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

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.

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.

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.

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 antenna mast is installed perpendicularly.
12. A map to aid antenna orientation. (Aircraft maps are ideal. Most airports sell them.)
13. A strong step ladder (in addition to extension ladders).
14. A magnetic stud finder.
15. A small, portable TV that operates on both standard house current (117 volts AC) and batteries.

Masts

Most antenna hardware catalogs list a wide variety of mounts and masts. Most however, are variations of a few basic types. By taking into account signal strength and ease of installation, it’s not difficult deciding which site, mount, and hardware to use.

A mast (Figure 4-1) is used in every installation. The mast is the vertical tubing that supports the antenna. Conventional masts are available in 5 and 10 foot lengths. Telescoping mast units (Figure 4-2) are

Fig. 4-1. Examples of 5 and 10 Fig. 4-2. A telescoping mast.

available in 20, 30, 40 and 50 foot lengths. Each type

foot mast sections.

is available in various wall thicknesses that provide different degrees of strength and rigidity. Your choice will depend on the height, weight, and size of the antenna being installed and also on wind conditions in the area.

MOUNTING SITES AND RELATED PROCEDURES Attic Installations

An attic installation (Figure 4-3) may work in areas where strong signals are present. In most cases, an attic installation is the easiest, fastest, most economical, and most convenient installation. There are a few conditions however that can prohibit an attic installation. Shallow attics that are obstructed by rafter supports may not accommodate the size antenna required for the installation. Most attics are not large enough to accommodate multi-antenna arrays and rotors. Also, aluminum foil on insulation, aluminum or steel siding, metal gutters at the attic level, and metal lath under older plaster walls all can interfere to some degree with reception.

To determine if an attic installation is suitable, take a test antenna, a field-strength meter and a portable TV up into the attic and check the signal level and picture quality. If the signal level is sufficient and there is room enough to properly orient the antenna, assemble the antenna in the attic and attach one end of the transmission line to the antenna terminals. Then prepare the mount for the antenna.

Several roof-type mounting brackets (Figure 4-4) and swivel mounts (Figure 4-5) are adaptable for use in attic installations. The mounting bracket is used to attach the short mast to a rafter or rafter support. The antenna is then mounted on the other end of the mast. The antenna however, must not touch the attic floor. Also, remember that the antenna should be attached to the mast right side up, even though the installation appears to be the reverse of an outside installation.

An alternative method of mounting the mast is to flatten one end of the mast with a hammer and drill a hole in it through which a nail, screw, or bolt can be inserted for securing the mast to a rafter or rafter support. However, this method requires more time and effort than does the bracket method.

Instead of using a mast, you may suspend the antenna from the inside of the roof with guy wires or nylon rope. But don’t let the guy wires touch the antenna elements. They will short out the antenna.

Once you have the antenna mounted or suspended, you are ready to run the transmission line. If at all possible, keep it indoors. Coaxial cable (Figure 4-6) is the best transmission line for any antenna installation. It should be used instead of twinlead even in attic installations. Selection and installation of the correct transmission line is described in the chapter beginning on page 15.

After you have run the transmission line, use a compass and field-strength meter to orient the antenna toward the signal source(s). Check the picture and sound on all channels before you tighten down the clamp that secures the antenna to the mast.

Some manufacturers make special antennas for attic installations. These antennas however, tend to be omni-directional. This means they intercept signals equally well from all directions. Consequently, they will also pick up interference more readily than a good directional antenna.

Chimney Mounts

Chimney Mounts (Figure 4-7) are used more frequently than other types of mounts, but they often are not the best option. Although they are relatively easy to install, the smoke and gases from a chimney can shorten the life of the antenna and significantly impair its performance.

A chimney installation is practical only if the chimney is sturdy and vertical. Never mount an antenna on a deteriorated chimney. During moderate too high winds an unguyed mast taller than 10 feet can exert enough leverage to break off an unstable chimney.

If you choose a chimney mount, use enough mast to place the antenna above most of the smoke and gases. However, to avoid overstressing the chimney, do not mount the antenna more than 10 feet above the top of the chimney. If the height of the antenna must exceed 10 feet to receive satisfactory signals, the mast must be properly guyed. (The correct method of installing guy wires is described in Chapter 7.)

