US1778750A - Transmission regulation - Google Patents

Description

Oct. 21, 1930. BRUCE 1,778,750

TRANSMI S S I ON REGULAT ION Filed Dec. 31, 1926 AAAMM "WHY firvemorx f07770/7d 5/2/66 Af/omey Patented I umranfsrA -as PATENT OFFICE EDMOND BRUCE, or m max, mew eraser, assroxon 'ro rntnrnom: mom. roams, mconromrnn, or NEW roux, N. 1., a conrou'rrou or mswronx TBANSMISSIQN REGULATION Application filed December 81, 1928. Serial 80,158,108. V

3 to the detector grid, The function o'zqi:

- This invention relates to wave transmis. sion, and particularly to short wave radio signaling.

An object of the inventionfis automatic 6 volume control of transmissiomand especially reduction of fading efiects in short wave radio telephony. r

In a successive detection receiver embodying the invention, D. vC. voltage drop across a resistance in the plate circuit of the last detector variably biases a grid of the first detector, to reduce fluctuations in the output of the last detector. I Fig. 1 of the drawin shows a double de- 1 tecti'on receiver; and 2 shows a tr ple. detection receiver. embodying. thev invent on.

In Fig. 1, a tuned circuit 1, comprising a variable tuningcondenser 2 anda loop antenna represented as an inductance coil 3, receives radio signaling waves,as for example, 5 cech signal modulated carrier waves,'a1'1d ehvers them from the half of the looprepresented by the upper halfofcoil 3,to thQlIlPllt circuit of a high fr uency detector 4, shown as an electric space liar e detector. The end of the loop represented y the lower end of coil 3 is connected to the grounded filament of the detector through Iii-condenser 5 which has. a capacity equal to the 'efiective input the loop is connected to'the grounded detector filament through a condenser 10 of negllgible reactan'ce for frequencies of the order of the resonantfrequency of tuned circuit 1. The loop is preferably rotatable as usual for obtaining directional selectivity, and the directional selectivity is increased by the connecting of the center of the loop inductance to earth-and the use of the condenser '5 for preventing unbalauce of the capacities connect ed to the loop, with respect to ground. The detector A. C. input circuit includes a coil :6 coupled to a beating oscillator 7, preferably of the electric space discharge type, 1n series with a grid biasing battery 19 and the condenser 10. The D. C. connection-between the filament and the grid of the detector 4 extends from ground through a resistance 11, conductor 1:2,"the grid biasingbattery 19 for the detector, coil 6, and upper half of coil of the detector 15 includes a telephon'e refrequency amplifier 16,'are delivered to de-i a 1 capacity of the detectorfand'the center of.

sistance 11 is brought out-hereinafter.

The output circuit of the detector connected'to the input circuit of a.low fruency detector '15 through an intermediate requency amplifier 16. Theoutput circuit ceiver 18, or other signal indicating means,

v in series withthe resistance 11 and a battery 17 for supplying space 'currentto detector 15.

By the action of detector 4, and beating oscillator 7 the frequency of thewaves re'- ceived'by loop 3, which may be, for example,

of the order of 10" cycles per second is changed to a lower frequency, as, for example, a frequency of the order of 300,000

selective amplification in an intermediate tector 15, which operates to reproduce-the .cycles. These lower frequency waves, after speech or other signal current of the'signal I modulated wave received by loop 3, to render the signal audible in telephone 18. The frequency range of the intermediate frequencyamplifier may extend, for example, from 295,000 to 305,0007cycles per second.

The balancing condenser 5 prevents the incoming wave from developing across the the circuit of vacuum tube oscillator 7.. If

coil 6 a voltage which would be induced in a a voltage were so induced in the oscillator, there would bedan'ger-that the oscillator would function as a self-oscillating detector developing a difference frequency which would be transmitted through the grid-plate 7 capacity of tube 4 and through intermediate frequency amplifier 16. r

Preferably the system isoriginally adjusted so that with no incoming signalthe D. C. grid bias of detector 4 is such that the point ofoperation on the grid voltage plate current characteristic is the point where the curva-- ture is the greatest,'and furthermore so that the beating oscillator peak voltage is at least I equal to the additional bias necessary to -cause plate current cut off. Then when signals are received, an additional negative bias is, applied to the detector grid due. to the dr across resistance 11, resulting in two taneous effects, one a shift downwardly to an operating point on the characteristic of detector 4 at which the curvature is less, and

the other, an effective reduction of the beating oscillator input, due to an increased portion of the wavebeing below plate: current cut oil".

