US 2284415 A
Description (OCR text may contain errors)
*May 26, 1942.l
H. E; GOLDSTINE 'RELAY SYSTEM Filed Nov. 29, 1939 Patented May 26, 1942 UNITED RELAY SYSTEM Y Hallan E. Goldstne, Rocky Point, N. Y., assigner to Radio Corporation of America, a corpora--` tion of Delaware Application November 29, 1939, Serial No. 306,608
3 Claims. ,(Cl. Z50-15) The present invention relates to the art cf signal relaying by ultra short wave radio and, more particularly, to a system for supplying a television signal to receivers which are near the relay system but not within the eld of the transmitters of the system. One method of utilizing a network of television relay stations to connect important cities involves the transmission of the television lsignals on an ultra high frequency of the order of hundreds of megacycles from one city l and at intervals of fty miles, or thereabouts, picking up the received signals, amplifying and retransmitting the signals through the medium of highly directive antennae and thus covering the entire distance between the cities. Due to the quasi-optical characteristics of the ultra high frequencies used the signals are transmitted only along line of sight paths and due to the extreme-directivity of the transmitting and receiving antenna of the relay station, as well as due to the high frequencies involved, being beyond the tuning range of television broadcast receivers, such receivers are unable to receive the programs.
An object of the present invention, therefore, is the provision of a television relay system which will supply a relayed television signal to a comparatively large area near the path of the television relay chain. In accordance with this object it is proposed that the television signal be transmitted by means of frequency modulation. At the desired locations where low frequency broadcast transmitters are to be located a pickupantenna within the field of a high frequency relay transmitter is established, or the signals are tapped off from an adjacent relay station amplifier. The picked up high frequency signals are heterodyned by means of a fixed frequency oscillator to the television broadcast band and then amplified in a number of stages at that frequency until the power is sufficient for prnner coverage of the area involved. This amplified lower frequency signal is then applied to a broadcast antenna in the conventional manner and radiated over the area to be covered. As a further feature of the invention means may be provided to alter the modulation index of this broadcast signal.
Further objects and features of the invention will be more clearly understood from the following detailed description which is accompanied by a drawing in which Figure 1 shows the layout of a television relay chain and a broadcast transmitter utilizing the principles of my invention with the amplifiers and converters shown in conventional Ablock form, and Figure 2 illustratesa modification of a portion of Figure 1.
In Figure 1, I have shown -a plurality of they ultra high frequency relay stations I0, each of which are placed at the top of acomparatively tall tower. These towers are spaced about miles apart, depending upon the characteristics of the terrain covered, and a balancing of the cost per foot of the towers against the cost of the relay equipment. Each of the relay stations Iii comprises a receiving antenna I2 withina highly directive reflector I3 and a similar transmitting antenna likewise within a highly directive transmittingreiiector I3. The receiving and transmitting antennas are connected by an amplifier which takes the signal as picked up by the receiving antenna, ampliiies it without frequency conversion and retransmits it to the next relay in the relay station Ill nearest the area to be covered by the broadcast signal and applies the signal taken therefrom to a frequency converter I5. If desired, the relay frequency signal may be picked up by asimple antenna between adjacent relay stations. Since the relay transmission is a frequency modulated signal the relay transmission may have its frequency changed to the conventional television broadcast band by means of a fixed frequency oscillator such as a crystal oscillator or a frequency controlled oscillator of any other convenient type at I5 and amplified at I6 for transmission by means of transmission line I 'I to the power amplifiers I 8. The amplified signal, of suiiicient power to cover the desired area, is then applied to the broadcast antenna I9 in the usual manner. Since a frequency modulated signal is used the amplifiers I6 and I8 need not be operated as linear amplifiers but need only respond linearly with frequency, thus decreasing the cost of the system considerably.
The frequency control device IEa may be either a crystal oscillator or automatic frequency control may be applied from the output of amplifier I6, as indicated by line F-I-C, to maintain the average frequency of the signal in transmission line Il and radiated from the antenna IS essentially constant. In some cases it may be desirable to reduce the frequency swing or modula- A trans--v tion index of the broadcast signal from that existing in the relay signal. is shown inFigure 2 wherein a demodulator 26 takes a portion of the signal'frorntransmission line I4, before it is applied to the frequency converter I5. The demodulated signal, of an adjustable amplitude controlled by amplitude control 21 One method of doing this is applied to a `frequency modulator stage 25. The frequency modulator 25 aplies the signal to Y' Vthe heterodyne oscillator in a manner to opDOSe the original frequency swing thereby degenerating. the frequency modulated signal output from converter I5 to any desired extent.
While I haveparticularly shown and described` quencies, said chain passing .near an intermediate area overwhich signals are to be broadcast, pick-up means adapted to Vreceive Ysaid ultra high frequency signals connected to one ofV said vrelayv stations adjacent .said area, an oscillator,v means for applying signals picked up :by said pick-up modulation index `of said lower frequency signals ,may be adjusted, and means for broadcasting v said lower frequencysignals over said area.
2. In a signal transmission system, a source of'frequency modulated high frequency waves, a frequency rconverter inc1uding an oscillator, means for applying said waves to said Vfrequency `converter oscillator so that they are heterodyned toa different frequency, means independent of said frequency converter means for demodulating said first mentioned highfrequency wavesl and means for modulating said oscillator in accordance with saiddemodulated waves in such sense fwith respect to the modulation of said frequency modulated signals that the modulation index of said resultant frequency modulated signals 'maybe adjusted.
rmeans to said oscillator so that said signals are heterodyned to a lower frequency, means forfrequency modulating said oscillator in a predetermined sense withrespect to the modulation of said frequency modulated signals whereby Vvthe 3. In a signal'transmission system wherein frequency modulated waves in one frequency band "are transformed to frequency modulated waves in another frequency modulated bandfby heterodyning in one path' :the first mentioned waves with wave energy of a predetermined vfrevlquency, theV method of Areducing the modulation rindex ofthe secondcmentioned of said frequency Vmodulatedr waves which comprises 'diverting a portion ofsaid first mentioned4 wavesr into a second path; demodulating in said' second path'said diverted portion of said rst mentioned waves and frequency'modulating said wave of predetermined frequency by said demodulated first wave. f Y f HALLAN E. GOLDSTINE;