______________________________________________________________ >> 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 >> Message delivered to [email protected] >> >> > ______________________________________________________________ > 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 > Message delivered to [email protected] > ______________________________________________________________ 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 Message delivered to [email protected]
