RADIO

Radio Record, Volume V, Issue 38, 1 April 1932, Page 3

RADIO

IN THE AFRICAN JUNGLE

Radio has penetrated yet another unknown sphere, and from the jungles of Africa have come the calls of the amateur operator. In this story is told how radio was employed by an expedition moving in the African interior to maintain communication with civilisation.

a Wwe our company was sent to film a \* picture in the heart of Africa, some means of communication between headquarters and the various -field units had to be maintained. Short-wave radio was selected as the means of communication, and as the expedition was necessarily limited to a small number of persons, we could not afford to take along a radio operator. I was selected, because of my interest in the amateur shortwave branch of modern science, to be the radio operator of our safari. From the remote places visited it was one of my duties to kee), in daily touch with the expedition’s temporary headquarters in Nairobi, British East Africa, and in some cases with the studios -at Culver City, 12,000 miles away, as well as the New York office. : When we left America our party included 20 people, and this number was augmented to 40 whites at certain stages of the safari, what with the addition of professional British hunters.and guides,*and additional white men, who acted as technicians in handling the necesssarily elaborate motion-picture equipment, camp managers, and so on. In addition we enrolled an army of native porters for carrying goods,

er cooking, personal service, etc. 1 mention these particulars to give some idea of the elaborate formation of the safari, which was said to be the longest and largest ever organised in Africa. We carried a quarter of a million dollars in equipment to these renaote places, and altogether lived a rather complicated and varied life, if primitive in some of its essentials. In addition to my regular work, the radio required considerable time, but was nevertheless a source of much interest, as radio enthusiasts will understand. The first consideration in selecting a radio outfit was performance, and this had to be sharply related to portability and endurance, Operating, as we were, far from a place where parts may be replaced, I had to rely on the ruggedness of the original equipment to an unusual degree. ' ( I chose an M-1 type transmitter and receiver, which is a portable set standard with the United States Navy. It works on a frequency of 4000 to 30,000 kilocycles both for sending and receiving. The power was derived from a gas-electric generator. The entire outfit weighed 300 pounds and could be broken into packages weighing from 40 to 60 pounds for convenience in carrying. The main object of our installation was to maintain regular schedules with Nairobi, regardless of our location. This was quite a problem, inasmuch as nearly as great difficulty is encountered in working short distances with short-wave ‘apparatus as in trying for extreme distance. Fading, swing, and other disturbing phenomena are more prevalent at short distances than at longer ones; and during our work recourse was

had to three of the bands-14,000, 7000 and 3500 kilocycles-accord-ing to what best suited prevailing conditions. The distance from Nairobi varied from forty to approximately one thousand miles, and communication was maintained throughout the trip, regardless of weather ° and other adverse conditions. : The man handling the Nairobi end was Mr. Sydney Pegrumse, . an amateur there, VO4CRE, who did remarkably good work on his . low-powered set. Our regular schedule was kept at 16.00 GMT, with . extra sessions fitted in, according to demand. . Den the period of our safari we handled approximately 600 messages, . totalling perhaps 18,000 or 20,000 words. The Nairobi connection was © the first consideration throughout the trip, taking precedence over any efforts at distance or other experimental work. However, we also made connection with amateurs in practically all parts of the world during. our spare time-this being carried on, ©

of course, along recognised amateur lines. Many interesting contacts were made with amateurs in | different nations: South Africa, France, Spain, . Germany, England, Belgium, Denmark, Czecho- | Slovakia, China, Malay States, Borneo, Philip- . pines, Russia, Mexico and the United States... Radio is now fostered under an enlightened policy in most of the African Governments, and we were specially licensed by the Kenya, Uganda, Belgian Congo, and Tanganyika Governments to’ handle traffic to and from Nairobi. These Governments showed us great courtesy and co-operar . tion. As to operation: All work was done in| the wavelength bands set aside for use by amateurs. The bands used most were the 7000 kilocycle and the 14,000 kilocycle bands... -or 40 and 20-metre bands respectively. Thé* 7000 k.c. band works best for moderate distances, and during the early morning, while the 14,000 is best for extreme distance and in the evening. The early evening and early morning proved the best hours for receiving. From about 5 p.m. to about 7 p.m. the 40-metre signals come in well from the east. From about 8 p.m. to 10 p.m, the "European gang" on 20 metres (14,000 kilocyeles) came along; and from 10 at night until around 2 a.m. the United States "buncly’ on 14,000 kc. came in excellent. Then there began a fade-out until daylight, and from then until noon or so the U.S. bunch on 40 metres came in very well again. This represents about the average condition, the time given being that for the parts of Africa in which we happened to be working. ‘Stations on the east coast of the U.S. and those in the Philippines (Continued on page 13.)

