US2065652A - Radio receiver - Google Patents

Description

0% 29, 1936. w. 1.. CARL'SON RADIO RECEIVER Filed Aug. 15, 1935 Rn wfi fi u r a mc L l l e d m -m w -kn-fim LQBQR mw Till Q EN 2 .2 m 2 a \H\ HN Patented Dec. 29, 1936 UNETED STATES PATENT OFFIQE.

RADIO RECEIVER of Delaware Application August 15, 1933, Serial No. 685,196

16 Claims.

My invention relates to radio receivers and particularly to receivers of the superheterodyne type designed to receive signals over a plurality of frequency ranges.

Various circuits have been utilized for adapting radio receivers, designed primarily for reception within the broadcast band, to receive signals within a different frequency band. One such circuit is generally known as a short-wave converter and consists of an oscillator and tuned radio-frequency circuit which may be connected to a conventional broadcast receiver at the proper point in the circuit whereby the high frequency or short-wave signals are converted to the intermediate frequency signals for which the broadcast receiver is designed.

The converter type of circuit is satisfactory in operation, but it is objectionable in that it is both expensive and lacking in compactness because of the additional apparatus required.

A circuit of another type involves switching different sets of coils into the radiofrequency and oscillator circuits for the different frequency ranges. This is objectionable in many cases both because of the switching and of the added space required for the extra coils and because of the added cost.

One of the main objects of my invention is to provide a simplified receiver suitable for operation over a plurality of frequency bands which may be made relatively low in cost and compact in construction.

A further object of my invention is to provide a superheterodyne type of receiver which does not require a change in the oscillator adjustment when switching from one frequency range to another, whereby the lining-up of the oscillator and the tuned radio-frequency circuits is facilitated.

In practicing one embodiment of my invention I design the receiver to receive signals within a band lying between 540 kilocycles and 1710 kilocycies, which will be referred to as the broadcast band, and within a narrow high frequency band lying between 2400 kilocycles and 2500 kilocycles, which will be referred to as the police band.

Reception within the high frequency band, within which police calls may be heard, is accomplished by utilizing the second harmonic of the output of the superheterodyne oscillator and by tuning the radio frequency circuit broadly to a rind-point in the high frequency band.

The radio frequency circuit is tuned to the high frequency band by connecting a small condenser in series with the tuning condenser, whereby a change in setting of the tuning condenser will have very little effect upon the capacity shunted across the inductance coil of the radio frequency circuit and, consequently, very little effect upon the tuning of that circuit. During reception within the broadcast band, the small condenser is short-circuited so that the tuning condenser is effective for tuning the radio frequency circuits in the usual way.

Other features and'advantages of my invention will appear from the following description taken in connection with the accompanying drawing in which:

Figure 1 is a circuit diagram of a radio receiver embodying my invention; and

Fig. 2 is a circuit diagram of one of the circuits of the receiver of Fig. 1, illustrating a modified form of my invention.

Referring to Fig. 1, the preferred embodiment comprises a tuned radio frequency amplifier which includes a suitable amplifier device such as an electronic tube 1 having, in the present example, an indirectly heated cathode 3, a control grid 5, a screen grid 1, a suppressor grid 9, and an anode H. The tuned input or signal selecting circuit of the vacuum tube I, designated by the reference numeral l3, includes a radio frequency transformer l5 having a primary winding I! and a secondary winding IS. The primary winding I1 is connected with a signal collecting means such as an antenna 2 I and a ground as indicated.

The secondary winding [9 is shunted by a variable tuning condenser 23 and a small adjustable condenser 25 connected in series therewith, the condenser 25 being provided for the purpose of tuning the input circuit l3 to a frequency in the middle of the high frequency or police band.

A switch 21 is provided in conjunction with the condenser 25 to permit it to be made ineffective and whereby the tuning condenser 23 may be connected directly across the secondary winding IQ for tuning over the broadcast band. In the present example and as a preferred arrangement, the switch 21 is arranged to short circuit the condenser 25.

The control grid 5 of the amplifier device or tube l is connected to a point tapped down on the secondary winding I9 in order to reduce the effect of the tube input capacity on the tuned circuit I 3. While this reduces the gain of the circuit somewhat, it permits making the receiver tunable in the broadcast band over the desired frequency range.

The output circuit of the amplifier tube I is coupled to the tuned input circuit 29 of the combined first detector and oscillator tube 3|. The output circuit of the vacuum tube I may be traced from the anode I I through the primary winding 33 of a radio frequency transformer 35, and through conductors 31 and 39 to a point of positive potential on a voltage divider means 4| which is connected with a power supply means 43. A radio frequency connection from the low potential end of primary winding 33 to the oathode 3 is provided through a bypass condenser 44 and a bypass condenser 46 shunting a portion of voltage divider 4|.

The tuned input or selecting circuit 29 of the first detector is similar to the tuned radio frequency circuit I3 above-described, and-includes the secondary winding 45 of the radio frequency transformer 35 which is shunted by a variable condenser 47 and a small adjustable condenser 49 connected in series therewith.

A switch 5| is connected across the condenser 49, this switch being operated simultaneously with and for the same purpose as the switch 21 by means of a common control as indicated by the dotted line connection 53.

The tuning condensers 23 and 41 are units of a gang condenser and are operated simultaneously by means of a common control as indicated by the dotted line connection 55. They are shunted by small trimmer condensers 51 and 59, respectively, for lining-up the tuned circuits over the broadcast band in the usual way.

The control grid 6| of the first detector is connected to a point tapped down on the secondary winding 45 in order to obtain the desired tuning range as explained above.

The connections of the low potential ends of the tuned circuits I3 and 29 to the cathodes 3 and 63 may be traced through conductors '65 and 61, respectively, to the common conductor 69, and through a grid biasing portion 'II of the voltage divider 4| and a conductor I3 to the cathode 3, this cathode being connected to the cathode 63 of the tube 3| through a conductor 15.

