US2462100A

US2462100A - Demodulator system for time modulated pulses

Info

Publication number: US2462100A
Application number: US663126A
Authority: US
Inventors: Max G Hollabaugh
Original assignee: Federal Telecommunication Laboratories Inc
Current assignee: Federal Telecommunication Laboratories Inc
Priority date: 1946-04-18
Filing date: 1946-04-18
Publication date: 1949-02-22
Anticipated expiration: 1966-02-22
Also published as: FR1014497A

Description

Ferb- 22, w49' M. G. HOLLABAUGH DEMODULTOR SYSTEM FOR TIME MODULATED PULSES Filed April 18, 1946 .INI/ENTOR. mx a. Hama/:UGH

Patented Feb. 22, 1949 DEMODUIJATOR SYSTEM'FOR' TIME. MODUIATEDPULSES Max: G. Hollabaugln,JacksonfHeightsg.Ni asfsignor to Federal, Telecommunication Laborwtories4 Inc.,` New. York, N., Y, a'. corporationof Delaware Application April 18, 1946-', SerialifNoi. 66351126;

9. Claims.

This invention` relatesA to demodulators. for time modulatedi pulse systems, particularly.` ot the multi-channel type;

Multa-channel. time modulated: pulse systems haveV been proposed; in which pulses, oiv different channels are interleaved and spacedwith respect to regularly repeated marker pulses or signals soaszto form av single train.A

An object of the present invention isthe provision of an improved demodulator for time modulated pulse systems.

Anothery object of thelpresent invention. is the provision of a combined demodulator andchannel selector for multichannel time modulated` pulse systems.

A feature of the present invention is they provision of a combined channel selector and demodulator characterized. by simplicity and rer liability.

Another feature oftliepresent invention is the provision of a demodulator for timemodulated pulses Whose characteristics vary substan tiallylinearly With the time modulation off the pulses.

Other andfurther objects of the-present invention willbecome apparent and the invention will be best understood from the following description of an embodiment thereof, referencebeing had tov the-drawings, in which:V

Fig. 1 is a block diagram of a multi-channel time modulated pulse receiver embodying my invention;

Fig. 2 isa schematic diagram of a selector-demodulator embodying my'invention; and

Fig. 3 isa set of curves used in describing the operation of the selector-dernodulatorV of Fig. 2.

Referring now to Fig. 1, the receiver system there shown is of the type particularlyl adapted for the reception of pulse trains of multi-channel time modulated pulses such as for example, as illustratedin curve A, Fig. 3, `vvl'iere a series of signal pulses I, 2,'3, d, etc., each forming` part of a separate'channel, follow a marker pulse 5. These series are repeated as shown in said figure to form part of a continuoustrain with the signal pulses being varied'- between the limits indicated by the dotted lines on either side thereof. The signal pulses are equally spaced from each other in their unmodulated position.

Such trainsv of pulses may be used to modulate a carrier'vvave which may be radiated and thereafter received on an antenna I5 and fed to a re;- ceiver I Where the carrier frequency is removed. Theu output cf receiveril" isfed` througrli` a plurality offchannels 8, 9, I0', II', each channel being designed tdneceiue pulses'belongingytolaseparate one o the-pulsechannelsv I:.4. respectively.' For Control pur-poses, an additional. channel t2; is provided attfne; output of the receivenn 1.3. Whieh channel isusedttoselect'. thesmarken-pulse asa-for enamplebr'meanszof. apulsewidth ortiine dura.- tion discriminatprorother typeert marlieeselectcrtt', the output, oie: the; markenselectorfbeing ing turn used tm synchronize aJrecta-ngulaznwave generator. le, whose-output iszthen fed` over; a line I5; tore delai/ device I6 im channel 8; the delay device IiB.- lis adjusted-,for thel purpose; of

delaying the; centrali ware. output. of generator La to determine'. which. of the f particular channels is togbe; selected.. in the selector-demodulator` ill to.` which;i the delayed: rectangular: wave from: delay device Iisrfed; Fori example, infchannel' S, the selecton-demodulatorf- I1; which. receiveswall the pulses', cnly'a-ccepts those of the desired channel. which: maybek forl example, g'and de'- modulates the time modulation off the pulses vof channel Ie and; feeds. its result-ing. output to-` any suitable utilization. device lIii The other signal channels. f, lil' andl Hf are similar to chai-melY 8 in that. they. have a corresponding.. delay :device Iii?, seleet'on-demodulator 'Il' and suitable-utilisa;- tion device 53;- but theA delays in the separate channels.Y differ to i selectdifferent pulsev` channels.

