A few years ago I built a parallel LC network from a roller inductor and a variable cap rated for approximately 2.5kv and have used it to match 20 meter EFHW many times. I run 500 watts into it from the kpa500 through a choke balun in the shack. I use (5) 8 foot radials for a counterpoise and I tape the wire to a 40 foot spiderbeam fiberglass pole in a vertical configuration. I have never had any problems with rf in the shack using this antenna with the choke. In fact I have more problems with rf from my 80 meter inverted-L than I do the EFHW. I built the antenna for field day use but I have had excellent results with it in several local and DX contests. I easily have over 3000 q's with this antenna and the only real complaint I have is that at times it can be a bit noisy. I originally built the box to match a 40 meter halfsquare but it works well on 20, 80, and 160 as well.
Sent from my iPhone > On Jul 14, 2016, at 8:01 PM, Don Wilhelm <[email protected]> wrote: > > Keep in mind that the original End Fed Half Wave antenna was the original > Zepp antenna. > A halfwave radiator that was fed from one side of a quarter wave transmission > line. > That antenna was trailed from a Zeppelin airship. The 1/4 wave transmission > line reduced the high impedance of the halfwave antenna to a low impedance > (see transmission line characteristics). The ideal characteristic impedance > for the 1/4 wave transmission line is 300 ohms - see the work of N3GO - "the > J-Pole according to N3GO" at http://knightlites.org/n3go_workshop/index.htm. > > Of course, the transmitters in those airships had adjustable amplifier tank > circuits which could match almost anything except a very high impedance - > that function has been moved to the ATU in recent times and the PA output > stage is designed to work into 50 ohms. > > If you want a modern-day example of the EFHW fed with 1/4 wave transmission > line, consider the J-Pole antenna that is popular for VHF - it is nothing > more than the original Zepp antenna oriented vertically. > > I have no idea how the "Zepp antenna" designation has been construed in > amateur radio circles to apply to a balanced center fed non-resonant radiator > but it has been so construed that we have to be careful when saying "I have a > Zepp (or Extended Zepp) antenna - it no longer means what it originally did. > > 73, > Don W3FPR > >> On 7/14/2016 8:38 PM, Walter Underwood wrote: >> I totally agree. End-fed half waves are tweaky. One terminal is the antenna >> wire and the other terminal must be something. The RF will find something to >> drive as the other “pole” of the antenna. There are no monopole antennas. >> >> It could be the outside of the coax, it could be a “counterpoise” (not fond >> of that term), or it could be your hand on the key. Ouch. >> >> I was using “ground reference” as the negative side of what you measure RF >> voltage against. Whatever that is. >> >> There might be an antenna topic with more voodoo than end-fed antennas, but >> I don’t know what it is. The EC-130J flies a long wire out behind it and >> broadcasts on medium wave. I guess the other pole of that antenna is the >> airplane itself. >> http://www.af.mil/AboutUs/FactSheets/Display/tabid/224/Article/104535/ec-130j-commando-solo.aspx >> >> <http://www.af.mil/AboutUs/FactSheets/Display/tabid/224/Article/104535/ec-130j-commando-solo.aspx> >> >> wunder >> K6WRU >> Walter Underwood >> CM87wj >> http://observer.wunderwood.org/ (my blog) >> >>> On Jul 14, 2016, at 5:14 PM, David Gilbert <[email protected]> wrote: >>> >>> OK, I can buy that ... except that the term "ground reference" as used by >>> you and Don doesn't really apply. The counterpoise is simply providing >>> some minimal balance to the high impedance at the end of the EFHW, and it >>> doesn't need to have anything to do with "ground". >>> >>> If the counterpoise is located at the rig (as I inadvertently thought Don >>> was suggesting) instead of at the end of the antenna then indeed the >>> feedline would radiate, and if located at the rig the impedance >>> transformation effect of the transmission line (depending upon it's length) >>> could easily put a low impedance there ... rendering a short counterpoise >>> essentially ineffective. >>> >>> For the record, I know how electricity works. >>> >>> Dave AB7E >>> >>> >>>> On 7/14/2016 3:42 PM, Walter Underwood wrote: >>>> The transmitter needs to drive into two terminals. That is how electricity >>>> works. If you do not provide a ground or a capacitive RF ground >>>> (counterpoise), the ground is the chassis of the transmitter. In a big >>>> grounded shack, that might be a stable reference. Otherwise, you need to >>>> provide a ground reference. Without that, the feed impedance changes every >>>> time you touch the rig. >>>> >>>> The ground reference does not need to handle much RF current, because of >>>> the high impedance feed (around 10 kOhms). Even a little capacitance to >>>> ground will stabilize the feedpoint impedance. >>>> >>>> A minimum length of coax feedline would reduce the SWR due to losses, but >>>> it would also provide an RF ground reference with currents on the outside >>>> of the shield. Currents on the inside of the shield are balanced, of >>>> course. >>>> >>>> Walter Underwood >>>> [email protected] >>>> http://observer.wunderwood.org/ (my blog) >>>> >>>> >>>>> On Jul 14, 2016, at 2:40 PM, David Gilbert <[email protected]> >>>>> wrote: >>>>> >>>>> >>>>> I'm confused why an EFHW should need a counterpoise. If it needs a >>>>> counterpoise it isn't actually acting like an EFHW. If it needs a >>>>> counterpoise that means there isn't enough choking impedance at the >>>>> feedpoint, and it means that the feedline is radiating with the >>>>> counterpoise acting as ... well, a counterpoise. >>>>> >>>>> Manufacturers state a minimum length feedline simply to have the feedline >>>>> losses help swamp out SWR variations along the line, and of course to >>>>> marginally lower the SWR. >>>>> >>>>> Dave >>>>> AB7E >>>>> >>>>> >>>>>> On 7/14/2016 1:03 PM, Don Wilhelm wrote: >>>>>> Andy, >>>>>> >>>>>> What happens if you connect to a dummy load? Does the KX2 tune it >>>>>> properly? >>>>>> If so, then you know the KX2 is operating into a 50 ohm load OK. >>>>>> >>>>>> Do you have an antenna analyzer? If so, then connect it to the antenna >>>>>> feedline and look at the impedance - both real and reactive - as well as >>>>>> the SWR. >>>>>> That will tell you whether the antenna is troublesome. >>>>>> >>>>>> You specifically said an EFHW - that should be a resonant antenna. If >>>>>> instead you have a random length wire (not a halfwave), and what is the >>>>>> matching device? >>>>>> Many EFHW antennas need a counterpoise to work - that is why many >>>>>> manufacturers state a *minimum* length feedline. >>>>>> >>>>>> If the problem is *not* the antenna, contact Elecraft support. >>>>>> >>>>>> 73, >>>>>> Don W3FPR >>>>>> >>>>>>> On 7/14/2016 2:40 PM, Andy Clift wrote: >>>>>>> Just received my KX2, but unable to get it to tune an EFHW wire. I’ve >>>>>>> tried a home made one and then tried a SOTABEAMS MultiBander that I’ve >>>>>>> used successfully with an FT-857. I’ve checked the continuity in the >>>>>>> wire and also the continuity in the KX2 between the BNC connector and >>>>>>> where the wire connects inside the KX2 (as I removed this to fit the >>>>>>> end panels). Battery is at over 11v. Any ideas please? >>>>>>> >>>>>>> ______________________________________________________________ >>>>>>> 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] >> ______________________________________________________________ >> 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]
