US1820898A - Transmission system - Google Patents

Description

Aug. 25, 1931. s. A. BARONE TRANSMISSION SYSTEM Filed Feb. '7. 1929 rINVENTOR. amo/1w,

4TT0RNEY SL m Q TL n H dlrmuHH Patented Aug. 25, 1931 j UNrrrznA STATES PATENT ori-ice :rj SALVATORE A. IBARJJNE,r OF FREEPORT, NEW YORK, ASSIGNOR, BY MESNE ASSIGN- A MENTS, TO FEDERAL TELEGRAPH COlvllAlil'Y, A CORPORATION 0F CALIFORNIA TRAnsivrrssoN SYSTEM An object of my invention is to provide a system for transmission ofk signaling energy of a modulated character. i c

Another object of my invention isto provide a broadcasting'system whereby low frerq mquency currents are caused to modulate a source of yhigh frequency energy without causing distortion of the low frequency currents. Y, f f

Another object yof my invention is to space the sidebands in the frequency spectrum apart from the carrier. l

i Another object of my invention is to shift aband of frequencies to a lower part of the frequency spectrum whereby a portion of said "26 band may be readily selected and to shift the selected band to a higher part of the frequency spectrum and spaced apart from the carrier. Still another objectvof my invention is to u provide a transmission system wherein the carrier frequency may be eliminated.

A further object of my invention is to provide means for eliminatingone set of the side band frequencies produced by modulation.

A still further object of my invention is to 'l providea meansfor controlling the vrelative amplitudes of the carrier and side band frequencies. e f j Other and `further objects Vof my invention will appear from the specification to follow andby reference to the accompanying drawingsinwhich: f Y.

Figure 1'is a diagrammatic illustration of the respective embodiments of 'my invention and is illustrative ofthepositioning of the 4U various units comprisingy the transmission system of my invention; c. y Fig. 2 is a diagrammatic il-lustratioii of the schematic circuit arrangement and electrical connections in the transmission system of my invention.

yIn Fig. 1a source of modulated high frequencyenergy 1 is connected to a local oscillator 2 and a combining device 3. Local oscillator 2 is connected to combiningfdevice 3 and modulator 5.' Combining device 3 is lcon- Applcation led February y7, .1929. Serial No. 338,235.

nected to filter system 4. Filter system 4 is connected to modulator 5. Modulator 5 is connected to load circuit 6. A general understanding of the system I employ can be had by reference to Fig. 1. The source of modulated high frequency energy 1 impresses voltages in the input circuit of 3. Local oscillator 2 is coupled likewise to the input circuit of 3. The two frequencies beat together and produce a third frequency in the youtput circuit of combining device 3. The

output circuit of 3 is coupled to the input circuit of filter system 4. The energy is properly filtered and comprises one set of side bands produced by modulation and no carrier, a carrier with the one set of side bands or the carrier alone,A as elected by the design of aforementioned' circuits and the filter system 4. The signal energy from filter 4 is coupled to the input circuit of a modulator 5, as is also the unmodulated energy of oscillator 2, producing a beat frequency in the output circuit of modulator 5. ,The output of modulator 5 is coupled to the load circuit 6 which may be a spa-ce radio radiating system or the input circuit of a wired radio system.

By referringto Fig. 2 the units comprising the transmission system and their electrical connections are shown. Ay source of audio frequency 7 is coupled to the input circuit of a vtlierinionic vacuum 4tube 23. rlhe plate circuits of therniionic vacuum tubes 23 and 24 are connected in multiple in respect to the direct current plate potential source 29. Oscillator circuit 9 includes thermionic vacuum tube 24., inductance 10 and condensers 33 and 33a. Oscillator circuit 9 is coupledto input circuit of thermionic vacuum tubecombining device 3 through inductance 11. Oscillater circuit 2-comprses thermionic vacuum tube 26 and grid and plate circuits 14. Oscillatory current from oscillator circuit 2 distributes to iuductance coils- 12 and 13. Inductance coil 12 is in series with inductance 1l and constitutes a part of the grid circuit of vacuum tube 25. Tliermionic vacuum tube 25 is caused to function as a combining tube determined by the value and polarity of supply 30. Mod'ulated high frequency energy from the modulator oscillator circuit l beats with the energy'from oscillator 2 and produces resultant frequencies in the output circuitV of combining device 3. The output circuit of combining device 3 is coupled to the input circuit 16 of filter system 4.v Filter system 4 includes inductances 18 and capacity 17in ade dition to the input circuit 16 and output circuit 19. The values of the inductances 18,

