US2240295A - Television receiver - Google Patents

Description

April 29, 1941. G. l. GRUNDMANN 2,240,295

TELEVISION RECEIVER Filed sept'. 29, 1937 Patented Apr. 29, 1941 24ans TELEVSIGN RECEIVER Gustave L. Grundmann, Westmont, N. J., assigner of America, a corporation to Radio Corporation of Delaware Application September 29, 1937, Serial No. 166,287-

(Cl. 17g- 5.8)

6 Claims.

My invention relates to television receivers and particularly to receivers designed for the reception of both pictures and sound.

In Patent No, 2,165,794, issued Juiy l1, i939, in the name of Ralph 'S'. Holmes and assigned to the Radio Corporation of America, there is described and claimed a television receiver which is designed to be used in combination with a short Wave broadcast receiver. By connecting the broadcast receiver to the intermediate frequency channel of the television receiver and by tuning the broadcast receiver to the intermediate frequency of the sound accompanying the incoming picture, this sound is reproduced by the broadcast receiver. This permits the design of a low cost television receiver.

It Vhas been found that when using a television receiver and a broadcast receiver of the superheterodyne type in combination as described above, certain, precautions should be taken or l voltage from the oscillator of the broadcastreceiver will feed into the television receiver and overload its Vsecond detector. Such overloading can be prevented by the use of a buffer sound amplifier through which signal is fed to the broadcast receiver but an additional amplifier vstage adds materially to the cost of a receiver.

vfor use with a broadcast receiver or the like con-` taining a frequency converting unit.

A further object of my invention is to provide an improved circuit for taking the sound signal from a television receiver.

In the preferred embodiment of my invention, I employ between the first detector and the first I. F. amplifier of the television receiver a band pass coupling filter or transformer unit of the type described and claimed in Patent No. 2,199,604, issued May 7, 1940, to Horace C. Allen and Gustave L. Grundmann, and assigned to the Radio Corporation of America. In this tran..- former unit the tuned primary circuit and the tuned secondary circuit are coupled by means of an inductance coil or other impedance unit such as a condenser common to the two circuits. The roadcast receiver is connected through a trap circuit to the high potential end of the above-mentioned inductance coil which will be .referred to hereinafter as the coupling coil.

The coupling coil and the circuit leading to the broadcast receiver are tuned to resonate et the I. F. sound carrier whereby sound signals are transferred efficiently to theV broadcast receiver. The trap circuit is tuned to the frequency of the oscillator in the broadcast receiver whereby voltage from this oscillator is not fed into the picture I. F. channel.

- The invention-vuil be best understood from the following description taken in connection with the accompanying drawing in which Figure lis a Ycircuit diagram of a preferred embodiment of my invention, and' Figures 2 and 3 are curves which are referred to in explaining'my invention.

Referring to Fig. 1 there is shownthe first detector tube' l0 and the first I. F. tube I l of my improved television receiver. The picture and sound signals on two separately modulated -carrier waves are supplied to `the first detector: l0 through a tunable selecting circuit l2 having a pass range wide enough to pass both modulated carrier waves. In the particular System being described, the two carriers are spaced 3.25 megacycles apart.

The tunable selecting circuit l2 may comprise two tunable circuits I3 and |11, the circuit I3 being a link circuit which couples the circuit lil to an input coil It. The 'coil I6 may be coupled through va transmissionline to a dipole antenna (not shown).

The first detector i8 may be of any suitable type such as a pentode 'having the screen grid and suppressor grid connected together for increasing the mutual conductance of the tube. A suitable operating voltage is supplied to these grids through a filter resistor Il provided with a filter condenser 1'3. The detector tube is selfbiased by means of a self-biasing resistor I9 in the cathode circuit, the resistor I9 being shunted by the usual bypass condenser 2l.

In order to convert the incoming modulated carrierY Waves'to I. F. signals, a tunable oscillator 22 is coupled in any suitable manner to the rst detector it; I'he vtuning condensers of the oscillator 22 and of the circuits I3 and l are ganged, as indicated by the broken lines, to permit tuning by the single knob 23.

