US1875157A - Compression and expansion of range of energy level - Google Patents

Description

Aug. 30, 1932. 1.. c. ROBERTS 1,375,157

COMPRESSION AND EXPANSION OF RANGE OF ENERGY LEVEL Filed June 29, 1929 D'amnglksion INVENTOR Z. a Rolfrlis ATTOR N EY Patented Aug. 30, 1932 in STATES PATENT Fries LELAND C. ROBERTS, 0F TOWAC'O, NEW JERSEY, ASSIGNOR T0 AMERICAN TELEPHONE AND TELEGRAPH COMPANY, AOORPORATION OF NEW YORK COMPRESSION AND EXPANSION OF RANGE OF ENERGY LEVEL Application filed June 29,

rangement of an amplifier and of two reistances connected in series, one of the resistances having a low temperature coefficient and the other a high temperature coefiicient. This use of resistances having different temperature coefiicients is disclosed in a different arrangement in my application filed of even date herewith and given Serial No. 374,919.

The present invention will be clearly understood when the following detailed description is read with reference to the accompanying drawing, which shows diagrammatically the circuit arrangements involved.

As indicated above, in the transmission of broadcast programs over telephone circuits, it is often desirable to compress the range of energy level of the currents in the telephone circuit. This may be accomplished by causing the currents of high energy level to be amplified less than those of low energy level at the input or sending end of the telephone circuit, whereby the differences of level transmitted over the circuit are made as small as is practicable. This compression demands, of course, a corresponding expansion at the output or receiving end of the telephone circuit in order that the normal range of energy level may be restored and transmitted.

Inthe drawing there is shown a transmission line, which it is understood may be a telephone line over which it is desired to transmit broadcast programs. At the left or input end of this line, an arrangement of re sistances FR and VR is connected through a transformer T, with the grid-filament cir- 1929. Serial No. 374,920.

cuit of a vacuum tube amplifier A and the mission line, the resistances FR and VH are .5

associated through the transformer T with the grid-filament circuit of the amplifier A and the plate-filament circuit of this amplifier is connected through a transformer T to the output of the circuit.

The resistance FR- is a resistance of low temperature coefiicient. The resistance VR is a resistance of high positive temperature coefficient and may take the form, as is indicated'on the'drawing, of a short, fine, tungsten filament in an evacuated bulb. Another form of resistance which may be employed is a hydrogen-iron ballast lamp designed to consume less energy than the ordinary commercial lamp of the type. VR presents a relatively low impedance to currents of low energy level and a relatively high impedance to currentsof'high energy level. The two resistances FR and VB are connected in series as shown. It will be noted that the voltage drop across the resistance FR is the one impressed through transformer T upon the input of amplifier A It will be understood by those skilled in the art that,

given this circuit arrangement, the apparatus at the input end of the line will function as a compressor of the range of energy level, giving less gain for the currents of high energy level than for the currents of low energy level. In other words, the difference of energy level is considerably diminished.

At the receiving end of the line, the resistances FR and VH are connected in series, as is the case at the sending end, but here the voltage drop across the high temperature coefficient resistance VR is impressed upon the input of amplifier A Since the voltage drop across VH is relatively greater for currents of high energy level than for currents of low energy level, the apparatus at this end of the circuit introduces more gain for the high energy currents than for the low energy currents and accordingly acts as an expander of the range of energy level.

Given a line substantially free fromdistortion it Will be obvious to those skilled in V s the art that the resistances FR ,VR ,FR and VR may be so chosen that the combination of the compressor, the line and the expander 5 Will introduce substantially no distortion.

'The ltrue'scope of the inventionis determined by the appended claims. Y

What is claimed is: in I s i 1; a transmission circuit, av fixed resist- I 'anceand a resistance varying with the energy level of currents flowing through it connected in series atthe sending-end of. the circuit, a

translating device at the sending end of the 'circuit, means for impressing ontheinput of said translating device-the voltage drop "across sa'id fixed resistance,a'secondfixed resistanceanda second resistance varying with the energy level of currents flowing through 1 it connected in series at the receiving end of i thecircuit', a second translating device at' the 1 receiving; end" o-fthe circuit, and means for impressing on the input of said second translatingdeViCe the voltage drop across saidsec- V "ond vvaryi ng resistance." s c i D 2. In a transmission circuitytwo resist- "ances of substantially difli'erent temperature coefilcientsi connected in series at the sending end of'the circuit, a translating deviceat the sending end of the circuit, means for'impressingion the input of saidtranslatingdevice the voltage drop across oneof said 'resistamies *two resistances ofsubstantially difierent tern- 5 perature c'oefiicients connected inseries at the ,7

receiving end of the circuit, a second translating device at the receiving end ofthe circuit, U i

and means for impressing on the input of said i secondf translating device thevoltage' drop across one of said: resistances'at the receiving end of the circuit, the resistance of which the f 4.0 voltage drop is utilized at the receiving end 1 being of relativelydifferenttemperature co efiicient fro'm 'the: resistance of Whichvthe voltage drop is utilizedvat the sending end. a a In testimony whereof, I have signed my name to this specification this 28thday of June51929. "1 LELAND GLRQBERTS.

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