US2280521A - Radio receiver - Google Patents

Description

A ril 21, 1942.

Filed May 17, 1940 \//s/aA/Az RANGE (545 T0 #45 Kc.) EAIVD mas/50o r0 moo/(a) D. E. FOSTER RADIO RECEIVER DEGENERAT/ON BAND P486 0000 70 I800 Kc.)

T g L mf OSCILLATOR 2 T0 BAND Q 7'0 BA/VD PASS /0 GR/D4 PASS /.5

r0 LOCAL 05c. 20

k/IVSUZA TIDN AMPLIFIER M (900m zaookc.)

IN VENTOR DUDLEY E. FOSTER ATTORNEY Patented Apr. 21, 1942 RADIO RECEIVER Dudley E. Foster, South Orange, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application May 17, 1940, Serial No. 335,650

7 Claims.

My present invention relates to radio broadcast receivers, and more particularly to a radio broadcast receiver of the superheterodyne type which embodies a single tuning circuit.

One of the main objects of my invention is to provide a superheterodyne receiver having a converter stage which has a wide band signal network transmitting collected signals thereto, and the converter being additionally fed with locally produced oscillations which are provided through a local oscillator network equipped with but a single tuning mechanism.

Another important object of this invention is to provide in a superheterodyne receiver a pair of wide band, band pass networks constructed to transmit signals over different portions of the broadcast range, a converter being utilized for selective connection to either of the pair of networks, and the converter being fed with locally produced oscillations which are the resultant oscillations provided by a fixed oscillator and a tunable oscillator.

Another object of this invention is to provide a broadcast receiver having a converter whose signal input network is adapted to pass the entire signal frequency range, and the converter having a connection to an oscillator network which comprises a local oscillator provided with means for tuning it over a range of ultra-high frequencies, and a second oscillator network which functions to heterodyne, or combine, the first oscillations and the output of a fixed oscillator to produce a range of local oscillations which are fed to the aforesaid converter.

Still another object of the invention is to provide in combination with a converter stage a signal input network which comprises two band pass stages of overlapping frequency ranges, and each band pass stage including means for preventing cross-modulation effects between different frequencies of said signal ranges.

And still other objects of the invention are to improve generally the simplicity and efficiency of superheterodyne receivers, and more especially to provide a superheterodynebroadcast receiver which is not only reliable in operation and simple to tune, but is economically manufactured and assembled.

The novel features which I believe to be characteristic of my invention are set forth in particularity in the appended claims; the invention itself, however, as to both its organization and method of operation will best be understood by reference to the following description taken in connection with the drawing in which I have indicated diagrammaticallyacircuit organization whereby my invention may be carried into effect. 1 i

In the drawing: 1

Fig. 1 shows acircuit diagram of a receiver embodying the invention,

Fig. 2 is a schematicview of the tuning control,

Referring to the drawing thereis shown in Fig. 1 that portion of the superheterodyne receiver which is essential to an understanding of this invention. The numeral l denotes the converter, or combined local oscillator and first detector, and may be a tube of the GA? type which employs a cathode 2, a plate 3, and five intermediate grids. The signal grid 4 is connected to the adjustable contact arm 5 of a changeover switch which has a pair of contacts 6 and I. The contacts "I andG each represent the high potential output terminals of a pair of band pass networks which pass overlapping portions of the signal frequency range. Thus, the antenna l', which has impressed upon it the waves of the signal broadcast range, feeds signal energy to the pair of band pass networks. Assuming that the signal range is approximately 545 to 1745 kilocycles (kc.), any signal waves that are impressed on the antenna I are transmitted to the pair of band pass networks.

One of the band pass networks may cover a range of 500 to 1300 kc., and may comprise an amplifier 8, which is schematically represented. The numeral 9 denotes the resonant input circuit of the radio frequency amplifier 8, and it will be understood that circuit 9 is adapted to pass with substantial uniformity signals in the 500-1300 kc. band. The output electrodes of amplifier 8 may be coupled to a second band pass circuit l0 whose primary and secondary networks are so resonated that the circuit l0 passes a band of 500 to 1300 kc. signals with substantial uniformity.

