While the text is as non-techinical as possible, there are certain terms and definitions which must be used. Presented here is a partial list of the "Cast of Chracters" used in the book. This is just one more way I've kept the answers to the questions meaningful and consistant. When you see an unfamiliar term in the text, the "Cast of Characters" is right at the front of the book for easy reference.

Cast of Characters

Antennas are simple. Just toss some wire in the air and viola .... Yeah, right!

Concepts and Definitions

I was going to put these few pages in the in the back of the book because I didn't want you to open this book and be faced with a lot of technical jargon, mathematics, and other confusing issues. However, since we are discussing a very technical subject, we need to be familiar with certain terms and concepts. So, meet the cast of characters presented in this saga.

All technical references in this publication are made to the ARRL Antenna Handbook, either the 12th, 14th, or 17th edition. This information is used with the permission of the ARRL. Various editions are used because each presents certain subjects differently. I encourage you to purchase a copy of the latest ARRL Antenna Handbook and keep it handy. That book often dedicates several pages to thoroughly explain what I have compressed into a single paragraph. If you don't understand a particular concept, please refer to the "handbook" for a complete explanation of the subject of interest.


Counterpoise

A counterpoise is a wire or system of wires, insulated from the ground. Its purpose is to serve as an artificial ground for an antenna. Generally, one or more conductors in a counterpoise are resonant on each band of frequencies on which the associated antenna will operate.
dB or decibel

The "bel" is the fundamental unit in a logarithmic scale for expressing the ratio of two amounts of power. It is named after Alexander Graham Bell. A logarithmic scale is necessary because the human ear perceives the loudness of a sound logarithmically. To the ear, the minimum detectable change in loudness is one decibel or 1/10 of a bel. This is for a trained individual, listening under ideal conditions. Under most circumstances, a change of 3 dB or doubling the power of the source signal will go unnoticed in typical on-the-air operations. It is important to have this reference for comparing performance and results.

The decibel is based on power ratios.

dB=10 log10 (P1/P2)

Voltage or current ratios can be used but ONLY when the impedance is the same for both values of voltage or current. When the impedances are the same, the number of decibels for a given power ratio is give by:

dB=20 log (V1/V2) or dB=20 log (I1/I2)

V=voltage
I=current

A value greater than zero indicates gain (i.e., 6 dB or + 6 dB). A value lower than zero indicates a loss (i.e., -6 dB).
Rather than working with logarithms, it is far easier to use a calculator or use a chart to look up dB values.

10

 "The magnitude and phase angle of the input impedance depends on the SWR, the (feed) line length, and the (impedance) Zo of the (feed) line. If the SWR is small, the input impedance is principally resistive at all line lengths; if the SWR is high, the reactive component may be relatively large. The input impedance of the line can be represented by a series circuit of resistance and reactance, where Rs is the resistive component and Xs is the reactive component. Frequently the "s" subscripts are omitted, and the series-equivalent impedance denoted as R + jX. The j is an operator function, used to indicate that the values for R and X cannot be added directly, but that vector addition must be used if the overall impedance is to be determined. (This is analogous to solving a right triangle for the length of its hypotenuse, where R and X represent the length of its two sides. The length of the hypotenuse represents Z, the overall impedance.) By convention, a plus sign is assigned to "j" when the reactance is inductive (R + jX), and a minus sign is used when the reactance is capacitive (R - jX)." (I will use this convention throughout this book)(This information is found in theIt is important to note that when you see the "j" operator with a positive value, the antenna is too long for the frequency being measured. Just the opposite is true if the "j" operator is negative. The antenna is too short. Nonresonant antennas are an exception. ARRL Antenna Handbook, 14th edition, pages 3-6)Since complex impedance (R +/- jX) is now indicated on readily available antenna test equipment, this simple factor is very valuable when adjusting antennas for best SWR.

Input impedance

Factors determining the Input Impedance of a transmission line.

Feed point impedance

The impedance at the feed point of the antenna may be expressed in terms of R + jX.
It is a hypothetical antenna radiating or receiving equally in all directions. Isotropic antennas do not exist physically, but represent a convenient reference antenna for expressing the directive properties of actual antennas.   Isotropic antenna

"The energy supplied to an antenna is principally dissipated in two ways: radiation of radio waves and heat loss in the wire and nearby dielectrics. The radiated energy is the useful part, but it represents a loss just as much as the energy used in heating the wire is a loss. In either case, the dissipated power is equal to I2R. With heat losses, R is a real resistance. For radiation, however, R is a virtual resistance which, if replaced with an actual resistor of the same value, would dissipate the power that is actually radiated from the antenna. This resistance is called the radiation resistance. The total power loss in the antenna is therefore equal to I2(R0 + R), where R0 is the radiation resistance and R the real resistance, or ohmic resistance." (ARRL Handbook, 17th edition, pages 2-6.)

   Radiation Resistance
 Symbolized by X. Reactance is the opposition to the flow of alternating current. A capacitive reactance (XC) is the opposition offered by capacitors, and inductive reactance (XL) is the opposition offered by a coil or other inductance. Both inductive and capacitive reactance is measured in ohms. In tuned circuits, resonance occurs when XC and XL have the same value (and opposite signs). They cancel themselves.   Reactance 

11

This is only two of the four pages covering the "Cast of Characters."

Note: The actual pages from the book are similar in appearance. I had to reformat the pages slightly to accommodate a web format without scanning in the actual page. Had I scanned in the original pages, a lot of detail would have been lost and the files would have been large. What appears above is very close to the original.

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