US1753445A

US1753445A - Signaling system

Info

Publication number: US1753445A
Application number: US140388A
Authority: US
Inventors: Russell S Ohl
Original assignee: American Telephone and Telegraph Co Inc
Current assignee: AT&T Corp
Priority date: 1926-10-08
Filing date: 1926-10-08
Publication date: 1930-04-08
Anticipated expiration: 1947-04-08

Description

April s, 1930. R. s. OHL A 1,753,445

sIc'JNALING SYSTEM Filed Oct. 8, 1926 v- & ATTORNEYS.

Patented Api'. 8, 1.9.30

. UNITED STATES PATENT oFFicE RUSSELL S, OHL, OF NEW YORK, N. Y., ASSIGNOR T AMERICAN TELEPHONEAND TELE- GRAPH COMPANY,'A CORPORATION' OF NEW YORK SIGNALING sYsTEM Application led Oct'ober 8, 1926. Serial No. 140,888.

quency signals in the form of high frequency venergy over a considerablevdistance, it is necessary to maintain the high frequency or carrier wave very constant in frequency. In order to receive and detect the energy present in, for example, a single side band of high.

frequency energy, it is often necessary to iny troduce some local frequency which may be employed to beat with the lside band,"the local frequency being maintained constant within verynarrow limits, in order that the 2o low freqluency signals may be faithfully rey produce A common practice for receiving a high frequency modulated signal is, first, to change the frequency of the signal to another frequency lowered in the frequencyspectrum, which may be amplified more easily than the higher fre uency originally received, and;

second, to etect the signal from the intermediate frequency. This is done by the wellknown means of beating the received high frequency signal with the unmodulated sinusoidal frequency of a .local oscillator to pro'-l duce an intermediate frequency which can.

then easily be amplified. One can readily see no more than the higher equency originally received, if itis essential to maintain high quality standards throughout the system. l'

In this invention, there will be shown, merely for the sake of illustration, a local oscillator which is connected tol a harmonic producer to produce a harmonic of the fre-` quency of the oscillator to vbe used as a local beating frequency to beat with a side band of high frequency energy. In order to main is employed to receive a side band of very tain the local beating frequency Aconstant within very narrow limits, a piezo-electric device is connected to the oscillator. In order to vary the `frequency sustained by the locall oscillator, means are associated with the that -the intermediate fre uency should vary .with partieularity 11i the appllded claims,

high frequencyv ener piezo-electric device for carefully adjusting its characteristic frequency with considerablel accurac Accordingly, the intermediate band o` frequencies resultin from beating processto be described hereinafter, will'be 55 well defined in the frequency spectrum. The

' same oscillator, controlled and varied as to its frequency by means of the piezoelectric device, is employed to bea-t with the intermediate band of frequencies, so that the low 60 frequency signals originally present in the 4fcvrm of high frequency energy are faithfully detected and reproduced.

Accordingly, it is an object of this inven` tion to associate the output of an oscillator with a band of high frequency energy so that by controlling and varyingythe frequency of the oscillator as conditions necessitate, the band of signals will be faithfully detected and reproduced. 7o

Another of the objects of this invention is to so relate an oscillator and a harmonic producer to means for receiving a band'of vhigh frequenc energy that the harmonic producer will pro uce a harmonic of the frequency of the oscillator, which may be carefully controlled and `varied as to its frequency, in order that an intermediate bandof signals corresponding to the original signals can be effected, which. may again be beaten with the frequency vof the oscillator similarly controlled and varied as to its frequency to reproduce theoriginal signals, with greater accuracy than `has heretofore been possible.

While the invention will be` pointed out the invention itself, both as to its further obfrom the detailed description hereinafter following, when read vin connection with the 0o accompanying drawing, showing one embodiy ment of the invention, merely for the purpose of illustration. l

Referring to the drawing, an antenna system comprisingv an antenna N and ground,

high frequency energy.. This side band of is impressed upon a first detector D1.v e reference character Q designates an oscillator which` sustains os- 100 'cillations of a very high frequency, such, for

