An array of dipoles are common for high power international broadcast stations. They accept a VSWR of about 2:1 from aprox 20 DB gain curtain arrays They almost always use open wire line. It’s mostly about TX output matching.
Sent from my iPad > On Jan 13, 2019, at 9:40 PM, Barry <[email protected]> wrote: > > Don et al, > I sense this discussion is targeting the use of a dipole on a single band. > What is being missed is that many of us use a dipole cut for for one band and > use it for the bands above. What we see are high SWRs on all of the higher > frequency bands. We use balanced feeds, open wire or ladder line, as far as > we can before we transition to coax. That transition is a good current balun. > What this does is control losses due to high SWR and keeps RF currents off > the outside of the coax shield. What has been said in previous notes might be > true, but they will prevent or make use of balanced feeders quite difficult. > > An 80 meter dipole used on 40 or 20, for example, is a pretty good > antenna. However, it begs to be fed with open wire or equal. That means no > balun can be used at the antenna feed point. The exception is to use very > expensive coax. :-) > > 73, > Barry > K3NDM > > ------ Original Message ------ > From: "Don Wilhelm" <[email protected]> > To: [email protected] > Sent: 1/13/2019 6:59:18 PM > Subject: Re: [Elecraft] Slightly Unbalanced dipole? > >> Al, >> >> If not placed at the antenna feedpoint (up at the antenna), then the >> feedline may radiate due to common mode current. >> For feedlines using parallel conductors, the problem is not as bad if the >> feedline exits at right angles from the radiator for at least a half >> wavelength. In that case, the common mode choke can be placed at the >> junction of the parallel line and coax. >> >> In all cases of a radiator fed with coax, a good common mode choke at the >> radiator feedpoint is necessary. Even though the RF on the inside of the >> coax is balanced, when the coax reaches the radiator, the side of the >> antenna connected to the coax shield sees two paths. One is the side of the >> radiator, and the other is the outside of the coax braid - it will dutifully >> split to follow both paths depending on the impedance of each one. A good >> common mode choke will prevent the RF current from seeing the coax shield as >> another conductor. >> >> A similar situation exists at the transition between parallel feedline and >> coax. >> >> 73, >> Don W3FPR >> >> >> On 1/13/2019 6:42 PM, Al Lorona wrote: > ______________________________________________________________ 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]
