Info

1.61"

1.78"

Fig 7—Boom to mast clamp.

Antenna Height ~ 11 feet

SWR Frequency (MHz)

bit more explanation. First, it is often quite efficient to work with half elements when modeling Yagis, because the assumption that you have a symmetrical antenna enables the software writers come up with a programs that run faster and handle bigger antennas. Thus, the taper schedule specifies just half an element, although this may be a poor way to actually build an element. Also, the schedule doesn't include any overlap required to actually join the elements—it's just the electrical model. Typically, I'll add about three inches to the smaller tubing— since it effectively uses up four 6 foot sections of '/« inch tubing. Finally, unless stated otherwise, spacing dimensions given by programs are center to center distances.

Fig 6 shows a drawing of the an tenna—I moved the boom off to one side for clarity. Remember, the boom is just a mechanical support. I designed the element clamps for minimal interaction, so it really isn't part of the electrical design. Thus, it would work just as well—or maybe even better—if you could magically suspend the elements in mid-air, without real supports that interact with the antenna.

Table 1 shows some SWR measurements made at the ARRL HQ parking lot with an SWR analyzer and a cable with 0.3 dB of loss. Cable loss makes the SWR look better. To correct for it, one can convert SWR to return loss and subtract out twice the cable loss, because the reflected power makes a round trip through the coax.

Fig 7 is a drilling guide for a boom-to-mast plate made out of lU inch 6061-T6 aluminum plate. I made this plate a long time ago and used it because it was available.

Notes

1Dr James Lawson, W2PV, Yagi Antenna Design (Newington: ARRL, 1986), no longer in print. 2http://web.wt.net/~w5un/ is Dave's Web page and http://web.wt.net/~w5un/ w5unqu97.htm ought to get you to the Quagi design, assuming it hasn't been moved.

3Dean Straw, N6BV, Ed, The ARRL Antenna Book, 18th Ed. (Newington: ARRL, 1997), ARRL Order No. 6133. ARRL publications are available from your local ARRL dealer or directly from ARRL. Mail orders to Pub Sales Dept, ARRL, 225 Main St, Newington, CT 06111 -1494. You can call us toll-free at tel 888-277-5289; fax your order to 860-594-0303; or send e-mail to [email protected]. Check out the full ARRL publications line on the World Wide Web at http://www.arrl.org/catalog.

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