US2451916A

US2451916A - Radio telegraph receiving system

Info

Publication number: US2451916A
Application number: US695530A
Authority: US
Inventors: Reynold S Chapin
Original assignee: PRESS WIRELESS Inc
Current assignee: PRESS WIRELESS Inc
Priority date: 1946-09-07
Filing date: 1946-09-07
Publication date: 1948-10-19
Anticipated expiration: 1965-10-19

Description

/Pf ma@ CHAP/N Oct. 1,9, 1948. R. s. cHAPlN 2,451,915

` RADIO TELEGRAPH RECEIVING SYSTEM Filed sept. 7, y194e /f/P/ j f QF fpm 1f DE? OWS /Pmcrq f #WP CO/VL/ HNP MT5/P ,/70 A70/P OSC/LL/Q/F 15A/V0 /E'F f/Pfa F of? H955 f6/WW- AMP ca/vu #f7/.D LHP @fsw/vof@ f/ /c f? @07 mi@ //y asc/mm? INVENTOR.

Patented Oct. 19, 1948 UNITED STAT RADIOk TELEGAPH RECEIHCIG SYSTEM` Reynold S; Chapin, Flushing, N. Y., assgnor toV Press Wireless, Inc., New' York, N. Y., a corporation of Delaware I I. Application september 7, 1946,' seial'No. 695,550

" 5 claims.

tems and more especially to such systems Wherein the telegraph information is represented by keyed off and on signals. I

In present day radio telegraphy, there are two generally used methods of transmission, one identified as make and break, and the other as frequency shift. In the make and break system, the radio carrier is keyed-on for one signal conditi-on, e. g., mark, and is keyed-off to represent space. In the frequency shift system, the radio carrier is continuously transmitted but the frequency is shifted to one value representing mark and another value representing space. One of the advantages of the frequency shift method is an increase in the signal-to-noise ratio as compared with the off and on system.

Accordingly, it is aprincipal object of this invention to provide an off and on radio telegraph system having certain of the advantages `of the carrier frequency shift system, and in particular the advantage of high signal-to-noise ratio.`

A feature of theinvention relates to a radio receiving arrangement for receiving telegraph signals of the olf and on carrierntype, having means to increase the ratio of signal-to-noise by automatically 'and artiically inserting `a carrier at the receiver when no carrier is beingy received from the transmitter, as for example during the reception of a space signal.` L f i Afurther feature relates to a novel arranges ment for selectively and artificially supplying a local carrier to a radio receiver which normally depends for its signal reproduction on the receipt of a carrier from a distant transmitter. i

A still further feature relates,r to the novel organization, arrangement" and` relativev inter-Y connection of parts which cooperate to provide an improved radio telegraph receivingksystern.

Inasmuch as the various components of a vradio telegraph and receiving'V system are, in

themselves, well-known, the invention will ybe illustrated in block diagrammatic form.` Only those parts of such a system as areinecessary to an understanding of `the invention and one method of carrying it into practice, are shown. The drawing shows any well-known suitable form v of radio transmitter I of the Well-known carrier off and on type,' comprising a carrier frequency generator II which can be keyed on and off by the telegraph keyer device I2. The keyed carrier is picked up by any suitable antenna I3, and is appliedto two radio receivers I4, I5, Ieach of which may be, although not necessarily,` ofthe superheterodyne type. Each receiver may `comprisea radio frequency amplifier stage,`a fre- A'" quencyvmixer or converterstage which is suppliedwithlocal high frequency heterodyne oscillations from the usual source II6,1II; an intermediate frequency amplifier stage, and adetector stage. The receiver I4 -is the main receiver whose output controls the `signal responder device I8. Preferably, the`detect0rstage of receiver I4 is vsupplied'with local audio frequency beat oscillations fromfsource I 9, and the resultant beat note is" passed through a suitable band-pass filter 20. The receiver I5 is an auXiuiary receiver and is employed for the purpose of supplying the intermediate frequency stage of receiver I4 with an intermediate frequencycarrier when no radio frequency carrier is being applied via antenna I3 to the input of receiver I4. For purposes of explanation, it will be assumed that when a'mark signal is being transmitted by the transmitter II) a radio'frequency carrier is picked up by the antenna I3, and when a space signal is being transmitted, nocarrier 1s picked up by the said antenna. "Connected to the intermediate frequency stage of receiver I4 is a localintermediateY frequency oscillator 2l Vwhich Vnormally generates a frequency within'the pass-band of the intermediate frequency circuits of receiver I4. The arrangement is such that when no radio carrier is being received bythe antenna I3, the oscillator 2| is effective to apply or inject the local intermediate frequency into the interme- 'diate frequency stage of the receiver I4. On the other hand, when a radio carrier signal is ibeing received by antenna I3, the arrangement Is such that the oscillator'ZI is controlled so that it does not apply any local intermediate frequency carrier to the intermediate frequency stage of receiver I4 within the pass-band of the said stage. It has been found `that when the receiver I4 does not receive radio carrier from the antenna I3, and in the absence of v oscillator 2|, considerable noise is present in the output of the receiver. On the other hand, by injecting Ythe intermediate frequency oscillations artifically from `the oscillator 2| as above described, this noisecontent in the output of the receiver I4 is greatly reduced if not entirely suppressed.