Securing the chimney-mounted antenna and minimizing the stress on the chimney requires the mounting straps to be properly spaced. The top strap should be placed as high up on the chimney as possible. If the chimney has a crown or projecting cap, place the top strap directly under it. The bottom strap should be placed 4 feet below the top strap. If the chimney isn’t long enough to permit this, place the bottom strap as far down on the chimney as possible. If the mast must be 10 feet above the chimney top, don’t use a chimney mount unless you can space the straps at least 30 inches apart. For masts less than 10 feet above the chimney top, the straps should be spaced no less than 24 inches apart.

Be sure the straps are level, with no kinks or twists. The easiest way to level straps is to line them up along the nearest course of bricks. Straps should be centered on the bricks – not over the mortar joint. Pull each strap tight, line it up so that it is level, and then tighten it just enough to hold it in place.

Before the straps are tightened completely, fasten the mast to the mounting bracket. (It is assumed that the antenna has already been clamped securely to the mast, and one end of the transmission line has been connected to the antenna terminals.) Align the mast so that it is vertical. Then completely tighten the mounting straps. Next, orient the antenna. Finally, tighten the clamps that hold the mast to the mounting. Be sure the clamps are tight enough to prevent the mast from being rotated by the wind load on the antenna.

Roof Mounts

There are two basic types of roof mounts: a base mount (Figure 4-8) and a tripod (Figure 4-9).

Tripods are stronger and more rigid than base mounts, but they are also more expensive. When given a choice, use a tripod.

However, if cost savings or limited space require it, a properly guyed base mount will usually work. Unlike a chimney mount, a base mount holds the mast at only one point, the bottom. Consequently, the mast also must be supported by guy wires, regardless of the mast length.

Correct installation of either type of roof mount requires great care and should not be attempted without a helper. Both types of mounts should be secured to the roof with either bolts or lag screws. These should be screwed into only solid wood like a rafter or a truss section. You can locate these with a stud finder.

If you must fasten the mount to the roof in an area where a bolt or screw cannot reach a rafter, send your assistant into the attic with a large square of wood 1-1/2” thick, to act as a backing plate. Have him hold this wood against the entry points of the screws or bolts so that the mount is firmly anchored in both the roof sheathing and the wooden block. This will give the mount needed stability.

When installing a base mount, attach the base plate to the roof in the manner just described, and place the mast (with antenna, guy ring, and guy wires attached), into the U-bolt that has been fastened loosely to the mount. Do not let the bottom of the mast touch the roof; it may tear a hole in the shingles.

Since a base mount must be guyed, an easy way to raise the mast is to first fasten one of the guy wire screw eyes to the roof peak on the end of the roof opposite the direction in which the antenna is lying. Run the end of the guy wire through the screw eye. Have your assistant slowly raise the mast while you pull the guy wire through the screw eye (Figure 4-10). When the mast is vertical, the guy wire you are holding will be approximately the right length for permanent installation. Temporarily secure this guy wire. Install the other guy wires while your helper holds the mast in a vertical position. Check the mast with a level as you tighten and permanently secure each wire. When the mast is vertical and each guy wire has been tightened, orient the antenna and firmly tighten the U-bolt (clamp) on the base mount.

Tripods, as noted earlier, are a stronger, more rigid type of roof mount. The most common tripod mounts are 3, 5, and 10 feet high. The 3 foot tripod is most commonly used.

A tripod mount can be installed and leveled before the mast is inserted. It should always be mounted so that the antenna can be folded down along the peak of the roof. This will enable you to lower it more easily should repairs or adjustments become necessary in the future. Even though tripods are very stable, any tripod-mounted mast over 10 feet high should be guyed.

Ensure the sturdiness of the tripod by anchoring. To protect the roof, use a pitch pad seal under each tripod leg (Figure 4-11). Coat all lag bolts with roofing tar or other sealant to prevent leaks around them. Roofing tar or silicone should be used liberally around all holes, bolts, screws, nails, and eye screws.

