I purposely overlooked the obvious error that broadcast band antennas are 1/2 wave length long. How many BCB stations has anyone seen with a free-standing transmitting tower between 400 and 1000 feet high?
Most BCB (0.5 to 1.6 MHz) antennas are 1/8 wavelength high (or less) which necessitates an extensive ground system. Even so an efficiency of 10% or less is not surprising. A half wave radiator a decent distance from the earth is much, much more efficient, no matter how it is fed (end, center, off-center). 73, Ron AC7AC -----Original Message----- From: Elecraft [mailto:[email protected]] On Behalf Of Rick Dettinger Sent: Saturday, February 11, 2017 9:54 PM To: Kevin - K4VD Cc: Elecraft Reflector Reflector Subject: Re: [Elecraft] EFHW 10% efficient is for a “short” end fed antenna and a ground rod or similar. Something near a quarter wave and a typical one or two wire counterpoise is much better. It doesn’t take much effort to get to 50% efficient with a quarter wave or longer wire, and a few short radials. After that, there are diminishing returns for a given amount of effort. The BC 120 radial, half wave long ground systems are a good example. And, as QRP and mobile operators have shown, contacts with a 10% efficient antenna system do happen! 73, Rick K7MW > On Feb 11, 2017, at 9:19 PM, Kevin - K4VD <[email protected]> wrote: > > So what we are saying here is that all the local and DX QSOs we make > from a picnic bench with an end fed or random wire thrown up in a tree > and a short or no counterpoise doesn't really happen or, at best, is a > fluke. The end fed is only 10% efficient (did I get that right) and > most of our QRP signals are going to heat worms. Pretty hopeless > situation I guess. I might have to just stick with the local repeater > and Google Hangouts for communications. > > Or, for those of you that are thinking the situation isn't so > hopeless, grab your portable antenna, head out to the campsite, throw > your wire up in the tree and I'll catch you on the air. Let's warm up the > worms. > > 73, > Kev > > > On Sat, Feb 11, 2017 at 11:54 PM, Ron D'Eau Claire <[email protected]> wrote: > >> 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] >> > ______________________________________________________________ > 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] ______________________________________________________________ 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]