The operation of' the selectoredemodulator- I'l' will' be best understood from the illustration of Fig. 2i` and the curves ofFFig; 3. Rectangular Wave generator I4 produces rectangular Wave control pulses I9" having a repetitionv frequency equal tothe repetition frequency of thernarker pulses and. havinga sumcient duration to accommodaterany-signa-l'pulse-,over its entire range of time displacement due to modulation. For example, in. one; given case, the signal pulse had a width or a halfmicrosecond andlhadVv a displacement of plus or minusone microsecond. The total time elapsingto cover the* signalpulse with its maximum displacement is a periodJ of two* and one half microseconds. The-widthof' the rectangular Wavey pulse leg was fourV microseconds and' was adjustable; The spacina'between' pulsesl at their central position Was five microseconds; The rectangular pulses t9L are delayed'- a sufclent amount in delay device l5 to select the particular channel desired; For example; referringy to curve B; Fig. 3, ther delay in delaydevice I6 was such as toselect channel 2 as'iwill beseen since the rectangularpulse' |19 substantially coincideswith pulse 2 and covers'the maximum time dis placement o saidpulse in either-direction.

The rectangular' pulse` I9 and the signall pulses are used to control the output of an electron discharge device as for example by being fed to the second and first grids respectively of a pentode 20 in the selector-demodulator |1. The pentode 20 is so biased that neither the rectangular pulse alone nor the signal pulse alone is su'icient to cause the flow of plate current, as is indicated by the conductivity levels 2| and 2'2 associated with vcurves A and B respectively. When, however, said rectangular wave pulse I9 coincides with one of the signal pulses, such as for example, signal pulse 2, the pentode 2U conducts and by the use of suitable shaping means consisting of condenser 23,

resistors

24 and 25, the plate current i is then so shaped as to producea negative pulse 26, curve 3, Fig. 3 at the rst grid of a second pentode 21 in the selector-demodulator 1. Pulse 26 has a very steep leading edge 28 and a substantially logarithmically-declining trailing edge 29. The rectangular pulses |9 which are applied to the second grid of pentode are also 'simultaneously applied to the second grid of pentode 21. Pentode 21 has a low cut-off level as indicated by the line 30 so that the rectangular pulse I9 is sufcient to start pentode 21 conducting. When, however, pulse 26 is applied to the first grid of pentode 21, pulse 26 has so large an amplitude that it immediately cuts 01T pentode '21 despite theA fact that rectangular pulse I9 is still being applied in a positive vectorial direction to the second grid of pentode 21. The resultant output of pentode 21 consists of pulses 3|, Whose leading edge coincides with the leading edge of pulses |9 and whose trailing edgel coincides with the leading edge of pulses 26. Since the leading edge of pulse 26 coincides with the leading edge of the signal pulse, as for example, pulse 2 in Fig. 3, the leading edge of pulse 26 will vary according to the time modulation of the signal pulse and likewise the trailing edge of pulse 3| will vary with the time modulation of the signal pulse. This is represented in Fig. 3. For example, pulse 2 in the first series is represented as being in its intermediate or unmodulated position and the resultant output pulse 3| has a given width. Pulse 2a in the second series is represented close to one extreme of modulation and theresultant output pulse 3|a is considerably wider than pulse 3|. Pulse 2b in the third series is shown at the other extreme of modulation and the resultant output pulse 3|b is narrower than pulse 3|. Accordingly, the duration of the output pulses 3| varies in accordance with the time modulation of the signal pulses. It will be seen that this variation is linear and is not determined by the transfer characteristics of the pentode 21. `The output pulses 3| may then be fed to any suitable integration device such as for example, a 10W pass iilter 32 and then to the utilization device I8 which may be for example, an amplifier and loud speaker system. l

While I have described above the principles of my invention in connection with specic apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of my invention.

I claim:

1. A demodulator for time modulation pulse systems in which a signal pulse varies from a given time position according to its modulation, comprising a control pulse source producing pulses of constant duration, said duration being at least as great as the maximum range of time displacement of the signal pulses dueto modui 4 lation, means for timing one of lsaid control pulses substantially to coincide in time with a corresponding signal pulse so that the control pulse has a xed time relationship to the unmodulated position of the signal pulse and covers the entire range of time displacement thereof, means responsive to the' coincidence of the timed control pulse and the signal pulse to produce a pulse having a relatively steep Wave front, current-control means responsive to the timed leading edge of the control pulse for initiating the flow of current and responsive to the steep pulse for halting the ow of current, whereby the resultant output pulse from said current-control means varies in duration in accordance with the time modulation of the signal pulse.