Wall Mounts

Many types of wall mount brackets are available. However, many of them are poorly made and will not withstand more than a moderate wind. Buy only the best quality wall mount brackets (Figure 4-12).

When installing a wall mount, space the brackets as far apart as possible (or practical). Generally, the farther apart you space the brackets, the stronger the installation will be. Be sure the brackets extend out from the wall far enough for the mast to clear the roof eaves. As with roof mounts, screw wall mount brackets only into solid wood, and use caulking or other durable sealant around screws.

Mounting from the Ground

Many times you will not want (or will not be able) to mount an antenna on the roof. One of the best alternatives to roof mounting is mounting from the ground (Figure 4-13). With a firm base support and one or more wall mount brackets, a ground mount installation is exceptionally sturdy and long lasting. A good ground mount may also eliminate the need of guy wires.

Correctly preparing the base of a ground mount is very important. The antenna mast should rest on something more solid and stable than just bare earth. If your installation site is on a solid deck or patio, the base is already prepared for you.

When you have to prepare the base yourself, dig a hold about 2 feet deep at the spot where the mast will contact the ground. Remember that the base hole must line up with the wall bracket(s) so that the mast will be vertical. A plumb line and bob suspended from the roof eave can be used to determine the correct positions of the base hole and wall brackets (Figure 4-13). Use bricks or flat stones in the bottom of the hole as a footing to prevent the base of the mast from moving. Concrete can also be used as a footing but you’ll have to wait for it to dry before you can put up the mast.

Once the base is prepared, mount a wall bracket at least 10 feet above the ground or as high as possible. Remember, the farther apart the wall brackets are placed, the sturdier the installation (Figure 4-13). If there is 5 feet or more left between the first wall bracket and the roof eave, add another wall bracket. Be sure the base hole and the wall brackets line up so that the mast will be vertical. This can be determined easily by suspending a plumb bob and line from the roof eave into the base hole. Also remember that the wall bracket(s) must extend out from the wall far enough so that the mast clears the roof eaves. Be sure the screws of each wall bracket are anchored in solid wood. Screw them into the wall studs.

Firmly clamp the antenna to the upper end of the mast. Insert the mast into the base hole or rest it on the deck or patio. Vertically position the mast by “walking” it up hand over hand. Rest it against the wall bracket(s). Loosely fasten the mast to the wall bracket(s). After determining that the mast is truly perpendicular, tighten the bracket(s) a little more. Next, orient the antenna. After the antenna has been oriented, securely tighten the wall bracket clamps around the mast. Finally, if a base hole is being used, fill in the hole and firmly tamp the soil around the base of the mast.

Telescoping Masts

A telescoping mast (Figure 4-14) is used in installations for which standard 5 or 10 foot lengths of mast stacked together would not be sufficiently strong or rigid. A length of telescoping mast is stronger and more rigid than the same lengths made up of standard mast pieces stacked together. Because of their additional strength, some telescoping masts used with ground mounts can be extended up to 15 feet above the roof line without requiring guy wires. Another advantage of telescoping masts is that they can be easily adjusted to odd heights without having to cut the tubing.

Because telescoping masts are heavy and require firm bottom support, they should not be used with chimney or wall mounts. However, because ground and roof mounts do provide bottom support, telescoping masts can be used with these mounts to provide additional height.

For extra strength when installing large antennas, use a telescoping mast that is one size larger than actually needed. This will permit you to attach the antenna to the mast section immediately below the topmost one. This section is larger and stronger than the topmost section because it is reinforced by the 1-1/4” diameter section that remains inside.

When installing telescoping masts 20 feet or shorter in length, lay the mast on the ground and extend it to the desired length. Prop up the small end on a stable support and attach the antenna and transmission line. Then connect the bottom of the mast to the base mount and walk up the mast to its vertical position. (Use a base mount that will swivel!)

For masts over 20 feet long, securely mount and guy the bottom section first. Then attach guy rings and wires to the rest of the sections. Mount the antenna on the upper section, secure its guy ring and the transmission line. Using a person to hold the guy wires to each anchor point, raise each section one at a time, starting with the top. Tighten the wires after the mast is fully extended.

