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Scanner Antenna Users Guide

Austin Antenna Logo

  by Austin Antenna

  The Leader in Multiband Technology

 Introduction

The broadband receivers and scanners with auto-tune, frequency scan and search capabilities have reached a fantastic state of the art level. The transition of these electronic devices from the not so long ago days of the crystal controlled units represents a quantum leap in technology. The new receivers and scanners have necessitated a need to provide broadband and multiband antennae to assure the maximum performance. While all this electronic wizardry has been in progress, similar technological advances have been made in the art of antennas.

The pricing of today's scanners and receivers ranges from approximately $200 to $5000. No small investment to be sure! One of the most overlooked parts of the system is the antenna. Most scanners come equipped with either a small telescopic whip or an even smaller coiled up wire housed in a flexible rubber sheath. This latter configuration is commonly referred to as a "rubber duck". While the terms are used in relationship to antennae, it is dearly understood by anyone skilled in the art of antenna technology that they bear very little, if any, relationship to a properly designed resonant device deserving to be called an "Antenna". One would probably get just about as much performance out of a "duck" or a "whip" attached to his or her scanner. These devices could more appropriately be referred to as "Wicks", which is a device that when suspended in some medium will pick up or absorb some of the medium on its surface. As an antenna, a wick performs equally poorly on all frequencies.
                   Austin Antenna's Multiband Scanner Antenna User's Guide Scanner Radio

Check out Austin Antenna's   Ferret Base    Spectra Mobile   Condor Portable

 Anatomy of an Antenna

Antennas commonly thought of by most people as "just a piece of wire" are anything but! The appearingly simple device is in actuality the by-product of one of the most sophisticated and complex sciences known as "Electromagnetics". To be classified as a "real antenna" the device must be properly designed:

1. To have a resonance at a specific frequency, band of frequencies or group of frequency bands.

2. To assure that the electromagnetic field created by the antenna is correctly positioned for maximum performance.

3. To present a correct feed impedance to the scanner or receiver.

While sounding terribly complex, this is really quite simple to understand. As a matter of fact it is considerably easier to understand than in many instances to accomplish. Taking things point by point:

 

 Resonance: 

Radio signals are electromagnetic fields formed by the energy radiating from the antenna of the source transmitter. For the scanner listener, these sources most usually are the police and fire base stations, trucks, cruisers, etc. These sources are operating on frequencies assigned to them by the Federal Communications Commission. Frequency is a way of describing the dimensions of an electromagnetic wave. Let's give it a try!

Example:

The Podunk Police Department is assigned the frequency of 155 MHz. [155 Megahertz, le, 155 million hertz.] By the way, megahertz used to be called megacycles, but a few years ago just when everybody had gotten real familiar with cycles, this was changed to hertz to honor the German scientist Heinrich Hertz for his accomplishments in electromagnetics and related fields. This information should provide some comfort to those who feel overlooked as Heinrich died about 100 years ago.

              OK- The equation: [A real brainburner.]

984 X 12 /Frequency in MHz=length of the wave in inches


             For Podunk 984 x 12 / 155 = 76.180 inches.

The most common antenna configuration utilized for transmission and reception is a length of 1/2 wave.

            492 X 12 / Frequency in MHz=1/2 wavelength

        So for Podunk this would be 76.180 / 2=38 inches.

When an antenna is designed according to this definition it is said to be resonant. No! It is not exactly as simple as this, but this definition is fundamentally true, and it is correct that an antenna that is resonant is significantly more efficient than anything that is not. It is also useful in understanding the elementary antenna criteria, and that the "whip" and the "duck" are not resonant at more than one frequency. So If your duck is 6" long and your whip is 15" long, they AIN'T working too good on the Podunk frequency. Got it ? ?

Austin Antenna's Multiband Scanner Antenna User's Guide Ferret Base Antenna
An Inside look at antenna
technology at its best.

Austin's Ferret Multiband Antenna

Check out Austin Antenna's   Ferret Base    Spectra Mobile   Condor Portable

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