Ha, ha!!! Well put Wes! Some mountain portables erect low "horizontal" antennas on the side of a steep mountain. The result is a very low angle of radiation because, even though the main lobe is "straight up" from the mountainside from the antenna, the slope puts that lobe at a fairly low angle relative to the earth.
73, Ron AC7AC -----Original Message----- From: Elecraft [mailto:[email protected]] On Behalf Of Wes Stewart Sent: Saturday, February 11, 2017 8:02 PM Cc: [email protected] Subject: Re: [Elecraft] EFHW It is with some reluctance that I smack this whole EFHW tarbaby, but here goes. Comments in no particular order: 1) A resonant antenna (even one that is self-resonant), e.g. one with a non-reactive feedpoint, isn't necessarily "efficient." A quarter-wavelength monopole over lossy earth leaps to mind. 2) A non-resonant antenna isn't necessarily inefficient. The ever popular G5RV isn't resonant on the band of interest (20M) but when fed appropriately, was as efficient as a resonant dipole. 3) Consider a BC band 1/2 wavelength vertical antenna. Does the station designer say, "Well, this EFHW doesn't really doesn't need much of a counterpoise, so I'll just throw a 100' long wire on the ground and call it good enough?" No, he install 120 radials that are even longer than the ones he would use under a 1/4 wavelength monopole. Devoldere in "Low-Band DXing, Chapter 9, Section 4.3 says: "Here comes another surprise. A terrible misconception about voltage-fed verticals is that they do not require either a good ground or an extensive radial system.'" Later in the same section he says, "Therefore it is even more important to have a good radial system with a voltage-fed antenna such as the voltage-fed T or a λ/2 vertical. These verticals require longer radials to do their job efficiently compared to current-fed verticals." 3) When you backpacking mountain goats say, "Hey my wire isn't a vertical, it's mostly horizontal", I say, if your radio is sitting on a boulder or the ground, it's a vertical and your wire-on-the-ground counterpoise proves it. Wes N7WS On 2/11/2017 2:33 PM, Ron D'Eau Claire wrote: > All efficient antenna systems are "resonant" (jX=0) but the shorthand > often used is "resonant" to mean "self resonant". That is true of any > 1/4 wavelength long radiator (again our common shorthand is usually > "1/4 wave > wire") or any multiple thereof worked against ground. It is also true > of any half wave length radiator or any multiple thereof. (Note that > these are electrical lengths, taking into account any surroundings > including the radiator itself.) > > While self-resonant antennas do not present a reactive load to the > source of RF power, the value of R, the resistance, may vary widely. > There is nothing magic about the 50 ohm load most of our transmitters are > designed for. > > However, a half wave radiator fed at the center presents a resistive > value near 50 ohms when fed at typical heights above ground (in free > space it is > 75 ohms). Half wave antennas became very popular after WWII because > 50-ohm coaxial feed line became abundant and cheap on the "surplus" > market and Hams were taking steps to deal with needing to avoid > interfering with the rapidly growing number of TV sets in nearby > homes, including the Ham's own living room. > > In the following decades, greater and greater demands on harmonic > suppression have led to Ham transmitters with output filters > specifically designed for a 50 ohm load instead of being able to match > a wide range of load impedances. > > So we have now moved the wide-range output network that was in > Grandpa's Ham transmitter out of the transmitter and into what we call an > "Antenna Tuner". > But, of course it does not "tune" an antenna at all. It's just a > matching network to be sure the transmitter is delivering power to a > load close to 50 ohms and non-reactive. > > 73, Ron AC7AC > > -----Original Message----- > From: Elecraft [mailto:[email protected]] On Behalf Of > Wes N7WS > Sent: Saturday, February 11, 2017 12:44 PM > To: Charlie T, K3ICH > Cc:[email protected] > Subject: Re: [Elecraft] EFHW > > jX = 0 > > Sent from my iPhone > >> On Feb 11, 2017, at 1:29 PM, Charlie T, K3ICH<[email protected]> wrote: >> >> Define "resonance". >> >> Chas >> >> -----Original Message----- >> From: Elecraft [mailto:[email protected]] On Behalf Of Fred >> Jensen >> Sent: Saturday, February 11, 2017 2:40 PM To:[email protected] >> Subject: Re: [Elecraft] EFHW >> >> Ummm ... A full-wavelength wire is not resonant? >> >> 73, >> >> Fred ["Skip"] K6DGW >> Sparks NV DM09dn >> Washoe County >>> -----Original Message----- >>> From: Elecraft [mailto:[email protected]] On Behalf >>> Of Lynn W. Taylor, WB6UUT >>> Sent: Friday, February 10, 2017 12:13 PM To:[email protected] >>> Subject: Re: [Elecraft] EFHW >>> >>> Just a reminder, folks. >>> >>> If it's not a half-wave, then it's a non-resonant wire. >>> >>> ______________________________________________________________ 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 Message delivered to [email protected] ______________________________________________________________ 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 Message delivered to [email protected]
