Radio doings (Dec 1930-Jun1932)

March, 1931 RADIO DOINGS Page Twenty-seven In a parallel resonance circuit these expressions become w LR and R/ w C so that the variation of these ratios has the opposite effect. Since we arc dealing in this case with parallel resonance, greater selectivity will be obtained with small values of L and larger values of C. Incidentally, as L is reduced, R automatically drops due to the lower DC resistance and also reduced distributed capacity. At 175 kilocycles the high frequency resistance does not climb nearly as rapidly as at the broadcast signal frequencies. The principal increase in resistance is due to the distributed capacity of concentrated inductances. In a layer wound coil the distributed capacity is actually lower when the coil is wound in many layers than if the same number of turns were wound in two layers, due to the fact that the capacities of the individual layers may be considered in series. Thus, when the number of layers is increased for a given number of turns, the coil approaches a single layer solenoid. The exact ratio of width to number of layers will vary in individual cases and can best be determined by experiment for any given set of conditions. FIG. 1 FIG. 2 ; j K i 8 1 1 f N Jl ■JT * 1 ! i -3 FIG. 4 -- [~~. , 1.0 > .3 5 / \ 6 1 '' a a ! i « j \ j \ 5 .o FIG. 5 J ^\ h t .6 a -8 l \ r 1 » / \ i h \ F IC. 7 FIG. 8 5 1 l 9 9 .6 1 \ & 8 .** ! / \ .A A 6 i A : GAIN OF A SINGLE STAGE In a parallel resonance circuit the equivalent series resistance is expressed L r = (13) CR Where L is in Henries C is in Farads R is the high frequency resistance in Ohms. With the usual range of L and C used at 175 kilocycles in inter The New KFI Interesting details of the 50-kilowatt transmitter being constructed hy Earle C. Anthony, Inc., under authority of a federal permit authorizing that power for KFI have been released by the broadcaster in an official announcement. The giant station will be located in a 30-acre tract in the vicinity of Northham, Los Angeles county, near the Orange county line at an approximate distance of twenty miles. This location was decided upon after exhaustive field strength tests by engineers, which proved that a perfect "circular pattern" was obtained at that point, insuring equal radiation in all directions. The exterior, visible features of the new station consist mainly of the two towers and the building that houses the transmitter. The towers will be 400 feet high, placed 700 feet apart, and placed so that they form, with the building, an almost equilateral triangle, the building being 495 feet from the middle point between the towers. Double insulation is a feature of the towers which have been purchased from and will be erected by the Pacific Iron and Steel Company at a cost of $17,600. The towers will be lighted in compliance with the Department of Commerce regulation for air traffic. The ground system, elaborate and advanced in design, includes the feature of having 20 miles of copper wire plowed into the ground. The transmitter itself, costing $153,000 is built by the RCA Victor Corporation and will be installed by them. It is of 50-kilowatt power with 100 per cent modulation. The electrical contract is handled by the General Electric Company. The prices quoted above for building, transmitter and towers do not represent the total investment. Costs of the propery, telephone installation, equipment, housing facilities for employees will appreciably increase the total. When television becomes a practical factor in broadcasting, the new KFI transmitter can accommodate the new art by the addition of a minor unit. These plans do not include studio facilities which will be handled separately. Programs will continue to originate in the Earle C. Anthony building at Tenth and Hope streets, telephone cables taking the programs to the transmitter in the same manner that KECA programs are now handled to the transmitter at Eighth and Beacon streets. According to engineering tests completed, the most appreciable result of KFPs increase of power will result in a much more refined and clear tuning, due to the difference between "noise lever' and "signal level." At 5000 watts, for instance, the "signal level" is high enough over the "noise level" so that tuning is only rarely affected with extraneous noise. But with the 50,000 watts the "signal level" is so high above the noise level" that it is possible to tune down without receiving noise to an extent impossible with the smaller wattage. This will be specially noted during daylight reception which will be materially improved. mediate frequency amplifiers and assuming high frequency resistances of from 50 to 100 ohms for the primaries, load impedances from 300,000 to 1,000,000 ohms may be realized, resulting in very great voltage amplification when 224 tubes are used. It will be noted here that while a reduction in the value of L will favor selectivity, it will result in a considerable reduction in the equivalent series resistance, thus reducing the gain per stage. In practice, a compromise may easily be effected, since the gain changes more rapidly than the selectivity. The gain of a single stage may be varied easily between 40 and 300 with values of L from 5 to 1 5 milhenries and with values of R from 40 to 150 ohms. Thus, it will be seen that the selection of the exact values will depend upon the conditions to be fulfilled in the individual case of design.