V of modulator 5.

the `capacity 17 and the input and output c ir-V cuits16 and 19 respectively, largely determine thevfunction of the filter and the suppression of the upper or lower set of side bands, produced by modulation, or one set of side bands and the carrier, The output 19 of filter system 4 is coupled to the input circuit Modulator '5 includes thermionic vacuum tube 27, input circuit 20 and output circuit 21. The grid electrode of thermionic vacuum tube 27 is 'supplied with a predetermined potential with respect to its cathode by' means of a source of direct current 31. The output energy from lter 4 and broadcastingy system we may assume that the.

output energy from 1 has a carrier frequency of' 600 kilocycles modulated by 1 to 10 kilocycles.` This produces one set of side' bands 590 to 599 kilocycles and a second set of side bandsI 601 to 610 kilocycles. The output energy from oscillator 2 has a carrier frequency Vof. 660 kilocycles and unmodulated energy the frequencies' of one set of side bands,v 61 to 70 lrilocycles correspondingvtoV the 'frequencies of theV other vset of side bands.

from' 2 produce aplurality Vof resultant frequencies and in the example cited some of these frequencies will be of the order of 60 kilocycles corresponding to the carrier frequency,y to 59 kilocycles corresponding to In the outputV circuit of combining device 3 the above mentioned frequencies will be pres# ent together with other frequencies outside the'r'ange of 550 to 70 kilocy'cles. The relative amplitude and wave form of suchr currents willdepend on the'charact-eristics of the circuits ,of' 1', 2.an'd 3. The current in the output circuit of 3 is transferred tothe filterl circuitfl;v Suppose that the filter is one of unifor-niattenuation for frequencies o'f 50 to 59ki`locy'cles and having a very high attenuation forall others. lt is evident that' by properly designing the ltenall or part of the 60 kiloc'ycle energy may be passed throughV the filter 4in which event, all or whatever.

desired portion of the 60 kilocycle carrier will be 'inthe final output circuit of the filter. The'o'scillator 2 supplies energy, having a frequency of 660 kilocycles, to the input circuit of modulator 5. By virtue of the intercombination of the 660 kilocycle frequency from 2 andthe bands of frequency from filter 4, the output of modulator 5 will containfrequencies of 710 to 719 kilocycles, 601 to 610 kilocycles and also the frequency 660 kilocycles from oscillator 2. The loadcircuit may have a uniform frequency characteristic for frequencies of 601 to 610 kilocycles and exclude all other frequencies.'

As another example of the operation of my broadcasting system, suppose the filter 4 is one of uniform attenuation for frequencies of 61 to 70 kilocycles and having a very high attenuation for all others. rl`he output of modulator 5 will contain frequencies of 721 to 730, 590 to 599 and also the frequency 660 kilocycles from oscillator 2. The load circuit 6 may be designed to have a uniform characteristic for the frequency band 590 to 599 kilocycles and exclude all other frequencies. i

The foregoing examples show that, in ac coi-dance with my invention, filter 4 may bedesign'ed to suppress either side band and reduce the carrier any desired amount in the band of frequencies received from combining device 3 and corresponding to the original frequencies of source 1. After modulation in 5, the voutput of filter 4 isl stepped up in thel frequencyspectrum and comprises two side bands of the carrier from source 2. These side bands are spaced from the carrier bya band width in' the frequency spectrum equal to thelowest frequencyin the output of filter 4. By proper design of the output circuit of modulator 5 and load circuit 6, and in accordance with my invention, either ofthe spaced side bands, or either side band and the car rier, or the carrier alone, may be sup-pressed. The selection of the desired band for transmission is` made relatively easy because of the separation of the side bands fromthel carrier. Y

ln either of the examples cited, instead ofl designing load circuitv 6 to transmit 601 to 610, or 590 to 599 kilocycles, the 710 to 719, or 721 to 7 30 kilocycles may be transmitted by the proper design ofthe load circuit.

