US2293148A

US2293148A - Television system

Info

Publication number: US2293148A
Application number: US380808A
Authority: US
Inventors: Ray D Kell
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1941-02-27
Filing date: 1941-02-27
Publication date: 1942-08-18
Anticipated expiration: 1959-08-18

Description

Aug. 18, 1942.

. R. D. KELL TELEVISION SYSTEM med Feb. 27, 1941 2 Sheetvs-Shneet 1 SY/VC.

GENERHTOH :Snvehtor Eazy D. Kell Gttorneg ug. 1.8, 1942.I R. D; KELL TELEVISION SYSTEM v2 Sheets-Sheet 2 4Filed Feb. 27, 1941 Ray alfeu vun E --HllllhA i the transmitter.

transmitting a composite signal consisting of Patented Aug. 1942 TELEVISION SYSTEM Ray n. neu, mamada, N'. J., signor to naam Corporation of America, a corporation of Deh-- Application February .27, 194'1, Serial No. 380,808

, y 70mm. (ci. 11s-69.5)

My invention relates to the transmission of television pictures and particularly to the transmission of pictures originating at a point remote from the main television transmitter.

In transmitting television pictures it is necessary to transmit synchronizing signals along with the picture signals in order to synchronize the scanning at a receiver with the scanning at This is usually accomplished by picture signal and of recurring line frequency and frame frequency synchronizing pulses, a

line frequency pulse occurring at the end of each,

scanning line and a frame frequency synchronizing pulse occurring at the end of each vertical deflection. v

The main television transmitter unit of a television system includes a synchronizing pulse generator for producing the above-mentioned line frequency and frame frequency synchronizing pulses. These pulses are mixed in the proper time relation with the picture signals originating at .the main transmitter unit.

without the necessity of generating synchronizing or driving pulses at the remote unit.

In practicing the invention, picture signals are transmitted'from a portable pickup unit over a cable or wire line to the main transmitter'unit. synchronizing pulses for controlling the deiiection of the cathode ray in the pickup tube are` transmitted over this line from the synchronizing pulse generator at the main transmitter unit to the portable pickup unit where they preferably Vare passed through a picture separating circuit and then applied to the horizontal and vertical deflecting circuits of the pickup tube.

`In one embodiment of the invention, the connection between units is a coaxial cable which has a non-reflecting termination at each end, that is, it is terminated in its surge impedance. As a result, a picture signal only is transmitted over the cable from the portable pickup unit to the main' transmitter unit, this picture signal being .delayed acertain amount by its passage through the cable.

It will be understood that this main unit may consist of apparatus which is rather widely separated as in the case of a transmitter in one building and the studio in another building several blocks away. In this case, it is the practice to have the synchronizing pulse generator located adjacent; to the studio.

When it is desired to pick up a television pic- Y ture at some remote point,\ as for example, when it is desired to televise a baseball game, it has previously been the practice to utilize a portable transmitter or pickup unit which includes a synchronizing pulse generator. Such a generator supplies synchronizing pulses for driving or controlling the deflection of the cathode ray in the pickup tube of the portable unit. and it also supplies synchronizing pulses which are mixed with the picture signal in the portable unit for transmission to the main unit. .The resulting lcom-V posite signal, after being transmitted either over a radio link or overa cable or wire line to the main transmitter, is caused to modulate the carrier` wave of the main transmitter. This use of a pulse generator at a portable pickup unit obvlously complicates the design.

, It is an object of the `'present invention to simplify the apparatus which is required forthe pickup cfa picture at a remote point.

A further object of the invention is to provide a means for and amethod of transmitting picture signals from a remote pickup unit over a wire line or cable to `a main transmitter unit At the main transmitter unit, the synchroniz' ing pulses which would normally become mixed with the picture signal are balanced out and there is mixed with the delayed picture signal the desired synchronizing pulses which have been delayed the same amount as the picture signal.

Thus there is produced the desired mixture of picture signal and synchronizing pulses for modulating the main radio transmitter.

In another embodiment of the invention the cable is so terminated at the portable pickup unit that a portion of the synchronizing pulse voltage which is transmitted over the cable is reflected back to the main transmitter unit wherebythere is transmitted vfrom the portable pickup unit to the main transmitterl unit the desired mixture of picture signal and synchronizing pulses. In this case also, it is necessary to balance out at the main transmitter unit the undelayed synchronizing pulses which would otherwise become mixed with the picture signal. The invention will be better understood from the following description taken in connection with the accompanying drawings, in which Figure 1 is a circuit and block diagram of a4 television transmitter system embodying my invention; and A l Figure 2 is a circuit and block diagram of another embodiment of the invention.

