US1823687A - System for frequency translation of electric waves - Google Patents

Description

Sept. 15, 1931. R. A. HEISING 1,823,687

SYSTEM FOR FREQUENCY TRANSLATION OF ELECTRIC 'wAvEs Filed Dec. 26, 1928 "'"IG. IBC

F/LTER /3 mwm/AL 'T Z2 WWWW IMPEDANCE /6 tZEME/VT INPUT 77 QUIPl/f FILTER M767? @PEW T wvs/vrop RA. HE/SING BY '2 e ATTORNEY Patented Sept. 15, 1931 UNITED STATES RAYMOND A. HEISING, OF MILLBURN, NEW JERSEY, ASSIGNOR TO WESTERN ELEC- TRIO COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK SYSTEM FOR FREQUENCY TRANSLATION 015 ELECTRIC WAVES Application filed December 26, 1928. Serial No. 328,504. PE

This invention relates to systems for frequency translation of electric waves and particularly to such systems wherein space discharge devices are employed.

Frequency translation is defined, for the purposes of this specification, as the process of causing electric waves comprised within a definite frequency range to generate or produce electric waves comprised within an- 10 other frequency range lying either above or below the first. In the art of communication by means of electric waves the process of frequency translation may thus include either modulation or demodulation and de- 15 tection.

An object of the invention is to effect frequency translation efficiently over an increased width of frequency band.

Another object "is to cause frequency trans- 29 lation to occur with substantially uniform efliciency at all frequencies lying within the operating band.

A' further object is to effect the efficient shift or translation uniformly, even though 25 the extent or frequency interval of the shif may be relatively small.

A device in common use for detecting modulated radio frequency waves consists of a space discharge tube having a relatively high resistance element inserted in the input or grid circuit and a condenser in shunt to the high resistance.

' The operation of the above mentioned detector commonly known as a grid leak detector may be regarded as follows. Electric waves of radio frequency are applied to the input circuit of a space discharge device and are by-passed by the condenser around the high resistance so that they establish a maximum of' potential difference between the grid and cathode of the discharge device. Due

to rectifying action, frequency translated waves are generated in the input circuit. The translated waves, being of much lower the condenser as if it were an open circuit. The high resistance is therefore effective in causing substantially the entire potential of the translated wave to be applied between the grid and cathode. This condition is fafrequency than the applied waves, react to vorable to the most efiicient amplification of the translated wave by the discharge device.

In certain communication systems employ.- ing frequency translating devices the grid leak detector has not come into use, because the frequency ranges occupied by the applied waves and the translated waves respectively are relatively close together. The result is that a condenser is not adapted to by-pass the applied waves, while at the sametime operating as a substantially open circuit for the translated waves. Furthermore, it is evident that the impedance of a condenser, over a frequency band which is relatively broad compared with the magnitudes of the frequencies included within the band, varies sufficiently to prevent uniformly eflicient operation of the circuit. "5',

The preceding statements apply to carrier systems in which a carrier wave of relatively low frequency is modulated by signal currents extending over an extended band of frequencies which are relatively close to the carrier frequency. While the invention is not limited to use with any specific type of system, it may be advantageously applied, for example, to carrier telephone systems :or television systems for use with wire lines.

To overcome the difficulties which are encountered in attempts to adapt the grid leak detector and similar devices for the purposes of frequency translation, in carrier wave communication systemsutilizing a relatively low frequency carrier wave, the present invention employs a suitably designed wave filter to by-pass the applied waves around a high impedance element in the input circuit of a space discharge device.

" The invention is hereinafter .more fully described with reference to the accompany.- "915 ing drawings in which:

Fig. 1' is a schematic representation of a frequency translating system embodying the invention; l I

Fig. 1A is a detailed diagram of a com- "55 bination of filters and impedance elements which may comprise the section of the circuit to the left of the line AA in- Fig. 1;

and Y Fig, 1B is a detailed diagram of aciri- 1130 cuit which may be substituted for the apparatus represented above the line B-B in Fig. 1.

In Fig. 1, there is shown a space discharge device 1 which includes a cathode, an anode, and a control electrode.

The catliode may be in the form of a filament 4; heated by current from a battery 5, which current is regulated by a resistance 6.

The control electrode may be in the form of a grid 7 and may be coupled to an input circuit 2 by means of an input transformer 8, the secondary winding of which is con nected between the grid 7 and the filament a.

