. QST . ector-type array hasa bandwidth of about 5 Mc. in these bands, com-pared to 8 or 12 Mc. for the conventional col-linear designs. The bandwidth of the directorbeam for 50 Mc. would be only about 2 Mc, andperhaps 12 Mc. or so at 420 Mc. These valuesare too low for full band coverage, so the designwould have to be for the parts of these bandswhich are of primary interest. The bandwidth isample for the 144^ and 220-Mc. bands withdesign centers at 146 and Mc. A close-spaced director, whether used withone or two driven elements, detunes the drivenelements and all elements have to be ma
. QST . ector-type array hasa bandwidth of about 5 Mc. in these bands, com-pared to 8 or 12 Mc. for the conventional col-linear designs. The bandwidth of the directorbeam for 50 Mc. would be only about 2 Mc, andperhaps 12 Mc. or so at 420 Mc. These valuesare too low for full band coverage, so the designwould have to be for the parts of these bandswhich are of primary interest. The bandwidth isample for the 144^ and 220-Mc. bands withdesign centers at 146 and Mc. A close-spaced director, whether used withone or two driven elements, detunes the drivenelements and all elements have to be made alittle longer than expected. For example, a direc-tor in this design is 39 inches long for the 2-meterband, and 253 2 inches long for the 220-Mc. , the driven elements can be tunedto resonance by a short stub, and the main trans-mission line tapped across this stub at the properpoint for impedance matching. There is, there-fore, no critical length for the driven elements in April 1955. such a system. Where two such 3-elenieiit baysare used a single stub can l)o used to resonate theentire system. In curtain arrays or with Yagis spaced a halfwavelength apart, there is a bucking action ofdirectors of one bay upon those of the other. Re-flectors spaced a half wave apart aid slightly inthe forward gain of a beam, especially in a 4-or 8-element design. Directors, on the otherhand, tend to cancel each others gain when usedat half-wave spacings between bays. It wasfound that ^s ^ ^-wavelength spacing mini-mized this efTect when two directors were used,but ^ 8 wavelength was not sufficient spacing fortwo bajs having four directors each in a broad-side beam, in tests at WGAJF. A 2-meter ver-ticall>-polarized beam of this type had a verysharp front lobe, with large side lobes and lessthan expected forward gain. When the two 6-element Yagis that made up this array were cutapart and stacked vertically, a considerable im-provement in forward gain resulted, and therewas
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectradio, bookyear1915
