Guy, OK, I missed by a factor of 10. I am using 2 elevated radials per band, and the physical direction is such the pairs are horizontally opposed - that should reduce the radiation from the radials to zero (or nearly so).
I first cut the radials 15% longer than the "formula" would indicate, and used my MFJ259B to determine the actual (X=0.00) resonance point. By changing the lentgth of the radial (one at a time), I was able to comee with a working antenna for 160, 80, and 40. While my antenna works well fot me, it is not a universal solution. 73, Don W3FPR On 12/20/2010 10:15 PM, Guy Olinger K2AV wrote: > 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
