When I first put up my vertical, I only had 40 and 20 meters and mounted them on the opposite of my house from the current feed point location, that is, in between and close to the rain gutter and the metal chimney liner. The feed point resistance on 40 was as expected but the feed point resistance on 20 was about 1/3 of what I expected. Moving the center parts and feed point to the opposite side of the house gave feedpoint impedances as expected. I have no idea if the chimney liner is grounded or not.
I haven't modeled the antenna but I still know how to calculate radiation restiances. Back in the day "when I had hair on top of my head) I was an antenna designer for Collins and for Hy-Gain and a consultant afterwards. Dunc, W5DC Byron Servies wrote: > On Dec 14, 2009, at 12:45 PM, Geoffrey Mackenzie-Kennedy wrote: > > >> While planning your antenna farm, have you considered using an antenna >> modelling program such as EZNEC which could be of great help to you. A free >> version comes with the ARRL Antenna Handbook. >> > > This is the approach I am taking, though I ended up buying EZNEC+ as I have a > lot of architectural metal in my 3-story town home over the Santa Cruz small > craft harbor. The first story is also stucco, which has a bunch of wire in > it as well, as are the other nearby homes in my complex. > > My goals are to try and determine why the placement of my current wire > dipoles is so poor, and then to see if I can model something that will have > theoretically better performance before I go through the effort of > constructing and hanging my next low-visibility antenna(s). > > So far, just looking at the plots as I add more of the large bits of metal in > my home to the model has been instructive. > > Byron KI6NUL > p.s. One of the first things in the EZNEC instructions is a word from the > author about how amateurs with limited space often wonder why their 3 > antennas do not work well, and he points out they really have 1 antenna with > 3 feed points due to their spacing. > ______________________________________________________________ > 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 > > ______________________________________________________________ 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
