US2441958A - Communication system - Google Patents

Description

May A25, 1948.

Afr @IAM/wrm? Filed July 1'7, 1944 L. DE ROSA COMMUNICATION SYSTEM 2 Sheets-Sheet 1 INVENToR. ou/s 4. DE @om ATTIP/VEY May-25, 1948. L. A. DE RosA v 2,441,958

COMMUNICATION SYSTEM Filed July 17, 1944 2 Sheets-Sheet 2 IN V EN TOR.

[0a/s 4. of Ras/l Patented MayV 25 1948 i-FICE- 2,441,95s v colvnwUNloATroN SYSTEM Louis A. de Rosa, West Brighton, N. Y., assigner to Federal Telephoneand Radio Corporatlon, New York, N. Y., a corporation of Delaware Application July 17, 1944Serial'No. 545,260

My invention relates to communicating systems, and more particularly to a simpliediorm of pulse generating system that is particularly suited for use in portable transmitters.

There are many instances where radio trans-f mitting equipment must be kept within certain prescribed limits both as to weight and to the number and variety of circuit elements employed. While this is often the case in apparatus intended for use on aircraft, itis almost universally" ior repair thereof is greatly facilitated. Further-'i15- more, a reduction in the number of circuit elements utilized correspondingly reduces the possibilityof electrical or mechanical failure of the transmitter.

It is accordingly an object of the present in' .20

vention to provide a simpliiied form of pulse generating system having relatively few parts.

It is a further object of the present inventio-n to provide a method of, and modulator means for,

generating pulses the recurrence rate ofv which l Y 500 ohms. Y

A lead II connects the anode 9 of triode 3 to' is varied in accordance with the envelope of the signal representing the intelligence to be transmitted.

The above and other objects I. accomplish by systems incorporating an electron discharge tubefo of the gas-filled type. By applying audio signals to the grid of this tube, the striking potential of the tube is caused to vary in accordance with the envelope of the signal. A resistance-condenser combination. having a small time constant rela-:135` I l example, the tube will become ionized when the tive to the period of the highest modulating frequency to be employed is connected in the cathode circuit of the tube so that the condenser will charge while the tube is conducting and will begin to discharge as soon as the extinction po-lo tential of the tube is reached. Due to the variation in the striking potential las a result `of the ,audio signal, however, this striking potential will be reached at diiferentpoints along the discharge curve of the condenser.V Thus the striking lecurrence of the tube/will be at a rate determined bythe grid voltage which, in turn, represents the instantaneous magnitude Vof the signal energy.

Further operational details will be found in the 3 Claims. (Cl. 179-1715) Fig, 2 is a set of curves useful in explaining the operation oi the system of Fig. 1; and

Fig. 3 is a schematic circuit diagram of one form of receiving system that may lbe employed inconjunction .with the transmitting system of Fig. 1.

In the circuit of Fig. 1 is shown a pulse transmitting system including a microphone or other sound pick-up device I connected to an amplifier 2.1 A gasffilled triode 3 such, for example, as an RCA 884 has its grid d connected through a coupling condenser to the output of amplier 2. A resistor 5 provides a negative bias from voltage C` on grid 4 for a purpose to be hereinafter described. -l Y A Between the cathode 6 of triode 3 and ground is connected a resistor l of fairly high value, Asay forV example '75,000 ohms.

A condenser 8 is shunted across resistor Anode 9 of triode 3 is provided with a D. C. potential of positive polarity from a suitable source. For the purpose of illustration, let this plate potential be equal to 150 volts. Between anode 9` and the source of plate potential Yis connected IaY resistor Il) of fairly low value, say

an ampliiier I2. The output of amplifier I2 passes through a clipping circuit I3 to an R. F. translator I4 and is thentransmitted from an- Y tenna I5.

' I'riodey 3 has Va certain striking potential.

-This potential varies in accordance with the grid Vbias on the tube.

In the case of the RCA 884 with-a plate voltage of 150 volts taken as an grid bias is approximately -l51/2 volts.

.Assume that tube 3 becomes conductive. In the curve aci. Fig. 2, the normal striking potential of the tube with constant grid voltage :due to its bias. is indicated by the horizontal line VVVI. When Vtube -3 first becomes conductive in any transmitting sequence, there is, of course, no charge on condenser 8, and such no charge condition is represented on wave I l by point I8 at the zero charge axis I9.

When tube 3 becomes conductive, current flows fthroughsaid tubeand charges condenser '8.-

Whenthe charge on condenser 8 reaches the first point indicated at 20 on wave I1, the potential drop across triode 3 is reduced to the point where extinction of the discharge in tube 3 occurs. This extinction level is shown in Fig. 2 as a horizontal line 2i. Upon extinction of tube 3, condenser 8 starts to discharge through resistor I to ground. Since resistor 1 is of a fairly high value as above mentioned, this discharge follows current flows through tube 3 to again build up th.V

charge on condenser 8 to the level 21|.,` Fig. 2.

