Radio and Television Today (Jan-Nov 1941)

UP THE LADDER TO FM SU (Continued from page 34) installations after lobe has been found, W2X.OY will come in strong or drop out entirely with a slight turn of antenna mast. "We then leave the radio for the customer to listen to for a night or two and if he buys we try to impress upon him the importance of buying the dipole type of antenna. CAREFUL ADJUSTMENT "In a location on a hill we use the ladder and demonstrating antenna to determine the orientation of a FM wire doublet such as tbe Stromberg No. 6 Antenna Kit. The results obtained from a dipole and reflector against a wire doublet is about five to one, due to the fact a wire V doublet suspended between two points cannot be raised and lowered or oriented close enough and while a TO-ohm line is supposed to be 70 ohms plus or minus, actually the plus or minus can be from 30 ohms to 100 ohms. Even though there has been some sales resistance to the dipole and its extra cost a demonstration as above generally convinces the customer. The final installation, correctly matching, orientation and ground reflection work, takes nearly a day. "One word about cheap transmission lines, while the current involved in receiving is infmitesimally small compared to the transmission, we have tried all sorts of lines from twisted lamp cord to Basset cable and have definitely found that the larger size wire No. 12 in EOl cable gives by far the best results and is easier to handle. "One thing a dealer or his service man should do is get acquainted with conditions in his territory such as having some method of determining the field strength of signal that is necessary to give the proper drive to get a good limiter action. This will vary in residential, business or rural sections. ANTENNA HEIGHTS "Here at my store, with autos starting and stopping on all sides of us, we have had to build the antenna above the building 85 feet. We also use a coaxial transmission line. "In residential sections the best working height above the ground is between 30 and 40 feet, making the transmission line as short as possible. Incidentally, in residential sections there is no great advantage in going much over 10 to 15 feet above the roof. In fact, the added resistance of EOl cable from length can offset the advantage of height. "On the map on page 34 are the relative positions of FM transmitters from Gardner, and the dipole and reflector orientation, the main lobe and small lobe off one side which gives us W2XOY. In locations farther south and nearer to transmitters than we are, a turnstile antenna would probably work out better. However, individual dealer's technicians will have to work out for themselves the type of antenna to use. Our condition in Gardner is different than that found in Worcester, 20 miles south. "I have tried stacked arrays as well as adding a director but the adjustments have to be made with the antenna absolutely in place and that requires tower construction too expensive for domestic use of radio. IMPRESSIVE REACH "Factory, engineers have! inspected our results from W2XOY and the reception is equal to W43B with about 5 per cent fade as indicated by the limiter grid voltage. This is not enough to be noticed by the ear. Alpine, W2XMN, at times fades maximum 85 per cent, but will hold up sometimes one hour at a time so that at home I listen mostly to W2XOY and W2XMN. "Based on reception of some seven or eight FM transmitters varying from 18 to 160 miles away, noticing the limiter drive against noise level and observing installations with different types of antenna from built-in to the best we have been able to construct, it is my guess that the dealer problem will divide itself into two distinct sections. Namely, installation in city and suburban locations, and in remote small cities and country. "However, dealers located within the square-mile service area specified by the FCC will be able to set up their radios using very simple antenna construction. They will do well to study the more complicated antenna because as transmitters increase their power, even though the radio will bring in perhaps six or seven programs, distant transmitters with their special programs are going to cover much more than the FCC anticipates. Theoretically the antenna can give the effect of the transmitting station increasing its power 200 and 300 per cent which would bring a distant signal above noise level. "FM bends over hills much more than at first supposed. I have a customer who enjoys W2XOY, 100 miles away, and the top of his antenna is back of a hill by about one tenth of a mile. The hill is more than twice the height of his antenna. EXCELLENT PROGRAMS "From results we have had in Athol, Mass., only 550 feet above the sea level and with the Hoosac Mountains between Heidelberg Mountain and Athol, when W2XOY increased from 1000 watts to 2000 watts there was a noticeable difference. When W2XOY goes to 20,000 watts the signal will bend and come in strong enough I am sure to give an excellent program. At another point in Athol 800 feet above sea level a customer now enjoys W2XOY. "All of which means with an antenna properly installed in remote sections, say in the neighborhood of 100 to 125 miles from a 50,000 watt, 10 bay turnstile transmitter, much better and greater distance will be had in the future. "To sum up, I believe that a radio technician should study U.II.F. the same as 5 meter amateurs do. "The dealer should not attempt to sell FM unless he can show the customer that FM is worth the price that a real FM receiver will cost." II. M. L. Capuon, Merchandising Editor CAP SAYS:— "MAKE ALL OUR DREAMS COME TRUE" • Not since the socket-powered radio made its debut, and swept the country with a tremendous buying wave, has the radio industry had an economic condition to compare with the present. We have : • A product which the public has long wanted. • More people with more money to spend than ever before in our nation's history. • More radio sets obsolete and crying for replacement than ever before. • Prices rising, the public buying — demand for quality superseding the search for prices. • And FM — a high quality, high price, high profit set which can make all others obsolete. And make the dreams of the industry come true. • But in the final analysis, FM will mean no more than we of the industry make it, though its potentialities are beyond the vision of many. 52 RADIO TODAY