15 ohms miscellaneous in series with 32 ohm radiation resistance, only 3%? Don't you mean 30%?
What were the lengths of the elevated radials and how many? 73, Guy. On Mon, Dec 20, 2010 at 8:27 PM, Don Wilhelm <[email protected]> wrote: > Dave, > > If you read the radial tuning procedure in Low-Band DXing, you will find > that it "all comes out in the wash". Yes, your statements are correct, > and in fact that is how I did mine. Although I did not resonate my > vertical monopole against any ground plane - I simply cut the lengths to > what was stated in the article, and then cut each radial to resonate > with that particular length of the "monopole". If the result was > slightly "off-center fed", so be it, the impedance and the resonance > point obtained were a good match for 50 ohm coax, and I left it at that. > > OK, so the ideal impedance of a vertical antenna is 32 ohms - I got > closer to 50 ohms which indicates a 15 ohm loss in signal efficiency. > It matches my feedline nicely, and I an willing to accept the the 3% > loss in efficiency that represents. > > The ground conductivity in my area is not the greatest, so I have > accepted the logical consequences of that fact. > > 73, > Don W3FPR > > > On 12/20/2010 8:06 PM, David Gilbert wrote: >> "I personally would not consider elevated radials that are non-resonant" >> >> >> I guess I'm having a difficult time with that comment. You can have a >> resonant system without the elevated radials themselves being >> "resonant" ... i.e, any two of them acting like a resonant dipole. If >> the elevated radials are shorter than a 1/4 wavelength, all that is >> required is that the vertical section be a little longer than a 1/4 >> wavelength to compensate. If the radials are longer than a 1/4 >> wavelength, the vertical section needs to be shorter than a 1/4 >> wavelength for resonance. >> >> Elevated radials are kind of like the lower half of a vertical 1/2 >> wavelength dipole except that it is "fanned out" for symmetry, and if >> the radials are longer or shorter than half of a 1/2 wavelength dipole >> the feedpoint simply behaves similarly to an off-center fed dipole. You >> can prove this to yourself with EZNEC ... start with a vertical section >> longer than 1/4 wavelength and see what length radials you need to have >> a resonant feedpoint. Then do the same thing with different lengths of >> vertical sections and see the effect on radiation pattern. I can tell >> you that it isn't a direct function of radial resonance. >> >> I could be wrong, but I don't see any need at all for the radials to be >> "resonant" on their own. You want system resonance and generally >> speaking, for radiation effectiveness you want as long a vertical >> section as you can manage. You might want to choose a vertical section >> somewhat longer than a 1/4 wavelength and radials correspondingly >> shorter than a 1/4 wavelength in order to take advantage of that >> "off-center feed" aspect I mentioned in order to get a 50 ohm match. >> >> The only situation where resonant radials might be required is if you're >> trying to decouple whatever is on the other side of the radials. In >> that case, the radials act like a choke to keep current on the feedpoint >> side of the resonant radials. You can see that effect with EZNEC as well. >> >> 73, >> Dave AB7E >> > ______________________________________________________________ > 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