2. A demodulator for time modulation pulse systems of the type in which a marker signal is followed by a signal pulse which signal pulse varies from a given time position with respect to the marker signal according to its modulation, comprising means responsive to the marker pulse for producing a control pulse` of constant duration, said duration being at least as greatas the maximum range of time displacement of the signal pulses due to modulation, means for delaying said control pulse to substantially coincide in time with the signal pulse so that the control pulse has a xed time relationship to the unmodulated position of the signal pulse and covers the entire range of time displacement thereof, means responsive to the coincidence of the delayed control pulse and the signal pulse to produce a pulse having a steep wave front, current-control means responsive to the leading edge of the delayed control pulse for initiating the ilow of current and responsive to the steep pulse for halting the ow of current, the resultant output pulse from said current-control means varying in duration in accordance with the time modulation of the signal pulse, and integrating means for translating the duration of said' output pulse into an amplitude characteristic.

3. A demodulator according to claim 2 wherein said control pulse producing means is comprised of a rectangular wave generator.

4. A demodulator according to claim 2 wherein said means responsive to the coincidence of the delayed control pulse and the signal pulse comprises an electron discharge device having at least oneA control element, means for biasing said device so that the control pulse alone or the signal pulse alone is of insuilicient amplitude to cause said device to conduct, but both signal pulse and control pulse together are capable of causing conduction of said device, means for applying said delayed control pulse to a control element of said device, means for applying said signal pulse to a control element of said device, a condenser connected to be rapidly discharged upon conduction of said device to thereby produce the steep wave front of the steep pulse.

5. A demodulator according to claim 2 wherein said current control means comprises an electron discharge device and further including means for impressing said delayed control pulse on said device to initiate conduction thereof, and means for impressing said steep pulse on said device for halting the conduction thereof.

6. A demodulator according to claim 2 wherein said means responsive to the coincidence of the delayed control pulse and the signal pulse comprises an electrondischarge device having at least one control element biased so as to conduct upon coincidence of the control pulse and the signal pulse, means for applying said delayed control pulse to a control element of said device, means for applying said signal pulse to a control element of said device, a condenser connected to be rapidly discharged upon conduction of said device to thereby produce a negative pulse having a steepvwave iront, and said current-control means comprises a second electron discharge device, means for impressing said control pulse on a grid of said second device to cause conduction thereof, and means for impressing the steep negative pulse upon a grid of said electron discharge device to halt conduction thereof.

7. A channel selector and demodulator for multi-channel time modulation pulse systems of the type in which a marker signal is followed by a succession of signal pulses, each forming part of a separate channel and each varying from a given time position with respect to the marker signal according to its modulation, comprising means responsive to the marker pulse for porclucing a control pulse of constant duration, said duration being at least as great as the maximum range of time displacement of the signal pulses due to modulation, means for delaying said `control pulse to coincide with a pulse of the channel desired so that the control pulse has a xed time relationship t0 the unmodulated position of the signal pulse and covers the entire range of time displacement thereof, means responsive to the coincidence of the delayed control pulse and the signal pulse of the desired channel to produce a pulse having a steep wave front, current-control means responsive to the leading edge of the delayed control pulse for initiating the ilow of current and responsive to the steep pulse for halting the flow of current, the resultant output pulse from said current control means varying in duration in accordance with the time modulation of the signal pulse of the desired channel,

6 and integrating means for translating the duration of said output pulse into an amplitude characteristic.

8. A channel selector and demodulator according to claim 7 wherein said means responsive to the coincidence of the delayed control pulse andV the signal pulse of the desired channel comprises an electron discharge device having at least one control element, means for biasing said device so that it conducts upon coincidence of the control pulse and signal pulse, means for applying said control pulse and said signal pulse to control the conduction of said device, a condenser connected to be rapidly discharged upon conduction of said device to thereby produce the steep wave front of the steep pulse.

9. A channel selector and demodulator according to claim '7 wherein said current control means comprises an electron discharge device,

means for applying said control pulse so that the leading edge thereof initiates conduction of said device, said control pulse having a duration at least equal to the total width of the signal pulse v REFERENCES CITED The following references are of record in the ile of this patent:

UNITED STATES PATENTS Number Name Date 2,416,088 Deerhake Feb. 18, 1947 2,421,025 Grieg May 2'?, 1947