Vent Pipe Mounting

Vent pipe mounting (Figure 4-16) secures the antenna and mast to the plumbing (gas) vent that comes up through the roof of the house. This type of mounting should be used only for the smallest antennas, and then only when economy absolutely demands it. Vent pipe mounts are not sturdy enough for medium and large antennas. Even a moderate wind or ice load may ruin the installation and damage your customer’s property.

Standard vent pipe mounting hardware is available. However, it should be used with great care. Most vent pipes are made of soft materials like copper or orangeburg, which are easily crushed or dented by the stress exerted by the mounting bracket.

Towers

Antennas are mounted on towers (Figure 4-17) when exceptional height (35 feet or more) is required for adequate reception or when an unusually large antenna array must be used. Although they are very sturdy installations if properly installed, towers can be very difficult and dangerous to erect. Tower manufacturers’ instructions and specifications usually include a large number of warnings and precautions that must be strictly followed. The best advice that can be given about tower installations before attempting one of your own, is to work with an experienced tower installer on one or more installations. If possible, have an experienced installer assist you with your first tower installation. If you do find yourself involved in a tower installation, be prepared for some heavy work and for the possibility of having to climb well above the height of the average roof.

If you must climb a tower, use an attachable work platform with a safety ring and safety belt. These are available from some tower manufacturers.

CAUTION: Before climbing any tower, first check the condition of the structure and the guy wires to make sure the installation is safe. Even a newly installed tower may have defects that make it dangerous to climb.

In most cases, a properly guyed 40 or 50 foot telescoping mast can be substituted for a 40 to 50 foot tower installation. It is not only easier and less dangerous to install, it is also significantly less expensive.

A detailed discussion about the various types of towers and the procedures for installing each of them would require more space than is available in this manual. The most accurate and helpful sources for such information is the extremely detailed instructions that most tower manufacturers provide with their towers.

Selecting and Installing Transmission Line

Transmission line or downlead, is the wire that carries the signal from the antenna output terminals to the receiver input terminals. Even the best antenna and the most expensive receiver will not produce an acceptable picture if the transmission line has not been carefully selected and correctly installed. The transmission line is more important than most people realize. Color television reception is sensitive and highly susceptible to interference from many different sources. Transmission line that is carefully chosen and neatly run by an installer who knows what he is doing will reward the customer with clear, distortion-free color TV reception.

The Two Basic Types

There are two basic types of transmission line: 300 ohm twinlead and 75 ohm coaxial cable.

Most antennas are 300 ohm balanced output. Therefore, an outdoor balun is required at the antenna in order to use 75 ohm coaxial cable. If a preamplifier with 300 ohm in put is used, a short length of 300 twinlead will be required between the antenna and preamplifier. Fig. 5-3 shows examples of baluns.

300 ohm twinlead (Figure 5-1) comes in various colors and thicknesses, is the least expensive, but requires more careful installation, and picks up interference signals if they are present. In modern installations, it is only used to connect between an antenna and a preamplifier.

Although more expensive, 75 ohm coaxial cable (Figure 5-2) is easier to correctly install, has a longer life, and does not pick up interference. Coaxial cable is round with a central conductor wire surrounded by plastic insulating material, a braided wire or aluminum foil sheathing, and a water-resistant outer covering jacket.

Most modern TV sets have a single 75 ohm VHF/UHF input. Older TVs frequently have a 75 ohm VHF input and a 300 ohm UHF output. In this case, a band separator will be required. Coaxial cable has many advantages over twinlead and is preferred by most installers.

Installing Twinlead

Start the twinlead installation at the antenna and work toward the receiver. First, assemble the antenna according to the manufacturer’s instructions. Carefully “snap-out” the elements and then mount the antenna on the mast.

Attach the twinlead wire conductors to the antenna terminals with lugs. Never twist bare wire around the antenna terminals. It is a poor connection that will deteriorate even more as rust and corrosion set in.

Next, pass the twinlead through a standout or standoff (Figure 5-4). Install the standout on either the mast or the antenna boom as recommended by the antenna manufacturer. Leave just enough slack to relieve tension on the antenna connections. Crimp the standout firmly enough to securely hold the twin-lead but not so firmly that it deforms the twinlead.