In'the output circuit of the first detector la there appears the I. F. picture signal and the accompanying I. F. sound signal, it being desired to supply the I. F. picture signal to the first I, F. amplifier il and to supply the I. F. sound signal to a broadcast receiver indicated at 24.

The band pass coupling circuit between detector ill and amplifier Il comprises a tunable primary coil 2G, a tunable secondary coil 21 kand a common coupling coil 28. A blocking condenser 25 is connected between coils 26 and 2l'.

Plate voltage is supplied to the plate of detector tube I through a filter resistor 29, the coupling coil 28 and the primary coil 26. A lter condenser 3| is connected between the high potential end of resistor 29 and ground.

Biasing voltage is supplied to the control grid of I. F. amplifier tube through a filter resistor 32 and a grid resistor 33. A filter condenser 34 is connected between the high potential end of resistor 32 and ground.

The above-described coupling circuit includes a tuned primary circuit coupled to a tuned secondary circuit. The tuned primary circuit may be traced from ground through the relatively large capacity filter condenser 3|, the coupling coil 28, the primary coil 26, and through the tube capacity and distributed capacity indicated at 36 back to ground. Capacity 36 is the tuning capacity, the nal tuning adjustment being made by means of the coil 26 which has an adjustable magnetic core.

'I'he secondary circuit may be traced from ground through the filter condenser 3|, the coupling coil 28, the blocking condenser 25, the secondary coil 21 and through the tube input capacity indicated at 37` back to ground. Here the tuning capacity is the capacity 37, the nal adjustment being made by means of the coil 27 which has an adjustable magnetic core.

It will be understood that the primary and secondary circuits are so coupled and tuned as to pass the band of picture frequencies and to re.. ject signals at other frequencies, especially to reject the sound signals.

The picture signals only appear in the output circuit of the I. F. amplier and are supplied to other similar I. F. stages connected in cascade. The screen grid and the suppressor grid of the amplifier tube assuming it is of the pentode type, are preferably connected together through a resistor 38 wherebythe mutual conductance of the tube is increased without causing oscillations. It has been found that in an I. F. stage there are undesired oscillations ifY the resistor 38 is omitted.

Referring now to the circuit which supplies the sound signals to the broadcast receiver 24, it comprises a conductor 4| leading from the high potential end of the coupling coil 28, a parallel resonant circuit 142-43, a tuning condenser 44, and a conductor 46 connected to the antenna terminal of the broadcast receiver. The ground terminal of receiver 24 is grounded as indicated. Preferably the conductor 46 is provided with a grounded shield' 41. Instead of the conductor 46 and the ground connection indicated at the broadcast receiver, a twisted shielded pair of conductors may be employed.

It has been found that the broadcast receiver chassis should be connected directly to, that is, grounded to, the chassis of the television receiver, whereby there is no potential difference between the two chassis. Otherwise, the conductor transferring sound signal from the television receiver to the broadcast receiver, acting as an antenna, will pick up interfering signals, such as automobile ignition noise, and cause noise in the broadcast receiver output.v

The sound signal circuit is tuned to the frequency of the sound signals, 9.75 megacycles in the specic case illustrated, by adjusting the condenser 44. The rejection circuit 42--43 is tuned to the frequency of the broadcast oscillator,

10.21 megacycles in the specific case illustrated,

by adjusting the inductance of coil 43, this coil being provided with an adjustable magnetic core.

Thus the circuit which is series resonant to sound signals may be traced from ground, through filter condenser 3|, coupling coil 28, conductor 4 I, circuit 42-43 which presents an inductive reactance, tuning condenser 44, and through the conductor 46 and capacity between conductor 46 and shield 41 back to ground. It will be apparent that sound signals are transmitted efciently to the receiver input coil 48 and that the signal from the broadcast receiver oscillator is prevented by the trap circuit 42-43 from reaching the television receiver.

The action of the above-described circuits is illustrated by the curves in Figs. 2 and 3. The frequency response of the circuit as measured at the control grid of the I. F. tube is shown in Fig. 2. It will be noted that the sound signal at 9.75 megacycles falls to one side of the pass range for the picture signals. It may be noted that the dip in the curve at 9.75 megacycles is caused by the presence of the series resonant sound circuit, this circuit substantially increasing the rejection of sound signal in the picture channel.

