Please don’t talk down to me or many other of us. I’ve been in this hobby for over 60 years and I know how things worked both then and now.
To answer your question about broadcast, many systems consist of series fed towers. In a practical world a tower presenting zero reactance is about 35 ohms and 50 ohm tower has reactance. Other heights have (generally) higher resistance and reactance. In all these cases an ATU at the tower. base is used to match both the coax and TX output. The other approach is a grounded tower with a unipole (or shunt feed) arrangement. Properly done the feed is tapped for zero reactance and the resistance is somewhere 250 ohms. Others tap for 50 ohms but the reactance is high. These arrangements also require an ATU at the tower base. On HF, the antenna is multiband and uses open wire feeder. Usually this goes straight to the TX which usually has a 300 ohm balanced output. These transmitters are still tube devices and their output networks accommodate the changing load. Sent from my iPad >> On Apr 19, 2020, at 7:39 PM, ab2tc <[email protected]> wrote: > Hi, > > I know nothing about BC transmitters and antennas but in our world of > amateur radio solid state transmitters it is imperative that the > transmission line presents a load close to 50 ohms resistive to the > transmitter. The transmitter doesn't care how this is accomplished as long > as it sees a good match to 50 ohms. The simplest, of course, it to have a > resonant antenna (close to 50 ohms resistive - resonance is no guarantee of > a 50 ohm load) and a good low loss 50 ohm coax transmission line. If the > antenna is far from 50 ohm resistive, a tuner (more correctly called a > matching network) is required somewhere between the antenna and the > transmitter. If the actual loss of the transmission line under the > mismatched condition is not too high, it's perfectly OK to have the tuner > close to the transmitter. If these conditions are not satisfied, the tuner > is best located close to the antenna feed point with the extra cost and > effort that involves. > > AB2TC - Knut > > > > W2xj wrote >> You can get an AT-615B from Array Solutions now and do this. I put 10 in a >> club station for our various wire arrays. They do everything you need. >> >> BTW I disagree about this 50 Ohm antenna thing. In my world of commercial >> high powered broadcasting 30 MHz and under, there are almost never >> resonant, matched 50 ohm arrays. >> >> Sent from my iPad >> >>> On Apr 19, 2020, at 8:41 AM, Richard Thorne < > >> rthorne@ > >> > wrote: >> <snip> > > > > > > -- > Sent from: http://elecraft.365791.n2.nabble.com/ > ______________________________________________________________ > 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]