Then as the signaling waves incoming to the loop decrease in strength, due, for example, to fading, the D. 0. plate current of detector l5 decreases and, hence, the IR drop across resistance 11 decreases, causing reduction of the negative grid bias of detector 4 and consequent shift upwardly to an operating point on the characteristic of detector 4 at which the curvature of the characteristic is greater, and also causing an increase in the effective beating -oscillator input. This tends to increase the output of the high fre-' quency detector and, therefore, counteracts the decrease in the strength of the signaling waves received by loop 3. 7 I

When the strength of the signaling waves received by the loop increases, the reverse action occurs, tending to cause a decrease in the output of the receiver. The system thus compensates for carrier fading by automatically readjusting the receiver gain. The use of such compensation enables satisfactory reception of speech in cases in which the receptionwould otherwise be unsatisfactory, due to violent fading.

' In the theoretical limiting case in which a change in the plate current of the second detector is just sufiicient to produce'in resistance 11 suflicient IR drop 'to cut off the cplate current of the first detector, the second etector voltage input, which that second etector plate current change represents, is the greatest voltage input to which a signal of any magnitude whatever can subject the second detector, because a greater voltage input to the second detector cuts off the plate current of the first detector and thereby completely destroys the signal.

' The system has a very largevolume control range per tube on which the grid bias variation is effected. With a system such as shown in Fig. 1, in which-the resistance 11 r was 20,000 ohms and the capacitylO was 1 mi, tests showed that an increase in slgnal change of bias does not produce danger of sing'n'g or characteristic resonant frequency shi control, when resistance 11 is 20,000 ohms and capacity 10 is 1 mf; the time constant BC or the control is 20,00ox10--=o.o2= second. This is sufliciently fast for ractically all cases of ordinary fading. he capacity 10 should be sufiiciently large to offer a low im dance path to ground for the high fre uencies and particularly to prevent interme iate frequency-feedback and singing.

In order to obtain a large range of volume control, a receiver should have available large-excess amplification. fForexample, if a signal amplitude fades, say, from its maximum to one-fiftiethof its maximum, the receiver should have available more than t mes excess amplification. The intermediate frequency v0 tage gain of the system described above may be, for example, 120,000

times at 300 kilocycles, or may be the largest amplification from which the tube noise can be tolerated.-

In the system described above, the wide frequencyrseparation between the A. C. output from tube 15 and the A. 0. input to tube 4 tends to prevent singing due to the feedbaokfrom resistance 11 to the input circuit of tube 4. p

Still further insurance against singing in a fading control system of this general type can be obtained by employing more than two stages of detection, and effecting the fading control by varying the bias of the grid of the first detector in response to the volume chan es in the output of the last detector. The equency of the input wave ap lied to the last detector will then be widely (lifierent from the frequency of the output wave of the first detector, and the danger of singing will' be reduced to a greater degree than in a double detection system.

Eig. 2' illustrates, by way of example, a triple detection system, when the switch 20 therein is closed and the switch 21 is open. The system is then like the system of Fig. 1, except for the insertion between the first intermediate fre uency amplifier 16- and the low uency etector 15, of the detector 22 and its eating oscillator 23 and-thesecond frequency: selective intermediate frequency amplifier 24 danger of intermediate frequency s nging is considerably reduced, compared with a double detection system, the capacitypf condenser 10 maybe greatly reduced, with consequent reduction in the time includes the limiting frequency zero, that is,

constant of the stemandwith resulting im rovement in t e operating speed of the fadin g control. Where it is desired to reduce the range of variation which the signals reduce in the input to the third detector, t a bias of the grids of both the first and the second detector may be caused to vary, simultaneously, in

