US1984451A - Short wave radio signaling - Google Patents

Description

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A. BAILEY SHORT WAVE RADIO SIGNALING Filed Sept. 15, 1931 IOOKC 111? 40011. Mod.

Speech Input Dec. 18, 1934.

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I I I L a I I .Elzmuzafor Patented Dec. 18, 1934 1 v UNITED STATES PATENT OFFICE SHORT WAVE RADIO SIGNALING Austin Bailey, Maplewood, N. J., assignor to American Telephone and Telegraph Company, a corporation of New York Application September 15, 1931, Serial No. 562,969

3 Claims. (Cl. 250-6) This invention relates to short wave radio sigoscillation of the detector-oscillator B. The rate naling, and more particularly to a super-regenof starting and stopping is governed by the freerative and double demodulation system for ulquency of a super-regenerative oscillator C,which tra short wave radio signaling. Its object is to for illustrative purposes we may assume to oscilsecure the combined advantages of the so-called late at about 3000 kilocycles. For best results super-regenerative and super-heterodyne meththis oscillator must be much lower in frequency ed in one system. than the incoming carrier and must also be much Briefly, the invention consists in double moduhigher in frequency than the side band frequency lation at a transmitting station followed at the separation from the carrier frequency. With the 10 receiving station bysuper-regenerative demoduillustrative 'values of frequencies already given, 10

lation, amplification at an intermediate frethis would mean that the frequency of the oscilquency, demodulation to signal frequency, and lator C should be much less than 100 megacycles such further amplification and reproduction as and much more than 100 kilocycles, and the value may be desired. of 3000 kilocycles mentioned above would be an The invention will be better understood by refappropriate value. l5 erence t0 th f w n Specification and accom- The details of the oscillator C are evident from p nying drawin in whi h Fi ure 1 shows in the drawing and it will be noted that it consists block form the elements of my transmitting staof a Hartley type of oscillator with the filament on,Fi 2 shows th r uit f the r iv n connected to the midpoint of' the tuning inducstation a d s. 3 and 4 show modifications t0 tance L1 and the positive of battery connected to 20 the transmit in nd r ceivin circuits f Fi s- 1 plate through a suitable choke. A single source and 2. of B voltage may be used for supplying the plate Referring more particularly to Fig. 1. th e circuit of the tubes in both circuit 13 and circuit is shown a source of spe h np at whi h C, there being appropriate choke coils and cons ppli s a su a l si a t a d at r densers such as are used in circuits of this type, 25

this modulator being supplied also from an oscilhi h r ell kn w in th art, later 3 with a frequen y o any Suitable value, The circuit B is a vacuum tube circuit which here indicated as 100 kilocycles for illustrative acts as a detector but under normal conditions its p p The p 0f themodulator 2 is efliciency as a detector is comparatively low. If

c us d thr u h a and-p filter which pa feedback is supplied from the output to the input 30 the ca ie frequency of 100 kilocycles and one this detection efliciency may be increased and as of its modulat o Si e a This, turn, is the circuit approaches the oscillatory condition used to modula a m higher Carrier the efliciencyrises to very large values. When,

q y, Such as 100 megacyeles, from the Oscilhowever, the oscillatory condition is establishedlabor 6. h u -p 0f themodulator 5 cohtaihthen detection immediately falls to substantially in t carrier and tWO Side bands may then be zero. When oscillations cease detection again amp fi to y Suitable Value by the amplifier commences increasing in efliciency as the estab- 7, h Output of Which is impressed 0h lishment of the condition for oscillations is again ing system here shown as an antenna 8 grounded approache In t circuit of Fig 2 t t 40 at 9. It will be understood, however, that any lishment d blocking of oscillations occurs at th 40 DD type i antenna System may be usedrate of 3,000,000 times per second and demodu- At the receiving Station there is an antenna lation between the carrier and its side bands comwhich here is shown as a Hertzian doublet, aling in 6 t t A occurs corresponding though again any antenna- Suitable for receiving number of times and during each one of these the Short Waves contemplated may be usedperiods of detection a moment of very high ef- 45 sociated with the antenna A is a super'l'egenficiency occurs just before the circuit B breaks erative detector 13, the association here being into oscillations. There is th nt in th shown as y means of a 10086 inductive fiouplingoutput of the circuit B a wave corresponding to The ci cu B Comprises 8 Vacuum tube with the modulation of the carrierfrequency,thiswave.

interconnected circuits constituting essentially however, being broken t large number of 50 an oscillator at the incoming carrier frequency. hort impulses. The envelope of these impulses,

Al o his Oscillator has pp to its ircuit, in that is, the modulation curve itself, is passed on addition to the normal bias, a variable voltage to the circuit D comprising a band filter adapted effective on both plate and grid which, during to pass frequencies in the neighborhood of 100 each cycle of its variation, starts and stops the kilocycles, eliminating such other components as may have appeared in the output of the circuit B.

