Tristao Tower Co

Box 115

Hanford CA 93230

Antenna Quad 144

The 11-element version of the long circular quad is designed for operation on 144 MHz up to about 146 MHz. Measured horizontal forward gain showed 15 dB gain over a dipole. Front-to-back was 21 dB for the horizontal pattern ratio (and not the vertical directivity of that pattern); and 1 measured 9 dB over a dipole for the vertical forward gain, and 12 dB vertical frbnt-to-back, Measurements were made on the linear scale of the SX-122 S-meter that was modified for elimination of contact-potential bias effects, and with increased control of i-f amplifier cathode current (meter electrical zero). By using a Parks Electronics' Lab Converter plus a JFET preamplifier, linearizing of the S-meter scale on the low end was obtained. These measurements are repeatable. An International Crystal secondary frequency standard provided the transmitting signal source on exactly 144.00 MHz, from a seventh-overtone crystal. The transmitting antenna was a simple lA\ groundplane that could be turned vertical or allowed to radiate horizontally, depending on the relative position of its case. The 1 3-element long circular quad was operated as a aiiiiiStfii receiving array for these tests. Antenna height was 70 ft above flat ground, thereby eliminating ground reflections,

Theory of the i 1-Element Circular Quad

Initial measurements - made by an organization having ties w it In Project Oscar - showed IN dB gain over isotropic (not over a dipole), since the pattern was obtained while ray antenna was transmitting on 10(30 MHz to a reference antenna receiving the signal. I am very grateful to those who made the icsts possible; however, there is one point I ha I should be cleared up; There is vertical polarization in the major lobe, which means some circular is generated. Repeat-able tests have shown on this J meter model that with 1 1 circular group-phased elements there's 9 dB/dipole forward gain on 2 meters; and \2 dB/dipole front-to-hack for the vertical pattern! According to W0HTH, some circular polarization is always present in most common antennas. If you try to test your own antenna, remember that the structure

under test cannot be operated in the transmit mode for reliable readings, Grouping the elements as shown in the photographs boosted horizontal receiving-mode gain by as much as 5 "real11 dB on the 18-e lenient structure- At present, the gain of an II-element circular quad is 15 dB/dipole, with an estimation of 18 dB/dipole possible with 18 properly phased {not like a yagi) elements.

Screen sezc is also a factor in reconciling gain expected with actual measurements. As you increase forward gain, front-to-back tends to decrease, wjih any major improvement in the forward lobe. This doesn't hold for yagi arrays, for example, since adding extra elements to make it "long" reduces the overall efficiency to such an extent that a slight increase in forward gain is the only effect, And, by adding even more elements, considerable power is dissipated as element "heat*1 if we could measure it! This is where I stopped further research and developed "driven" parasitic director groups. Getting back to screen size, you can expect an increase of 2 dB by increasing screen size from 4 to 8 ft

Fig. I. This photo shows the completed \ I-element 2 meter circular quad. Screen size is on/y 4 ftt and found to be inadequate, unless it could be increased to 200 inchesl An 8 ft diameter screen reflector wouid have cost $48 for materials alone! Forget about "chicken wire" and you'd need a "cherry picker** for hardware ck?thr because of the weight.

1970 Amateur
Fig. 2< Carl Day made 29i round trips before final ground readings were taken as being acceptable.

diameter: however, ( would expect front-to-back ratio to increase to only 24 dB + Hopefully, the horizontal forward gain would be 17 dB/dipole!

Construction

Figure 1 shows the completed 1 i-element 2 meter quad, I he boom is made of thin-wall aluminum TV mast and is quite strong. 1 he screen is a braced, two-part structure covered with half-inch Maeklanburg-Duncan "expanded aluminum" mesh (chicken wire won't do!). The top set of guys is attached at the 60 ft level-

Figure 2 shows the antenna man's position at the 40 ft level; and the tower is back-lighted nicely against a darkened sky. i his photo shows most clearly the connecting tower bolts and the aluminum Foam flex transmission line taped to it. Note especially the slipknot of rope around the first director in the first (common) group. You can sec the element wiring il you look closely

Tower Radioamateur Hbx
Fig. 3. Seen here is one of those crucial moments when "you don't know tf he can make it bur you don't dare ask/" Since this was a success with a 4 f\ screen, a later modification to include a driven, reverse-phased aluminum clement certainly made the job easier.

Figure 3 shows perhaps the most hazardous or in-between position of the lowei and 11-element quad. He made it!

(But 1 had some doubts because of guy wire breakage the day before.) The lop of the gin pole is at SO ft. I was on the ground pulling up on the line streaking dmvn to the left. This shot is included in the article to show how a steeplejack or tower construction man can safely erect this antenna. Incidentally, boom length is HI ft and screen diameter is 4 ft.

Tower Radioamateur Hbx

Fig, 4. The array is in position, with ropes gleaming in the sunlight. Use of a rugged gin pole is an

I I

essential

Figure 4 is a dramatic one. With erection tines streaming in the wind Carl Day is tightening down the mast bolts prior to connecting the RG-8/U to the aluminum Foam flex. We used a Dill Tower TV tower for a rugged S10-per-section mast. Rohn 11 i in. heavy galvanized mast is used to rotate and support the i I-element quad.

Figure 5, a close up of the d riven-element connections, reveals the screen-mesh structure. The round 9 in. flat plate is connected lo the aluminum A-frame struts^ The plate is made from M-IO yellow brass. Plate-to-boom attachment is accomplished using right-angle shelf brackets which are thoroughly bolted to the boom with 3/16 galvanized roundhead machine screws. Rivets are used to hold the screen to the A-frame. From this position we can also see where the boom was electrically broken

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