US2223431A - Means for touching up radio photographs - Google Patents

Description

J. E. SMITH MEANS FOR TOUCHING UP RADIO PHOTOGRAPHS 3, Filed Aprjil 20. 1939 :Si i i5 minar/VIV mma/rdn! mannaro@ mom/avrai l//V Z/ 4/ 6/ que.' I L I 5 afar/nn inviati AAAAAAA ATTORNEY.

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Patented Dec. 3, 1940 PATENT OFFICE MEANS FOR TOUCHING Ur RADIO i PHOTOGRAPHS James Ernest smith, Brooklyn, N. Y., assigner to Radio Corporation of America, a corporation of Delaware Application April 20, 1939., Serial No. 269,055

` 2 claims. (c1. 17a- 6.7)

This invention relates to photo radio reception.

In facsimile andfother photo radio transmitting systems 'the received signal often fades to, and below, the noise level during adverse multipath effectsin the upper atmosphere. The effects Vappear as pronounced'streaks in the received picture.` These streaks are either white or black, .depending upon the polarity of modulation. It is an object of my .invention to touch up the streaks in receivedV picturesldue to fading and Another object of my invention is to add local indications that convert the' white or black streaks in fading effects to gray so 'that they are not particularly noticeable.

Other Objectswill appear in the following description, reference being had to the drawing in which:

Fig. 1 is a block vdiagram illustrating a photo radio transmitter.

` Fig. 2 isia block and diagrammatic illustration of a receiving4 systemj employing my invention.

Fig.' 3'v shows graphs' illustrating principles of my invention. 7 f

Fig. 4 shows the voltage attenuation curve of the demodulator.

While my invention is useful with other forms of modulation I have illustrated it in connection with facsimile and other photo radio systems in which themodulations are produced by Varying the frequency of the carrier.`

Referring to Fig. 1, scanning device I has its varying output feeding into modulator 2 varying la sub-carrier frequency produced by low frequency generator 3. The varying frequencyfoutput containing the picture modulations pass into modulator 4 which varies the amplitude of radio frequency generator 5. Theoutput of modulator 4 passes into transmitting apparatus 6 and the signal is radiated by antenna 'I. 'Ihe scanning apparatus` I, frequency modulator 2, generators 3 and 5, amplitude modulator 4, transmitting apparatus 6 and antenna 'I may be of any desired form and the details of these are no par-t of my invention. Consequently they are shown and described only generally for a clearer understanding of my improvement which resides particularly in the receiving system. At the receiver end of the system the modulated'signal is received on antenna 8 and is amplied, detected and further amplified by the receiving apparatus 9. The output of receiver 9 therefore consists of the variable subcarrier frequency which `contains the frequency modulations imposed at the distant transmitter.

In general this also will contain modulations and fade-outs produced by static and other atmospheric causes. This low frequency output from receiving apparatus B passes into limiter I0 which cuts off portionsof the negative and positive halves of .the waves and thus eliminates the amplitude modulations produced by fading.' Complete fade-outs, or fade-outs that descend into the noise level, are not eliminated by limiter I0 and it is here that my improvement enters. output of limiter Ill is fed into a switching device II which preferably is` of the electron type described in my joint application, Serial No. 270,332, led April 27, 1939. The particular type of switch forms no part of my invention claimed l5 herein randtherefore to simplify `the disclosure i and aid in its understanding I have illustrated the switch I I 4diagrammatically only, but it would be understood that the `details of this switch will not beof the simple type actually disclosed. As 20 Ihave thus illustrated it, the output of the limiter I0 has control lines I3'feeding into control coil I4 and output lines VI 5, the continuity of which is controlled byswitching device Itunderv control of coil.I4'. The switching device I6 also controls 25 the continuityof local generator IIwhich produces thetouching Iup energy that eliminates the-white or blackstreaks caused byffading; as previously referred to. The output lines I8 from the switch II are connected to a'frequency de- 30 modulator converter I9 which may be of any `sort but for simplicity of disclosure I have shown it as a high pass lter containing series capacity and shunt inductance. The output of the converter passes into 'appropriate rectifying and re- 35 cording apparatus generally indicated at 2t. The receiving, detecting and amplifying apparatus 9 and the rectifying and recording apparatus 20 may be of any sort as these devices are old and well known. The limiting apparatus I0 may 40 also be -of any desired type but preferably it would be that shown in my joint application above referred to.