Referring to Fig. 1, `the' television transmission system comprises ay main transmitter unit and a portable pickup unit as indicated by the legends, these two units being connected by a y impressed upon -chronizing pulses appearing coaxial cable in the particular example illustratcd.

The main transmitter unit, as previously mentioned, may consist of a main radio transmitter containing some o! the terminal equipment and a several blocks away and containthe terminalequipment, there line or the like connecting the cerned, this equipment, comprising the main transmitter unit, may be considered as located at one point. It comprises a radio transmitter -at the remote point.

Theportablepickup unit c onprises a suitable pickup device or vcamera I6 which preferably 'comprises a cathode ray pickup tube such as the well known Iconoscope, or a low velocitybeam pickup .tube such as that described in Patent No. 2,213,175, issued August 27, 1 940, to Iams et al.

The'portable pickup unit also includes horizontal and vertical deiiecting circuits I1 and IB for applying the desired saw tooth waves tothe cathode ray pickup tube for effecting the desired The synchronizing pulses y which have been transmitted over the cable are suitably amplified by means of an ampliiier 20 and then applied to a synchronizing separator circuit 2l which is so designed as to prevent the passage of picture signals therethrough. pass through to the deilecting circuits I1 and I8 whereby the scanning in the camera IB is controlled by the synchronizing pulse generator I I at the main transmitter; y

The picture signal output of the pickup camera I6 is amplified by an ampliiier 22 and supplied to an output tube 23 of the cathode follower type. The output impedance of the cathode follower 2l has the correct resistance for so terminating the cable I4 that it is a non-reflecting termination.

The picture signals appearing across the cathode resistor 24 are supplied through the cable I4 to an amplifier 26 in the main transmitter unit.

It will be evident that, at the portable unit, the'picture signals supplied from the output tube 23 are unavoidably impressed upon the input circuit of the amplier tube 20 as well as. upon the cable li. It is for this reason that the synchronizing pulse separator 2I is desirable for preventing these picture signals from being impressed upon the deilecting circuits I1 and I8.

It will also be evident that, at the main transmitter unit, the synchronizing pulses supplied from the output tube I3 to the cable Il are also the input circuit of the amplifier tube 26. Since these synchronizing pulses have been delayed a negligible amount, there being only the delay introduced by the ampliiier I2- I 3, it is apparent that they must be removed from the delayed picture signal appearing at the input circuit ofthe tube 26, the picture signal having been delayed a substantial amount by the This is accomplished by .balancing out the synat the input circuit of tube 26 by means of synchronizing pulses of opposite polarity which may be fed over a con- So far as the present invention is con-- are suitably amplied as by means of amplifier I lThe synchronizing pulses escano ductor 3| to an

amplifier

22, 32 and 23 having a common plate resistor I3.

With the clrcuitthus -far described there would appear across .the common plate resistor 33 -only the rdelayed picture signal. The desired mixture of picture signal and synchronizing pulses is obtained by taking synchronizing pulses from the the amplifier tubes output of a suitable amplifier'stage such as the amplifier stage I2 and feeding them through a delay network 3d to an amplifier tube 3B which has as its plate resistor the above-mentioned common plate resistor 33. By means of the delay network 34, the synchronizing pulses may be delayed exactly the same amount as the picture signals whereby these delayed synchronizing pulses and the delayed picture signal are combined at the output resistor 3,3 to produce the desired composite signal for transmission to a radio receiver by means of the transmitter I6.

It will be noted that in the example illustrated, the output tube I3, like the output tube 23, is of the cathode follower-type, the output impedance I5 of the tube having the correct resistance to provide a non-reflecting termination for the cable lli. It will be understood that these output tubes are not necessarily of the cathode follower type, although thisA type vof output tube circuit has certain engineering advantages.

In Fig. 2 there is illustrated an embodiment of the inventionin which the cable or wire line has a reecting termination at the portable pickup unit. In Figs. 1 and 2, like parts are indicated by the same reference numerals.

The portable pickup unit shown in Fig. 2 is the same as that shown in Fig. l except that the cable vterminating cathode follower 23 is given a different resistance value whereby the synchronizing pulses which are supplied over the cable II fromv the output tube I3 are partially reflected. The result is that there is transmitted over the cable from the portable pickup unit to the main transmitter 4unit the desired correct mixture of picture signals `and synchronizing pulses.