'Ihe response characteristic at the broadcast receiver end of the conductor 46 is shown in Fig. 3. It will be seen that the response at the 9.75 megacycle sound signal is very good, while the response at the broadcast oscillator frequency of 10.21 megacycles is very poor.

From an inspection of the curves in Figs. 2 and 3 it will be apparent that, if the 10.21 megacycle signal from the broadcast receiver reached the television receiver, it would cause trouble, as this signal falls within the pass range of the picture signal amplier. The frequency of 10.21 megacycles for the broadcast receiver oscillator was selected for the purpose of illustration because it is common for such receivers to have an intermediate frequency of 460 kilocycles. Assuming that receiver 24 is designed for an I. F. of 460 k. c. and that the sound carrier is 9.75 megacycles, it is required that the oscillator in receiver 24 operate at 10.21 megacycles to give the required frequency difference of 460 k. c. where the oscillator is operating at a higher frequency than the incoming signal in accordance with usual practice.

While the broadcast receiver may be connected to a separate broadcast antenna for the reception of regular broadcast sound programs, it is preferred to provide means whereby the television antenna and transmission line may be utilized as the broadcast antenna.

Referring to Fig. l, the midpoint of the input coil I6 is connected to a switch arm 5| whereby the midpoint may be connected either to ground through a contact point 52 or to a conductor 53 through a Contact point 54.

The conductor 53 connects the contact point 54 to the conductor 46 whereby, when the switch arm 5| is in the dotted line position, the sound signals in the broadcast range are supplied from the dipole antenna and transmission line (not shown) to the broadcast receiver 24 over conductors 53 and 46.

Preferably a switch 56 is provided between conductor 46 and condenser 44, this switch being thrown to the dotted line position when switch arm 5| is in the dotted line position, for the purpose of disconnecting the circuit 4|, 42-43, 44 from the conductor 46 and thereby improving the eciency of the broadcast reception. If the cir- If the switch 56 is employed, it is preferred to y have it ganged with switch I asindicatedby the broken line 51. Also, switches 5|; and 55 should be ganged with the television receiver power switch 58 as indicated by the broken line 59. Thus, when the power switch 58 is turned on, the switches 5I and 56 are moved to the proper positions for combined picture andsound reception. When switch 55 isturned oiff the switches 5| and 56 are moved to the positions which cause the television antenna and transmission line to function as the broadcast receiver antenna.

I claim as my invention:

1. In a television receiver of the superheterodyne type having a first detector and an intermediate frequency amplifier for the reception of picture and sound signals, a band pass coupling network connected between said detector and said amplifier and having a pass range for passing the picture modulated intermediate frequency carrier wave substantially to the exclusion of the sound modulated intermediate frequency carrier wave, said network comprising a tuned primary circuit having a primary coil and a coupling impedance unit, and a tuned secondary circuit having a secondary coil and including said coupling impedance unit, and a circuit connected to the alternating current high potential end of said coupling impedance unit for supplying the sound modulated intermediate frequency carrier wave to a frequency converting unit having an oscillator therein, said circuit including a parallel resonant circuit tuned to the frequency of said oscillator, and means for making said circuit and said coupling impedance unit series resonant at the frequency of said sound modulated intermediate frequency carrier wave.

2. In a television receiver comprising a first detector and an oscillator coupled thereto for converting an incoming picture modulated carrier wave and an incoming sound modulated carrier wave to an intermediate frequency picture signal and to an intermediate frequency sound signal, said modulated carrier Waves having a certain frequency spacing, an intermediate frequency amplifier tube, a band pass coupling network connected between said detector and said amplier tube and having a pass range for passing the intermediate frequency picture signal to the exclusion of the sound signal, said coupling network comprising a tuned primary circuit including a coupling impedance unit and a tuned secondary circuit including said coupling impedance unit, and a circuit connected to the alternating current high potential end of said coupling impedance unit for supplying the sound signals to a frequency converting unit having an oscillator therein, said circuit including a parallel resonant circuit tuned to the frequency of the oscillator in said converting unit and a reactance unit in series with said parallel resonant circuit and having such reactance that said circuit and said coupling impedance unit are series resonant at the carrier frequency of said intermediate frequency sound signal.