This intermediate frequency is now amplified to any desired extent in the circuit E, there being bridged across the input circuit of the first of such amplifiers an impedance of value to properly terminate the filter D in a manner well known in the art. The amplification in the circuit E is carried on at such frequencies as to give the usral advantages of superheterodyne reception, in p articular this being at a frequency which gives freedom from the noises and other disturbances characteristic of many audio frequency amplifiers.

The output of the amplifiers E, along with oscillations from the oscillator G, are now impressed upon a second demodulator F, the frequency of the oscillator G, which in this case would be kilocycles, corresponding to the intermediate fre quency of theoscillator 3 in Fig. 1. The output of the circuit F will then contain, among other things, a reproduction of the signal frequency supplied in the circuit 1 of Fig. 1, and such signal is segregated by means of a suitable low pass filter H. Further amplification of this voice frequency or other signaling frequency and its reproduction in any appropriate device, such as a loud speaker, or transmission to remote points, may now take place in the circuit 1.

Various modifications of the circuit as thus far described may be made. Thus, for instance, instead of the double modulation described in connection with Fig. 1, it would be possible to modulate a frequency of 100.1 megacycles directly with the speech eliminating all but one side band. Still another modification might consist in modulating the 100 kilocycle oscillations with the speech message, passing these through the usual band filter, modulating the 100 megacycle carrier and then suppressing all but one side band, say the upper side band, by means of selective circuits so that the transmitted wave would then consist essentially of a carrier of 100.1 megacycles modulated with speech. The modification of the transmitter of Fig. 1 to obtain the results indicated above is obtained by introducing at some point of the circuit such as 3-3 the circuit portion shown in Fig. 3, which portion may consist of any of the suitable means known in the art for eliminating the carrier frequency and one sideband. At the receiving station in this event it would be necessary to supply a generator of 100 megacycles which, combined with the incoming modulated carrier would then give an output of 100 kilocycles with the upper and lower speech modulation and this may after amplification be detected directly with the elimination of G. This modification of the receiver circuit of Fig. 2 may be obtained by having the IOO-megacycle oscillator connected as shown in Fig. 4 at G and in this event it will not be necessary or even desirable to use the 100-kilocycle generator G.

By means of such systems as described, it is thus seen that use is made of the extreme sensitivity of a super-regenerative receiver without introducing large amounts of audio gain which are apt to introduce considerable noise especially if used in mobile services such as is frequently the case for ultra short wave signaling. Another advantage of this system is that much greater se-. lectivity can be obtained and the noise is reduced below the values which would be expected if double demodulation alone were used on a signaling carrier and two side bands of the ordinary broadcasting variety.

What is claimed is:

1. In a radio signaling system for ultra short waves, a receiving station at one end to receive a carrier frequency modulated with an intermediate frequency and its message side band, the receiving station comprising a detector oscillator for detecting the received wave down to intermediate frequency, means for periodically increasing the detector efiiciency to a high value at a frequency high compared to the intermediate frequency, and means for amplifying said intermediate frequency output and for demodulating it to signal frequency and a filter preceding the last demodulator element.

2. In a radio signaling system for ultra short waves, a transmitting station, means thereat for modulating a speech signal against an intermediate carrier frequency, means for modulating this output against a high carrier frequency, a selective circuit for eliminating the high frequency carrier and one of its side bands, a receiving station comprising a super-regenerative detector and a source of the high frequency carrier, a filter passing the detector side band of modulated intermediate frequency, an amplifier therefor, and a detector to detect the modulated intermediate frequency to signal frequency.

3. In a radio signaling system for ultra short waves, a receiving station at one end to receive a carrier frequency modulated with an intermediate frequency and its message sideband, the receiving station comprising a circuit for detection to intermediate frequency, said circuit being brought to a highly efficient unstable state periodically at a frequency high compared to the intermediate frequency, a second circuit for demodulating the resulting wave of intermediate frequency to signal frequency, and a band-pass filter in the output of the detector to pass a narrow band including the intermediate frequency.

AUSTIN BAILEY.

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