Thoroughly spray the antenna connections with an

acrylic insulator such as Krylon. This will retard corrosion and rust. Also, seal the end of the twinlead if foam is used as part of the twinlead insulating material. This will prevent moisture absorption.

Twinlead must not be run close to metal. Metal interacts with the twinlead conductors. This causes signal mismatch, resulting in inefficient signal transmission through the line.

Horizontal runs of twinlead also act as an antenna. This causes two or more sets of identical signals to reach the receiver at different times producing ghosts on the TV screen. It may also cause “suck out,” or loss of signal.

Some types of twinlead also develop high attenuation (increased impedance) in wet or humid weather. This causes severe signal loss.

If an antenna rotor is used, never run the twinlead and rotor wire through the same standout. The wires and signals will interact, and the quality of the TV picture will be decreased. Use two evenly spaced mast standouts for the top 5 feet of mast or in-line double standouts designed to carry both rotor and transmission line. Use additional standouts as necessary to keep the twinlead away from the mast. Standouts should be at least three inches long. Twist the twinlead once every three feet to prevent wind lashing (Figure 5-5).

Use additional standouts at ends and turns to keep the twinlead away from eaves, gutters, drainpipes and any other metal surfaces. When running twinlead indoors, drive staples or tacks only in the center portion of the insulation between the conductors. Do not use any staples or tacks large enough to “bridge” the conductors. This will short the conductors. Run twinlead directly to the back of the set from the wall, floor, or baseboard. Don’t leave more twinlead than absolutely needed. Extra twinlead will coil up and act as additional antennas. This causes ghosting and signal loss.

Installing Coaxial Cable

Because 75 ohm coaxial cable is shielded (Figure 5-6), it is completely unaffected by contact with metal structures, and it will not pick up unwanted signals as twinlead does. Also, its performance is not affected by moisture, and it generally has a much longer life span than 300 ohm twinlead.

Aluminum/mylar-equipped coaxial TV cable provides superior low-loss performance. (Examples are Channel Master coaxial cable model numbers 9533, 9539, 9540, and 9544.)

Begin installing coaxial cable by first connecting the “antenna end” to a balun. (The balun is not necessary if the antenna is one of the few with a 75 ohm output.) Attach the input lugs of the balun to the antenna terminals. Apply acrylic insulator or silicone grease to the connections. A weather boot (Figure 5-7) should also be installed over the connections.

Next, run the coax through a standout mounted on the boom or the mast. This will prevent the weight of the transmission line from creating stress on the antenna connections. From this point on however, the coax may be taped to the mast at appropriate intervals. Use plenty of good-quality vinyl tape to secure it. (If you also are installing a rotor, sufficient slack must be left in the transmission line between the mast and the antenna to permit rotation of the antenna. Also, coax and rotor wire can be run together without interaction or signal distortion. See Chapter 22 for details about rotor installation.

These are precautions that must be observed when installing coax:

1. Do not bend coax too sharply. This may collapse the dielectric and ruin the necessary spacing between the center conductor and shield.

1. Do not crush or deform the coax. Ghosting and smears may result.
2. When attaching connectors to coax, do not nick the center conductor. This will cause a stress point that will probably break the next time the wire is flexed.
3. Remember that in almost all cases baluns are required to match the 75 ohm coax impedance to the 300 ohm impedances of the antenna output and the TV input.

GENERAL GUIDELINES FOR INSTALLING TRANSMISSION LINE

Both coax and twinlead should be run as directly as possible to the receiver. Avoid excessively sharp bends or turns. You should also try to use one continuous transmission line without splices. (However, if necessary, two lengths of coax can be joined with a splicing connector (Figure 5-9). Also, keep the line away from anything with sharp or jagged edges.

Fig. 5-8. A splicing connector should be used to join two lengths of coaxial cable.

Run the transmission line into the house through an attic or basement section if possible. Never run the line through a window or door. This invites damage to the line and is the mark of a careless installer.