The anode may be in the form of a plate 9 supplied with space' current from a battery 10 through a choke coil 11 and coupled to anoutput circuit 3 by means of a blocking condenser 12;

The input circuit 2 includes the input terminals 13, 14 which are connected to an input. filter 15. The output terminals of filter 15 are connected serially to a resistance 16, a terminal impedance element 17, the. primary winding of transformer 8. The resistance 16 is shunted by the input circuit Of a by-passing filter 19 which latter terminates in a resistance 20.

Terminals 13, 14 may be connected to a source of. waves which it'is desired to subject to the process: of frequency translation to a source of carrier waves for determining the degree or frequency interval of the translation.

The input filter 15 is adapted to pass the applied waves withoutmaterial loss of energy. The by-pass filter 19 is designed to provide a low impedance path for the ap plied wave around the resistance 16.

The terminal impedance element 17 is a compensating means, the value of which may be adjusted in conjunction with the values of the; elements of filters 15 and 19, in accordance with well known principles of filter design, to make the combination of filters and: terminal impedance function substantially as: if composed of two entirely independent filters...

The ratio of turns in the respective windingsof input transformer 8 is so chosen that the input impedance of device 1 when transferred into the circuit 2 by the transformer e-ifectis of relatively low value. By suitable design the impedance which is thus transformed may conveniently be caused to a have a value substantially equal to the output impedance of the filter 15. The impedance: of the filter may conveniently be chosen with a view to obtaining a design which comprises elements in sizes which are eco-' nomical to manufacture.

It is desirablethat the output impedance :of .filt'er 15 should match the input impedance of transformer 8 as closely as practi cable, sothat the combination may produce the largest possible potential differences between the grid 7 and the filament 4. In order to effect this result, it is obviously essential that filter 19 operate to by-pam the applied waves around the resistance 16, so that the applied waves do not produce a potential drop across the resistance 16.

The by-pass filter 19 is designed with reference to the additional requirement that the by-passing function shall be selective as to frequency, so that it is effective for the applied waves but not for the frequency translated waves which it is desired to produce.

If an extended band of frequencies is to be produced by frequency translation, the filter 19 may be designed as a band-pass lter to transmit to its farther terminals with small or negligible attenuation all cur rents having frequencies lying within. the hand. For frequencies within the band, the filter 19 may be regarded as transparent, thus causing resistance 20 to be effectively placed in parallel connection with resistance 16. In most instances, the resistance 16 may be omitted without detriment to the opera tion of the system, its function being performed by resistance 20.

Input circuit 2 operates upon. the applied waves in conjunction with the grid-cathode circuit of discharge device 1 to produce. frequency translated waves which. are then repeated in amplified form in the output circuit 3 by means of the amplifying action of the discharge device.

The output circuit 3 comprises the output filter 21 and the terminals 22, 23, which latter may be connected to a load circuit of any desired form.

The'manner. of operation of the system to produce frequency translated waves may be regarded as follows: The applied waves are supplied to the system in such manner as to produce a maximum amount of potential difference between the grid 7 and the filament 4.

By means of the rectifying action of the space discharge path between the grid and cathode a frequency translated wave is pro duced which may be regarded as being generated in the space path. Resistance 16 or resistance 20 or a combination of the two is reflected into the grid-cathode circuit as a resistance for the frequency translated wave which is large in value relatively to the internal resistance of the space path, thereby causing substantially the entire potential of the translated wave to be effective between the grid 7 and filament- 4 to produce an amplified wave of maximum amplitude in the output circuit.

While the transformer 8 is shown connecting circuit 2 with grid 7 and cathode 4, its use is not indispensable to the operation of the invention.

The transformer may therefore be omitted. In some cases the exigencies of circuit design may make it desirable to alter the ratio of turns and other design factors relating to transformer 8 or to connect the transformer between terminals 18, 14 and the source of waves to be applied to circuit 2, instead of 111 the position shown.

In some instances the element 17 maybe omitted, or it may be placed in shunt 111- stead of series relation to the terminals of the primary winding of transformer 8. Again it may be placed in some other part of circuit 2. In other instances the input filter 15 may be replaced by a transformer or by one or more resonant circuits tuned to the frequencies of the applied waves.

In some cases, it may be inconven ent or inexpedient to make the value of resistance 20 relatively extremely high. This may be due to difficulties in designing the by-pass filter 19 to uniformly and only slightly attenuate all frequencies lying within the frequency band of the translated band. In such cases, if the value of resistance 20 1s somewhat lowered, the efficiency of translation may be slightly reduced, but it will be more uniform.

When desired, either of the filters 15 and 19 may be of the low-pass or high-pass type or one may be a low-pass and the other a high-pass filter. In either case, it will in general be importantto prevent overlapping of the transmission bands of the respective filters.

