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Off Air Antenna Installation Guide
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Posted: 12 Jul, 2007
by: Admin A.
Updated: 12 Jul, 2007
by: Admin A.
INTRODUCTION

he information in this manual has been gathered from some of the most experienced antenna installation professionals in the country and compiled by Channel Master® field engineers. It is intended for technicians who are, or plan to become professional antenna installers. Any handy “do-it-yourself” consumer can mount an antenna , run transmission line and pull in some kind of a signal. But only a professional can select and precisely install the correct antenna and assure his customers years of superior TV/FM reception.

Back in the 1940s, TV antennas were actually manufactured by hand at the installation site. Each antenna was assembled, piece by piece, at the customer’s home. Channel Master eliminated this time-consuming labor by introducing the first preassembled TV antenna , providing excellent reception in all areas and at reasonable prices.

Today medium-to-high gain , broadband antennas are essential for good reception. Even the most expensive color TV or FM stereo receiver can’t perform to full potential without the strong signals that only a quality antenna system can provide.

Advanced antenna theory and design is not included in this manual. The greatest emphasis is on practical, time-tested methods and procedures for properly installing TV and FM antennas. With this foundation of knowledge, you can build your reputation as a professional antenna installer–one who is capable of assuring his customers the finest performance from today’s sophisticated TV and FM equipment.

A WORD ABOUT ANTENNA SPECIFICATIONS

Sensitivity ratings are based on optimum conditions over unobstructed terrain. What lies between a transmitter and an antenna installation will have a direct bearing on what type of antenna is appropriate.

Factors to consider are: the power output and height of a transmitting antenna tower, the type of terrain between the tower and the receiving antenna , and the size and number of buildings that lie in the path of the transmission.

All Channel Master VHF/FM and UHF/VHF/FM antennas have sensitivity classifications such as “fringe,” “suburban,” “deep fringe,” etc. These classifications are designed to indicate at what distance from a TV transmitter the antenna will provide the best reception. Our antenna lab has computed the following chart as a general guide:

Area Designation For VHF For UHF
Deepest Fringe 100+ miles 60+ miles
Deep Fringe 100 miles 60 miles
Fringe 80 miles 45 miles
Near Fringe 60 miles 40 miles
Far Suburban 50 miles 35 miles
Suburban 45 miles 30 miles
Far Metropolitan 30 miles 25 miles
Metropolitan 25 miles 15 miles

Additional performance information is available from Channel Master upon request. Write to:

Channel Master

P.O. Box 1416 1315 Industrial Park Drive Smithfield, NC 27577

Or contact us through our site on the World Wide Web at:

www.channelmaster.com

CHAPTER ONE: ANTENNA SELECTION

asically, a receiving antenna is a device for intercepting the electromagnetic waves or signals, sent from a transmitter . Some antennas are simple vertical poles; others are small wire loops attached to the back of a TV set.

In this manual, we will discuss the outdoor TV antenna design with which most of us are familiar: a central horizontal boom with small elements attached at right angles.

The main receiving element of an antenna is called the dipole (Fig. 1-1). All of the other antenna parts are designed primarily to help the dipole do its job. The dipole consists of two half-elements to which the transmission line is attached. It is the element around which the other antenna parts are designed and positioned.

BASIC TV ANTENNA TYPES

TV antennas can be grouped in four major functional categories: VHF/FM, UHF, UHF/VHF/FM, and FM only combinations.

VHF and FM Antennas

Most VHF (Very High Frequency ) antennas are engineered to receive TV channels 2 through 13. They also will receive the FM radio band, which is located between TV channels 6 and 7. FM only antennas are available also (Figure 1-6). Channels 2 through 6 are known as the low band. Channels 7 through 13 are referred to as the high band. Some VHF antennas are designed to receive only one band, either the low or high band. Antennas designed to receive both the low band and the high band are called VHF/FM broadband antennas (Figure 1-2).

TV channel 1 “disappeared” in the early days of TV because of a change in frequency assignments by the Federal Communications Commission (FCC). A reshuffling of FM, Amateur, and other bands removed TV from the frequencies previously reserved for TV channel 1. Because the other 12 TV channels were already numbered 2 through 13, the channel 1 designation simply was dropped.