The contact I is connected to the high potential side of the secondary circuit of the band pass transformer l0, while the opposite side thereof is grounded. The unby-passed resistor H may be inserted in the cathode lead of the amplifier 0 so as to provide sufficient degenerative feedback to the grid thereof thereby to prevent cross-modulation effects between the various sig nal frequencies passed through the 500-4300 kc. network. Those skilled in the art are fully acquainted with the manner of constructing a wide band, band pass network, as well as the specific manner of providing degeneration in the amplifier circuit 8. It may, also, be pointed out that the degenerative amplifier 8 will improve the linearity of amplification.

The second band pass network is constructed to pass signals in the 1000-1800 kc. range, and comprises an amplifier I2 which includes a degenerating unby-passed resistor I3 in its cathode lead. The input circuit I4 of the amplifier I2 is constructed to pass the 1000-1800 kc. signal band, and signal circuit I4 is magnetically coupled to the antenna circuit I. The output circuit I5 of amplifier I2, as in the case of circuit I0, is a network capable of passing the wide 1000-1800 kc. band. The contact 6 is connected to the high potential side of the secondary transformer I5, while the opposite side thereof is at ground potential.

The plate electrode 3 of the converter tube I is connected to the high potential side of the resonant primary circuit I6 of the intermediate frequency (I. F.) transformer I1, and the secondary circuit I8, as well as the primary circuit IB, is tuned to the operating 1. F. value. By Way of illustration let it be assumed that the operating I. F. value is 455 kc. In other words, there is produced in the output circuit of the converter signal voltage of the I. F. value, and the I. F. voltage may be passed through the transformer I! to one or more I. F. amplifiers. The amplified I. F. signal voltage is demodulated in any well known type of second detector network, and the modulation voltage is amplified in one or more modulation voltage amplifier stages. Any desired type of reproducer may then be employed for reproducing the amplified modulation voltage. The networks following the I. F. transformer I! are not shown, since those skilled in the art are fully acquainted with such networks.

The signal grid 4 of the converter tube I is located between a pair of positive screen grids. The local oscillation voltage is injected into the converter tube by a network to be presently described. The oscillation grid I3 is located adjacent the cathode 2, and the second grid-may be established at a positive potential. Local oscillations impressed ongrid I9 will be of a diiferent frequency from the signal frequencies. Specifically, it is desired that the local oscillation range comprise 900-2300 kc. In such case by virtue of the electronic coupling action within the converter tube there will be developed in the output circuit of the converter tube intermediate frequency energy Corresponding to that signal carrier frequency which differs from the selected oscillation frequency by the operating I. F. value of 455 kc.

Considering now the local oscillation network, there is provided an oscillator 20 which is tunable over a range of 5 to 6.2 megacycles (mc.). The local oscillator network 20 may be constructed in any desired manner, and the construction will be chosen so that oscillations in the specified frequency range will be efficiently produced. The tunable tank circuit of the oscillator is represented by the numeral 2 I, and comprises an inductance coil 22 which has arranged within it for lateral displacement a metallic plug, or cylinder, 23. Preferably the metallic plug-23 should be of brass, and it is provided with an actuating device 24 so that the plug 23 may be displaced within the coil 22. Referenence is made to my pending application Serial No. 319,831 filed February 20, 1940 for a detailed disclosure of the construction of the typecf tuner that may be em- Iii) , to 2200 kc.

ployed in the tank circuit 2| of the oscillator 20.

