What Stuart says about radials is quite true, but there is another important reason for a tuned radial (or other ground connection) other than to improve the efficiency of an end-fed wire.
Consider the end-fed dipole; it's probably the most extreme example of what I'm talking about. Fed at the end, a dipole (1/2 wave radiator) presents a very high impedance to the source. Hence, the RF voltage at the feed point will be very high. Without a ground on the ATU and rig, the whole rig will tend to "float" at a high RF voltage. At QRP you may not notice any RF "bites" or "burns" (although you certainly can get burns at less than 5 watts under the right conditions) but other problems abound. RF gets into the controllers and other logic in the rig causing erratic operation, and just touching the rig may detune the whole system, because of your body capacity to ground. An electrically 1/4 wave long "radial" connected to the rig ground can prevent these problems since a 1/4 wave wire has an impedance of only 35 ohms. That means that the rig case and ground will see an impedance of only 35 ohms, maximum, to ground even though the feed point at the "hot" side of the antenna connection may be looking into thousands of ohms. The Elecraft ATUs, like most tuners, can't handle the very high impedance of an end-fed dipole. Still, they can match to a sufficiently-high impedance that RF on the rig can easily become a problem, as many have reported here on the reflector. Usually a 1/4 wave long wire, elevated a few feet off the ground (over 6 feet if it's where people might walk into it) is a good investment. Another approach, as Stuart observed, is a wire on the ground that will capacitively couple to it and help hold the RF voltage on the rig down. Ron AC7AC _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