Thus, it will be seen that the condenser 8A is 'not' normally completely discharged tothe zero. level The horizontal line I6 represents the normal striking potential oi tube 3 as determined by its bias, in the present example approximately -151/'2 In the above-described operation it has Volts. been assumed that the grid voltage is of constant value, in which case the series of points 2E!A representing Vperiodic maximum" charged conditions of condenser 8 will be'edually spacedv apart in time, this spacing being, ot course, determined by the" time constant of the resistance-corldenserV combination 'I- as well as bythe operating characteristics of, and the voltages.on, the particular tube employed.

HIf now an audio signal voltage isl applied to grid 4 from microphone. I through` amplifier 2,`

theV normal striking potential oi tube 3; vvillfY be varied. This is illustratedfby. the wave 24 of curve a, which shows the signal voltage superposed on the grid bias voltage. Due to, this variance in the striking potentiaLvthe time duringj which condenser 3` discharges before the striking potential is reached willi vary correspondingly. As shown for example inportion.25 o f waveV I'I, the discharge time of the condenser isl applieciably shortened, resulting a change, in the recurrence rate oi points 2:0,A along extinction level 2I.

Each time that tube 3 strikes.,a,l Voltage pulse is produced in the output circuit I.;I., as shown in the Curve o 0f Fig, 2,- This. uulsefhas asharp leading edge 2e produced when the tube strikes, followed by a curved trailing` edge 2.1. As s oon as the, tube becomes;extir iguishedv anodeqs immediately takes the potential oi thev positive source.V

Due to the fact that the pulses of curr/eb,V are produced during conduction o f tube 3, thesel pulses will be spaced apartV intime anJ amount; approximately equal to the spacing or pointsA 2,0.-representing the corresponding` chargings oi?l conamplier I2 and then clipped at a-level such as 28. by a known clipping circuit-latoiresult Vinthe series of pulses 29 of curve-c. Theclipping circuit I3, however, maybe omitted-ifldes'ired, the.

pulses of curve b in that casebeingapplieddirect to translator la. The pulses oi curves; or` or, c, as-the case may be, are used `to modulatefa-carrier wave in a conventional translating device I4 whereby a series of pulses 30 of R. F. energy as shown in curve d is produced for transmission from antenna I5.

To receive the pulses produced by the circuit of Fig.' 1, a system such as shown in Fig. 3 may be employed. This system comprises an R. F. detector and amplifier 3! which may be of any suitable type. The output of detector and amplifier 3l is applied to an integrating circuit 32 which reproduces the envelope of the original audio, Wave as applied to grid 4 of Vtriode 3 in Fig; 1*: The audio wave mayrthen be used to energize a reproducing apparatus such as the tem, it is to `be clearly understood that this discription is made by way of example only and not as a limitation on the scope of my invention asset forth in the objects and the accompanying claims. i

denser 8 to the extinction leyel` 2|;of tlnetuloe.

` The pulses of curbe h are amplified by an 'If claim: u Y Y 1. A pulse modulator system comprising afreely-running relaxation. oscillator including; a gridcontrolled gaseous discharge tube,AY an anodecathode circuit coupled tosaid; tube, asource of potential coupled to4 theanodefcathode. circuit of said tube, time-constant means coupledftothe anode-cathodeV circuit Vand including. a condenser adapted-tobenorrnally chargediand: discharged.-y at a rate controlled; byV thepotential on thel grid kof sa idtube, meansfor biasing said. grid to normally ignite said tubeata; givenrate,V to thereby normally produce pulses of: a given ,repetitionrate inthev anode-cathode. Circuiti thereof, a source of varying amplitudey audio. frequency signal'. voltages, andmeansior applying saidvoltagesto the grid of said tube to varyits rate of .ignition and consequently the repetition frequency of said pulses.

2. Apulsemodulator. systemaccording toclaim 11 wherein said; time; constant; means.. is. a. circuit including a resistor in. parallel with; saidV condensensaid circuit; being connected inseries in the anodefcathode circuit, said. condenser being charged ,uponignitionoigsaidvr tubeanddischarged through said resistor. u

3. kApulse modulator,A system according to-cla-im 1,V further including a clipper for. clipping away the base `portion of- `saidpulses .to .thereby produce on its. output, peaked pulses modulatedin time in accordancevvith the amplitude off the signal voltages.y

LOUISIA. DE ROSA;

importations.; CITED The following references are of; record'in.. the leeofcthis patent:

UNrIED STATES EATENTS N umberA Name Date.

1,387,237:V Finch- Nov; s, 1932 2,227,596 Luci:- Jan. '1; 1931 2,280,707 Ken Apr. 21, 1942 2,238,554 smith Juneso, 1942 2,292,100 Bussi Aug. 4, 1942 2,329,137l Richards sept: v; 1943

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