It will be understood that displacement of the plug 23 with respect to the coil 22 varies the tuning of the oscillator tank circuit over the specified 5 to 6.2 mc. range. At this point it is noted that the variable inductance tuner 22-24 is the sole tuning mechanism of this receiver. The oscillation output of circuit is impressed upon the grid 25 of a mixer tube 26, which may be of the 2A? type if desired. The cathode of the tube 26 is grounded through a biasing network 21, and grid 25 may be grounded through a grid leak resistor 28 in order to establish the grid at a desired negative bias. The second grid, or anode, electrode 30 of tube 26 is connected to a source of positive potential through a tank circuit which is fixedly resonated to a frequency which may be, by way of illustration, 4 mo. The oscillation grid 3I is magnetically coupled to the fixedly tuned tank circuit 32, and hence the cathode, .grid 3| and anode-electrode 30 co-operate with the tank circuit 32 to provide a fixedly tuned oscillator which is adapted to produce oscillations of the 4 mo. value.

Since there is injected into the tube 20 oscillationsfrom oscillator 20 which are selected from a range of 5 to 6.2 mc., and since the fixed oscillator produces oscillations of 4 mc. value, it will be clear that in the output circuit of tube 26 there will be developed a voltage varying in frequency through a range of l to 2.2 mc. The output circuit of tube 26 is indicated by numeral 40, and it will be understood that it comprises a pair of tuned circuits which are constructed to pass a band of 900 to 2300 kc. Of course, the band pass network may be constructed in any desired fashion so that it may readily transmit voltage of frequencies lying in the specified band pass range. The band pass circuit 40 is utilized in the output of tube 26 so that the sum of the 4 mc. energy and the 5 to 6.2 mc. energy will not be transmitted to the oscillation grid I9. It will be understood that there will be transmitted to grid I9 voltage of a frequency in a range of 1000 All frequencies below 900 kc. and above 2300 kc. will be rejected.

It will now be seen that tube 20 and its associated circuits function as the second oscillator which is fed by the tunable oscillator 20, and that the output of the second oscillator is fed to the oscillation grid I9 in the manner of the usual superheterodyne practice. If there is impressed on the grid 4 a plurality of signal frequencies, assuming contact arm '5 has been switched into connection with contact 1, the selected oscillation frequency impressed on grid I9 will beat with that signal frequency of the 500-1300 kc. range which will produce the I. F. value of 455 kc.

In operation, then, the switch arm is adjusted to that one of contacts I and 6 which will feed to signal grid 4 the wide band of signal frequencies which includes the desired signal frequency. Simultaneously, or subsequently if desired, the brass plug 23 is then adjusted within coil 22 to tune oscillator 20 to that setting which will produce in the output circuit 40 of oscillator 20 that oscillation frequency which when heterodyned with the desired signal frequency results in the production of the I. F. energy of 455 kc. If desired, the switch 5 may be mechanically coupled to the actuating device 24 in such a manner that when the brass plug 23 is adjusted to the high portion of the frequency range of oscillator 20 then simultaneously the switch arm 5 will be connected to contact IS. The reverse will, of

course, be true when the brass plug 23 is adjusted to the lower portion of the frequency range of oscillator 20. Such a construction is shown in Fig. 2. It will, also, be understood that the actuating device 24 will have associated with it a calibration dial so that the necessary and desired setting of the tuning knob may readily be had.

Of course, more than two parallel band pass networks may be utilized to feed the converter. As many band pass circuits will be employed as is necessary to cover the entire desired signal frequency range. In the present case each band pass circuit covers about 800 kc. and with the I. F. of 455 kc. no image or I. F. response will be present in the output of the converter. The oscillator 20 is chosen to operate in the mo. range because at that range, or higher, sufficient inductance change can be produced for coil 22 by the use of brass, copper or other types of movable plugs to give a l to 1.5 mc. tuning range.

It will now be appreciated that the entire broadcast range is covered in the present receiver by merely varying the position of the metallic plug 23. Further, better image and I. F. interference response is had than with present broadcast receivers. By virtue of the degenerative amplifiers used in the parallel band pass networks there is had freedom from other spurious responses.

