US1508565A - Loading system - Google Patents

Description

J. MILLS LOADING SYSTEM Sept. 15, 192.4. 5 1,508,565

. Filed March 29. 1923 fiy/ //7 yen/0n John /7///J Improvements in Loading Systems,

Patented Sept. 16, 1924..

UN IT D S TE JQHN .IVIILLS, or wyomine, amnesty, assrcnortaownsrpaivannotate coi/i]- ma mcoaroaaran, or NEW YORK, N. 2., .AQOBPQRATIQ YD NEW $03 LOA ING SYSTEM.

To all whom it may concern, I

Be-itlknown'that I, J OHN MILLS, a citizen of -the United States, residing at Wyoming,

in the county of Essex, State of New Jer sey, have invented-certain new and useful Which-the ifollowingis a-full, clear, concise,

ZLIl'Cl BXtLGt description.

'This invention relates to'communication over loa'ded dines and'ha's for an object'yto improve the transmission of signals, voice currents :in particular, over loaded lines.

The advantages of light loaded telea phone lines having a "high natural cut off frequency have been pointed out in thespplication'of Carson, Clark and-Mills, Serial fects dueto unequal rates of propagation of the various frequencies of importance 1n speech. The important voice frequencies may be taken to'be included in the range well known that satisfactory speech transmission may be had witlra range considerably smaller than this. fF-req uencies higher than 2500 vcyclesoare present in speech and aidintelligibi-lity if they can be transmitted without distortion. In long lines, however, even if extra light loaded, the time required for transmission of thehigher frequencies may be relatively so great that the resulting distortion or so called transient effects may outweigh the advantages of having these frequencies transmitted.

In accordance with this invention substantially uniform speed of transmission of the important voice frequencies is obtained by using high cut off light-loaded lines and the distorting efiect of the higher frequencies is eliminated by preventing them from reaching the receiving station. The cut off frequency of the line should be substantially above the highest frequency to be utilized in speech transmission and with certain lengths of line should be twice as great or more. The upper speech frequencies may be suppressed by any suitable means such as low-pass wave-filters which may be located at repeater stations or at any suitable point or points between a transmitter at one end of the line and a receiver at the other end.

The invention will be more fully understood from the following description and cla-imstaken in connection with the accompanying drawings in which: i

Fig. 1 illustrates graphically a -.fundamental characteristic of a loaded line, and

Fig. 2 illustrates schematicallya portion of a system embodying the invention. The curve in Fig.1 shows the rel'ative time of transmission of the" various fre quencies on a loadedline' up to its cutoff frequency. The abscissa: are given in terms fi h vi a t i Wlii -f ap -s a equ ncy a a var abl and f; .KQP QIS it the cut off frequency. "The ordinates are given I asla function of according to the as varia e -.an :iairepres nt th t me Of ra mission o zer fr qu ncy Th equ fraction 1 t -t sin f/fg i f/fo' Itiwillbe. seen that .overa frequency range from 0v to betWeen*0.6 and.:O.'7 of the entire range. .up to. the cut off .1 frequency, the gliderence in I retardationonly attains about} .10 but for frequencies closeztothe cut.- off frequency it increases rapidly and may become as great as 50% or more. In units of time the disparity in time of transmission will of course be greater for long lines than for short lines. Hence, for voice transmission it may be that there will be a net improve ment by omitting these higher and much retarded frequency components.

In Fig. 2 is shown a system of the four wire type in which a substation S is con nected by a two wire line 10 and a balanced transformer 12 to the unidirectional lines 14 and 16. The artificial line N performs the usual function of preventing any substantial amount of feed back from line 16 to line 14. A similar arrangement (not shown) terminates the distant end of the four wire circuit.

The line 14 is provided with any desired number of repeaters such as shown at It and R and the line 16 is provided with oppositely directed repeaters R R etc. The lines 14 and 16 which may be small gau e cable lines are provided with loading coi s 20 of such values and spacing that the lines have a high critical orcut 01f frequency, say

in which 2i; represents time I 5600 cycles. Reference to Fig. 1 will show that if the critical frequency of the line is 5600 cycles, the time of transmission of frequencies below 2500 cycles will be fairl uniform. Low pass filters indicated at 1 and F are accordingly provided to suppress the speech frequencies above 2500 cycles or at least to reduce their amplitude at the receiving station to a harmless value.

While the invention has been described as applied to a four wire system, it obviously is adapted for use in other types of systems and maybe applied thereto in a great variety of manners Within the scope of the appended claims. 1

The invention claimed is:

1. A telephonev system comprising a loaded line having a critical frequency such that the higher speech frequencies are transmitted substantially slower than the frequencies of principal importance to intelligibility and means for reducing the efficiency of transmission of said higher frequencies.

2. A telephone system comprising a loaded line having a critical frequency such that the higher speech frequencies are transmitted substantially slower than thefrequencies of principal importance to intelligibility and means for reducing the efliciency of transmission of said higher frequencies, the range of frequencies having their transmission reduced being at least one third as great as the range of frequencies freely transmitted.

3. A telephone system comprising a loaded line having a critical frequency such that the higher speech frequencies are transmitted substantially sloWer than the frequencies of principal importance to intelligibility and a wave filter for attenuating said higher frequencies.

4. A telephone system comprising a loaded line having a critical frequency such that the higher speech frequencies are transmitted substantially slower than the frequencies of principal importance to intelligibility and a wave filter for attenuating said higher frequencies, said wave filter havlng a cut off frequency of the order of one half said critical frequency.

5. A telephone system comprisinga loaded line having a critical frequency of the order of6000 cycles and means for substantially suppressing speech currents above a frequency of the order of 2500 cycles.

6. A telephone system comprising a loaded line having a critical frequency of the order of 6000 cycles, means for supplying speech currents to said line, and a low pass filter in said system in the path of said speech currents and having a cut off frequency of the order of 2500 cycles.

7 A telephone system comprlsing a loaded line having a critical frequency such that the higher speech frequencies are transmitted substantially slower than the frequencies of principal importance to intelligibility and having a length such that the actual time lag of said higher frequencies is substantial, and a wave filter for attenuating said higher frequencies, said wave filter having a cut off frequency sufiiciently lower than said critical frequency to produce a net gain in intelligibility. y

In witness whereof, I hereunto subscribe my name this 20 day of March, A. D. 1923 JOHN MILLS

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