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The Swiss Quad Antenna at ZS6PP |
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The Swiss Quad Antenna at ZS6PP Rotatable Antenna with Phased ElementsBy E.P. Towers, ZS6PP This antenna, designed originally by HB9CV, has not yet received widespread attention in the Western Hemisphere. Measurements made by the designer indicate that its performance is superior to the conventional two-element quad, while the structure is much simpler and sturdier.
After conducting extensive experiments, HB9CV was so successful in simplifying the construction and design of the quad that he filed a patent application in 1960 for an entirely new concept of this antenna, and named it the "Swiss Quad."2 Since then, the design of this antenna has been treated in additional articles by others.3 Reference to this previous material is recommended for full information. In constructing a Swiss Quad for 20 meters, the author found that he had to modify and adapt details suggested by these articles. In response to requests from other hams around the world for information on his design, these notes from his own experience and that of others who have constructed similar antennas are presented. Due acknowledgment is made here to the inventor and to the authors of earlier articles. Refer to the sketch of Fig. 1 for a general idea of what the Swiss Quad looks like. It differs from the conventional quad electrically in that both elements are driven - with a phase difference of 180 degrees. Construction is simplified by making the horizontal members of aluminum tubing sufficiently rigid to support the weight of the vertical members, which are made of wire, thereby eliminating the customary spreaders. Additionally, the horizontal members are bent in such a manner as to provide the desired element spacing without the need for a boom. The author's antenna is fed with coax line and gamma match, as shown in Fig. 2. Supporting Mast The vertical members are 230 inches long for 14,250 kc. Thus the supporting mast must be about 20 feet long, plus sufficient length at the bottom for mounting in a rotator socket or tower bearing. It may also be desirable to add rigidity to the antenna by extending the mast 2 or 3 feet above the top horizontal members so that the outer ends of these members can be guyed to the mast with nylon cord. In any event, it will usually be necessary to splice sections of tubing together to obtain the necessary mast length. A method of splicing that the author found satisfactory is illustrated in the sketch of Fig. 3. Sections of 2-inch 10-gauge dural tubing were used for the mast. Further strength can be added by applying a self-guying or truss system to the mast. However, the author did not consider this necessary. Mounting Brackets The horizontal members are fastened to the mast at the cross-over points by means of two brackets (one for the top set, and one for the bottom set). The brackets are made up of three pieces of aluminum or steel angle, as shown in Fig. 4. An alternative that would avoid welding would be to use wider angle stock which would provide space for attaching the element-supporting angles individually to the mast with U bolts and serrated yokes. If this method is used, care must be taken to make sure that the two angle pieces are oriented at exact right angles to each other. (The welded arrangement assures this automatically.) The antenna elements must be insulated from the brackets. To accomplish this, the author cut sections of flexible 1-inch polyethylene pipe to lengths slightly longer than the bracket. The pipe was then slit lengthwise so that it could be spread and forced over the 7/8-inch aluminum tubing of the elements. The angles should be notched as shown to allow the clamps (gear-type, stainless steel) to secure the elements firmly. The top bracket can be mounted permanently on the mast before assembling the antenna. Mounting of the bottom bracket should be postponed until later. Elements The sketch of Fig. 5 shows the dimensions of the horizontal antenna members used by the author for 14,250 kc. All four members are made identical. Forty-five degree bends are made at equal distances from the centers of a 16-foot length of 7/8-inch 18-gauge aluminum tubing which forms the center section. (Borrow a conduit bender from your local electrician, or have him do the job; otherwise, the tubing is sure to kink when the bends are made.) The ends are slit to take extensions of 3/4-inch 16-gauge tubing. The junctions are secured with stainless-steel gear-type hose clamps. The ends of the extensions should be flattened and drilled for screws that will be used to fasten the horizontal members and the vertical wire members together. The extensions are not added until final assembly. Assembly The assembly can be started by laying the mast, with upper bracket attached, across the tops of a pair of stepladders at least 5 ft. high. Clamp the top pair of horizontal members not too tightly in the bracket while their positions are adjusted so that the members cross each other at their exact centers. Then twist the members in the bracket, if