If your entry is through shingles or shakes, remove one of the shingles and drill a hole for the line through the wall. Use a brace with an extension bit to drill through the insulation, plaster, and/or drywall. After you run the line through the hole, replace the shingle, and you’ll have a neat, waterproof entry.

Note: Always make a drip loop (Figure 5-9) at the entry point so that water will run off the line and not into the house.

If you are running the line through wooden siding, drill a hole through the wall, run the line through and then seal the entry point with caulking compound for weather protection.

For an entry through brick, concrete, or stucco, use a hammer and star bit or a carbide-tip masonry drill bit. Again, caulking should be used to weatherproof the entry.

CAUTION: Before making an entry hole, always carefully check the interior surface of the wall for electrical fixtures or wiring that may be in the path of the drill bit. Do not enter near electrical wires or outlets especially when using twinlead.

Indoor runs of transmission line should be concealed as much as possible. With twinlead this is a practical necessity because it should be shielded from unwanted signals whenever possible. Coax should be concealed too, but mostly for neatness. If possible, run the line in closets, behind walls, behind baseboards and moldings, or up through the floor from the basement. Snaking the line down between wall studs however, is difficult and time consuming. Consequently, it shouldn’t be done unless the customer has demanded it and has agreed to pay the extra cost. Before attempting to conceal the line behind baseboards and moldings, be sure that you can replace them exactly as they were without damage.

There are various couplers, amplifiers, and wall outlets that are useful in many installations. Because these devices usually come with detailed instructions, their installation will not be described in detail here. However, we suggest the following general procedures and guidelines:

1. Use only plastic outlet boxes or plaster straps for 300 ohm twinlead.
2. Locate TV outlets near electrical outlets. However, avoid running twinlead parallel to the electrical wiring in the wall. (Coax is not affected by the electrical wiring because it is shielded.
3. When running transmission line from a coupler or amplifier, be sure it runs to the outlet(s) as directly as possible. The shorter the run the better.
4. Twinlead lines running in and out of any device should never be run close or parallel to each other.
5. If you must use twinlead outdoors, select the kind with a black polyethylene jacket. The sun’s ultra-violet rays will not penetrate it, and it will not crack or chip in extreme heat.

Choosing the correct type and best quality of transmission line and then installing it correctly, is one of the keys to a customer-pleasing TV antenna installation. Don’t skimp on quality. “Cheap” transmission line can be very costly in the long run. Most so-called “cheap” lines not only produce excessive attenuation and poor impedance matching, but also are made of poor grade polyethylene which deteriorates rapidly. This makes it necessary to replace an installation within a relatively short time. Because the dollar difference between “cheap” and quality line is minimal, it always pays to invest in the best.

Grounding an antenna is not just the law, it is good common sense. Because the antenna is usually the highest point on the house, it is highly susceptible to lightning strikes.

Grounding the Mast

The NEC requires that the antenna mast and mount be grounded directly. No splices or connections are allowed in the ground wire between the mast and the ground rod.

First, attach one end of a No. 8 or No. 10 copper or aluminum ground wire to the antenna mast (Figure 6-1). One of the bolts on the mount can be used as a fastening point. Masts that are painted or coated must have their coating scraped off around the area where they contact the mount. This will ensure an electrical connection between the mast and the mount. It is vital to get a good, solid connection. (Once the mast is attached to the mount, any scraped off portion that is exposed should be recoated with paint or other sealant.)

Next, run the ground wire to ground as directly as possible. Standard wire staples can be used to secure the ground wire against the side of the house. Avoid making 90Ëš or sharper turns with the ground wire. A lightning charge has difficulty making such a turn and therefore may discharge into the house. Make ground wire bends as smooth and as gradual as possible.

The ground wire must be connected to a ground rod (Figure 6-2). Water pipes or plumbing fixtures are not acceptable. A good copper-coated steel ground rod driven at least 3 feet into the ground is required. Special clamps that provide a solid connection between the ground wire and ground rod should be used.

