US2474249A - Multichannel carrier communication system - Google Patents

Multichannel carrier communication system Download PDF

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Publication number
US2474249A
US2474249A US750148A US75014847A US2474249A US 2474249 A US2474249 A US 2474249A US 750148 A US750148 A US 750148A US 75014847 A US75014847 A US 75014847A US 2474249 A US2474249 A US 2474249A
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group
frequency
channels
band
frequency range
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US750148A
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English (en)
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Hodgson Kenneth George
Fairley Frank
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International Standard Electric Corp
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International Standard Electric Corp
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J1/00—Frequency-division multiplex systems
    • H04J1/02—Details
    • H04J1/04—Frequency-transposition arrangements

Definitions

  • the present invention relates to multi-channel signalling systems.
  • the output of the second modulator contains the wanted and unwanted sidebands and also the input frequencies which lie in the frequency range of the basic group.
  • the unwanted sidebands and the input frequencies can easily be eliminated by filters, but in the groups adjacent to the basic group the frequency space between the wanted sideband and the band in which the input frequencies lie is so small that filters have to be used of an extremely sharp cut-off characteristic in order to eliminate the input band without introducing distortion into the wanted sideband.
  • the modulators are balanced to reduce the transmission of the input frequency, the'lter requirements are very difficult to meet. In order to overcome this difficulty, one could provide a frequency gap between the basic group and the adjacent groups. This, however, would reduce the number a of transmission channels within the available total frequency range.
  • a multi-channel signalling system employs a basic group of channels occupying a primary frequency range, other groups of channels each occupying the whole or part of the primary frequency range, and comprising means for translating such other groups to frequency ranges outside the primary frequency range and is characterised in this that groups of channels which are translated to occupy positions in the frequency range adjacent to the primary frequency range have bandwidths which are less than the whole bandwidth of the primary frequency range.
  • FIG. 1 and 2 serve to illustrate the underlying principle of the invention
  • Figs. 3 and 4 illustrate arrangements of known multi-channel alternating current telegraph systems
  • Figs. 5, 6, and '7 serve to illustrate the principle of the invention as applied to the arrangement shown in Fig. 4.
  • the arrow I indicates a basic group of n channels in the primary frequency range from f I to f2.
  • the arrow 2 indicates another group of nchannels, extending from the frequency 'fl to f3.
  • the said other group is translated to assume a frequency range extending from f2 to (f2-i-J3-fl), as indicated at 4. It will be seen that anuninterrupted frequency range is utilised without any substantial gap, that is to say, the frequency range from f!
  • a third group 5 of n-y channels may be modulated by the frequency (f4-HI) indicated at 1, whereby the group, by using the lower sideband, is translated to the frequency band 6, ex-
  • the transmitted groups of frequency bands are now I, 4, and 6 (indicated by arrows in full lines) and cover an uninterrupted frequency range.
  • the groups 4 and 6, adjacent to the basic group I each comprise fewer channels than the basic group I. If' it is desired to transmit groups of channels of equal widths, the system so far described may be modified as will now be explained with reference to Fig. 2.
  • the basic group of n channels is again indicatedby the arrow I.
  • the frequencies of the subgroup 2 are modulated by the frequency (f2-H3) as indicated at 3, and the sub-group I'Il is modulated by the frequency (2]2-1-33- f I as indicated at I I.
  • lf lower sidebands are used, the subgroup I is translated to assume the finaly position 'tV as in Fig. 1, and the sub-group I9 is translated to assume the final position I2. It will be seen ythat the groups I, 4 and I2 occupy an uninterrupted frequency range, while sufficient gaps exist between the translated group 4 and the input group 2 on the one hand and the translated group lf2 and the input group Ill on the other, for easing the filter design.
  • a third group of n channels may be broken up into two sub-groups l'3- and I4 comprising respectively n-y and y channels, and extending fromf4 to f2 and from JIl to f4 respectively.
  • the group I3 is modulated by the frequency (f4-HI) as indicated at I 5, and the group I 4 by the frequency (2fI-l-f4-f2) as indicated at I6. If, again, lower sidebands are used, the sub-groups I3 and I4 are translated respectively to thepositions Il and I8, extendingifrom (fI
  • the groups I8, II, I, 4, and I2 (indicated by arrows in full lines) occupy It is, however, possible to use upper sidebands in the translating operation and suppress the lower sidebands, the modulating frequency used for the translation being the difference of the two boundary frequencies of the basic group. Since the modulating frequency in this latter case would be comparatively low, it is usually preferable to employ the lower sidebands.
  • the principle of the invention may be used in connection with multiple channel carrier telephony and with multi-channel Voice frequency telegraphy. It is also obvious that the invention isx not restricted ⁇ to systems using two subsequent modulations but may with equal advantage be used in connection with systems using more than two such modulations.
  • Fig. 3 diagrammatically illustrates such. a system of known type arranged for unidirectional operation. For the reverse direction, the same frequencies are used along a second communication channel with equipment at the sendingl and the receiving ends similar to those indicated in Fig. 3.
