US2180944A - Television and like receiver - Google Patents

Description

Nov. 21, 1939.

TELEVISION AND LIKE RECEIVER Filed Jan. 22, 1936 INVENTO .A. L/ 5 BY 7%? ATTORNEY -A. A. LINSELL 2.180944 Patented Nov. 21, 1939 UNITE 2,180,944 TELEVISION AND LIKE RECEIVER Alfred Aubyn Linsell, London, England, assignor to Radio Corporation of America, a corporation of Delaware Application January 22, 1936, Serial No. 60,162 In Great Britain March 11, 1935 5 Claims.

This invention relates to television and like receivers and more particularly to such receivers wherein picture reproduction is efiected by means of a cathode ray tube reproducer.

It is well known in radio receivers generally and more particularly in radio receivers employing so -called automatic volume control means, to provide an indicator for indicating the correctness of tuning of the receiver, Indeed for receivers of the automatic volume controlled type, the provision of such an indicator is especially desirable since it is difiicuit to tune such a receiver by ear owing to the action of the automatic volume control means. Many different forms of tuning indicator have been proposed among these proposals being that of using as indicator a small cathode ray tube the cathode ray beam of which is arranged to be deflected across a fluorescent screen in accordance with received signal strength so that when the receiver is accurately tuned to incoming signals the deflection of the beam is a maximum.

The present invention also proposes to employ a cathode ray tube as a tuning indicator, but according to the said invention the cathode ray tube which is employed as a tuning indicator is the normally provided picture reproducer tube of a cathode ray tube television or like receiver, means being provided whereby the same tube can perform the dual function of tuning indicator and picture reproducer.

The invention is accordingly economical to embody since the one cathode ray tube is utilized for the two functions, while, as regards the function of tuning indication, the invention has the advantage of enabling an accurate and easily readable indication to be given since the cathode ray tube is the normal picture reproducer tube and is thus a relatively large device.

The invention is illustrated in the accompanying drawing which shows diagrammatically various embodiments thereof, wherein Fig. 1 is one form of arrangement for carrying out the aims and objects of the invention;

Fig. 2 shows ways and means to prevent damage to the fluorescent screen of a cathode ray tube when the tube is being used as a tuning indicator;

Fig. 3 shows a modification securing the same effect as the arrangement of Fig. 2;

Fig. 4 illustrates a still further modification; and

Fig. 5 represents a still further modification where a separate screen is used for tuning inicat nt Referring now to the drawing and first to Fig. 1 thereof where the invention is applied to a cathode ray tube television receiver wherein radio reception is effected upon the superheterodyne principle, incoming modulated carrier Wave signals received upon an aerial l are subjected at 2 to such high frequency amplification as is desired and the amplified resultant mixed with locally generated oscillations from an oscillation generator 3 in the input circuit of the usual 10,

first detector or mixer stage 4 of a superheterodyne circuit. The anode or output circuit of this stage includes in series with the primary of the usual intermediate frequency coupling transformer I.T. (whose secondary feeds into the usual 1 5 intermediate frequency amplifier 5) a resistance 8 which is in series between the said transformer primary and the source ll of anode potential for the first detector valve 4 the series combination of resistance and anode source being shunted 29;}

by a condenser 9. The intermediate frequency amplifier is'followed by the usual second'or demodulating detector 6 by which the original modulation e. g. sound signals representing-sound accompanying the transmitted picture, is reob- 2M5:

tained to be reproduced e. g. by a loudspeaker I. A variable tapping point upon the source H, valve 9, and the junction point of the resistance 8 with the primaryof the transformer LT. are

connected respectively to two contacts l0, I2, of

a double pole double throw switch device I3 two other contacts I1, l8, of which are connected to the normally provided generator source (not shown but which may be of any desired type such as shown by British Patents 394,597; 401,990; 35;,

402,134; 402,629; 403,283 or U. S. 1,613,954 or. many other patents and/or publications) giving saw-toothed or other similarly shaped potential or current waves for producing one component of scanning of the cathode ray beam in the nor- 40 to opposite'terminals of one of the normally pro- 45 vided co-ordinate beam deflector means of the tube, e. g. as shown to one pair l4, I5, of electrostatic deflector plates of the tube. The other connections of the cathode ray tube may be as well known, per se, and as these form no part of the 50 present invention they need not be herein described. The connections of the double pole double throw switch device l3 are such that in one position (the upper position as shown) potentials setup across theresistance 8 plus a fixed,

' the normally provided coordinate deflector means potential from source I I are applied to the deflector plates l4, I5, of the tube I6, so that when the said switch device is in this position the tube acts as a tuning indicator. When the switch device is in the other position the appropriate source (not shown) of saw-tooth waves is connected to the deflector plates M, l5, so that when the said switch device is in the said other position the tube operates as in the normal way for picture reproduction. For tuning, the switch device is thrown over into the first mentioned position and for picture reproduction it is thrown back into its second mentioned position.

