Radio Digest (Oct 1923-July 1924)

May 10, 1924 RADIO D I G E S T — Illustrated Why Don't I Hear Los Angeles Every Night? Sets Not Always to Blame for Non-Reception By Wilson N. Durham "W HY don't I hear Los Angeles? I have spent $600 for the best Radio set that I could buy and still I do not get the West Coast." You have all heard these or similar questions, perhaps you have asked them. The answers given have probably been many and varied and possibly disappointing to the listener who thinks that he can always increase the distance over which his set will receive by increasing its sensitivity. The Radio public seem to believe that long distance reception can always be attained if the receiver is sensitive enough. This belief has very probably resulted from a consideration of the claims of results obtainable by employing Radio frequency amplification, that is, amplifying the incoming energy before it is changed in form by the detector tube. A consideration of the theory of Radio frequency amplification alone would logically lead to such a conclusion. "Increase the sensitivity of your receiver and you will increase your receiving range." This theory alone is not correct and we will try to tell you why. Speed of Electromagnetic Waves The electromagnetic energy emitted from the antenna of a broadcasting station is believed to radiate in every direction and to go on and on into space, with diminishing strength, but nevertheless continuing forever at the astonishing speed of 186,000 miles per second. The greater the power of the transmitter, the greater will be the strength of the received signal at a given distance. It is to be noted, however, when considering the amount of power required for Radio transmission that due to absorption, reflection and refraction of the electromagnetic waves the question is almost as difficult to answer as the question, "How far can a man's voice be heard?" Over a quiet lake in the evening a man's voice may carry two or three miles, while on a city street the same voice would carry but 500 feet, on account of disturbing noises in the city. Atmospheric disturbances make the range of a Radio broadcasting station almost as indeterminate. It can be seen then that there are two important factors, in addition to the sensitivity of the receiver, governing the distance over which it is possible to receive; the decrease of signal strength as the distance from the transmitter increases and the presence of atmospheric disturbances of varying intensity. These atmospheric disturbances include the Radio frequency electrical noises resulting from the operation of electrical machinery such as motors, trolleys, elevators, arc lights, etc., and static, which is the electrical noise caused by electrical charges in the atmosphere itself, by electrical storms and discharges of electricity between the clouds. This is the cause of the crashing sound sometimes heard in the headset or loud speaker resembling thunder crashes during summer storms. The ratio between the signal intensity and the static intensity determines whether or not the signal will be heard. If the signal is stronger, it will be heard, if weaker, it may not be heard at all. Force That Carries Transmissions Through Ether Let us consider arst what affects the strength of the transmission from the broadcasting station. As has been noted, the electromagnetic waves set up by the transmitter are propagated in all directions through the medium we call the ether, at a velocity equal to that of light. As the distance from the transmitter increases their intensity decreases, due to the waves spreading out in ever-widening circles and absorption by the different media through which or over which the waves may travel. Many investigations have been made to determine to what this energy absorption is due, and many interesting facts disclosed. Signals from a certain station may be very much stronger at night on account of an absorptive effect of light rays on them during the day. At night, due to variations in atmospheric conditions the energy losses in transmission are decreased. In practice it is generally found that transmission is very much more effective at night than in the daytime; the distance over which it is possible to receive being increased sometimes two or three times or more. Another interesting fact in connection writh the variation in transmission is the fact first recorded by Marconi in his early trans-Atlantic tests. When the line of sunrise or sunset is between the two stations, transmission is very difficult and the signal received very weak. This phenomenon is still apparent and considerable interruption is experienced at times even today with our tremendously powerful trans-Atlantic telegraphic transmitting and receiving station. It seems as though the twilight lines act as either a reflector or absorber of the Radio waves. Strength of Received Signal The strength of the received signal varies also with the seasons, the effective distance being much greater in winter than in summer. The reason for this seasonal variation of signal strength is considered as being due to the absorption of the waves by vegetation, thus causing a marked decrease during the summer months. This seems to be a reasonable conclusion in view of the fact that trees have been successfully used as antennae, thus demonstrating their energy absorbing qualities. This may also explain why it is possible to receive much greater distances over water than over land with the same transmitting power. It has been