jhs%Mitre-Bedford@sri-unix.UUCP (09/25/84)
Phased verticals might be especially attractive if implemented as center-fed wire verticals. I have been running a single such vertical on 20-15-10 for several years with excellent results. It is basically a Zepp antenna mounted vertically in the tallest tree near my house. It is 32 feet long and center fed at the moment with "Radio Shack's Finest" black, foam-filled "ultra low loss" TV twinlead. I use a Heathkit tuner with ferrite balun to get the balanced feed. On 20 Meters 32 feet is a half wave, and the antenna gives 0dBd (dB relative to a dipole) of gain. It has a low radiation angle because of the symmetry of the current distribution on the wire about the center feed point. Since it does not depend on a reflection in the ground to obtain the desired pattern, it works very well with no radials. On 10 Meters, this antenna is two half waves in phase, and gives a gain of about 2 dBd. On 15 it is in-between. It will be usable on the in-between new bands when they are authorized. The RS twinlead has performed amazingly well. It has handled the output of my 2KW PEP (input) amplifier with absolutely no sign of complaint, even though the twinlead passes through an aluminum storm window frame at one point with only a few layers of ducting tape to increase its insulation strength. The signal reports I get with the antenna are almost always stronger than the reports I give out, even when I am running low power. The same antenna can be "extended" into the "extended double Zepp" configuration for 10 Meters, which means just lengthening it to 44 feet. This gives 3.0dBd gain on 10 Meters. It then would also be fairly useable on 10 MHz and all the bands from there up to 10 Meters. NOTE: Increasing the length beyond the magic 10/8 wavelength (44 feet for 10 Meters) causes a null in the pattern to begin to appear broadside to the wire, i.e. at the horizon. Therefore lengths greater than 44 feet are undesirable if you want the maximum gain at 10 Meters. Arrays of such antennas could be used to obtain directionality. However, some thought would have to go into what spacings and phase relationships to use to make it work on all of the indicated bands. One possibility is to use the "W8JK" configuration, in which two such wires are spaced fairly closely and fed out of phase. Then broadside radiation cancels, giving 4 or so dB gain in the orthogonal direction, i. e. horizontally in the plane of the array. This configuration exhibits a low radiation resistance, however, and should probably be fed with open-wire line much heavier than the TV twinlead I have been using. Its advantage is that the principle could be adapted to work over more than an octave in frequency. For those wishing a simple but effective antenna for 10-30 MHz, the simple center-fed vertical works very well and is extremely easy to put up. Especially if you have a bow and arrow with spinning reel affixed to the bow, as I do. I use basically the same antenna on 40 and 80, only that one is mounted horizontally as I don't have any 130-foot trees. It is fed with open wire line. This antenna could also be used on 30 Meters if I had a rig to feed it At its present 40-foot height, this antenna gives excellent results out to about 1000 miles and satisfactory results for DX. 73, de W3IKG