US2141756A

US2141756A - Multirange receiver

Info

Publication number: US2141756A
Application number: US73989A
Authority: US
Inventors: Alfred A Linsell
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1935-04-26
Filing date: 1936-04-13
Publication date: 1938-12-27
Anticipated expiration: 1955-12-27
Also published as: GB455649A; FR804837A

Description

Dec. 27, 1938. A, A, UNSELL- 2,141,756

MULTIRANGE RECEIVER Filed April 13, 1936 FREQUENCY CHA NGER sw/rm o seArm/a MEMBER 547 INVENTOR ALFEED A. L/N$ELL 'ATTORNEY Patented Dec. 27, 1938 PATENT OFFICE MULTIRAN GE RECEIVER Alfred A. Linsell, Sydenham, London, England, assignor to Radio Corporation of America, a corporation of Delaware Application April 13, 1936, Serial No. 73,989 In Great Britain April 26, 1935 3 Claims. (Cl. 250-20) This invention relates to radio receivers and more particularly to multi-range tunable receivers adapted to receive over difierent wave length ranges.

Broadcast receivers for sound and music signals are at present in widespread use and it is common to construct such receivers to be tunable over two wave length ranges corresponding respectively to the so-called medium wave broadcast range (at present'from about 250 to 550 meters) and to the so-called long wave broadcast range (at present from about 900 to 1900 meters). It is expected, however, that there will shortly be established in Great Britain a public service of television transmission upon short wavesprobably upon waves in the neighborhood of 7 meters longand the object of the present invention is to provide an improved economical and easily operated receiver which can be employed for broadcast reception over a plurality of wave length ranges of which one includes a short Wave'range for television signals. The problem of extending a radio receiver which has been constructed to receive sound signals on the ordinary present broadcast waves so that it may receive also television signals on short waves involves more than merely making provision for the reception of signals within the further short wave range, for it will be appreciated that the width of frequency spectrum occupied by television signals is much more than that occupied by sound signals. Sound signals can be (and by international agreement at the present time are) accommodated within a band of frequencies equal to the carrier 15,000 cycles, but the modulation frequency range involved in television may easily extend up to 2 megacycle or more. 7

For the purpose of convenience in description, radio receiving apparatus adapted to receive carrier frequency energy modulated with sound or music signals, will be hereinafter referred to as sound broadcast receiving apparatus.

According to the main feature of this invention a radio receiver capable of receiving over a plurality of wave length ranges of which one is a short wave television range, comprises sound broadcast receiving apparatus preceded by a heterodyne arrangement adapted to transform '50 received short Wave television modulated signals for broadening. the modulated carrier frequency channel or channels in the sound broadcast receiving apparatus to the extent necessary to enable saidchannel or channels to pass the relatively wide band occupied by television signals and for fixing the tuning of the said broadcast J5 receiving apparatus at a predetermined value corresponding to said intermediate frequency. Thus, although a radio receiver in accordance with this invention may be left, after sound broadcast reception, with the controls for the '10 variably tunable carrier circuits of the sound broadcast receiving apparatus anywhere within the range of variation (e. g. anywhere between 250-550 meters or 900-1900 meters depending upon the wave length upon which sound broad- 16 cast reception has been last effected) the arrangement is made such that when the receiver is changed over to television reception said circuits are tuned to a predetermined frequency chosen as the intermediate frequency for such 20 reception.

Where the reception of low definition television signals-i. e. television signals which do not occupy a Width of spectrum materially different from that occupied by a sound program- .25 is contemplated, it is not necessary to broaden the carrier frequency channel or channels in the sound broadcast receiving apparatus for such apparatus will serve, unaltered, for low definition television. :30

