I agree with Bob. The KX1 does very well with nothing in between it and an end fed wire.
The most important thing is to have an RF ground at the rig - especially when using a wire that's 1/4 wavelength or less long as we often must do when travelling light. For my KX1 I carry two 33 foot lengths of wire soldered to a BNC male connector. One goes to the "hot" center pin and the other connects to the shell of the ANT connector. If I can, I get both of wires "in the clear". If the parts near the rig run roughly parallel to each other, they'll act like a "feed line" but that's not at all important (Note that "balanced" feeders do NOT need to be evenly spaced and exactly parallel. Variations of several inches or even a foot or two won't matter at HF). Accordingly, if you put both wires up in the air, be sure they have an enclosed angle of greater than 90 degrees over as much of their length as possible. Otherwise they may end up acting like a length of unterminated feed line. If only one wire is up "in the clear", that's fine too. I try to keep the one connected to the shell off the ground to act like a "counterpoise". In that event I'll usually adjust its length to 1/4 wave on the band I'm working most: 23 feet when on 30 meters or 16 feet on 20 meters. I've marked the wire with tape at those two lengths. That makes a very good 20/30 meter antenna and a decent 40 meter antenna. On 20 meters 33 feet is 1/2 wavelength long, which makes the feed point impedance very high. That's ideal to minimize the need for a good RF ground at the rig since the power is shared between the feed point impedance and the ground impedance. High feed point impedance and low ground impedance means most of the power will flow into the antenna and the least amount will be "lost" in the ground. On 20 the "ground" is important to hold the case of the KX1 at a low impedance. Otherwise, you may notice the SWR varies widely as you touch the rig: it'll be "floating" at the relatively high voltage present at the end of the 1/2 wave wire. On 40, the feed point impedance will be about the same as the impedance presented by the "counterpoise": approx. 35 ohms for each so the power is shared between them. What is very important to avoid is trying to use a 1/4 wave wire (or shorter) with no ground on the rig. In that case only a tiny fraction of the RF will be radiated. So what about 80? If there's room, I'll put up 66 feet of wire but I usually don't even carry that with me in my little "rig pouch". Getting the height and length needed for efficient operation on 80 is usually more effort than it's worth for me, so I operate 80 with the KX1 rarely with a temporary antenna. It will put out a bit of a signal using the 33 foot wire and the ATU easily finds a match, but it's a very inefficient setup at best. There are two ways a balun can improve the matching range of any ATU: 1) Under some conditions baluns get quite lossy (i.e. act like resistors) so they 'broaden' the apparent bandwidth of an antenna just like a good dummy load in parallel with your antenna will make the tuning very broad. 2) A balun might (by accident) change the impedance at the feed point to something the ATU can match. A much better and more compact way to avoid 1) and achieve 2), if needed, is to adjust the length of your antenna (or counterpoise) a bit until the KX1 ATU finds a good match. If that's not practical, consider adding a small inductor in series with the radiator. A coil wound on an old plastic pill bottle or 35 mm film container with a tap point every few turns is ideal. The coil adds inductive reactance (depending upon how many turns you use) and changes the feed point impedance accordingly. I recommend an air-core inductance since any iron core (such as most baluns use) can saturate under some conditions and become lossy. Ron AC7AC ______________________________________________________________ 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
