Uss Wheeling Antenna

"S, A. Schelkunoff, 'Antennas of

Arbitrary Size and Shape/' Proc,

Ddrr Antenna

Fig, 2. 77?e DDRR antenna is shown here installed aboard the U.S. Navy communications ship U.S.S. Wheeling. The antenna is seen mounted ait on the root of the helicopter hangar\ Operating efficiently even though exposed to the weather, the antenna was later covered with a pillbox fiberglass radome housing (official US. Navy photograph).

impedance3 of a cylindrical vertical conductor monopoly antenna over ground having a conductor radius "a" and length h. It is an average value because of the variable nature of l he posi monopok anten na's characteristic impedance wiih length h, Sc helkUnoff s equation (1-2.0) looks ^o simple in form and very similar to

!The symbols Kc and Km are used to denote the characteristic impedance of the horizontal and vertical monopoly antenna transmission lines, respectively, instead of Z

0, in order to jvoid getting these values confused wiih the Z0 of the standard transmission line we will use to feed the DDRR antenna.

(M.0), yei ii is loaded with e I e c t r omagnetic dy na mite ! We will discuss just how ¡n Pari U. Here we can honestiy say that, aside from Ohm's Law, this simple hlile formula may become one of the most useful expressions known to the ham fraternity for getting quick and easy practical answers to real antenna problems of all kinds. Oh yest if vou mufiiply the answer you get from 11-2,0) by two, it gives the average characteristic impe-dancc (Ka) of a balanced doublet antenna in free space of total length (2 h) formed fro mi two identical "monopoles1 of length h and cylindrical conductor radii

Tuning the DDRR

Armed with the simple formula (1-i.O) and the seemingly simple equation (1-2,0), we are fully equipped now to move on Lo design our DDRR for resonance and tuning over the width of the entire 75 meter band (or a bit more). Turning to Fig. 3(c), the DDRR antenna is now illustrated as being an antenna system composed of Ato distinct rf transmission lines, one connected to the other. Pleasu do not let ihe drawing fool you. The first transmission line section, of electrical length h° and characteristic impedance Km, shown "lying over on its side" still represents the vertical post of the DDRR antenna, it is just easier lo indicate the post in this way when it is represented as an rf transmission line. In our "model- drawing of the DDRR antenna system of "open wire" lines, we have two terminals to represent the ground plane end of the post; terminal IG is ground at a point where the base end terminal (1A) of the post connects to it. At a distance of Ii away from the post base, the top end of the monopole transmission line has a second terminal (2A). However, "ground" is now labeled 2Gt and represents a circle drawn on the ground

ELECTRICAL "MlRRQH" HMA&E PL ANE J

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