US 2201554 A
Description (OCR text may contain errors)
s. cLo'rHlER Er AL METHOD lAND SYSTEM FOR TELEVISION TRANSMISSION Filed oct; 2o, 1937 May 2l, 1940.'
Patented May 21, 1940 PATENT oFFlcE METHOD AND SYSTEM FOR TELEVISION TRANSMISSION Stewart L. Clothier, East Orange, and Harold C.
J., assgnors to Kolorama Laboratories, Inc., Newark, N. J., a corporation of New Jersey Application October 20, 1937, Serial No. 169,958
Our invention relates to improvements in methods and systems for television transmission.
One of the present, accepted methods in television broadcasting is to employ a transmitter for sending the synchronizing and the video or picture signals on an ultra high frequency carrier wave, and to employ another transmitter, operating entirely independently of the other, for sending the sound signals also on an ultra high frequency carrier wave which,l however, is separated from the first-mentioned carrier wave by 3.25 mc. The two transmitters have their own, separate oscillators for generating the two respective ultra high frequency carrier waves. These oscillators are entirely disassociated from and operate entirely independentlyof each other.
At the receiving station. in selecting a Ygiven television broadcasting station it is the practice to adjust the receiver for the best sound reception, in which case the receiver is .automatically adjusted for the best television reception. This is accomplished by virtue of the fact that rthe conventional receiver embodies a common oscillator and two independent intermediate-frequency amplifiers. These two intermediate-frequency amplifiers are adj-usted to two intermediate-frequency bands whose separation is 3.25 mc. This manner of operation is dependent upon the accuracy with which the fixed relationship between the two ultra high frequency broadcast carriers is maintained, and for this purpose, complicated and expensive frequency control equipment has heretofore been required to keep the two carriers fixed at the respective frequencies, or at least close enough so that the separation does not vary far enough from 3.25 inc. to cause poor television reception atthe receiver. The difliculty, in this connection, becomes apparent when it is realized that a variation of only .05% in each of the two transmission carrier frequencies might cause a maximum variation of nearly 50 k. c. in the separation between the two frequencies when the two carrier frequencies are, for example, 48 mc. and 51.25 rnc. respectively. and the intended, constant separation therefore 3.25 mc.
With the foregoing in mind, it is one of 4the objects of our invention to provide an improved method and system for television transmissionr which avoids the disadvantages referred to in the methods and systems used heretofore. and, particularly, which eliminates the necessity for the use of complicated and expensive frequency control equipment for maintaining constant the operating action of the two oscillators for obtaining the two ultra high frequency carrier waves.
Another object of our invention is the provision of an improved method and l.system for television transmission by which a fixed relationship and separation between the two ultra high frequency transmission carriers is maintained in a reliable and eicient manner.
Other objects and advantages will hereinafter appear.
In accordance with our invention, two independently operating transmitters are used to transmit, respectively, the picture and sound signals, the frequency of operation ofone of the transmitters is controlled by a first oscillator operating at a fixed frequency, and the frequency of operation of the other transmitter is controlled by the joint effect of said oscillator and a second oscillator operating at a fixed frequency.
More particularly, in accordance with our invention, a master, crystal-controlled oscillatorzis lused to develop a substantially fixed, ultra high frequency carrier Wave on which picture and synchronizing signals are broadcast by a first transmitter. A mixer circuit is supplied with this ultra high frequency and also with the frequency from the output circuit of a second crystal-cone trolled oscillator operating at a substantially fixed frequency different from said first-named frequency, whereby there is developed a second ultra high frequency carrier wave, the frequency of which is the algebraic sum of the respective frequencies in said output circuits. It is on this second, ultra high frequency carrier wave that the sound signals are broadcast by a second transmitter operating independently of the first transmitter. a
Our invention resides in the novel method and combination of character hereinafter described and claimed.
For the purpose of illustrating our invention, an embodiment thereof is shown in the drawing, in which:
Figure l is a block diagram of a television broadcasting system constructed and operating in accordance with our invention; and
Fig. 2 is a schematic representation of the television channel in which the system in Fig. l-opcrates.
With reference to the drawing, the numeral lli designates a iirst transmitter and power amplifier supplied with synchronizing signals and video or picture signals by the units shown and which are constructed and combined in a conventional manner. These units are a video pick-up device Il, an amplifier I2 for the video signals, a modat 3.25 mc.
ulator I3, a generator Ill for producing the synchronizing signals, and an amplifier l5 for the synchronizing signals.
The reference numeral I6 designates a second transmitter and powei` amplifier operating independently of the first and supplied with sound signals by a sound pick-up device l', an amplifier i8 for the sound signals, and a modulator i9, all constructed and combined in a conventional manner.
