Note that the article referenced suggests avoiding multiples of 1/2 wavelength if you are trying to feed it with a 50 ohm transmitter with *no* matching network or ATU. That is not true for a system that includes an ATU.
The closer you can get to 1/2 wavelength, the more efficient the antenna will be for a given 'ground' setup providing your ATU can match the transmitter output to the impedance. That's because at 1/2 wavelength relatively little current flows into the antenna and so relatively little current flows into the "ground" system, which greatly reduces losses in the "ground" system. Ground system losses are the majority of losses in an end fed wire. (I put ground in "" because it is really just a low RF impedance point, whether it connects to the earth or not. It can just as well be a 1/4 wavelength counterpoise, a gazillion wires, or anything in between.) Indeed, exactly 1/2 wavelength would be the ideal length for an efficient end fed wire except that most automatic tuners cannot match the very high impedance present or handle the very high RF voltages involved at the feed point. Many old manual tuners could, which is why they are physically huge, using variable capacitors with very wide spacing, big ceramic insulators, etc. So the "trick" for highest efficiency in an end fed wire with modern compact tuners is to get as close to 1/2 wavelength as the tuner can match. Unfortunately that can only be done on one band, but if you do that on the lowest frequency band you are usually good across the HF spectrum since the swing in impedance value from maximum to minimum gets less and less with each wavelength multiple. Depending upon your tuner's matching range and other factors, you may still find another band where the impedance is out of range. In that case the only solution is to find a compromise length if you really want to quickly hop all over the HF spectrum. 73, Ron AC7AC -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Calvin Sent: Friday, November 09, 2012 2:01 PM To: Joseph Trombino, Jr Cc: [email protected] Subject: Re: [Elecraft] Random length wire for use with KX3 Hi, this looked like a good article that talked about random wire lengths. http://www.hamuniverse.com/randomwireantennalengths.html I am interested in trying it out when my Kx3 arrives. 73's KA7MAY Sent from my iPad On Nov 9, 2012, at 2:33 PM, "Joseph Trombino, Jr" <[email protected]> wrote: > Howdy Gang: > > Nice WX tomorrow for our neck of the woods (southeastern North Carolina) so I'm gonna take my KX3 out and play radio. > > I have the internal tuner installed and am wondering if anyone has had success with a particular length of antenna wire with the tuner in the KX3?? > > I usually use a PAR EFHW for 40/20/10M but wanted to play with something different and also give the internal tuner a spin around the block. > > So, what lengths of wire have been used successfully with the KX3?? > > Many thanks for any info....will be on the air shortly after lunch time...1800Z or 1900Z....will be looking for you around the QRP watering holes on CW. > > 73, Joe W2KJ > I QRP, therefore I am > ______________________________________________________________ > 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 ______________________________________________________________ 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
