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]