The invention is illustrated in the accompanying drawing wherein Figure 1 shows diagrammatically a portion of a receiving circuit em. bodying the invention, Figure 2 shows a form of indicating dial that may be used, and Figure 3 :35

separate local oscillator and'frequency changer valves may be provided. The tuning'controls for the local oscillator and the input circuit of the .50 frequency changer are preferably gang controlled from a common handle as indicated by the line 5. Beat frequency energy from the frequency changer is applied (after further amplification, if desired) to the input circuit of the 55 sound broadcast receiving apparatus which input circuit thus serves as a beat frequency circuit for television reception on short waves. This input circuit may consist of a coil 6 included in the grid cathode circuit of a valve I and arranged to be shunted (for sound reception on broadcast waves) by a tuning condenser S adapted to tunesaid coil over the sound broadcast wave length range in question. The said tuning condenser is in series with switch contacts 9, it, which are opened when the receiver as a whole is to receive short wave television signals, the switch 3 being, in these circumstances, moved into a position (the position shown) in which the tuning condenser is cut out of circuit and instead there is shunted across the coil 6 a small fixed condenser H shuntedby a resistance I2. This combination l l, i2, is put in circuit for shor wave reception through contacts 53, ill. The small fixed condenser H is of such magnitude as to tune the coil 6 to a predetermined fixed frequency corresponding to the beat frequency from the frequency changer 3 and the resistance [2 is of such magnitude as to make the coil 6 when thus tuned, suificiently flatly tuned to pass the range of television modulation. For sound a broadcast reception an ordinary broadcast aerial M is coupled to the coil 6 and the switch s is moved into that position (not shown) in which the said coil 6 is tuned by the variable condenser 8 and the combination ll, I2, is out of circuit.

In the receiver illustrated in Figure 1 the sound broadcast receiving apparatus is itself of the superheterodyne type and accordingly the output of the valve 1 is mixed with local oscillations from a second local oscillator 4 and applied to the input circuit of another frequency changer valve M. This input circuit is arranged in'similar manner to the input circuit of valve 1 and includes a switch 5 having contacts 9', Ill, 13' which in one position causes said input circuit to be tunable by a variable condensert' over the desired sound broadcast wave range and to have a narrow pass range while in the other position the switch open-circuits the tuning condenser and switches in a small condenser and shunt resistance combination I I, I2 which fixedly tunes the input circuit coil 6 to the predetermined frequency and gives it the desired wide pass range. The output from this mixing valve M is coupled to a fixed tuned further intermediate frequency amplifier as in the usual way. Each of the intermediate frequency tuned circuits of this amplifier (only the first stage of the said amplifier is illustrated, this stage including the valve 15) is shunted by-a resistance 16 when the switch s is in the position shown contacting switch contacts l1, l3, for television receptionso that each resistance I6 broadens the pass range of its associated circuit sufiiciently for the television signals. All the other intermediate frequency stages (if any) are like that illustrated and therefore it is not thought necessary to show such further stages nor the rest of the receiver which is as well known per se, and includes thenecessary demodulating and translating apparatus together with filters and/or change-over switches for enabling television or sound reproduction to be effected. 7

It will be seen that in Figure 1 for short wave television reception, the variably tunable carrier stages of'the sound broadcast receiving apparatus are fixed tuned to a predetermined frequency, and act as intermediate frequency stages as respect the incoming short waves, while the pass band of the carrier stages of the said sound broadcast receiving apparatus is widened to pass the television signals. For sound reception on broadcast waves the said sound broadcast receiving apparatus operates in the normal manner. Preferably all the switches above described are gang controlled, indicated schematically by the dash line 26, with a switch a which, in the sound reception position, switches in the broadcast receiving aerial [4 so that for television reception the operator has merely to throw the switch control into the position appropriate to television reception and then effect tuning merely by varying the control handle to which the tuning reactance of the first local oscillator 4 and that of short wave tuned circuit (or cir cuits) are ganged. Only one such short wave tuned circuit is actually shown, namely the circuit 2.

r 'In the embodiment of Figure 1 when television reception is to be effected the variably tunable carrier stages of the sound receiving broadcast apparatus are fixed tuned to a predetermined frequency by connecting small shunt condensers (l I, ll) thereacross. The provision of such shunt condensers is not, however, necessary and by suitable design the self-capacities of the inductances (G, 6) in the tuned circuits in question may be caused fixedly to tune the said cir- .1

cuits to the desired predetermined frequency.