UHF Antennas

UHF (Ultra High Frequency ) antennas are designed to receive TV channels 14 through 69, the UHF TV band. The UHF TV band originally extended from channel 14 to channel 83. However, the FCC now has reassigned channels 70 through 83 (also known as the translator band) to mobile communications use. Although there still are many antennas capable of receiving all 82 channels, the translator band (former TV channels 70-83) is useless to the TV viewer. UHF TV antennas come in a wider variety of shapes and sizes than

ANTENNA SELECTION

VHF/FM antennas. The wider variety of UHF designs (Figure 1-3) is possible because they don’t require the long elements that VHF/FM antennas do.

Combination UHF/VHF/FM Antennas

Combination UHF/VHF/FM TV antennas are designed to receive both the UHF and the VHF/FM bands. Although the use of separate antennas for each band is ideal for peak reception, high-performance UHF/VHF/FM combination models are readily available and are becoming increasingly more popular. Examples of combination UHF/VHF/FM antennas are shown in figures 1-4 and 1-5.

HOW TO SELECT THE RIGHT ANTENNA

There are many bands and hundreds of TV antenna models available. However, choosing the right one is relatively easy if you are aware of a few basic reception and TV antenna characteristics.

First, “good reception,” or production of a snow -free color TV picture, requires a signal level of about 1000 microvolts (µV) = 1 millivolt (mV). To deliver this signal level to the receiver, the antenna requires a certain antenna gain . The amount of gain required is dependent on the distance between the station’s transmitting antenna and the receiving antenna . The required type of antenna therefore depends on the channels to be received and the distance and direction of the customer’s home from the transmitting antennas. These facts are readily available for any area, but be sure your information is accurate and complete. Call a local TV station if you have questions. Most TV stations are willing to help TV antenna installers because they also benefit from the improved reception to the station’s viewers.

Be sure to discuss with your customers the number and types of channels that are receivable. This may sound basic, but your customers may not understand the difference between VHF/FM and UHF. They also may not be aware that with the right equipment they may be able to receive out-of-town channels, some of which may carry sports programs that are locally blacked out. The most important points to remember when selecting an antenna are its gain , sensitivity classification, directivity, and front-to-back ratio.

Gain

The gain of an antenna indicates the relative strength of signal it can deliver to a receiver. Most manufacturers list the gain of their antennas in decibels (dB). The higher the antenna gain , the stronger the signal at the antenna output terminals. In most cases, the larger the antenna , the higher the gain .

Channel Master® SMARTenna® UHF/VHF Antenna

If you are in doubt about the amount of gain required, select an antenna that is slightly larger than you think is actually needed. The performance of all components deteriorates slightly during the years they are exposed to rain, sun, wind, and corrosion. Consequently, to ensure quality reception for a longer period, choose an antenna with a little more gain than is necessary. (Note: Excessive gain may cause overloading. Therefore, choosing the antenna with the highest gain might create more reception problems than it cures.)

Sensitivity classifications are used to indicate the type of reception area for which the antenna is designed. Certain ranges of gain are best suited for certain types of areas. The appropriate range of gain for a specific area is what a manufacturer is indicating when labeling an antenna . Outer Suburban or Near Fringe Table 1-1 is a chart of typical sensitivity classifications. It indicates in miles, how close an antenna must be to the transmitter to produce the best signal level. The classifications are somewhat general because reception conditions at various sites within a particular type of area may be different.

DIRECTIVITY

Direcitivity is the ability of an antenna to intercept signals from only one direction and reject those from other directions. Directivity indicates the antenna ’s ability to intercept signals arriving at its front and reject signals coming from the sides and rear. Generally, the more highly directive an antenna , the better it can reject signals from the sides and rear.

The front-to-back ratio of an antenna can be helpful when attempting to determine its directivity. Front-to-back ratio is expressed in decibels (dB) and can be found in the literature accompanying a new antenna . This ratio indicates an antenna ’s ability to reject signals coming from the rear (rear rejection). For example, an antenna with a front-to-back ratio of 25 dB will receive about 18 times more signal strength from the front than from the back.

In most cases, an acceptably accurate estimate of an antenna ’s directivity can be made by comparing its specified front-to-back ratio with the relative sensitivity classifications listed in Table 1-1.

The sensitivity classifications in Table 1-1 are intended only as general guidelines for evaluating directivity. Other factors, such as the antenna ’s beamwidth , can affect its directivity. Beamwidth is related to an antenna ’s overall gain and indicates how wide or narrow the antenna ’s reception area is. For example, if two antennas have the same front-to-back ratio, the one with the highest overall gain will have the narrowest beamwidth and consequently, will be the most directive.

