Let me add that even a quarter wave vertical is rarely a perfect match. The 50 ohm point is almost never the same as the j0 point. HF broadcasters don’t even try for a match. Typically open wire line is used and the match is achieved at the transmitter output network. They pump up to 500KW into VSWRs over 2:1.
Sent from my iPad > On Mar 31, 2019, at 6:03 PM, Fred Jensen <k6...@foothill.net> wrote: > > I also disagree. AM broadcast verticals are designed to achieve a desired > pattern and main lobe elevation angle. Over flat ground, 225 degrees will > optimize the ground wave coverage. However, higher powered stations will > then suffer from self-interference at the coverage edges because the sky wave > and ground wave interfere. It's common to shorten the antenna a bit to > perhaps 195 degrees or so which tends to reduce the self-interference. Once > the pattern and main lobe angle have been defined, the feed point is matched > to the transmission line with an appropriate network. Neither 225 degrees > [5/8 wave] nor 195 degrees are resonant lengths and both require a matching > network. > > Many hams do not have the luxury of resonant antennas on every band. It > seems perfectly reasonable to employ some sort of matching network to match > the feed point to the coax on bands where it is not resonant AND/OR does not > present a 50 ohm load to the coax and needing to do so does not imply there's > something wrong with the antenna. > > 73, > Fred ["Skip"] K6DGW > Sparks NV DM09dn > Washoe County > >> On 3/31/2019 9:44 AM, W2xj wrote: >> I would disagree. Most high power commercial operations use non-resonant >> mismatched antennas. Typically there is either a tuner at the antenna or >> open wire is used. >> >> Sent from my iPad >> >>> On Mar 31, 2019, at 12:13 PM, Ken G Kopp <kengk...@gmail.com> wrote: >>> >>> If an antenna is showing a VSVR of 3:1, something about the situation >>> is wrong, and most likely it's -not- the antenna. Fix the problem … feed >>> the antenna power where it's resonant, assuming the antenna is actually >>> resonant on the amateur band of interest. Expecting a tuner to compensate >>> for a problem external to an antenna is unreasonable, IMO >>> >>> 73! >>> >>> Ken - K0PP >>> > > ______________________________________________________________ > 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
