In the case of SWBC the matching happens at the TX. Sent from my iPad
> On Jan 6, 2019, at 5:15 PM, K9MA <[email protected]> wrote: > > The really attractive thing about open line, and even window line, is that > its loss is so low you can use it at a very high SWR, and take care of the > matching at the station end. This is especially useful for multi-band > antennas. The famous G5RV, for example, will work just exactly the same fed > with window line and a tuner as it will with the usual matching section. > > 73, > Scott K9MA > >> On 1/6/2019 16:09, W2xj wrote: >> And those broadcast stations generally work within a 2:1 VSWR range. >> >> Sent from my iPad >> >>> On Jan 6, 2019, at 4:51 PM, Bob McGraw K4TAX <[email protected]> wrote: >>> >>> Correct on all points. >>> >>> That is the reason I gave my feedline type, and length and antenna length >>> alone with specific balun type and common mode choke type. Any old ragged >>> combination of chunks of wire and feed line is not assured to work and is >>> largely the reason many hams shy away from balanced feed systems. They >>> tried it once, it didn't work well thus they deemed all balanced feed >>> systems as being "bad". While the facts are, a balanced system correctly >>> installed and with correct lengths, it is the lowest loss feed of any >>> system reasonably available. Which is one of the reasons most short wave >>> broadcast stations used balanced feed systems. >>> >>> 73 >>> >>> Bob, K4TAX >>> >>> >>>> On 1/6/2019 3:40 PM, Don Wilhelm wrote: >>>> All, >>>> >>>> I think a bit of extended study on transmission lines and their impedance >>>> transformation characteristics is in order - refer to any ARRL antenna >>>> book, even those from the 1950 an 1960 era, not much new has been added, >>>> other than baluns. The feedpoint impedance to the transmission line can >>>> vary from quite low to quite high dependent on the frequency, the length >>>> of line, and the load at the far end. It does NOT depend on the >>>> characteristic impedance of the transmission line. The ARRL TLW program >>>> can do a lot of computation for you. >>>> >>>> You may be able to adjust the length of the transmission line so there is >>>> a moderate shack end feedpoint impedance on all bands of interest and be >>>> able to use a good current balun which has either a 1:1 or 4:1 >>>> transformation ratio. You have to measure the transmission line at the >>>> point where you intend to install the balun to be sure which to use. >>>> >>>> Yes, just hanging any balun on any length of parallel feedline connected >>>> to any length of antenna and expecting it to work without problems is just >>>> not going to happen in all but exceptional cases. >>>> How many cases where you see "this antenna works great" do you see any >>>> mention of how long the parallel feedline may be. Most hams simply ignore >>>> that, but it is likely the most important part of how the antenna works >>>> and what type of balun of you need to use. >>>> >>>> Your experience may be very different with the "same" multiband antenna >>>> than your local ham or that in the artic >> ______________________________________________________________ >> 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] > > > -- > Scott K9MA > > [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]