@ne of the advantages of my broadcasting system, as should be obvious from theforegoing specification, is that with the system l employ it is; possible tol operate a. greater number of transmitters in a given frequency band without interference. i

It is evident that the. suppression of the carrier'and one vset of side bands could be accomplished by a filter inserted between the source of modulated high frequency energy and the load. A band pass filter for high frequencies is considerably more dificult to make than would vbe a filter for thev same band width and cut-off characteristics'at lower frequencies. VThis invention makes it possible to'use a'lower frequency ilterin spite of the fact that the transmitted energy is at higher frequencies. I do not intend to have my invention limited to the foregoing specifications nor to the accompanying l-drawinga and I realize that many arrangel"ments may be employed Without departing from the spirit of my invention as defined in the appended claims. f

lWhat I claim as new andy desire to secure lo by Letters Patent of the United States is as follows: A

1. In a radio broadcasting system the combination of a modulated source of high frequency energy, an unmodulated source of high frequency energy, means for combining said modulated and unmodulated energy, a filter system and means for impressing said combined energy on the input circuit of said filter system, a modulator and means for coupling said modulator to the output circuit of said filter system and to said unmodulated source of energ. and means for coupling the output of sald modulator to a load circuit.

2. In a broadcasting system comprising in combination means for producing modulated high frequency energy, means for producing unmodulated high frequency energy, vmeans fer causing said modulated and said unmodulated signaling energy to produce resultant sources of signaling energy, filter fmeans for eliminating one of said sources of energy, means associated With said source of unmodulated high frequency and said filter 35 means for producing a beat frequency and a load circuit associated With said last mentioned means for the transmission of signaling energy having frequency characteristics as determined by said aforementioned means and said load circuit.

3. In a signaling system, a source of modulated signaling energy, a source of unmodulated signaling energy,'means fo-r causing said modulated and said unmodulated energy to produce resultant sources of signaling` energy, means associated With the first mentioned means for selecting a plurality of said sources of signaling energy, modulating rmeans associated with said selecting-'meansand said source ofunmodulated signaling energy, and a load circuit associated with said modulating means for the transmission ofthe desired signaling energy.

4. In a signaling system the combination ofa source of modulated energy, a source of unmodulated energy, means for causing said sources of energy to produce a result-ant source of energy, filter means associated with '60 said means, modulating means associated e5 modulating means whereby said carrier and one s et'of side bandsy are transferred'ft'o said( sources of energy, filter means associated with said means and having such frequency characteristics as to offer a uniform and low impedance to desired energy of desired frequencies and having a high impedance to other energy of other frequencies, modulating means associated with said filter means and said source of unmodulated energy and a load circuit having a uniform and loW impedance to desired frequencies and having a high impedance to all other frequencies and means for transferring said energy from said modulating means to said load circuit.

6. A high frequency transmission system comprising a' source of unmodulated high frequency oscillations, a source of'modulated high frequency oscillations, means for combining the oscillations from said sources, and obtaining the beat frequencies resulting from said combination, means for selectively filtering said beat frequencies, means for modulating high frequency oscillations from the first mentioned source With oscillations in the output circuit of said filter, and means for transmitting a selected portion of the last named modulated high frequency oscillations.

`7. A high frequency transmission system comprising a generator of high frequency oscillations, means for modulating the output of said generator, a second generator of high frequency oscillations having a different frequency from the first mentioned generator, means for combining the outputs of both said generators and obtaining a band of frequencies of a lower order, means for filtering said band, means for modulating oscillations in the output circuit of said filter and high frequency oscillations from said second generator, and a. tuned circuit associated with the second mentioned modulating means for selecting a portion of said last named modulated high frequency oscillations.

8. The method for transmitting a selected portion of a band of modulated high frequency oscillations which comprises, modulating a source of high frequency oscillations to produce a carrier and two side bands, spacing said side bands in the frequency spectrum apart from said carrier, and transmitting a selected portion of said carrier and said bands.

9. The method for generating modulated high frequency oscillations Which comprises beating unmodulated high frequency oscillations With high frequency oscillations modulated With a band of audible frequencies,ob taining therefrom an intermediate band of super-audible frequencies, selectively filterlos ing Isaid intermediate band, Aand VCausing .said

`intermediate band to modulate. additional hie-gh frequency Ioscillations whereby the last mentioned high frequency oscillations Vcomprf'seracarrer and two side bands each sepa- AIa'eid inthe .requeneyspectrum from said carrier.

In testimony whereof I a-ix my ysigne-ture.

- SALVATORE A, BARONE.

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