D. C. I

What is claimed is: 1. A receiver for speech modulated high frequency carrier waves, comprising a frequency changing unit including an electric high frequency and connected .to said electric space discharge device for beating down said space discharge modulating device a' source of voltage of frequency different from said higher frequency, means forsclectively amplifying the waveof changed frequency to the exclusion of said waves of'high freq quency, and means for detecting said selected mentione wave to produce speech currents, said last to the first detector to appl thereto a voltage of such magnitude an direction as to tend to control the volume fluctuations in said speech currents due to fluctuations in the strength of said high fre uency waves. v

v2. A receiver for big frequency waves comprising a detector for changing the frequency of the received wave, means for amplifying thewave of changed frequency, a second frequency changing detector, a second means for am lifyin the wave of redduy said second detector, and means for detectin the amplified wave from said second amp means,

said last mentioned means comprismg a vacuum tube device with a connectlon to the first Y detector to apply thereto a potential of such 3. A receiver for high frequency waves comprising a'detector for changm the frequency of the received wave, means or amplifying-the wave of changed frequency, a second frequency changing detector, a second amplifyin means for amplifying the wave of reduce frequency delivery y said second detector, and means for detecting the amplified wave from said second amplifying means,

said last mentioned meanscoinprising a vacuum tube device with a connection to the first detector and a connection to the second detectorto apply to said detectors potentlals ofcomprising a plurality of frequency changmeans comprising a connection,

ingdetectors, an amplifier, for each of the waves produced by said frequency changing current into uni-directional current comprising space discharge devices including a pluralityof rectifiers for supplying current to a load "circuit, impedance elements and sources of biasing potential individual to said space discharge devices, and coupling means interconnecting said devices, said impedance elements and coupling means being current responsive to ary the conversion efiiciencies of said rectifiers in accordance with fluctuations in the alternating current. V

6. A wave detecting, system controlled in respect to detection efficiency by means of and in accordance with selected characteristics of the Waves to be detected, comprising a pluralityof space discharge devices, an input circuit for supplying waves to 'said devices, individual means for biasing each of said devices, an output circuit for transmitting detected currents to a load circuit, and means for utilizing a portion of said detected currents for varyingthe biasing potential applied to a plurality ofsaid devices.

7 A receiver of high frequenc energy comprising means for reducing the requency of the received energy, means for producing a uni-directional current from the reduced frequency energy, and means controlled by said uni-directional current for applying a variable potential tosaid frequency reducing means to control its operation.

8. A radio receiver comprising means for changin the frequency 'of the received wave, means or producing a uni-directional current from the wave of changed frequency, and means supplied with said uni-directional current for controlling the operation of said frequency changing means in accordance with a variable 0 aracteristic of said received wave.

9. A radio receiver comprising means for changing the frequency of the received Wave, means for producin' a. uni-directional current from the wave 0 changed frequency, and means supplied with said uni-directional current to control ,theuoperation of said fredetectors,'means for detecting the lowest quency changing means to maintain constant the current output of said receiver in spite of variationsin said received wave;

v 10. In a system for receiving waves of given frequency including a space discharge device, means to apply waves of said given frequency to the control electrode of said de vice, means for changing the frequency of the waves in the output circuit of said system to 1'4 v a mem 0. different frequency 1eve1-,'metmsto derive from said waves of changed. frequency a negative voltage, and connections for applying said negative voltage to the control electrode of said discharge'device to vary the gain of said system, said system including a means preventin the application to said ccntrol electrode 0% wave'components having the same frequenc ylevel asthe' received Wave. 11. In a wave receiving system comprising 10' a plurality of space discharge devices, means to impress waves of the received frequency on certain of said devices, an amplification control comprising means for impressing 15 upon the control electrode of certain of sai devices a potential, which becomes more negative with increasing output and less negative with decreasing output, whereby said output is maintained substantially constant with varying input and means to avoid singing in said system, due tofeed-back, comprising frequency changing means producing a Wave from which said negative potential is exclusiveiy derived and which differs in frequency 0 by a large amount from the received frequency. V

In Witness whereof, I'hereunto subscribe in; name, this 23rd'day of December, A. 3)., 19 6.- ,o w EDMOND BRUCE.

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