A couple of observations based on antenna principles and my personal experience:
1) A dipole is a dipole no matter where it's fed. A 1/2 wave dipole (Hertzian antenna) is more efficient than anything shorter (no matter how often the manufacturer puts "magic" in the ad copy :-) although, with great effort shorter antennas can come close. Jerry Sevick, W2FMI (SK) demonstrated how to build short, efficient grounded (Marconi) antennas for Hams. But they require extensive, well designed ground; not something generally practical for portable use and not even practical in many fixed station locations. 2) Antennas longer than 1/2 wave are also very efficient. Even at multiples of 1/4 wave, the impedance is never as low as it is for a 1/4 wavelength radiator. A simple "counterpoise" wire will usually provide good efficiency even at the odd 1/4 wavelength multiples where the feed point impedance is at a minimum. 3) The matching device earchi uses is a simple auto-transformer. The voltage at the top (antenna end) of the coil will be very high, requiring good spacing and excellent insulation. (Many will recognize the design as being similar to a Tesla Coil. It IS a Tesla coil!) A personal experience was when I ran a 1/2 wave long wire with a matching network at the rig that had a nylon banana jack for the antenna wire connection. It was housed in a metal box. At about 10 watts output on 40 meters, the nylon melted! But just because nothing smokes or melts at QRP power levels does not mean the system is efficient. That only means that the heat produced by the loss doesn't raise the temperature high enough to destroy the materials. You can still be throwing away much or most of your RF as heat in a poor connection or bad insulator. My rule is to be as careful with proper insulation and low resistance connections at 1 watt as I would be at a kilowatt. 73, 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