found that there are many AT ALL DEALERS $1-85 Condenser ,00025-MF 35c vm % Build for Success! -""tofSigyt ^^^k I ^ sure *hat your detector tube is working at :=7^£^*o?'a k ^\ ? its highest efficiency by using a Bradley leak ^^T^^^fe^J J M *or S1^ 'eak control. This remarkable ad°h^2$\\if M instable grid leak has a perfectly smooth and stepless range from J^ to 10 megohms and is unaSected by atmospheric changes. It is highly endorsed by Flewelling, Crosley, Kennedy, Radio News and has been adopted as standard equipment in all Amrad highAudion(DeForest)DV-6, 2 Megohms priced sets. g • i : ! ! ; ^SeTohms Be sure your set is made perfect by installing C-301-A 2 Megohms a Bradleyleak. Try one, tonight. UV-199 2 to 5 Megohms uv-200 I..... .2MegohmS ALLEN-BRADLEY CO. UV-201-A 2 Megohms 2g0 Greenfield Ave. Milwaukee, Wis. THE PERFECT GRID LEAK places whore it is difficult to receive signals from certain stations, or pei from any station. These localities wc load BPOtS, and can be attributed to many causes. In the cities it ofton happens that there is a shielding or absorb* ing effect due to many steel structures. In the country, and the mountains particularly, deposits of ore may greatly reduce the strength of the received signal, for the main energy of the wave is absorbed before it reaches the receiving station. This effect is also noticeable in ship to shore communication. It is sometimes impossible for a ship located near north shore of an island to satisfactorily communicate with a land station on the south shore even though the two stations are separated by but a few miles; while it becomes easily possible to carry on the communication when the ship is one hundred miles north of the island. So much for the factors affecting the signals radiated from the broadcasting station. Now let us consider the static. Atmospheric Disturbances Seasonal changes also affect the intensity of the atmospheric disturbances due to the electrical charges in the ether. In summer the static greatly increases over its average strength for the winter months and therefore becomes troublesome at times when distance reception is desired. When electrical storms are in the immediate vicinity of the receiving station it may be possible to hear only the local stations. There is always a great amount of electrical disturbance in the large cities due to the operation of electrical machinery. Its intensity depends upon the locality in which the receiving set is located. Sometimes disturbances of this sort make distant reception impossible regardless of the type receiver that may be employed. Naturally the man who has bought the finest set available expects the finest kind of reception, and it is sometimes difficult to explain to him why he cannot get results in spite of the apparatus he uses. Without knowing the cause of the trouble he immediately puts the blame on the equipment or the unfortunate dealer. We have seen that the ratio of signal to static strength is the determining factor in the distance over which any receiving set will satisfactorily operate, and unless the signal is louder than the static it cannot be heard clearly. No matter how weak the static may appear with the average receiver, it may alv be made strong enough to result in the same crashing sound, if a very sensitive I used. Let us suppose that we such a receiver, a super-heterod for instance, which has facilities for obtaining very great Radio frequency ampli<<n; that it is set up for operation in Philadelphia; that it is a favorable night for reception; and that we succeed in picking up the West Coast clearly and with very little static disturbance, cannot this same performance be duplicated any night? This is the question many are asking. Not the Same Every Wight On the following night, perhaps, the same set is tuned to the same station at the same time as on the night before, but, with the same adjustments and the same amplification, n are heard. Why? The signal was there the night before could be tuned in with far less amplification, while tonight increasing the amplification merely increases the crackling in the receivers. If the signal is brought !n at all it is so very weak as compared to the noise that it is not enjoyable. One of two things has happened: Kither the signal strength has actually dropped below that of the previous night or the static strength has increased so that the ratio of signal to static is not as favorable as the night before and is so loud that the signals cannot be heard. This is the answer to our question. Los Angeles cannot be heard tonight because the ratio of signal to static has changed and no receiving apparatus obtainable for home use today can bring through the desired signal. If the sensitivity of the set is increased, the static roar increases and the signal strength increases, but both in the same ratio, and if the signal was not audible before it will be no more audible with the increased sensitivity. Therefore (Continued on page 28) Magnavox Radio Reproducer M r can be used with any receiving set, and requires no battery for its operation. MAGNAVOX Reproducer Ml RESULTS secured by thousands of satisfied users prove that Ml is the universal Radio Reproducer, operating equally well under practically every condition, and may be connected as simply as a head set. cT&agnavox eTiCi can he had of good dealers everywhere, $55.00 5-10 THE MAGNAVOX CO., OAKLAND, CALIF. New York Office: 350 West 31st Street Canadian Distributors: Perkins Electric Limited, Toronto, Montreal, Winnipeg