US1988275A - Equal wavelength broadcasting - Google Patents

Description

Jan. 15, 1935. H. HARBICH EQUAL` WAVELENGTH BROADCASTING Filed Sept. l1, 1931 Y W 111' afney Patented Janl5, 1935 *UNITE-Dama `rinata EQUAL wAvsLeNern sacapcasrnie Hans Harbich, Berlin-Steglitz, Germany, as-

' signor to C'. Lorenz Aktiengesellschaft,.Berlin- Tempelhcf, Germany, a ccmpariy `7 *Appliance september 11, 1931, serial-n0'. 562,425 1 In'Germany September 13, `19.3,@

" 4' claims. (ci. 25e-f2) f,

This invention relates generally to radio trans` same wavelength 'are supplied from'a cer`itralv station withl afundamental frequency which is multiplied at the transmitters to form the carrier frequency; and` in the other of which, synchronization of the transmitting apparatus at each of the different stations is effected by local means. Both these arrangements, however, result in disturbed areas between the `transmitting stations in which the magnitudes of said disturbed areas are dependent on the magnitudes of thedegree of control of the apparatus in the individual transmitting stations.

According to the present invention,` it is proposed to limit the degree of modulation control, so that it never exceeds a predetermined value, by automatically regulating the amplifiers in each transmitting station.

Another object ofthe invention is to keep the size of the disturbed area constant, this size being dependent solely upon the degree of modulation chosen` for the individual transmitting stations.

A further object of the invention is to position the disturbed area over a predetermined locality between the transmitting stations.

An embodiment of the invention is illustrated in the accompanying drawing, wherein: Y

Fig. 1 represents the disturbed area between two transmitting stations using earlier methods of modulation;

Fig. 2 represents the disturbed area between two transmitting stations using a method of modulation according to the present invention;

Fig. 3 is a schematic representation of two transmitting stations, each receiving the same program from a microphone in a central station and operating on the same wavelength.

In Figs. 1 and 2, A andV B are broadcasters simultaneously transmitting on equal wavelengths. The hatched area between the two stations represents the disturbed area where the signals of each station are distorted.

v In Fig. 3, where a schematic broadcasting systemv employing the invention is shown, two broadcast stations and a central station are indicated as A, B and C, respectively. At the central station C there is a microphone M and an ampliner V. At each of the broadcasting stations there is a modulation-amplifier MV, an amplitude-liiniter F, and a transmitter S, together with the necessary antennafground connection and connecting land lines to the central station C. Y

" In the event of modulation, the disturbed area between-the two transmitting stationsemittinguwaves of the same frequencywill bei' very/large, in fact, comprising' practically -the entire territory between and around said transmitting stations.

However, if the modulation be reduced to 30% the ratio of the field strengths considered at a predetermined point may amount to 1: 2 without any distortion becoming noticeable.

If the modulation be still further reduced to 20%, a ratio of eld strengths amounting to 1: 1% would be permissible at the predetermined point.

For example, assuming transmitting stations.

Thus, a maximum limit for the percentage modulation is determined by experiment which gives a minimum disturbed area. This percentage when determined is used as a fixed maximum above which the modulation-amplifier MV (Fig. 3) Will not pass energy to the transmitter S. Therefore, the modulation-amplifier functions merely to prevent excessive modulation. The maximum percentage modulation of the individual broadcasters is so limited by the automatic regulation of MV, that the size of the disturbed area between broadcast stations emitting waves of the same frequency is kept a constant minimum.

The location of the disturbed area between the broadcasters depends upon the ratio of the `amplitudes of the carrier frequency of the individual transmitters.

If the broadcasters do not possess the same amplitude of carrier frequency, the disturbed area is shifted toward the This area can,

ThllS limits of amplitude fcr the carrier frequencies are determined, which place the disturbed area where itgives the least trouble to broadcast re- CGlVeI'S The maximum amplitude of the individual broadcaster is so limited by the automatic regulation of the amplitude-limiters F (Fig. 3) that the disturbed area is positioned over a predetermined locality.

In carrying out this method of control over the disturbed area between broadcasters, care must be taken that the percentagel modulation of both transmitters is the same, since it can be easily proved by experiment that in such a case the smallest area of distortion will occur between the broadcasters. This is further achieved through devices for limiting the fieldl strength which will take care that the transmission eiiciency of the broadcaster` is the same, even though there is a differentv amplitudejof rthe carrier frequency. It is not necessary to describe devices, such as variable antennacouplers, for limiting the transmission eciency of v a broadcaster, since these arrangements are well` ,from-two transmittinggsta-t-ions which comprises the following steps, modulating-and amplifying signals, andadjusting'the degree of:m0dulation `s o as to reduce to a minimum the area ofthe interference in the reception froin'said stations.

2. Method according to claim 1 characterized by the step of adjusting the amplitude of the carrier frequencies to determine the location of said interference.

3. Method of equal wavelength broadcasting from two transmitting stations comprising the following steps, modulating Aand amplifying signals at` said stations, broadcastingsaid-signals from said stations,adjusting the'degreeA of modulation to a point for reducing to a minimum `the area of the interference in the reception vfrom said stations, and determining the location ,ting` stationY ,the` degree-of Y modulation tol a point for reducing to a minimumythe area of 'thea inter.-

ference in ythe'freception Afrom said stations; and

determining.` the location of. said' interference by;adjustingthe amplituderatiossof the unmodiulated transmittersl atx-said transmitting stations.

HANS HARBICI-..I

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