- example, as 2,500,000 cycles. This oscillator ma be of any well-lmown type, but it is prefera ly of the-vacuum tube type familiar to the art. This .oscillator may also be of the untun'ed type, and may of itself vary in freuency considerabl requency. In or er to maintain the frequency of the oscillator O constant in frequency within very narrow limits, and in order to render the frequency characteristic of this oscillator O adjustable as conditions necessitate, a piezo-electric device is connected thereto, which comprises a piezo-electric crystal PE which is placed between two conductive electrodes L1 and L2. The conductive electrode L1 is rigidly fixed to an ad'- 'justable thumb screw'T so that as the thumb screw is moved inwardly or outwardly, a corresponding change will take place in the dis-l tance between the'piezo-electric crystal PE andthe conductive electrode L1. Obviously, the width ofthe dielectricr` such, for example, as air, between the conductive electrode L1V and the piezo-electric crystal PE may be y changed by manipulation of the thumb screw T. The piezo-electric device may preferablybe located in a box or othercontainer which electric crystal PE any means may, for example, be madeof hard rubber, bakelite, or other insulating material. Means may also be provided for accurately determining the displacementof the thumb screw. It is to be understood,however, that itis within the scope of this invention to provide whatsoever for rendering a fine adjustment of `the space between the piezoand one or both of its conductive electrodes, so that in effect the frequency characteristic of the piezo-electric crystal may be adjusted and varied with precision.

- v. Inan oscillator with which a piezo-electric device is associated, which comprises a piezoelectric crystal vibrating between conductive electrodes, it has been found that the frequencyof oscillations sustained bythe oscil- .lator may be controlled and varied as to frequency by adjusting the size of the gap existing between the Vpiezo-electric crystal and its I conductive electrodes. Generally, as the space between the crystal and its conductive elec.

trodes changes, a corresponding change is produced in the frequency of the oscillations sustained by the oscilla-tor. -More particularly, as the distance between the piezo-electric crystal and its conductive electrodes is 'inJ A creased, the frequency of the oscillations sustained by the oscillator Will, under certain conditlonis, also be increased, and .v1ce versa.

This is exactly what takes place when thepiezo-electric device, comprising the piezoelectric crystal and the conductive electrodes L1 and L2, is associated with the oscillator O. Briefly, the fre uency of oscillations sustained by the oscillator O may be controlled from its characteristic be of any well-knowntype,

22,500,000 cycles. This harmonic is transmitted to the first detector D1, and is employed to beat with the incoming side band of high frequency energy, whichl may, for example, be a band of signals between 20,000,000 and 20,005,000 cycles. This detector D1 may also but it is preferably of a vacuum tube type. -By beating the frequency of the harmonic with the incoming side band of high frequency energy, another band of signals is produced which is displaced in the frequency spectrum. In the particular case given for the purpose of illustration, this intermediate bandof frequencies may have the limits' of, for example, 2,495,000 and 2,500,000 cycles. The output of the detector D1 is impressed upon a filter F which may be of any well-known type, but preferably of the type disclosed in the patent to G. A. Campbell, No. 1,227 ,113, dated May 22,I

1917. This filter freely transmits the band y of signals resulting froml beating the har.- monic of the oscillator O with the incoming side band of high frequency energy, and substantially suppresses all frequencies above and below the limits of said band. The filter F is connected to an intermediate frequency amplifier A which is employed to amplify the Aband of signals transmitted by the first detector D1 and the filter F.- This intermediate frequency amplifier A may, of course, be of any well-known type, but it is also prefcrably of the vacuum tube type. After Y amplification by the amplifier A, the intermediate band of signals is impressed upon a secondV detector D2.

, The frequency sustained by the oscillator O, which is controlled and varied as to frequency by means of the piezo-electric device, is now transmitted to the second detector D2, which may also be of any well-known type, but which is preferably of they vacuum tube type. The second detector D2 beats the frequency of the oscillator O with the intermediate band of signals transmitted by the filter F' and the amplier A. Accordingly, the original signals, which were lreceived by the antennal N in the form of a side band of high frequency energy, are faithfully detected and received by a headset R. It will be fairly obvious that if the oscillator O were not controllable and variable as to its frequency by a device such as is shown herein, i. e., a piezoico? Ois possible to maintain such a high quality in transmission as has not heretofore been possible.