In the modification partly illustrated in

Fig ures

2 and 3 wherein the variably tunable carrier circuits of the sound broadcast receiving apparatus are converted into fixedly tuned intermediate frequency'carrier circuits for television reception, the required fixed intermediate carrier frequency tuning is obtained without the need for providing any switches afiecting the tuning of the stages in question, but merely by so arranging the tuning controls as to ensure that for television reception the circuits in question are tuned by their normal controls to a predetermined frequency, preferably the lowest frequency in their tuning range' For example in a receiver wherein the variably tunable carrier stages of the broadcast receiving apparatus are tuned each by a variable condenser in a gang of condensers operable by a common control knob the gang shaft which is operated by a knob t2 carries a pointer I 9 moving over a scale 20 marked with the broadcast tuning range (for example 250 to 550 meters) and there-is provided an additional mark 2| on the scale below the 250 meters mark this'additional mark being labelled Television. A convenient arrangement is shown in Figure 3 in which the tuning knob 22 drives the gang shaft 23 through a friction clutch 24 and the said gang shaft has a television reception, the necessary resistances are switched into the carrier circuits of the sound broadcast receiving apparatus to broaden the acceptance band thereof to the extent necessary for television reception.

Although in the above described embodiments the use of shunt resistances for the purpose of broadening the acceptance band of the sound broadcast receiving apparatus is referred to, obviously other expedients known per se, may be resorted to without departing from the spirit and scope of the appended claims.

Having now particularly described and ascertained the nature of my invention and in what manner the same is to be performed I declare that what I claim is:

1. A receiving system for the selective reception of sound signals transmitted on a carrier within the broadcast band and of television signals transmitted on a carrier within a widely separated frequency band, comprising a vacuum tube amplifier having an input circuit tunable to desired frequencies Within the broadcast band and capable of passing a narrow range of modulation frequencies, said input circuit being constituted by an inductance and a variable condenser, and means for converting said tunable input circuit to a fixedly tuned circuit which is resonant to a frequency within said widely separated frequency band for television signals and which is capable of passing a range of modulation frequencies several times wider than the range of modulation frequencies passed by the tunable circuit in the reception of sound signals, said fixedly tuned circuit being constituted by said inductance and a parallel combination of a resistance and a capacity connected in shunt to said inductance,

said converting means comprising switch means for selectively connecting in shunt to the in ductance the variable condenser or the parallel combination of said resistance and capacity.

2. A receiving system for the selective reception of sound signals transmitted on a carrier within the broadcast band and of television signals transmitted on a carrierwithin awidely separated frequency band, comprising a vacuum tube amplifier having an inductance connected to the input electrodes thereof, a variable condenser adapted to be connected across said inductance to form therewith a circuit tunable to desired frequencies within the broadcast band and capable of passing a narrow range of modulation frequencies, a fixed condenser and a shunt resistance adapted to be connected across said inductance to form therewith a fixedly tuned circuit which is resonant to a frequent within said widely separated frequency band for television signals and which is capable of passing a range of modulation frequencies several times wider than the range of modulation frequencies passed by the tunable circuit in the reception of sound signals, and means for selectively connecting said variable condenser or said fixed condenser-resistance combination across said inductance.

3. A receiving system for the selective reception of signals transmitted in widely different channels of the frequency spectrum, such as for example, a sound signal channel having a carrier in the broadcast hand between 250 and 550 meters and requiring modulation frequencies of about 10 kc. wide, and a television signal channel having a carrier below about 100 meters and requiring modulation frequencies several times wider than those of the sound signal channel, comprising a conventional sound broadcast receiver provided with at least one resonant circuit constituted by an inductance and a shunt variable condenser which are tunable to a frequency within the broadcast band and are capable of passing only a limited band of modulation frequencies, a circuit responsive to television signals in a channel below 100 meters coupled to said sound receiver, means adapted to cooperate with said inductance of the sound receiver to resonate at a frequency in said short wave channel and to pass the rela-