While I have indicated and described a system for carrying my invention into effect, it will be apparent to one skilled in the art that my invention is by no means limited to the particular organization shown and described, but that many modifications may be made without departing from the scope of my inventon, as set forth in the appended claims.

What I claim is:

1. In a signalling system of the type employing a converter tube provided with a signal input electrode and an oscillation electrode, an intermediate frequency output circuit for the tube, a signal input circuit, fixedly resonated to pass a wide band of desired signal frequencies, coupled to the signal grid, a variably tuned oscillator functioning as the sole signal selection device of the system, a network for reducing the frequency of the oscillation energy output of the said oscillator to a substantially lower value, and means for impressing the reduced frequency energy on said oscillation electrode.

2. In a signalling system of the type employing a converter tube provided with a signal input electrode and an oscillation electrode, an intermediate frequency output circuit for the tube, a

signal input circuit, fixedly resonated to pass a wide band of desired signal frequencies, coupled to the signal grid, a variably tuned oscillator functioning as the sole signal selection device of the system operating over a range of the order of 5 megacycles, a network for reducing the frequency of the oscillation energy output of the said oscillator to a substantially lower value, and means for impressing the reduced frequency energy on said oscillation electrode.

3. In a signalling system of the type employing a converter tube provided with a signal input electrode and an oscillation electrode, an intermediate frequency output circuit for the tube, a signal input circuit, fixedly resonated to pass a wide band of desired signal frequencies, coupled to the signal grid, a variably tuned oscillator functioning as the sole signal selection device of the system, a network for reducing the frequency of the oscillation energy output of the said oscillator to a substantially lower value and such that it differs from the desired signal frequency by the said intermediate frequency, and means for impressing the reduced frequency energy on said oscillation electrode.

4. In a signalling system of the type employing a converter tube provided with a signal input electrode and an oscillation electrode, an intermediate frequency output circuit for the tube, a signal input circuit, fixedly resonated to pass a wide band of desired signal frequencies, coupled to the signal grid, a variably tuned oscillator functioning as the sole signal selection device of the system operating over a range of the order of 5 megacycles, a network for reducing the frequency of the oscillation energy output of the said oscillator to a substantially lower value and such that it differs from the desired signal frequency by the said intermediate frequency, and means for impressing the reduced frequency energy on said oscillation electrode.

5. In a signalling system of the type employing a converter tube provided with a signal input electrode and an oscillation electrode, an intermediate frequency output circuit for the tube, a signal input circuit coupled to the signal grid, a variably tuned oscillator, a network for reducing the frequency of the oscillation energy output of the said oscillator to a substantially lower value, and means for impressing the reduced frequency energy on said oscillation electrode, said signal input circuit comprising a pair of band pass networks of overlapping wide desired signal frequency ranges, and means to selectively connect a desired one of said band pass networks to the signal grid.

6. In a signalling system of the type employing a converter tube provided with a signal input electrode and an oscillation electrode, an intermediate frequency output circuit for the tube, a signal input circuit coupled to the signal grid, a variably tuned oscillator, a network for reducing the frequency of the oscillation energy output of the said oscillator to a substantially lower value, and means for impressing the reduced frequency energy on said oscillation electrode, said signal input circuit comprising a pair of fixedly tuned band pass networks, each passing a different part of a wide signal frequency range, and means responsive to tuning adjustment of the oscillator for selectively connecting a desired one of the band pass networks to said signal grid.

'7. In a superheterodyne receiver including a signal input network fixedly resonated to pass a wide band of desired signal frequencies, a local oscillator tuning over a frequency range of the same extent, but being appreciably higher in value than said desired range, the oscillator tuning being by means of the motion of a metallic mass relative to the oscillator coil, a second oscillator fixedly tuned, a first converter tube to which is applied the output of the variably tuned and the fixed tuned oscillator, the output of the said first converter tube being applied to a second converter tube, the input signal of the desired frequency band being likewise applied to the second converter tube, and an intermediate frquency amplifier connected to the output of the second converter tube.

DUDLEY E. FOSTER.

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