Radio today (Apr-Dec 1939)

Basic principles to be followed when setting up and installing television receivers. Correct antenna an absolute necessity. Recognizing common forms of interference. So important is proper installation of a television set that one of the leading manufacturers made the following statement, "The best receiver we know how to build can easily prove unsatisfactory, unless the receiver installation is equipped with the correct type of antenna properly installed." Correct installation of a television set is not generally so difficult as commonly thought — in most cases it is merely the application of straight-forward engineering principles. Occasionally, there will be some tough nuts to crack, and the serviceman should be prepared to handle them. While this article will in general apply to all receivers, the serviceman is urged to follow the manufacturer's instructions insofar as specific procedure is concerned. INITIAL SET-UP First of all is the initial adjustment of the television receiver after it has been unpacked. Some manufacturers will be shipping the picture tubes separately to guard against breakage. If the tube is enclosed in a protective sleeving, the sleeve should not be removed until the tube is ready for placement in the receiver. One type of sleeve that is being used is so designed that the sleeve remains on the tube after installation in the set. The top portion or cover is removed after the tube is fitted into the socket thus insuring maximum protection against injury from breakage. The antenna should be placed as high as is practical. Di-pole is rotated for best signal pick-up, usually at 90° to station. Some manufacturers are suggesting that the serviceman wear gloves and goggles whenever handling the picture tubes. After the tube has been inserted in the socket, the high-voltage lead or leads should be clipped into place according to manufacturers' instructions. KEEPING PIC CLEAN When the tube has been installed, the viewing end or screen should be wiped clean of all fingerprints. "Windex" or similar preparation and a soft cloth are recommended. Before the protective glass over the viewing end of the tube is set in place, the inside surface should be cleaned and polished. Likewise, before the set is put into operation, the outer surface of the glass should be cleaned. If a mirror is employed, that too must be kept clean so as to insure clear pictures. Before the receiver is tuned in on a signal, there are several preliminary adjustments that should be made on the receiver. In the case of a set using a magnetic deflecting yoke, there is a yoke adjustment that might have to be made. With the set turned on, the sweep signals will paint an image of lines that is suitable for preliminary adjustments. PRELIMINARY ADJUSTMENTS Movement of the yoke along the axis of the tube affects the size of the image on the screen. The further the yoke is away from the screen, the smaller the image will be. If the yoke is too near the screen, there may be cutting at the corners of the picture. Generally speaking, the yoke should be as near the screen as possible without cutting of corners. The horizontal and vertical size controls also affect the size of the image. These controls should be adjusted so that the image almost fills the screen. The yoke is rotated so that the edges of the image are square with the mask. This is known as orientation. In the case of electrostatic deflection, the tube itself is turned. The centering controls will permit placement of the image in the center of the tube. With an image slightly smaller than the mask, the image is centered so that the margin at the top equals that at the bottom. Also the margins on the side should be equal. TESTS WITH RECEIVED SIGNAL The size controls are later adjusted so that the image just fills the screen when a signal from the television station is tuned in. The image from a television signal will be slightly less in size than the image painted by the sweep circuits alone. The installation up to this point has been handled without the aid of a signal from the air. Whether or not the dealer does this work in the store or the customer's home is a matter of choice. If it is done at the store, the serviceman will have a chance to test the receiver connected up to an aerial, thereby checking the entire receiver before delivery to the customer's home. Then, if there is any trouble at the home in getting a good picture, the serviceman will know definitely that the trouble is external to the receiver. ROOM ILLUMINATION Wherever possible the receiver should be so placed in the home that a direct glare from either natural or artificial light does not fall upon the face of the cathode-ray tube. The received pictures may be viewed under a variety of conditions where it is not always convenient to darken the room completely. Adjustments made to meet these conditions will not cause damage to the receiver. Viewing the pictures in as dark a room as possible is always at an advantage as it permits the setting of the Intensity and Contrast controls in a manner that will give picture tone values more correctly relating to those actually used in the studio from which the picture is transmitted. ANTENNA INSTALLATION The antenna installation is the greatest unknown. Only by actual trial will one discover whether or not satisfactory pick-up can be obtained at a particular location. When a line of sight to the transmitter antenna is obtainable, it is generally possible to obtain good pictures. In certain instances reflections may occur that cause more than one picture to appear on the screen from one station. The cure for the reflected signals that cause ghost images is to place the antenna in such a position that only the main signal gets to the receiver. Elimination of ghosts will be discussed further along in this article. The first step in locating the aerial, which generally will be the di-pole or doublet type, is to find a high point on the roof from which the television transmitting aerial is visible. The receiving antenna is placed so that the di-pole is at right angles with the line of sight to the transmitter. If visibility is poor or there are obstructions, the directions can be determined from a map. After the aerial has been placed and the transmission line run to the receiver, the next step is check the image on the receiver. The image should be sharp. The size controls 7 8 RADIO TODAY