Assume for purposes of explanation that a mark signal 'is being transmitted. Under these conditions, a D. C. signal appears at the output of receiver I5 which is applied through a low-pass filter 22, inorderto increasethe ratio of signalto-noise., This D. C. signal is applied to a reactance tube orreactance modulator 23 of any well-known type,rthe' output of which is coupled to the oscillator 2 I, so that when a signal is passed On the other hand, when no radio frequency carrier is being received corresponding for example to a space signal, no D. C. signal appears receiver Whose detected output controls a telegraph signal responder, an auxiliary radio receiver for producing at its output a control signal when the radio carrier is keyed-on, a local injection oscillator for the main receiver, means responsive to the presence of said control signal to render said local oscillator ineifective to inject .carrier into said main receiver so as to affect said signal responder, the last-mentioned means being effective in the absence of said controlled signal to render said local oscillator effective to inject carrier into said main receiver to increase the .ratio of signal-to-noise when the radio carat the output of receiver I5. Under these condii tions, the reactance tube 23 causes the oscillator 2| to generate a sustained intermediatefrequency v carrier which is within the pass-band of the intermediate frequency stage of receiver 5M.' Preferably, although not necessarily, the injected frequency from oscillator 2I is slightly different fromf the normal intermediate frequency of the receiver I4,I which norm-al intermediatefrequency is produced at the output 4of the mixer stage of receiver I4 by heterodyning the received carrier with the local oscillator I1.; AHowever kkthe injected frequency is within the normal pass-band of this intermediate frequency stage. Thus, when the 'injected intermediate frequency signal is detected and heterodyned with the signal from-the local beat frequency oscillator I9, thereis produced an audio frequency in the output of the receiver I4 which is slightly different from the normal beat frequency at the output of receiver I4 when a radio frequency mark signal is applied to the input of that receiver. When a radio frequency mark signal is being received, the receiver I4 functions in the normal way to produce at'its output an audio frequency beat note determined by the detected signal and the beat frequency oscillator I9. Since the oscillator I9 is continuously operating, the output of the receiver I4 for a received radio frequency mark signal will be an audio frequency tone of a specie frequency, which is diierentfrom the tone which is created when no radio frequency carrier is being received, but which results from the injected local carrier. y

Preferably, the low-passlter 22 isadjustable to correlate it with the keying speed of the received signals so as to increase a'ratio of signalto-noise. Likewise, if desired, the vsensitivity of the reactance tube 23 and the oscillator`2l can be adjusted to correlate them with the keying speeds in the received signals vso as further increase the ratio of signal-to-noise.

While one particular embodiment has been disclosed, it will be understood' that various changes and modifications may be made therein without departing from the spirit and scopeof the invention.

What is claimed is: l 1. A receiving arrangement for radio telegraph signals of the carrier on and olf type, comprising a main radio receiver whose output con- 2. A receiving arrangement for on and off radiotelegraph signals, comprising a. main radio rier is keyed-off.

3. A receiving arrangement according to claim 2 in lwhich said main receiver is continuously suppliedwith beat frequency oscillations to produce inf-the output of said main receiver two different audio frequency beats, one correspondingto reception of a keyed-on radio telegraph signal and the other corresponding to the keyedoff telegraph signal.

` 4. A receiving arrangement for on,and off radio telegraph signals, comprising a main radio receiver whose detected output controls a telegraph signal responder, an auxiliary radioreceiver, said main receiver being the type having an intermediate frequency carrier stage; a local intermediate frequency carrier generator, and means controlled by the detected output of said auxiliary receiver for rendering said intermediate frequency carrierv generator effective to inject local intermediate carrier frequency into said intermediate frequency stage within the pass-band of said stage, the last-mentioned means being responsive to the reception of radio telegraph carrier to render said intermediate frequency carrier-generator ineffective to inject intermediate frequency carrier into said main receiver within the pass-band of the said intermediate frequency carrier stage.

5. A receiving arrangement for a telegraph receiving system comprising a main signal receiving channel, an auxiliary signal receiving channel, a local carrier oscillator for artificially injecting a carrier frequency into the main receiving vchannel when the received carrier is keyed off, a reactance modulator device for controlling the frequency of said local oscillator .said reactance modulator being controlled to the detected output of said auxiliary receiver, said main receiver being of the superheterodyne type having` an intermediate frequency stage and said local oscillator being arranged to generate a carrier lfrequency which is within the pass-band of said intermediate frequency stage but is different from the normal intermediate frequency of said main receiver when receiving keyed-on telegraph radio signalsand a beat frequency oscillator is connected to the detector stage of said main receiver to produce two `different .audio frequency signals correspondingy respectively `to the reception of a keyed-on and keyed-off radio telegraph signal.

y REYNOLD S. CHAPIN.

REFERENCES CITED The following references are of record in the le of `this patent:

UNITED STATES PATENTS Number Name Date 1,740,833 Ranger Dec. 24, 1929 2,125,953 Prochnow Aug. 9,1938 .2,316,017 Peterson Apr. 6, 1943