The exact form of the output circuit 3 or of the plate circuit of discharge device 1 is not a part of the present invention. In general, however, it will be desirable to design these circuits for efficient operation of the plate circuit as an amplifier and repeat er of such waves as are to be utilized in the load circuit.

Referring now to Fig. l-A a particular circuit embodying the invention will be described. Only so much of the circuit as lies to the left of line AA in Fig. 1 is shown and it will be understood that the portion of the circuit to the right of the line is the same as shown in Fig. l.

The input filter 15 consists of two branches. One branch consists of a series resonant circuit connected in series with the terminals 13, 14 and the other consists of a parallel resonant circuit shunted across the output terminals of the filter. Resistance 16 has been omitted.

The by-pass filter 19 includes a condenser shunted across its input terminals, an inductance in series with one side of the filter circuit, and a series resonant circuit shunted across the output terminals which are connected by the resistance 20. The terminal impedance element 17 is a series inductance.

Fig. 1B illustrates an alternative circuit which may be substituted for the portion of the system of Fig. l lying above the line B-B.

In Fig. 1-13 the resistance 20 is bypassed by one or more shunt paths, represented in the figure by the series resonant circuits 24, 25 and 26. Each circuit may be tuned to a frequency which it is desired to by-pass around resistance 20.

In general, circuits constructed in accordr ance with the invention will accentuate all translated waves having frequencies to which the filter 19 is transparent and will amplify all applied waves which are bypassed by said filter. The system of the invention may, therefore, be used to simultaneously amplify waves of selected fre quencies, while detecting or translating waves of other frequencies.

hat is claimed is:

1. The combination comprising a space discharge device having a cathode, an anode and a grid for controlling the discharge, a high impedance in circuit with said grid,

and a filter for transmitting into'said high impedance with substantially uniform attenuation the frequencies lying within a definite band and adapted to form an electrical by-pass of relatively low impedance around said high impedance for other frequencies a wave filter, providing substantially nniform attenuation for frequencies lying wit-hin a definite band and relatively great attenuatlon for other frequencies lying close outside said band, for 'operatively associating said high impedance means with said grid andcat-hode, whereby the potential difference derivable from said frequency translated waves is caused to occur between said grid and cathode.

3. The combination comprising a space discharge device having a cathode, an anode and a grid for controlling the discharge, a high impedance in circuit with said grid, a plurality of sources of waves to be amplified by said discharge device, said waves having predetermined frequencies, and a circuit resonant at a plurality of said predetermined frequencies connected in shunt to said high impedance.

4:- A system for frequency translation of electric waves comprising a space discharge device having a cathode, an anode, and a grid for controlling the space discharge, means for causing the electric waves to es tablish a potential difference between said grid and cathode to produce frequency translated waves, a high impedance means, and a plurality of coupled resonant circuits for operatively associating said high impedance means with said grid and cathode, whereby the potential difference derivable from said frequency translated waves is caused to occur between said grid and cathode.

5. A system for selectively amplifying waves of certain frequencies and translating Waves of other frequencies comprising a space discharge device having a cathode, an anode, and a grid for controlling the space discharge, means for causing said waves to establish a potential difference between said grid and cathode to produce amplified waves and frequency translated waves, a high impedance, and frequency selective means for associating said high impedance with said grid, said means being operative at the frequencies of said frequency translated waves lying within a definite band to increase the efliciency of translation to a substantially uniform value and inoperative at other fre-.

quencies lying close outside said band.

6. A systemfor frequency translatlon of electric waves comprising a space discharge 7 device having a cathode, an anode, and a grid for controlling the space discharge, means for causing the electric waves to establish a potential difference between said grid and cathode to produce frequency translated waves, and frequency selective means associated with said grid and cathode having a substantially uniformly high impedance throughout an extended band of frequencies, whereby all frequency translated waves having frequencies lying within said band are produced by the system with substantially uniform efiiciency irrespective of their frequency, and having a relatively low impedance for other frequencies lying close outside the edges of said band.

7 A system for frequency translation of electric waves comprising a space discharge device having a cathode, an anode, and a grid for controlling the space discharge, means for causing the electric waves to es tablish a potential difference between said grid and cathode to produce frequency translated waves, a wave filter providing substantially uniform attenuation forfrequencieslying within a definite band and relatively great attenuation for other frequencies lying close outside said band and having input terminals connected in circuit with said grid and cathode, and output terminals connected together through a high resist-- ance, whereby said resistance is operatively associated with said grid and cathode with respect to frequency translated waves.

In witness whereof, I hereunto sign my name this 21st day of December, 1928.

RAYMOND A. HEISING.

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