Grounding the Transmission Line

It is not just the height of an antenna that makes it susceptible to lightning strikes. Antennas and transmission line can accumulate static electrical charges that also increase the changes of lightning hitting an installation. To properly “draw off” this static electricity, a small device known as an antenna discharge unit (Figure 6-3) must be included on the installation. The antenna discharge unit (also called a “lightning arrestor”) is connected to the transmission line at a point close to where the transmission line enters the house. One end of a ground wire is attached to the discharge unit. The other end of the wire is connected directly to the ground rod.

Installation of the antenna discharge unit is very easy, and detailed instructions come with each unit.

An antenna installation is not adequately grounded unless both a mast ground and an antenna discharge unit are installed correctly.

Guy Wire Installation

The materials needed for a standard guy wire installation are: guy wires, a guy ring(s), screw eye, and turnbuckles (Figure 7-1). Six-strand, 18 or 20 gauge galvanized steel guy wire is recommended for general use. (The 18 gauge wire is recommended for high-wind areas and installations over 20 ft. above the uppermost support.)

are run through holes in the guy ring. The wire then is wrapped around itself at least six times (Figure 7-5).

Ideally, the guy wires should extend out from the mast at a 45Ëš angle, and should be anchored in screw eyes placed 120Ëš apart (Figure 7-6). (If four guy wires are used, they should be anchored in screw eyes 90Ëš apart.) Be sure each screw eye is firmly anchored in solid wood at least five feet from the base of the mast. After the guy wires are installed, cover each screw eye with roofing tar.

If the installation requires more than one set of guy wires, use separate screw eyes for each wire. A single screw eye may not be anchored solidly enough to hold two or more guy wires. A good quality screw eye should be used, and it should be at least 5” long and 5/16” in diameter. For guying a tall ground-mounted mast, use heavy-duty ground stakes.

rotor or rotator is a mast-mounted, motor-driven device (Figure 8-1) that permits the TV viewer to conveniently rotate (orient) the outdoor TV antenna in any direction. It is started and stopped by a manually operated control unit (Figure 8-2) that is placed indoors near the TV set. A multi-conductor wire carries the power and control signals from the

Automatic Rotors

The control unit of the automatic type rotor (Figure 8-2) has a direction-calibrated knob (or dial). When this knob is turned to the desired compass direction, the drive unit automatically turns the antenna to that direction and then stops it.

indoor control unit to the mast-mounted drive unit.

Installing the Rotor

To install a rotor, first assemble the antenna and attach it to a short section of mast. (This short mast section later will be installed in the top part of the drive unit.) If the antenna is large and has boom braces, the short mast section must be long enough to accommodate the boom braces and possibly a rotor alignment bearing. A 3-1/2 foot section should be long enough. Use a shorter section if the antenna is small.

A rotor should be considered when the desired TV signals arrive at the receiving site from widely spaced directions that cannot be accommodated by the relatively narrow beamwidth of a single, fixed-position antenna. With a rotor, a viewer can conveniently orient the antenna in the direction of the desired channel’s transmitting tower, or in the direction that provides optimum reception of a particular channel. A rotor also permits convenient “fine tuning” of the antenna direction to compensate for variations in signal direction caused by changing atmospheric conditions or other signal-distracting conditions. Additionally, the rotor permits elimination of adjacent-channel and other types of interference that in some cases, can be solved by slight reorientation of the antenna.

Attach the transmission line to the antenna, and set aside the antenna and mast.

Remove the bottom (or access plate) of the drive unit housing and attach the rotor wire (Figure 8-3). (Rotor wire is available in many different styles; however, the most practical and economical kind has only three conductors. An example is Channel Master Rotor Wire Model No. 9554.) All Channel Master antenna rotors use 3 conductor rotor wire. To attach the rotor wire to the drive unit, first strip back the insulation on all conductors and solidly twist together the wire strands that make up each conductor. Be sure there are no loose strands; they may impair the performance of, or short out the rotor. Use connecting lugs to attach the wires to the rotor terminals.

The “reference wire” is either wider or is a different color than the other conductors. Connect it to terminal No. 1. Connect the middle wire to terminal No. 2, and the third wire to terminal No. 3. If you use four or five-conductor wire, attach the third, fourth, and fifth wires to terminal No. 3. (Figure 8-3 shows the rotor wire connections to the drive unit.)