It will be obvious that While a single oscilv lator has been shown herein, which is controllable and adjustable as to its frequency by means of a piezo-electric device, tWo oscillators may equally Well be employed, each equally controllable and adjustable as to its `\-\rfquency by a common piezo-electric deviceVL or bysepalatemieazgexletricdevices, within the scope of this invention. y

Itwill also be understood that While this invention has beenshown herein, for the purpose of illustration, embodying a double' detection system, the principles of this invention may be applied to numerous other systems and to various `embodiments ofl such systems Without departing from the spirit of the invention and the scope of the appended claims. L'

What is claimed is:

- l. In a signaling system, the combination of means for receiving a band of signals of high frequency, an oscillator, piezo-electric means for controlling the frequency of said oscillator, said piezo-electric means including means to vary its vibratory characteristic in order to correspondingly vary the frequency of said oscillator, aifeans-ffcirfheatingsaidn Meno-electrically.'controlled and varied frequency with the band of signals of high frel quency to produce a corresponding band of signals displaced in the frequency spectrum,

and means for again beating the piezo-electrically controlled and varied frequency with the band o-f signals displaced in the frequency spectrum -to derive and detect the original signals.

2. In a signaling system, the combination of means for receiving aA band of signals of high frequency, a local oscillator, piezo-electric means for controlling and varying the frequency of the local oscillator, means for producing a harmonic of the frequency of said oscillator similarly controlled and varied as to frequency by said piezo-electric means, means for beating said piezo-electrically controlled and varied harmonic With the band of signals to produce a corresponding band of signals lowered in the. frequency spectrum, and means for beating the piezo-electrically controlled and varied frequency of said oscillator with the band of signals lowered in the frequency spectrum to derivel and detect the original signals.

8. In a signaling system, the combination of means for receiving a band of signals of high frequency corresponding to "voice frequency signals, an oscillator, means for beating the frequency of said oscillator with the band of signals of high frequency to produce YVwill be accurately derived.

quency spectrum, a piezo-electric device associatedA with said oscillator including means for controlling .and varying the frequency of said oscillator, the latter device including a piezo-electric crystal-placed between two electrodes and a screw-threaded member for varying the spacing of said electrodes, and means for beating' the contro-llediand varied frequency of said oscillator with said band of signals changed in the frequency spectrum so that the original voice frequency signals 4. The combination of means for receiving a band of signals of high frequency corresponding to voice frequency signals, an oscil# lator, means for kbeating the frequency of said oscillator with the band of signals so as to produce another band of signals changed in the frequency spectrum, a piezo-electric struc-- of saidoscillator with said -band of signals changed in the frequency spectrum so that the original voice frequencyv signals may be accurately derived and reproduced.

5. In a signaling system, the combination of means forreceiving a band of signals of high frequency corresponding to voice fre- "quency signals, anoscillator, means for producing a harmonic of the frequency vof said oscillator, means .for beating the harmonic of the frequency of said oscillator With the band of signals to produce another band of signals changed in the frequency spectrum, piezo-electric means for .controlling and varying the frequency of said oscillator, and means for beating the piezo-,electrically controlled and varied frequency ofsaid osclllator With said band of signals changed in the frequency spectrum so that the original voice frequencysignals may be accurately detected, derived and reproduced.

6. In a signaling system, the combination of meansfor receiving a side band of hi h frequency energy characteristic of signa s, means for generating a high `frequency Wave, piezo-electric means which may be manipulated for adjusting the frequency of'said latloo frequency wave with the received side band of high frequency energy characteristic of signals to produce another band of energy i changed in the frequency spectrum and characteristic of the same signals, and means for beating the latter band of energy with the Yadjusted high frequency Wave so as to accurately derive and detect said signals.

7. In a signaling system, the. combination of means for receiving a side band of high frequency energy characteristic of voice fre-v quency signals, means for locally generating a high frequency wave, means for producing a harmonic of said high frequency wave,

piezo-electric means for controlling the 'frequency of said harmonic, said piezo-electric means includingmeans for varying its vibratory period in order Ito correspondingly vary the frequency of the harmonic derived from said high frequency' Wave, means for beating the controlled and varied frequency of the harmonic with the received side band of high frequency energy characteristic of voice frequency signals to produce another band of energy changed in the frequency spectrum and characteristic of the same voice frequency signals, and means or'beating the latter side band of energy with the high frequency Wave locally generated so as to de' rive and detect the original voice frequency signals.

In testimony whereof, l have signed my name to this specification this 6th day of October, 1926.`

RUSSELL S. OHL.