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CHAPTER EIGHT: ANTENNA ROTORS
A rotor or rotator is a mast-mounted, motor~riven 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 indoor control unit to the mast-mounted drive unit.
. 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.
Automatic Rotors The control unit of the automatic type rotor 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
Installing the Rotor
To install a rotor, first assemble the antenna and attach it to a short section of mast. Cfhis 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.
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. (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.)
The wires must not touch each other or the housing after they are connected Cover each connection with an insulating material to prevent corrosion and rusting. Then reinstall the bottom (or access plate) of the housing.
Next, attach the drive unit to the main mast. After this is done, insert the short mast (with the antenna attached) into the top of the drive unit (Figure 8-4).
An alignment bearing (Figure 8-5) is absolutely necessary for large antennas or arrays to prevent excessive pressure on the drive unit. If you are installing a rotor alignment bearing, the main mast must extend far enough above the drive unit to hold the bearing in place (Figure 8-6).
An antenna (or array) large enough to require an alignment bearing should also be guyed above the level of the drive unit. Most alignment bearings have "eyes" for attachment of guy wires. A separate ball bearing guy ring should be used with an alignment bearing that does not have eyes for guy wires. It is attached to the mast above the alignment bearing. If the rotating mast is exceptionally long, use a ball bearing guy ring in addition to the guyed alignment bearing.
As previously mentioned, a loop of transmission wire must be left between the antenna and the drive unit to prevent the line from becoming tangled in the antenna or otherwise restricting rotation. Be sure the housing of the rotor drive unit is properly aligned with the antenna terminals. To properly align the rotor with the antenna, always install the drive unit with the front (the side of the unit without fixtures), facing away from the antenna terminals (Figure 8-8). This will allow the transmission line to be looped into a snap-on standout approximately 3"4" below the rotor on the rear of the drive unit housing (the side with clamps for the main lower mast).
When the rotor and antenna have been properly aligned, tighten the clamps holding the top (antenna) mast and run the rotor wire down the main mast. The best way to do this is to use 7" standouts or in-line double standout; (for transmission line and rotor wire) mounted with nutbuckle and strap, spaced equal intervals along the main mast. Taping the rotor wire to the mast may be acceptable for some smaller installations.)
Coaxial cable should be used with all rotor installations to void interaction that can occur between rotor wire and 300 ohm twinlead. If you must use twinlead, keep it at least 3" away from the rotor wire and mat at all times. Again, the use of in4ine double standouts before the rotor (Figure 8~9) is recommended.
The rotor wire should be connected to the control units in the same manner as it was connected to the drive unit. The reference wire is connected to terminal No. 1 , the middle wire to terminal No.2, and the third wire to terminal No.3. Leave enough rotor wire at the control unit to permit movement of the unit to any point in the room.
The final step in a rotor installation is to synchronize the control unit with the drive unit. For fully
automatic control units, turn the control dial (knob) clockwise to the due north setting and allow the antenna to rotate until the control unit stops it. Then, turn the dial counterclockwise to due north, again allowing the antenna to rotate until the control unit stops it. The installation is now synchronized.
The process is the same for semi-automatic control units except that you must depress the clockwise and counterclockwise buttons one at a time until the antenna stops at north in both rotational directions.Anytime you believe the installation is out of synchronization, repeat the above process.
Control units come with small adhesive stickers that can be placed on the control unit housing to indicate the best antenna position for each channel. When you have determined the best antenna position for a channel, place a sticker with the channel number in the appropriate spot on the control unit housing. The rotor installation is now complete.
CHANNEL MASTER ROTOR PAGE
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