  • the equipment for one channel comprises a telegraph modulator MI for modulating a frequency fl with direct current telegraph signals, a bandpass filter BFI which transmits the frequency fl' with the telegraph sidebands, and at the receiving side a bandpass filter BFIy and a detector DI for converting the alternating current signals for operating the telegraph equipment, the transmitting and receiving sides being connected by any suitable transmission Vpath such as a cable.
  • the equipment for the channels 2, 3 n is similar to that of channel I, the output of all the transmitting bandpass filters being connected in parallel to one another and. to the line, and likewise the inputs of all the receiving bandpass filters being connected. in parallel to one another and4 to the line.
  • Fig. 5 represents the attenuation frequency characteristics of the sending or receiving band filters BFI to BFn.
  • the frequency with which a group of channels is modulated is the sum of the frequencies representing one-boundary of the group that is to be translated, and the corresponding boundary of the translated group.
  • a basic group of n channels is derived by direct modulation by means of modulators MI Mn and bandpass filters BFI BFn, the modulated frequencies being demodulated by detectors DI Dn.
  • Another group of n channels is derived by modulators M1I M111. and bandpass filters BFlI BFln and a second modulation of channel frequencies fl to fn by means of group modulator GM using a carrier frequency fx.
  • GBF represents a group band filter and P represents coupling means to separate the basic group of channels from the other group of channels.
  • similar coupling means P separate the basic group of channels from the group modulated channels, which pass through the group band filter GBF to the group demodulator GDM using the same carrier frequency faz.
  • the system so far described is also known.
  • Fig. 6 shows the attenuation frequency characteristics of the band filters BFI to BFn and the characteristic of the group band filters GBF.
  • the requirements of the group band lter GBF at the sending end are that this filter shall pass one set of sidebands derived from modulation of frequencies fI to fn by the carrier frequency fri: with a minimum attenuation, whereas it shall attenuate the input frequencies fI to fn sufficiently to avoid interference between the said input frequencies and the primary frequencies f I to fn of the basic group of channels which have not undergone a second modulation.
  • this filter At the receiving end the requirements of this filter are similar. It is difficult or impossible to design a lter to achieve this purpose without allowing a gap within the frequency range actually transmitted between the channel n of the basic group of channels and the adjacent channel of the group modulated channels, and at least one or possibly two such -channels would be lost in the frequency spectrum available for transmission.
  • a basic group is derived by direct modulation by means of modulators MI Mn and band pass filters BFI BFn.
  • a second group of channels fl to fn, where fm is lower than fn is derived by modulators M1I Mlm and band pass filters BF1I BFlm.
  • the group band filter GBF is used to select the lower sideband and to suppress the carrier frequency and the upper sideband.
  • the lower sideband is applied to the line through a coupling device P such as a hybrid coil.
  • a number of channels equal to n-m are formed by modulation in modulators M1(m+ 1) to Mln by carrier frequencies f(m+ 1) to fm.
  • a multi-channel signalling system comprising modulating means and filter means for creating a basic group of channels occupying a primary frequency range and impressing said group on a transmission line, modulating means and filter means for creating another group of channels occupying a part of said frequency range from one boundary thereof to an intermediate frequency, group modulating means for modulating said other group of channels with a frequency equal to the sum of said intermediate frequency and the frequency of the other boundary of said range, filter means for selecting the lower side band from the output of said group modulating means and means for impressing said lower side band on said line.
  • a multi-channel signalling system comprising modulating means and filter means for creating a basic group of channels occupying a, primary frequency range and impressing said group on a transmission line, modulating means and filter means for creating another group of channels occupying a part ofv said frequency range from one boundary thereof to an intermediate REFERENCES CITED frequency, group modulating means for modulat-
  • modulating means and filter means for creating a basic group of channels occupying a, primary frequency range and impressing said group on a transmission line
  • modulating means and filter means for creating another group of channels occupying a part ofv said frequency range from one boundary thereof to an intermediate REFERENCES CITED frequency
  • group modulating means for modulat-
  • filter means for UNITED STATES PATENTS selecting the upper sideband from the output of Number Name Date said group modulating means, and means for im- 2,270,385 Skillman Jan. 20, 1942 pressing said upper sideband on said line. 2,274,535 Dixon Feb. 24, 1942 KENNETH GEORGE HODGSON. 10 FRANK FAIRLEY.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Mobile Radio Communication Systems (AREA)
US750148A 1946-04-08 1947-05-23 Multichannel carrier communication system Expired - Lifetime US2474249A (en)

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BE (1) BE475938A (en, 2012)
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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3007361A (en) * 1956-12-31 1961-11-07 Baldwin Piano Co Multiple vibrato system

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2270385A (en) * 1938-10-10 1942-01-20 Hartford Nat Bank & Trust Co Multicarrier transmission system
US2274535A (en) * 1940-10-19 1942-02-24 Bell Telephone Labor Inc Carrier wave system

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2270385A (en) * 1938-10-10 1942-01-20 Hartford Nat Bank & Trust Co Multicarrier transmission system
US2274535A (en) * 1940-10-19 1942-02-24 Bell Telephone Labor Inc Carrier wave system

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3007361A (en) * 1956-12-31 1961-11-07 Baldwin Piano Co Multiple vibrato system

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BE475938A (en, 2012)
CH262120A (de) 1949-06-15

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