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Steve Nosko wrote:
"Are the patterns in the handbook all equal power division?" The subscript says: "The two elements are assumed to be thin and self-resonant, with equal-amplitude current flowing at the feed-point." I think the "Antenna Book" authors were familiar with Kraus` Fig. 11-11 on page 290 of the 1950 edition of "Antennas". Kraus` Fig. 11-11 is similar to the "Antenna Book" Fig 11 on page 8-8 of the 19th edition. Kraus makes a point of G.H. Brown`s equal power observations. I am familiar with the negative-resistance tower occasionally found in a broadcast array. John E. Cunningham says in the "Complete Broadcast Antenna Handbook": "In an array of four towers or more, the resistive part of the driving-point impedance of one or more of the towers often has a negative value. This means that the tower obtains its energy through the mutual impedance between it and the other towers of the array. This is a confusing situation, but if it is carefully thought out, it will cause no serious problems. We know the following things concerning the negative tower: 1. The tower must carry a current of the proper magnitude and phase. 2. The direction of this current is 180-degrees out of phase with what it would be in a tower having a positive base resistance. 3. We need some method of controlling the magnitude and phase of the tower current. The simplest, although not the most efficient way of handling the negative-resistance tower is to terminate it through a matching network to a resistor, as swhown in Fig.11-15. The energy that the negative tower actually gets from the other towers is thus dissipated in the resistor. The magnitude and phase of the current may be controlled by the parameters of the network. Naturally, this isn`t a very efficient arranngement, particularly if the negative tower handles a substantial amount of current. The preferred way to handle a negative tower is to feed the energy back to the power divider, where it will be passed back into the feeder system again. In this way, all of the energy is radiated rather than some being dissipated in a resistor. Figure 11-16 shows an arrangement for recovering power from a negative-resistance tower.----" Since I can`t do diagrams, I suggest finding a copy of the book. It`s a good one. Best regards, Richard Harrison, KB5WZI |
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