3. In a television receiver of the superheterodynetype having a=rst detector andan intermediate frequency amplifierv for the receptionof picture and soundA signals, a bandi pass coupling network connected-between said detector and-said amplifier and having a pass range for passingfthe picture modulated intermediate frequency oarrier wave substantially to the exclusion ofthe sound modulated intermediate frequency carrier wave, said network comprising a tuned primary circuit having a primary coil anda coupling coil and av tuned secondary circuit having a secondary coil and including said coupling coil, and a circuit connected to the alternating current high potential end of said coupling coil for supplying the-sound modulated-intermediate frequency carrier wave to a frequency converting unit having an oscillator therein, said circuit including aparallel resonant circuit tunedv to the frequency of said oscillator and means for making said circuit and said coupling coil series resonant at the frequency of said sound modulated intermediate frequency carrier wave.

4. In a television receiver comprising a iirst detector and an oscillator coupled thereto for converting an incoming picture modulated carrier wave and an incoming sound modulated carrier wave to an intermediate frequency picture signal and to an intermediate frequency sound signal, said modulated carrier waves having a certain frequency spacing, an intermediate frequency amplifier tube, a band pass coupling network connected between said detector and said amplifier tube and having a pass range for passing the intermediate frequency picture signal to the exclusion of the sound signal, said coupling network comprising a tuned primary circuit having a primary coil and a coupling coil and a tuned secondary circuit having a secondary coil and including said coupling coil, and a circuit connected to the alternating current high potential end of said coupling coil for supplying the sound signals to a frequency converting unit having an oscillator therein, said circuit including a parallel resonant circuit tuned to the frequency of the oscillator in said converting unit and a condenser in series with said parallel resonant circuit and having such capacity that said circuit and said coupling coil are series resonant at the carrier frequency of said intermediate frequency sound signal.

5. In combination a television receiver and a frequency converting unit, said converting unit including an oscillator, said receiver comprising a tunable selecting circuit for selecting a picture modulated carrier wave and its accompanying sound modulated carrier wave, means including a first detector for converting the output of said selecting circuit to an intermediate frequency picture signal and to an intermediate frequency sound signal, an intermediate frequency amplifier, a coupling network connected between said first detector and said amplier and having a pass range for passing the intermediate frequency picture signal substantially to the exclusion of the sound signal, said network comprising a tuned primary circuit having a primary coil and a coupling coil and a tuned secondary circuit having a secondary coil and including said coupling coil, and a sound signal circuit connected between the alternating current high potential end of said coupling coil and an input terminal of said frequency converting unit, said sound signal circuit including a parallel -resonant circuit tuned to the frequency of the oscillator in said converting unit and also including means for making said coupling coil and said sound signal circuit series resonant at the frequency of the intermediate frequency sound signal.

6. In combination, a television receiver and a frequency converting unit, said converting unit including an oscillator, said receiver comprising a tunable selecting circuit for selecting a picture modulated carrier wave and its accompanying sound modulated carrier wave, means including a first detector for converting the output of said selecting circuit to an intermediate frequency picture signal and to an intermediate frequency sound signal,an intermediate frequency amplifier, a coupling network connected between said first detector and said ampliiier and having a pass range for passing the intermediate frequency signal substantially to the exclusion of the sound signal, said network comprising a tuned primary circuit having a primary coil and a coupling coil and a tuned secondary circuit having a secondary coil and including said coupling coil, and a sound signal circuit including a conductor having a grounded shield connected between the alternating current high potential end of said coupling coil and an input terminal of said frequency converting unit, said sound signal circuit including a parallel resonant circuit tuned to the frequency of the oscillator in said converting unit and also including means for making the circuit including said coupling coil, said sound signal circuit and the capacity between said conductor and said shield series resonant at the frequency of the intermediate frequency sound signal.

GUSTAVE L. GRUNDMANN.

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