In this composite signal the picture signal and the synchronizing pulse have been delayed the same amount even though the picture signal passes through the cable only once, whereas the reflected synchronizing pulses pass through the cable twice. This'is because the picture signal at the output of the camera I6 has been delayed by an amount equal to the amount the synchronlzing pulses have 4been delayed by. passingfrom resistor 33 without any of the main unit to the portable unit since it is these delayed synchronizing pulses which are controlling the horizontal and vertical deflection in the camera pickup tube.

At the main transmitter unit it is necessary to balance out those undelayed synchronizing pulses which are fed from the output tube I3 to the amplifier tube 26. This is accomplished in vthe same manner as previously described, synchronizing pulses being fed through the amplifier tube 32 to balance out the undesired synchronizing pulses of oppositevpolarity appearing in the common plate resistor 33. The result is that picture signals and synchronizing pulses mixed in the proper time relation appear across the plate the synchronizing pulses of the wrong time relation being present.

In this embodiment of the invention, as in the.

preceding embodiment, the end of the cable Il at the main transmitter unit preferably is terminated in its surge impedance to avoid reflection.

From the foregoing description it will be apparent that by employing my invention, thev 4pickup unit, means unit fol-

amount of apparatus in the portable pickup is substantially less than that required when lowing the usual remote pickup technique.

` I claim as my invention:

1. In a television system, a main transmitter unit, a remote pickup unit, a wire line connecting said units, a synchronizing pulse generator located at said main unit and connected to transmit synchronizing pulses over said line to said in said pickup unit for transmitting picture signals over said line to said main unit, and means at said main unit for balancing out certain undelayed synchronizing pulses which would otherwise become unavoidably mixed with said picture signal.

2. In a television system,v -a main transmitter unit, a remote pickup unit, a wireline connecting said units, a synchronizing pulse generator located at said main unit and connected to transrmit synchronizing pulsesoversaid line tu said pickup unit, a cathode raypickup unit at said remote unit and connected to transmit picture signals over said line to 'said main unit. means comprising deficting circuits for causing the cathode ray of said tube to scan a certain area, a picture' separating circuit located between said deilecting circuits and the junction point of said wire line and the output connection of said cathode ray pickup unit. and means at said main unit for balancing out undesired synchronizing pulses whereby the output oi' said 4main unit consists only of picture signals and synchronizing pulses occurring in the desired time relation.,

3. In a television system,` a' main transmitter unit, a remote pickup unit; a wire line connecting said units and having a nonreiiecting termination at said remote unit, -a synchronizing pulse generator located at said mainl unit and connected to transmit synchronizing pulses over said line to said pickup unit, means in said pickup unit for transmitting picture signals over said line to said main unit. means at said main unit for balancing out certain imdelayed synchronizing pulses which would otherwise become unavoidably mixed with said picture signal, andmeans at said main unit for mixing ldelayed synchronized pulses with the delayed picture signal.

4. In a television system, a main transmitter unit, a remote pickup unit, a wire line connecting said units and having a reflecting termination at said remote unit, a synchronizing pulse generator located at said main unit and connected to transmit synchronizing pulses over said line to said pickup unit, a cathode ray pickup unit at said remote unit and connected to transmit picture signals togetherwith reflected synchronizing pulses over said line to said main unit. means comprising deiiecting circuits for causing the cathode ray of said tube to scan a certain area, a picture separating circuit connected to prevent picture signals from passing into said deilecting circuits. and means at said main unit for balancing out undesired synchronizing pulses whereby the output of said main unit consists only of picture signals and synchronizing pulses. occurring in the desired time relation.

5. In a television system, a main transmitter unit, a remote pickup unit, a wire line connecting said units, a synchronizing pulse generator located. at said main unity and connected to transmit synchronizing pulses pickup unit, means in said remote pickup unit for transmitting picture signals over said lineto said main unit, a picture signal amplifier at said main unit, said amplifier lhaving an input circuit connected to said wire line to receive said picture signals whereby' undelayed synchronizing pulses areunavoidably impressed upon said ampliiler, and means at said main unit forhalanc-v ing out said undelayed synchronizing pulses.

6. The-invention according to claim 5 wherein,

said wire line has a nonreiiecting termination at said remote pickup unit.

7. lI'he invention according to claim 5 wherein said wire line has a tion at said remote pickup unit.

RA'Y D. KELL.

overV said line to said Partially reflecting termina--