Phil, As others have responded, attempting to tune the end of a half-wave wire is beyond the range of most tuners, including the KAT2. Your added wire provided a compromise length, because the feedpoint impedance was reduced.
Because the impedance of the EFHW is high, my favorite tuning section for a half wave antenna is a parallel tuned tank circuit - the radiator connects to one side of the parallel circuit and your counterpoise (or ground) connects to the "cold end". Tune the paralled tank circuit for resonance near the operating frequency (and make it a permanent part of the antenna). Then wrap a few turns around the ground end of the inductor and use that "link" to connect to the KAT2. The fixed tuned circuit will handle the high impedance, and the impedance of the "link" will be much lower (depends on the square of the turns ratio). The KAT2 will do the job of matching into that link as you move about the band. In other words, you make a fixed "tuner" that becomes part of your EFHW dipole (no variable capacitor to tune the antenna - use a fixed capacitor that resonates with the inductor approximately mid-band. The KAT2 will tune quite nicely into the link winding and produce a low SWR. The alternative is to use a non-resonant wire length that provides a sufficiently low impedance as to be within the matching range of the tuner. The W3EDP antenna is one of those examples. Use that approach if you want to use the same antenna wire for multiple bands. As I recall, the W3EDP radiator is 85 feet long and the "counterpoise" is 17 feet for use on 80 meters and up. Half those lengths would work on 40 and up. I look at the W3EDP as "sort-of" an off-center-fed" dipole - the counterpoise does not have to be on the ground to work well. 73, Don W3FPR On 8/23/2011 7:00 PM, Phillip Shepard wrote: > I have been using my K2 with an MFJ tuner to feed an end fed halfwave wire > for portable use (like SOTA). The 20m antenna is 33' long and I use one or > two 16' counterpoise wires. It seems to work well for what it is and 10W. > I just built and installed the KAT2 ATU into the K2 to lighten my pack by > the loss of the MFJ. The KAT2 tuner checked out fine on the bench, but it > had a very hard time getting a good match to the antenna. In AUTO mode, it > only got the SWR down to about 5:1. I put it in ALT mode, and it spent a > long time searching before it got down to between 3:1 and 4:1, depending on > the 20m frequency. I added about 2" of wire to the antenna, and the tuer > got down to about 2:1 to 2.5:1. I added another foot of wire (now 36'), and > it got down to about 1.5:1. Five or six feet added yielded a perfect match > (1:1). So I now have a 39' wire for 20m use. > > Is this normal? Should the KAT2 be able to more easily match the 33' > halfwave antenna? Thank you. > > 73, > Phl, NS7P > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > 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:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