Radio in the Jungle. (Continued from page 3) came in best, considering distance. Some of the east coast stations, both on 20 and 40 metres, were extremely reliable. The Philippine bunch was as regular as clockwork each evening, although static sometimes got too bad to read them. There was considerable heat lightning in Africa, and also a frequency of thunder showers in a land where clouds are always present along the rim of the sky. There are also frequent atmospheric disturbances due to the great changes in temperature from day to night. lLightning.always causes interference, my experience showing that this is more the case on the 40-metre band than the 20, and most of ail on the 80. As a rule, the higher the wavelength, the greater the interference from lightning. "Blind spots" were also occasionally encountered. A. possible explanation of this is the presence of great bodies of metallic ore. At times this condition gave considerable difficulty in keeping up the average work. Conditions in different parts of the country vary to a great extent, both in reception and transmission, and it was difficult to maintain any sort of stan- dard when shifting about from place to place. My confidence in our "outfit" was justified by events, as there was_ remarkably little technical trouble under the conditions encountered, and deterioration was slight. My most-seri-ous single difficulty, and one that threatened to put the radio out of com--mission and thus leave the expedition considerably handicapped. was the failure of the generator while we were on the Victoria Nile, near the Nile’s source and quite remote from ‘other means of communication. Following a period of overheating, the generator was overhauled, and upon being reassembled the output dropped to about two-thirds normal. Fortunately, the equipment for producing lights in the jungle, operating our electric refrigerating plant and other equipment, is extensive... I was enabled to commandeer a new generator of a different type which arrived "on location" at this time, having come by native dug-out canoe and crosscountry portage. This new generator was adapted to run from our Kohler lighting plant. Since then, the gasoline motor rig has been used only when away from the Kohler plant, or in emergencies. The greatest itéms of deterioration were the dry batteries used in the re- ceiver, which had to be replaced, usually, one a month. In fact, that is about the only item of deterioration about the set. The storage batteries lasted well indeed, and I could see no change in any of them during the ten months of use. The spares I carried consisted of two transmitting valves, six receiving valves, several insulators, and a quantity of wire for antennas, transmitting grid leaks, transmitting grid and blocking condensers, two receiving grid leaks, and earphones and earphone plugs. The chief mechanical difficulty I encountered was with the gasoline engine. It required a good deal of attention, particularly if the gasoline was not of the best quality, which, of

course, was .often the case. Gasoling ‘was carried in great quantity with the expedition-we had a lighting genera~ tor which alone consumed 12 to 15 gallons an hour when in use. Damp weather occasioned a certain amount of trouble with the receiver, giving rise to noise through corrosion. This was easily’ remedied by drying and cleaning. There was no trouble with the transmitter, with the exception of grid leaks-a rather unusual condition, but a troublesome one, probably due to humidity. My greatest physical difficulty when reachnig a new location was the erection of the antenna, One of my native assistants, whom I named "Grid Leak," had become quite expert at getting the wires clear of trees and brush. The aerial problem was of but little moment. when considering only the Nairobi. schedule, as I usually had power to spare from almost any sort. of a set-up-but when attempting DX -work, the location of the antenna was of extreme importance. Since necessity is the mother of invention, I worked out one improvement in the Zeppelin type of antenna which may be of interest to others who have to consider portability and save time as well. The improvement consisted of a.-set of detachable feeders! The Zeppelin type of antenna proved to be about the most satisfactory for general use. The mast furnished with the set is perhaps more convenient, but not as efficient, so a "Zepp" was made up in a permanent form, and an arrangement made whereby it could be readily reeled up for portability. For the benefit of the general reader, the Zepp rig. consists of a length of wire suspended (usually horizontally), ealled the radiator or "sky wire." This is coupled to the set by a pair of wires known as "feeders." One wire of this set is fastened to one end of the radiafor; the other wire parallels it, but is not connected to anything at the top, simply being fastened to an insulator. It is quite necessary to the operation of the Zepp that these twe wires be held parallel to each other and at a non-variable distance of a few inches apart-any swinging or changing of their relative positions acts to the detriment of the antenna. In ordinary cases of set installation the feeders are run down from the radiator to the set and fastened permanently, being spaced by. insulating strips, every three feet or so, along the length. [Owing to heavy pressure on space, we have been compelled to withhold the remainder of this article from publication until next week.-Ed. ]