Radio Broadcast (May 1928-Apr 1929)

SEPTEMBER, 1928 WORKING ON 5 METERS 265 Tm)y'' m)y QjlTT a ^ Primary R R Detail R o OR R O R "Broadside'Antenna ® Osc. Sec. 9 E H T Douglas, Lawrence.Kansas © Vallouri balanced oscillator 2 E.B. Phelps,Jamaica,L.I. (D 2 C S M West,Stapleton,N.Y. © Folded antenna Equivalent to an r.f.line 10 A, Kruse.West Hartford.Conn. FIG. 2. TRANSMITTING ANTENNAS FOR 5-METER WORK The Douglas antenna was equipped with the feeder system shown in the diagram to permit its erection a long way from the badly screened station. The "detail" shows a cross-sectional view of a reflector system occasionally used with this antenna. The circle A represents the antenna and the circles RRR represent reflector wires parallel to the antenna and arranged in an approximate parabola. The number and placement of the wires, R, was varied. The whole arrangement can be laid on its side to become a horizontal system. The W est antenna is a normal \-wave antenna with a coupling and tuning system at its center. The condenser needs but two plates. The system is roughly go inches long, counting the coil length. The balanced Vallauri oscillator needs no r.f. chokes. The Phelps antenna is voltage fed at one end by a tuned circuit con pled to the oscillator. The antenna ammeter, A, is 50" from the high end. The "broadside" antenna consists of a series of 100" half-wave antennas connected by ymeter tuned circuits. All of the half-wave sections operate almost in phase and give broadside transmission almost like that of Marconi's beam stations. In all the diagrams "osc" is the oscillator as shown in Fig. I. In all cases the inductance and capacity inthe secondary circuits must be such as to tune to 5 meters. ence that a long wire such as is normally used for broadcast reception is as good as anything. It may be connected to the coil, Li, as suggested in the diagram of the double-detection receiver (Fig. 3) or may be given a separate primary. There seems to be little choice. The antenna series condenser, C3, when used, consists of a "vernier" condenser with all but one fixed and one movable plate removed. If the attachment of the antenna to the set stops oscillation one may be sure that the antenna is too closely coupled. It should then be clipped on nearer the filament end of Li, the setting of C3 made smaller, or the primary coil (if any) put farther from Li. RECEPTION AND TRANSMISSION LJAVING the apparatus all together with * ' some current [in the sending antenna and some sign of proper action on the part of the receiver, we are ready to try communication by radio to supplement the letter communication that has previously taken place with other 5-meter experimenters. Before going on with this it is well to make sure of the thing first preached about — that the set really turns out a signal that it is possible to make head or tail of. To do this the sending set is put into action with some kindly neighbor or friend to punch the key or talk into the "mike" and the receiver is set up in another part of the house or perhaps in the front yard. The friend or neighbor had better be warned that he is in for a session of several hours and must not get impatient at the long silence that opens the proceedings. First of all the receiver will probably take a notion not to oscillate, though there is no real justice in this as it does not have an antenna at the moment. The second discovery is probably in the nature of noise in the receiver, or unsteadiness at the transmitter which must be remedied. However, be of good heart — it is far easier to do this than to go through the silly performance we staged. We did not take the precaution just suggested and when our first sets were in operation we spent a month or so in listening at 120 miles for signals that eventually turned out to be wholly in the Choctaw language. Eventually the transmitter and the receiver will be gotten into decent shape and will agree to work on a sporting basis — half the time. Then one is ready to take the field. WHAT CAN BE DONE AFIELD DEFORE another transmitter is available to work with, one may do some very enchanting things near the station by wandering about with receiver, wavemeter and screwdriver, testing for the manner in which the radiated power is scattered about the vicinity — which is usually surprising enough. These tests require the set to run while the owner is absent, and as the patience of the friend or neighbor was exhausted in the first tests one must make up an automatic key of some sort. C. H. West of station 2CSM created some sort of an affair from an alarm clock and a relay which made dashes for hours at a time and later drove a disc with the station call on it. He says it was not artistic but effective. Boyd Phelps at 2EB went to the opposite extreme and created a motor-driven key with a notched cam 18 inches across and half an inch thick, transmitting therewith the station call and the word "test." One need not feel at all guilty about such operation, or even about "laying a book on the key," provided that the thing is done outside broadcast reception hours, for there are not enough 5-meter men about to worry over. Having the set operating under automatic keying one may first take the screwdriver or the metal-shell pencil (not an advt.) and go about the house testing the lighting sockets, water faucets and other metal objects for the presence of r.f. Usually it will be found. This effect should be cut down as far as possible by getting the sending set clear of all wiring, including that in the walls. When the pencil test or screwdriver test does not reveal r.f. about the house try opening the circuit of the General Radio meter and putting in a flashlamp or a little Walbert " panelite" (60 mA, 5 volts) bulb. Tune the wavemeter to the transmitter and go about hunting along wires, pipes, etc., with it. Do not be too sure that you have removed r.f. when a "hot spot" disappears; it may only have shifted. Having finally gotten as much r.f. as possible out of the pipes, wires, metal lath, bathtub and kitchen stove we may hope that some fair part of the power is in the antenna and departing from it. At about this point it will be found that this is so, at least to the degree that the antenna transmits the stuff to nearby houses and causes hot spots to appear in them. If one of them happens to be in the family radio receiver that receiver will not work when the 5-meter set is going — or rather it will produce loud grunts and growls in place of music. For this reason it was said that these things should be checked up and the busy broadcast hours avoided. In some cases the thing is bad — in others totally absent. Be sure.