The operation of the 'system will be as follows:

The scanning apparatus will modulate the sub- 45 carrier frequency of generator 3 and 6 and the varying frequency output will amplitude-modulate the radio frequency carrier 5. 'Ihe subcarrier may be of any desired low frequency but a band within the range of 800 cycles to 2000 50 cycles mentioned in my joint applicati-on above referred to will be found satisfactory.

The output of modulator 4 passes into the transmitting apparatus 6 at the transmitting statien and is radiated by antenna I. The antenna 55 The 1 Cil 8 of the distant receiver in Fig. 2 will receive the modulated radio frequency carrier and this will be appropriately amplied at radio frequency, detected and amplified at audio frequency by the receiving apparatus 9. The output of this receiving apparatus is illustrated by graph A in Fig. 3, where the varyingk frequency of the modulated sub-carrier is clearly indicated. The fading effects are also indicated in this graph and between the points a and b it will be noted that substantially a complete fade-out has occurred; When the wave is passed through the limiter l the output will be as indicated by graph Bof Fig. 3. This of course has the variable frequency present in graph A but thepeaks havev been eliminated by passage through this device, but ythe wave is substantially completely blocked out betweenV the lines a and b, asin-'graph A. When ythis portion of the wave reaches the .switch ll the control device typified by Ill,r I6, will switch out the control lines 'l5 from limiter vI0 ,and will switch in the local oscillatorl1. This local oscillator will therefore fill in the graph-'at al with energy of the sameamplitudre ,and constant frequency 'as'indicated Obviowlylimiter Ilor another limiter can be placed after the switch Il amplitude for the local energi7 if desired so that'the output will have the same as well as that coming from the receiver.

If the upper limit of the modulation band F2 (Fig. 4) is 2000 cycles, and the, lower limit F1 is 1000, then the frequency of local oscillator Il will be adjusted to have a frequency of Fo substantially half way between these two values. This means ythat when the fade-out occurs as between the lines a, b, in graph A instead of having a white streak or a black streak, asthe vcase maybe, there will be a gray portion which is neutral and `will be substantially unnoticeable.

As soon as the point B is reached, the voltage,

in coilfd will be such as to lthrow the switch I6 to pass the energy in lines I tothe frequency demodulator I9 and interrupt the source.v

In this way as the ,signal fades out or into the noise level instead `ofthe blackxork white. streak in any particular type of recorder, agray portion will beproduced that has a less harsh'orfpleasing appearance. In other words, my 'improvement vautomatically touches up the defects of the recorded picture somewhat analogous to the touching up of a picture by a photographer, but of course it is done at high speed by the electron type of switch and it is entirely automatic. Instead of using my improvement with frequency modulated signals which areV converted into varying amplitude signal voltages V1, Vo V2, by the varying frequencies, as indicated in"`Fig.4, it will be quite apparent that the same effect can be produced when variable amplitude modulation is produced by the scanning apparatus, as the constant output and constant frequency of local generator Il would still produce a medium amplitude that would produce gray in the picture.

In disclosing my improvement I have necessarily referred to particularl apparatus but this has been by way of example only and various modifications may be used without departing from the spirit of the invention.

Having vdescribed my invention, what I claim is:

l. In signalling apparatus, a source of frequency modulated signal waves, a local source of oscillations having constant frequency intermediate the upper and lower limits .ofthe frequency modulation of the signal waves, means .for limiting the amplitude ofthe frequency .modulated waves to eliminate spurious amplitude increase, and means to demodulate the frequency modulation of the signal waves when the signal strength is above a predeterminedfvalue and to demodulate the constant frequency modulation of the local source when the signal is therebelow.

2. In signalling apparatus, asource of frequency modulated signal waves, a' demodulator for converting the rfrequencymodulation into amplitude modulation, a local source of oscillations having a constant frequency intermediate the upper and lower limits of the frequency modulation of the Ysign-alwaves, means for limiting the amplitude of the 'frequency modulated waves tol eliminate spurious amplitudeincrease,

and means for connecting therdemodulator to the limiter to receive the signal wave whenit is above a predetermined amplitude and to the local sourcev

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