Adjustment as to the extent of deflection in the cathode ray tube when the tube is employed as a tuning indicator may be obtained by moving the variable tapping point upon the source I I;

Although in the embodiment illustrated in Figure 1 the potentials for securing deflection when the tube is employed as a tuning indicator are obtained from the plate circuit of the first detector valve l, obviously potentials which may be used in precisely similar manner may be derived from any part of the receiver where a component corresponding to received carrier frequency signal strength is present.

If desired instead of applying the potentials which are to give tuning indication to one of of the tube, tuning indication may be efiected through the medium of a small electro-magnet suitably positioned adjacent the cathode ray beam so as to be able to deflect the same, and having a winding which is energized (when the switch device is in the tuning position) in dependence upon received signalstrength. When the switch device is in its other position the electro-magnet winding is open circuited. In this way any need to alter the connections of the normal coordinate deflector means of the tube is avoided.

In order to avoid risk of damage to the fluorescent screen of the cathode ray tube, due to the cathode ray beam impinging for a long time upon one spot thereof when the tube is being employed as a tuning indicator, it is (as illustrated in Figure 2) preferred to constitute the double pole double throw switch device by a'set of push button operated contacts so arranged that except when the push button (B) is held down the cathode ray tube is connected as in the normal way for picture reproduction i. e. circuit is made between contacts I1 and I8 and plates Id and I5 the push button being spring biased as by a spring I9 so that it has to be held down against the spring all the time the tube'is to be used as a tuning indicator.

In another arrangement in which risk of damage to the fluorescent screen is also avoided, the tube is provided as represented in Figure 3 (which is an end view of a tube) with an auxiliary strip ASof fluorescent material below (or by the side of) the normally provided fluorescent screen FS which is scanned during picture reproduction. In this case the circuit arrangement may be such as before, except that means are provided for applying to the co-ordinate deflector means other than that to which the carrier component is applied for tuning indication, a potential or current such as will deflect the cathode ray beam to strike the auxiliary screen. Thus with this arrangement' when the tube is to be used as a tuning indicator a predetermined bias is applied to one co-ordinate deflector means and potentials corresponding to received carrierstrength are applied to the other. Except when the tube is thus in use as a tuning indicator the potentials applied to the deflector means are the normal saw-toothed scanning potentials for causing the cathode ray beam to explore the normal picture screen of the tube. Alternatively, instead of applying bias to one co-ordinate deflector means so as when tuning to deflect the cathode ray beam on to the auxiliary screen, the same result can be achieved by using a small permanent magnet which is mechanically or otherwise interlinked with the switch device so that when said switch is in the position in which it allows the tube to be used for tuning indication, the magnet is moved to such a position that it influences the cathode ray beam to deflect it to strike the auxiliary screen.

In a still further modification which is represented schematically in Figure 4 and which is a variant of the last described embodiment, the tube again has two fluorescent surfacesFS, AS, at its end, one (FS) being the usual picture screen and the other (AS) an auxiliary strip like screen for use for tuning indication purposes. In this embodiment, however, the tube is provided with two electron guns 20, El one (2i!) positioned to cooperate with the normal picture screen FS and the other (H) positioned to co-operate with the auxiliary screen AS. The two guns may be entirely separate as shown, or they may be constructionallyunited; e. g. there may be a common cathode and an anode member with two separate apertures. When the tube is required to be used as a tuning indicator the potentials from a suitable circuit in the receiver are applied to a pair of deflector plates 22- (or a deflector coil) associated with the gun 25 which directs its beam towards the auxiliary screen. The other gun has associated therewith the usual television signal control grid and co-ordinate deflector means for causing scanning over the main or picture screen of the tube. With this arrangement the tuning indicator may be left in use all the time since it can operate independently of picture reproduction. Further, in such a case the auxiliary screen AS may be constituted by fluorescent material which is deposited on a thin metal strip connected to the cathode of the associated electron gun 2i through a circuit including a direct current permeable impedance 23 and a source 2 2 of potential in series and the voltage drop set up across this impedance (or-a part thereof) may be used for automatically controlling the gain of the receiver which is to be tuned in accordance with the indications given on the auxiliary screen. In such a case the accelerating anode 25 associated with the gun 2| should be connected to the usual source of controlling potential provided for the automatic volume control action. It will be appreciated that the voltage drop set up across the impedance 23 will (once the receiver has been tuned in) vary in dependence upon incoming'signal strength and the said voltage can accordingly be applied in any manner well known, per se, for gain con- 1 trolling purposes e. g. as grid bias to an amplifier valve'or valves, so as to increase the receiver gain when the incoming signal strength decreases and vice versa. In Figure 4, for the sake of convenience in representation, the end of the tube is shown at right angles to its correct position.