necessary, so that they lie in the same plane, at right angles to the mast. Clamp the members firmly in this position while hole centers are marked at the exact centers, and in the mast bracket, as shown in Fig. 4. Drill the holes for sheet-metal screws, attach soldering lugs, line up the members accurately again, and tighten the clamps. Wire the three lugs together with the shortest possible leads. Do not allow the leads to touch the bracket at any point. The author found this precaution necessary to obtain a satisfactory matching adjustment. The end extensions can now be added, and the telescoping adjusted to give the widths shown in Fig. 1. The two extensions in each element should be maintained at equal length, of course. Give all four ends of the horizontal sections a slight upward bend to help compensate for the weight of the vertical wire members. The vertical wires can be made of No. 14 copper wire, or stranded wire of equivalent cross section. No. 8 aluminum TV ground wire is also suitable. If solid wire is used, stretch the kinks out, and try to avoid reintroducing them during the assembly. Measure off the vertical lengths shown in Fig. 1. Mark the wires plainly at the measured length, then add several inches for adjustment. Attach the top ends of the wires securely to the ends of the top set of horizontal members. Then spray all connections with acrylic, or apply other suitable protection against corrosion, or loosening of the securing bolts. At the center of the clearest available space, drive a section of pipe whose inside diameter is slightly larger than the outside diameter of the mast into the ground. Swing the mast vertically and insert the bottom end into the pipe. If an extension can be added temporarily to the mast to bring the lower horizontal members at step ladder height above ground, so much the better. (It may be necessary to guy the mast temporarily with rope.) Temporarily clamp the bottom mounting bracket to the mast, while the mounting and adjusting procedure described previously for the upper set of horizontal members is repeated for the bottom set. Be sure that the longer extensions are on the same side of the mast as those of the upper set, and that the sets are lined up as accurately as possible in the same plane. At the conclusion, give the ends a slight downward bend. Attach the vertical wires temporarily to the bottom horizontal set at the measured points. Then slide the bottom bracket down on the mast until the vertical wires are reasonably taut, and reclamp the bracket. Adjustment The author made the matching section of 3-conductor plastic-insulated electrician's house wire, conductors in parallel. The wire was spaced about 1/200 wavelength (about 4 inches for 14 Mc.) from the elements by means of a series of aluminum clamps spaced at intervals, as shown in Fig. 6. (In some other instances, it has been necessary to use either wider or closer spacing to obtain a match.) The insulation was removed from the wire only at the ends for connection to the adjustable clamps, and at the center for connection to the feed line. Notice that the matching taps must be made at equal distances from the cross-over point. The distances from the taps to the ends of the horizontal members will not be equal because of the difference in lengths of the reflector and director members. The matching taps were set initially about halfway between the bends and the ends of the horizontal members. A short length of line terminated in a loop of 2 or 3 turns of wire was connected to the feed point. Resonance was then checked by coupling a grid-dip oscillator to the loop. All four lengths of the vertical wires were then adjusted equally until the g.d.o. showed resonance at the desired center frequency. The bottom bracket was then repositioned to bring the vertical wires taut, and the bracket was fastened permanently in place. The line was then connected and the matching taps adjusted for minimum s.w.r., keeping the taps at equal distances from the cross-over point. The author found that there was no change in the s.w.r. when the antenna was elevated to full height. Those with tilt-over towers should have no difficulty in mounting the antenna. Those with fixed towers will probably have to feed the mast up through the tower, fasten on the top horizontal members, raise the mast, and then attach the bottom set of horizontal members. Results No attempts were made to establish the gain of the antenna in respect to a dipole. On receiving, signals can be heard that just aren't there on a dipole. With the bottom of the antenna 35 ft. above ground, and an input of 150 watts, performance on transmitting has been excellent to all points on the globe. Judging from S-meter readings, the front-to-back ratio appears to be better than 20 db. 1 Ross, "How DX Kings Rate Antennas," QST, January, 1964. 2 Baumgartner, "The Swiss Quad Beam Aerial," R.S.G.B. Bulletin (England), June, 1964. 3 DL-QTC (Germany), October, 1964. Amateur Radio Bulletin (Australia), April, 1965. Radio ZS (Republic of South Africa), August, 1965. Posted December 1, 2013 |
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