> If you do modeling, please be aware that the pro's know that all modeling > programs on the planet terribly underestimate ground losses.
Another trap to avoid is thinking that (all other things being equal), more radials on a vertical will somehow result in better low-angle radiation. Well, it does, but only to the extent that the radials are also improving the entire vertical field strength profile through a minimization of ground loss. The radials are not improving low angle radiation independently without improving overall radiation efficiency. Medium and far-field ground conductivity rules when wanting efficient low-angle radiation from a vertical (or vertical dipole) at angles lower than about ten degrees above the horizon. The mid to far field conductivity and geography also applies to horizontal antennas atop a tower, for example. The best real-world example I've ever seen of this is W4ZV's study of the W3CRA site. A few pictures and graphs are worth ten thousand words. Same general rules apply to 160m/80m four-square arrays. It's just that to get directivity and low-angles from a horizontal antenna up in the air on those bands requires some pretty darn tall mounting structures (especially 160m) that are beyond the capabilities of most station owners. So, four-squares on the lower bands offer a good compromise. I've lived with verticals for the last fifteen years and it's only been the last two years that I've had a horizontal wire antenna up for operation on 80m-10m. Unless there's no way of getting wire up in the air -- or unless I were immediately adjacent to salt water, an all-band vertical would be an antenna of last choice for me (perhaps small loops would be dead last!). I've also come to this conclusion for my own operating if I've got just one all-band (80m-10m) antenna: (1) Flat top dipole at 0.15 - 0.20 wavelength high on 80m; (2) Open feeders; (3) and Remote ATU. Justification: On 80M, I'm mostly interested in regional 75m contacts and DX to a much lesser extent. On 40m-10m, my interest in lower angles increases as frequency increases. On 40m and above this is pretty much satisfied. Open feeder length chosen so that the ATU sees a reasonable (under 1K Z, but more than 25 ohms on all bands, all operating frequencies), high-quality open feeder spacers to minimize ATU changes and line loss with precipitation. Paul, W9AC ______________________________________________________________ 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
