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1925 __ A Kit for the Radio Detective
Comment : “How to Use a Sensitive, Portable Receiver to Find Interference of All Sorts Some Radio Tests of Great Value and Interest to the Experimenter.That is the kind of a radio compass station that can travel almost anywhere. That station is not too wide to go through doors nor too heavy for a youth. It is not too heavy for an old chap either, but of course if an old chap carries it in and around public places, it will probably be due to a lack of the dignity that usually comes with age, or due to youthful spirits, or because he wants to learn facts about interferences and the reception of radio to the extent of braving the remarks of others. The radio compass station operator, in this case, is the means of transportation or beast of burden and, if he travels in public places, he may be referred to as a beast of burden. Somebody will surely say he is an "ass." Also, inexperienced young dogs and snappy dogs may bark at him. The wise humans and dogs will behave quite properly. That kind of transportation for a compass station does not produce electrical disturbances to interfere with the compass readings. Also the operator is the pivot. Operator, receiver and coil turn together, which prevents changing tuning because all parts remain relatively the same. An automobile carrying a loop cannot go up stairs and in narrow places and the ignition has to be shut off to use the radio compass. Also a coasting automobile often moves too fast to detect sources of interferences or variations in receiving ability. Those of you who go camping in places where human transportation is the only available transportation, will recognize that thing on my back and shoulders as a special form of pack board made with braces over the shoulders instead of straps. This special pack board is just as available to carry fishing gear as to carry scientific instruments. When using the special pack board for radio compass work, the radio receiver is supported by the braces in front of the operator, where he can see the dials and make adjustments. Almost any kind of sensitive fairly long range receiver will do if the tubes require very little battery. The receiver in the photographs includes a regenerative detector and three stages of audio frequency, using peanut tubes that require about one volt and one fourth of an ampere each. Forty volts were used in the plate battery. That receiver was not built especially for this kind of use. It was chosen because it was convenient and light in weight. The compass coil, as can be seen, is mounted at one side. It consists of eighteen turns of No. 23 cotton covered wire, about three eighths of an inch apart. The coil frame is of very light spruce and fitted together with screws. A folding coil would do about as well, but it might not be as strong for its weight. A clip is provided so that eight, twelve, or eighteen turns may be used. Also, the little coil in series with the loop that couples to the tickler is tapped, so altogether a range of from 200 to about looo meters can be covered in receiving, with the tube oscillating. An oscillating tube is sometimes better for picking up disturbances. Now that radio receivers are located practically everywhere, there are too many possible sources of interference to cover the interference subject by articles stating where interferences may be found. Another kind of education is necessary. We have got to train a lot of local disturbance finders. Some local radio detectives with radio compasses are needed to do the finding and spreading of information. When broadcasting first started, the uninitiated blamed all interference on amateurs and static. Now in the summer time a great deal of interference is blamed on natural static that comes from defective electric lighting and power circuits. ' Also, winter and summer, some one short range notorious interference is blamed for what other local interferences do. A chap's own bed warmer may be causing the interference that he blames on the Blank electric light company. To stop interferences, first, find the interference producer; second, use your best influence to have that interference cease. Power companies are glad, usually, to do their share. Individuals are almost always reasonable about such matters, once the true situation has been presented to them. Those who take the trouble to do this radio investigating will find it decidedly interesting. They will do not a little to advance the radio art in their locality. Especially will they advance the art, if they tell others how they do it and the results they get. [...] A radio compass station made up in the form of a pack is much easier to carry than a suit case arrangement, and it leaves the hands free. One can carry about fifty pounds on a pack board as easily as one can carry twenty pounds in a suit case. And a pack board radio compass, as shown in the photos, weighs only about twenty-five pounds. By using a lighter receiver and smaller batteries, that can be reduced to ten pounds. By going to extremes and using radio-frequency amplification only it could be reduced to five pounds or less. Also all the equipment could be included in one package. TO FIND the cause of a disturbance, put the pack board compass on, turn on the filament battery and tune-in the disturbance with the detector oscillating, if tuning is necessary. Then turn around until the disturbance is loudest and then till it is weakest or out. Those two positions should be at right angles and the disturbance should be in the direction of the wires in the compass coil when the disturbance is loudest, that is it should be either in front or back of you, providing it is from some place some distance away and there are no conductors in your immediate neighborhood. Then walk forward until the disturbance gets weaker or stronger. If it gets weaker, turn around again and if the direction of the wires is the same for maximum disturbance, walk in the opposite direction. If everything is ideal for compass work, you probably will walk right up to the cause of the disturbance. If the interference comes from a neighbor with a regenerative detector and you set your radio compass so it oscillates, you probably will be able to follow the squeal right up to the neighbor's