The frequency 0f operation of the first transmitter l is controlled by a first, crystal-controlled, master oscillator 2D operating at a fixed frequency of 12 mc. for example. This frequency is doubled to 24 mc. by a frequency doubler 2l, and again doubled to 48 mc. by a second frequency doubler 22, whereby a 48 mc. television carrier wave is developed. It is on this ultra high frequency carrier wave, which is amplified by an amplifier 23 and supplied to the television transmitter Ill, that the picture and synchronizing signals are broadcast.
In lieu of using a second, independent, and ultra high frequency oscillator for controlling the sound transmitter I6, as heretofore, we employ a crystal-controlled oscillator 24 operating at a fixed frequency materially lower than the fre,- quency of operation of the master oscillator 20. That is, in the particular embodiment of our invention disclosed, the second oscillator 24 operates at the fixed frequency of 3.25 mc., as against the frequency of 12 mc. at which the master oscillator 2Q operates.
A mixer circuit 25 is supplied from the output circuits of both the master oscillator 20, after multiplying to the desired ultra high frequency, and the second oscillator 24, whereby there is developed a second carrier wave the frequency of which is, in this case, the sum of the respective frequencies in said output circuits, that is, 51.25 mc. It is on this second, ultra high frequency carrier wave, which is amplified by an amplifier 2S and supplied to the transmitter I 6, that the sound signals are broadcast.
Since the frequency of operation of the second oscillator 24 is relatively low, variations in its output frequency represent but a negligible percentage of the 3.25 mc. as compared to what would otherwise be the case if this oscillator operated at the ultra high frequency of 51.25 mc. to develop the sound carrier independently of the iirst oscillator 20, as heretofore. For all practical purposes, therefore, it can be said that the operation of the second oscillator 24 remains fixed Therefore, although the frequency of operation of the master oscillator might vary, the separation of the television and sound carriers will remain substantially fixed since this separation in our improved method and system is always the frequency of operation of the second oscillator 24.
If it is desired that the sound carrier be lower in frequency than the television carrier by the 3.25 mc. separation, the mixer circuit 25 is made to subtract the frequency of the second oscillator 24 from the ultra high carrier frequency developed by the master oscillator 20. In other words, the frequency of the sound carrier is in any case the algebraic sum of the respective frequencies in the output circuits of the two oscillators.
An example of a mixer circuit for combining the frequencies of two oscillators is given in the publication Radio, issues of June and July, 1936.
From the foregoing it will be seen that in our improved method and system, separation between the ultra high frequencies of the television and sound carriers is maintained constant in a relatively simple and eiiicient manner, and regardless of occurring variation in the frequency of operation of the master oscillator for developing the television carrier.
While but one embodiment of our invention has been disclosed, it will be understood that various modifications, within the conception of those skilled in the art, are possible without departing from the spirit of our invention or the scope of the claims. For example, any other suitable means may be employed for developing the ultra high frequency television carrier wave, instead of a crystal-controlled oscillator and the associated frequency doublers. Likewise, any suitable, stable, separation oscillator may be used, although we prefer the use of a crystal-controlled oscillator for this purpose.
We claim as our invention:
l. A television transmission system comprising a first radio frequency transmitter including an antenna system, means including an oscillator for developing a rst ultra-high frequency carrier Wave and means for modulating said first carrier wave at audio frequencies; a second radio frequency transmitter including a separate antenna system, means including a separate oscillator for developing a second ultra-high frequency wave differing infrequency from the first carrier wave, and means for modulating said second carrier Wave at video frequencies; one of said oscillators being crystal-controlled and operated at the dcsired separation frequency and interlocking and maintaining a fixed separation in frequency between the two carrier waves.
2. In a television transmission system, a rst transmitter including an antenna system, means for developing and supplying picture signals to said transmitter, a second transmitter operating independently of said first transmitter and including a separate antenna system, means for developing sound signals and supplying the same to said second transmitter, means comprising a crystal-controlled master oscillator operating at a substantially fixed frequency and developing' an ultra high frequency carrier wave supplied to said first transmitter, means comprising a second crystal-controlled oscillator operating at a substantially fixed frequency materially lower than said first-named frequency, and a mixer circuit supplied from the output circuits of both said oscillators and operating to develop a second carrier wave the frequency of which is the algebraic sum of the respective frequencies in said output circuits, said second carrier wave being supplied to said second transmitter, said respective carriers thereby being interlocked and maintained separated by the constant frequency of said second crystal-controlled oscillator.
STEWART L. CLOTHIER. HAROLD C. HOGENCAMP.