Figure 5 shows a still further embodiment wherein the tube is provided with a separate screen for tuning indication. The tube of Figure has an electron gun 26 with two electron outlet apertures 26a 262) preferably arranged as shown to give two perpendicular cathode ray beams one of which passes through aperture 26a and is employed as in the usual way for picture reproduction and the other of which passes through aperture 26b to a screen AS on the side of the neck of the tube and upon which tuning indication is given. Between aperture 26b and screen AS is a grid 21' which is connected, either permanently or through a switch (not shown) intended to be closed while tuning, to a suitable point in the receiver-e. g. the live end of resistance 8 of Figure 1whose potential varies with incoming signal strength. Accordingly the brightness of the spot formed on the screen AS will depend upon tuning adjustment tuning idication being thus given in terms of brightness of the fluorescent spot instead of in terms of the position thereof. If position indication rather than brightness indication is preferred the grid 21 may be replaced by suitable deflecting plates connected to be energized in dependence upon tuning adjustmente. g. as are the plates l4, N3 of Figure 1. In this case of course the screen AS must be big enough to accommodate the deflection.

Having now described the invention, what is claimed is:

1. In a television apparatus, means for receiving separate image and sound signals on related carrier waves, means for simultaneously tuning the receiver to both carriers, means for separating the sound signals from the image signals, a cathode ray tube having means therein for developing a cathode ray beam and a target area upon which the developed beam produces luminous effects, means for controlling the intensity of the developed cathode ray beam in accordance with the received image signals, means for causing a traversal of the controlled cathode ray beam across the target area in two mutually perpendicular directions according to a pre-established pattern of traversal to produce on the target area indications of the received image signal intensity, means for deflecting the developed cathode ray beam in only one of the two directions of deflection in accordance with the tuning of the received sound signals to indicate proper tuning of the image and sound signals, and a switching means for selecting in one position the reproduction of image signals on the target area and in a second position an indication of the tuning of the receiver.

2. In a television receiving apparatus, means for receiving separate image and sound signals of related carrier waves, means for simultaneously tuning the receiver to both carriers, a cathode ray tube having a luminescent electro-optical image producing screen surface and an auxiliary screen surface positioned adjacent the first-named screen surface, an electron beam developing means for causing luminous indications to develop upon the tube screens at the point of beam impact, means for causing the developed cathode ray beam to traverse the image screen according to a pre-established pattern of traversal in each of two mutually perpendicular directions, means to control the intensity of the developed cathode ray beam upon the tube screen in accordance with the intensity of received image signals, means for controlling the position of the developed cathode ray beam upon the auxiliary screen in accordance with the tuning of the received sound signals to indicate proper tuning of the image and sound signals, and means to select between image signal indications and tuning indications.

3. The apparatus claimed in claim 2 comprising in addition a voltage source and impedance element serially connected between the electron beam developing means and the auxiliary screen, and means for controlling the gain of the receiver means in accordance with the current flow through the impedance.

4. In a television receiving device, means for receiving image and sound signals on separate carriers having a fixed spacing, means for simultaneously tuning the receiver to both carriers, a cathode ray tube having electron beam generating means and a fluorescent screen, means for producing visible indications of the received image signals on one portion of the screen, means for producing visible indications on another portion of the screen of the tuning of the received sound signals to indicate proper tuning of both carriers, and switching means to select in one position only image signal reproductions and in a second position only tuning indications whereby proper tuning of the receiver to the image and sound signals may be assured.

5. The apparatus claimed in claim 4 comprising in addition resilient means for normally maintaining said last named means in said one position whereby the image signals may be reproduced.

ALFRED AUBYN LINSELL.

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