house. Then if you "squeal on" or "tell on" him to the other broadcast receiving neighbors they will probably join with you for a persuasive conference with the interfering neighbor. Of course if he is a stubborn Scotchman you may have to call on the Presbyterian preacher for aid. If he is a dealer in stubborn water called "Scotch," boycott him. If you have a drop of Scotch in your blood, please forget this. If your drop of Scotch is in a bottle, offer it to your interfering neighbor. If the disturbance is caused by the lighting or power circuits of the public service company that you all are buying service from, the correction should be easy. Some of the power companies who have high voltage lines want to know when people hear such disturbances on their lines because such noises may mean leaking insulation which will break down some time and shut down their service. Some of the present interfering apparatus was made or is owned by the General Electric, Westinghouse, Western Electric, and Bell Telephone companies. Those companies are also.interested in broadcasting, therefore they should naturally want to prevent interference from their machines and devices, and want to know what you find. There are a lot of effects that may make the spotting of the source difficult which, if you are not in a hurry to find a particular source, are very interesting. If the disturbance is carried bv a wire line overhead or underground, the disturbance will be loudest when the horizontal wires are parallel to it, and the disturbance may follow the line for a considerable distance. IF YOU have a large mass of metal in the house like a large futnace, all broadcasts and all disturbances may be loudest when the coil is pointing toward the furnace no matter which side of the furnace you may be on. That is providing you are alongside the furnace. You may get the same result from a tall iron structure or a wire coming down a tall pole. If there are wire lines running along one side of your lot you may get a broadcast station on the other side and not at all or in a different direction on the wire line side. Generally speaking any conductor you pass close to will produce a change in apparent direction or in volume. Another interesting thing is that to get zero sound in finding directions the coil must be tilted sometimes. This is done by leaning over sidewise. [...] If you live in a part of the United States where summer thunder storms are common occurrences, it will be interesting to pick up their directions and follow them around, away, or over. When they are overhead or all of them are far away in several localities, the static will probably seem to come equally strong from all directions. The pack board radio compass is a good device for comparing the receiving characteristics of different localities because you have the same apparatus to use in all the places instead of a different antenna and different ground connection in each place. For example: I used it at Bremerton, Washington on Puget Sound and then went up on Mount Rainier and concluded that the strength of broadcasts from KGO at Oakland was about five to ten times as strong at Bremerton than I found them in Paradise Valley on Mount Rainier. [...] One evening, recently, I was out with the pack set checking up on the absorbing and direction changing effect of some wire lines. Going around the block I live in about dusk, I passed the Kitsap Inn. I noticed a woman on the porch, but not being so young as most radio engineers I was more interested in radio effects and did not pay any attention to her. I do not know whether she was a new comer to the neighborhood or whether she was peeved by my inattention. Anyhow she telephoned in to the Bremerton Police Department that there was a crazy man going around with a radio set on his head. A few minutes later, a mechanic who was ambitious to become a sleuth, came along and paid attention to the lady on the porch and being informed of my conduct followed me at a safe distance. This man with the positive sleuth bias seemed to believe that I was carrying a diabolic ray apparatus which I was trying to train on the Navy Yard which is about a mile and a quarter long. At any rate, something like that was telephoned to the Bremerton Police about the time 1 was passing across the street that separates Bremerton from Charleston. After the first alarm, the Bremerton police came to look for me, after the second alarm a Charleston policeman was added to the posse. Not finding me they called out the sheriff. The neighborhood afterward told me that police were seen searching even behind garbage cans. 1 don't know whether any of them looked in a garbage can or not. This went on for about two hours and in the meantime 1 went home and set my pack com- pass on a table along side of a tuned antenna wire, plugged in the loud speaker and sat down. A little later an automobile full of men pulled up just below my house on the wrong side of the street and made so much noise that I thought they were full and went out on the porch and sat down on the steps to pet the dog and watch the men. About that time one of them said, "There is a fellow sitting on the porch of that house, maybe he knows some- thing about it." Whereupon he came over and asked me if 1 had seen a fellow going around with a radio set on his head. 1 said, No, but that 1 had been going around with one on my back shortly before. Then he started in to ask questions about like most people ask when they meet me wearing the pack compass. Others came up until there were eight or nine of them and the questions seemed rather unusual, which caused me to ask why all the delegation and so much interest. I didn't know they were police because they were in plain clothes. Then they told me the whole story and 1 invited them in and let them listen to concerts.Altogether we had a very enjoyable evening. They told my friend McCall, the mayor, and Mac told the newspaper reporters and. I don't expect ever to hear the last of it.”. (Robert H. Marriott,“A Kit for the Radio Detective”, In “RADIO BROADCAST”, Vol. VI, no. 3, JANUARY 1925, Garden City, N. Y., DOUBLEDAY, PAGE & COMPANY, 1925, pp. 463-469)
Urls : http://www.archive.org/stream/radiobroadcast06gardrich%23page/462/mode/2up (last visited )

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