ANTENNA SELECTION

An antenna with a relatively narrow beamwidth generally is best suited for areas where interference from sides is a problem. An antenna with a broad beamwidth is best suited for areas where a broad beam is needed to capture the signals from widely separated stations, and where interference is minimal. Beamwidth information, if included by the manufacturer, is usually displayed by use of polar plots like the one in Figure 1-6.

Selecting the most suitable antenna becomes easy with experience, but selecting quality materials should be the first decision to make before starting any installation. High-performance color reception usually requires highly sensitive equipment. In the long run, it pays to use the finest equipment available, from the antenna down to the receiver end of the transmission line. The slight additional cost should be considered an investment in longer system life and optimum performance.

CHAPTER TWO: SAFE INSTALLATION PROCEDURES

here are extremely important safety factors to consider. Learning and following simple safety precautions can, quite literally, save your life. Following safe procedures also helps prevent costly damage to your equipment and your customer’s property.

No list of safety tips can cover every potential hazard. Consequently, careful planning, common sense, and good judgment must be used at all times.

  1. Locate and avoid power lines and other wires in the work area.
  2. Do not climb on a wet or icy roof.
  3. Do not attempt high installations on windy days.
  4. Do not hesitate to turn down a job that seems too dangerous.
  5. Use only the sturdiest commercial-grade ladders. (Types with wide, slip-preventive rungs and bases are essential. Avoid types with round rungs.)
  6. Do not position ladders at an angle steeper than 70Ëš. Steeper angles can cause a ladder to slip sideways.
  7. Dig the base of the ladder into the ground if possible.
  8. Do not place ladders on slate that is wet or hot. Wet or sun-heated slate is very slippery.
  9. Do not climb on roofs that have curled or worn shingles. (Old shingles break easily or pull out.)
  10. Wear seasonable clothing that is neither too tight nor too loose. Wear snugly-fitting rubber-soled, low-heeled shoes or boots.
  11. Wear a pair of durable but flexible protective gloves whenever they will not interfere with the work process.
  1. Carry a well-equipped first aid kit in your truck.
  2. Keep a couple of cans of wasp and hornet spray that will shoot with a long stream.
  3. Have an effective insect repellent handy during spring and summer months. (Wipe off your hands after applying it.)
  4. Any antenna mounted on 20 or more feet of mast requires more than one person to install.
  5. Carefully survey the job before beginning the installation to locate secure handholds, dangerous conditions (such as power lines and weak roofs), and the safest and most convenient placements for ladders.
  6. Do not climb onto a roof when there is no one else around.
  7. Be sure all of your helpers know and follow safe procedures.
  8. Do not step into roof valleys (the area where two roofs join); they often are weak, even on new homes.
  9. Do not install antennas under large, overhanging tree branches if it can be avoided.
  10. Buy only the best quality tools and equipment. Besides lasting longer, top-quality tools and equipment generally do not break or bend as readily as do cheaper products.
  11. Antennas must be installed away from power lines a distance equal to at least twice the combined length of the mast and antenna .
  12. Refuse to perform jobs that are not directly related to the antenna installation. If you do and a liability problem develops, your insurance probably will not cover it.

Thoroughly plan every installation. Carefully think through the job, and don’t take dangerous shortcuts.

CHAPTER THREE: MOUNTING FOR OPTIMUM SIGNAL STRENGTH

deally, an antenna should be mounted at the point where the signals are the strongest, though often this is impractical or impossible. Also, the antenna should be mounted where it can be easily serviced should repairs or adjustments be required in the future. So carefully “aiming” (orienting) the antenna and adjusting its height often can overcome the problems created by installing it in a slightly weaker signal area.

In an area where there is a relatively short, unobstructed signal path between the installation and the transmitting towers, you can mount the antenna just about anywhere and receive sufficient signal. As you move deeper into the fringe areas however, there may be significant differences in signal strength at various points on the roof. This is where careful antenna selection, precise orienting, and accurate adjustment of the height become essential. The careful installer should be able to locate a spot where there is both a usable signal and sufficiently easy access to the antenna .

Large trees can present reception problems and nearby high-voltage power lines can cause interference that cannot be completely eliminated. Consequently, the further the antenna is from large trees and high-voltage lines, the better the reception will be.

WALKING THE ROOF FOR OPTIMUM SIGNAL STRENGTH

“Walking the roof” is usually the best way to find the spot on the roof where the strongest signals are present. First, attach a small TV antenna to short mast (4-6 feet). Attach one end of a short transmission line to the antenna terminals. Attach the other end of the transmission line to the input jack of a field-strength meter. Then walk to the most suitable mounting areas. Point the front of the test antenna in the general direction of the transmitter tower(s). Slowly, rotate the antenna while carefully watching the field-strength meter. (Most field strength meters are equipped with shoulder straps that free both of your hands for manipulating the antenna .)

