Bill, you are close to the famous Zeppelin antenna. It was a single-frequency antenna. The idea was to move the RF field as far as practical from the airframe. RF arcs between elements of the duraluminum airframe were to be avoided, especially up near the top of the airship where there was always some leaking hydrogen finding its way out through the top vents on the covering.
The original antenna was 1/2 wavelength long and fed at one end by 1/4 wavelength of open wire line. At the antenna end, one of the two wires in the transmission line was connected to the 1/2 wavelength long radiator. The other wire terminated at an insulator, and nothing else. Since the 1/2 wavelength radiator presented a very high impedance to the feed line, very little current flowed in that side of the feed line into the antenna. Since the other side of the feed line went to an insulator, there was very little current flowing there too (some current would result from typical leakage at the insulator). The end result was decent current balance and minimum radiation from the feed line from the balanced output of the transmitter to the actual connection to the radiator. Since the feed line was electrically 1/4 wavelength long, the very high impedance at the antenna was transformed into a very low impedance at the transmitter. The weakness in your design will be the transformer. Even at QRP levels, very high voltages can occur at the end of a half-wave radiator and so in your transformer. It's pretty easy to build an open wire line to handle the voltages without voltage breakdown. Not so easy in a transformer. 73, Ron AC7AC -----Original Message----- From: Elecraft [mailto:[email protected]] On Behalf Of Bill Frantz Sent: Saturday, February 11, 2017 2:52 PM To: [email protected] Subject: Re: [Elecraft] EFHW The next time I experiment with end fed antennas, I want to try a matching transformer at the end of the antenna wire of about a 50:1 matching ratio. That way I will have an impedance in the feed line of about 50 ohms and minimize coax loss. Now if I am connecting the antenna directly to binding posts on the side of the KX(2/3), the loss won't matter. But if I am using a length of RG174 for a light weight feed line, the lower loss will be very nice. Adding Don's recommended 0.05 wave length "counterpose" in the binding post scenario sounds useful. With a coax feed, the coax should perform that function. Now, where am I all wet? 73 Bill AE6JV --------------------------------------------------------------------------- Bill Frantz | "I wish there was a knob on the TV to turn up the 408-356-8506 | intelligence. There's a knob called "brightness", but www.pwpconsult.com | it doesn't work. -- Gallagher ______________________________________________________________ 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 Message delivered to [email protected] ______________________________________________________________ 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 Message delivered to [email protected]
