Just for fun once, I decided to make the smallest possible antenna and see if I could make any contacts. I wound about 30 week of #12 solid insulated wire around a 3/4" PVC pipe. Parallel to it and electrically in series, I created a tunable tubular capacitor using copper pipe and a threaded brass rod. You screw the rod in to increase C and out to decrease.
Using these strictly guesstimations, I found I had good SWR across the entire 20 meter band with about 1.7:1 on the edges. I mounted it on an 8' aluminum mast which was also connected to the shield side of the coax. I got on with my little Yaesu FT-840 and in 5 minutes I had a pileup of stations wanting an explanation for my report of an 18" vertical. I guess the efficiency must have been only a couple of percent. But, there it was, the smallest possible vertical for 20 meters! I worked about 15 countries that afternoon with it. Doug -- K0DXV Ron D'Eau Claire wrote: > I'd like to be clear when I wrote earlier that a small transmitting loop is > very inefficient. > > I didn't mean they don't work, only that they only radiate a small part of > the RF applied to them compared to a larger antenna. > > Consider a typical mobile "whip" antenna. They're terribly inefficient too > but people get out with them, sometimes working DX when band conditions are > good. > > Of course mobiles generally run more than the 10 watts or so a K2 produces, > but contacts are made with QRP power and such antennas all the time. > > One way to make a given antenna "larger" is to use a higher frequency band. > It's a matter of the antenna's size in wavelengths or fractions thereof that > is important. That's why small antennas do so much better when the sunspots > are active and the higher frequency bands are open. > > Ron AC7AC > > > > ______________________________________________________________ > 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