USING A FIELD-STRENGTH METER

A small, battery-powered portable TV is helpful for determining general reception quality. However, there is no better way to determine actual signal strength than to use a field-strength meter (Figure 3-1). It is one of the best investments you can make. The meter will save you so much time and trouble that it will quickly pay for itself.

Field-strength meters come with detailed operating instructions. Below are general characteristics and operating procedures that apply to most field-strength meters.

A field strength meter has an input impedance of 75 ohms. Most television antennas have an output impedance of 300 ohms. For accurate measurements these two impedances must be “matched.” Attach a balun (matching transformer) to the antenna terminals and run coaxial cable from the balun to the meter input jack. (TV coaxial cable has an impedance of 75 ohms.)

Most field-strength meters will measure the strength of both VHF and UHF signals and will separately measure each channel . Most field strength meters will also separately measure the picture and sound signals of each channel .

The ideal is to get the strongest signal possible. When this is not possible and you need to sacrifice a little strength, connect the test antenna output to a battery operated, portable TV set and check the picture and sound to ensure that the signal levels are adequate for acceptable reception. The TV will also help you better explain reception possibilities and problems to your customers.

A field-strength meter indicates signal strength in microvolts (uV) and decibels relative to one millivolt (dBmV). One microvolt is one-millionth of a volt, or 0.000001 volt. The microvolt reading is probably the easiest to use. As a general guideline, a signal level of 50 uV at the antenna output terminals is the weakest usable signal; however, it will require strong preamplification to provide acceptable TV reception.

Antenna output signals of 500 uV and above are considered adequate. Any signal level below 1,000 uV will require preamplification.

To use the field-strength meter, orient your test antenna in the direction of incoming signals and activate the meter. To orient the actual installed antenna in an area where several channels are coming from the same general direction, aim the antenna to obtain the highest reading with the field-strength meter set on the highest channel to be received. (Channel 13 is the highest VHF channel , and 69 is the highest UHF channel .) As a result, this will orient the shortest antenna element as well as properly align remaining elements. Of course, if the channels are coming from different directions, you will have to take separate readings for each and adjust the antenna (s) accordingly.

ADJUSTING THE HEIGHT FOR OPTIMUM SIGNAL STRENGTH

Just as the received signal strength varies with the mounting site and the direction in which the antenna is pointed (oriented), the height at which the antenna is installed will also affect signal strength. A few feet up or down may make a big difference in the level of the received signal(s), especially on UHF channels. Watch your field-strength meter as you slowly raise and lower the test antenna .

The height at which you ultimately mount the antenna depends on two things: signal strength and practicality. You should mount the antenna only as high as necessary, even if your meter indicates that the signal level continues to increase as you raise the antenna . Choose the height at which you get the highest signal level without having to resort to guyed mast and other more expensive and difficult to install equipment. Your objective should be to get as close as possible to an unobstructed “line of sight” between the transmitter tower(s) and the receiving antenna so that the signal clears all large buildings and other obstructions.

In some cases, obtaining adequate signals may require the installation of a multiple array. A multiple array is two or more antennas set at different heights on the same mast (Figure 3-2). Ideally, these antennas should be spaced seven feet apart so that they won’t interact with each other. If this is not practical, try to mount them at least five feet apart. When installing more than one antenna on a mast, try to mount the largest (heaviest) at or near the mast support. This will help prevent excessive strain on the mast during high winds.

CHAPTER FOUR: TOOLS, MASTS & HARDWARE REQUIREMENTS

Tools

The majority of the tools and equipment you will need for most installations are apparent. The following is a list of useful tools and miscellaneous materials that might also come in handy.

  1. A complete set of nut drivers (spin-tights).
  2. A set of ratchets and sockets.
  3. A pocket compass, for orienting the antenna and setting up the rotor when the compass bearing(s) of the transmitter tower(s) is known.
  4. A drill brace with a wide assortment of bits.
  5. A good quality leather tool belt.
  6. A crimping tool for fastening coaxial connectors.
  7. Caulking compound for sealing the holes where transmission line enters the house.
  8. Roofing tar (plastic roof cement), for sealing around screws on the roof.
  9. Silicone grease for waterproofing coaxial cable connectors.
  10. A sledge hammer for driving in ground rods.
  11. A level or plumb bob for ensuring that the