, It will be noted that the radio frequency connection from the tuned circuits I3 and 29 to the cathodes is through the bypass condenser 46 shunting the biasing resistor portion 'II.

The detector electrodes, which are enclosed in the same envelope with the oscillator electrodes,

comprise the cathode 63 and control grid 6|, above referred to, a screen grid I9 and an anode 8|. The screen grid 19 and the screen grid 1 of the radio frequency amplifier tube I are connected through conductors 83 and 85, respectively, and through a conductor 81 to a point of positive potential on the voltage divider 4|. lhe screen grids have a radio frequency connection to ground through a condenser 86 and a condenser 88 as indicated.

The detector anode BI is connected to the primary winding 89 of a tuned intermediate frequency transformer 9|, and receives an operating potential through a resistor 93 and a conductor 95 from a positive point on the voltage divider 4|, as indicated.

The oscillator electrodes comprise a control grid 91, an anode electrode 99 and the cathode 63 which is common to the detector and oscillator. By utilizing a common cathode 63, the detector and oscillator are coupled through the common electron stream. It is to be understood that any suitable oscillator and coupling circuit may be employed in practicing my invention, but

the oscillator shown in Fig. l is especially satisfactory as it is rich in second harmonic.

The frequency determining circuit I66 of the oscillator includes an inductance coil I 6| which is shunted by a variable condenser I63 and a fixed condenser I65 connected in series, the fixed condenser I65 having a larger capacity than the minimum capacity of the variable condenser I63. The variable condenser I63 is one unit of the above-mentioned gang condenser and is tuned simultaneously with the condensers 23 and 41 by means of the common tuning control indicated by the dotted line connection 55.

The fixed condenser I65 is employed in series with the variable condenser I63 for the purpose of making the oscillator track with the tuned radio frequency circuits as described in Carlson Patent No. 1,740,331, and forms no part of my present invention.

The oscillator variable condenser I63 is shunted by a small trimmer condenser I6! for the purpose of lining-up the oscillator with the tuned circuits I9 and 29.

The high potential end of the inductance coil I6I is coupled to the oscillator control grid 91 through a coupling condenser I69 and a grid leak coupling resistor |I3 to cathode, while the point between the fixed condenser I65 and the variable condenser I63 is provided with a radio frequency path to the cathode 63 through a circuit which may be traced through the conductors I II and 69, the bypass condenser 46 and the conductors I3 and I5 to the cathode 63.

The plate circuit of the oscillator is coupled to the tuned oscillator circuit I66 for producing sustained oscillations by means of an inductance or feedback coil H5. The plate circuit of the oscillator may be traced from the plate electrode 99 through the feedback coil I I 5 and through the resistor 93 and the conductor 95 to the voltage divider M. A radio frequency bypass condenser II! is connected between the upper end of the resistor 93 and the conductor I I I.

It will be apparent that when the switches 27 and 5| are closed, the receiver functions as a conventional superheterodyne receiver, the oscillator beating with the incoming signal to produce an intermediate frequency signal output in the detector plate circuit which is transferred through the tuned transformer 9| to the second detector indicated at II 9. In the embodiment being described, an intermediate frequency of kilocycles is employed.

When the switches 21 and 5| are open, the radio frequency tuning condensers 23 and 41 are made substantially ineffective since they are connected in series with condensers having, rela tively, very small capacities. In one embodiment of my invention, the low capacity condensers 25 and 49 have capacity values ranging between 3 micro-microfarads and 16 micro-microfarads, while the tuning condensers 23 and 41 each have capacity values ranging between 18 micro-microfarads and 405 micro-microfarads. Since the condensers 25 and 49 will generally be set in the middle region of their range, at 9 micro-microfarads, for example, it is evident that the capacity of the series combination of condensers is not varied appreciably by varying the capacity of the large condenser, even when the large condenser is set near its minimum capacity value.

The secondary windings I9 and 45 are given considerable distributed capacity so that they have a natural resonant period in the neighborhood of the police band. In order that the selecting' circuits may always .be tuned to themiddle of the high frequency or police band, the distributed capacity of .each secondary winding is made such that together with the tube input capacity, the secondary windings are normally tuned to a frequency slightly above said high frequency band. i

The assembled apparatus is then adjusted with the switches 21 and 5| open, the small condensers Z5 and 49 being adjusted to a value such that the circuits I3 and 29 are. tuned to-the middle of the high frequency or police band. In the particular embodiment being described, the condensers 25 and 49 are adjusted to tune the circuits I3 and 29, respectively, to a frequency of z i lokilocycles.

As previously stated, the tuning at the police band is so broad that signals at all frequencies lying between 2400 kilocycles and 2500 kilocycles are passed by the tuned circuits I 3 and 29. Within this bandthe desired station is selected solely by adjusting the oscillator frequency to a value such that the difference between the second harmonic of the oscillator signal output and the frequency of the incoming signal is 175 kilocycles. From the foregoing description of the tuned circuits I3 and 29, it will be understood that although the condensers 23 and 4'! are rotated at the same time the oscillator frequency is adjusted, there is substantially no change in the tuning of these circuits.

The oscillator may be designed to supply a fundamental frequency oscillation which is either 175 kilocycles above or below the frequency to which the selecting circuits are tuned in the broadcast band. In the preferred embodiment the oscillator is adjusted to supply the higher frequency oscillations, but it will be seen that, in either case, the second harmonic falls within the range required for reception within the police band.

It will be apparent that, within the police band, a station can be received at either one or two oscillator settings, but that two stations will never be received at one oscillator setting since the frequency response range of the fixedly tuned selecting circuit is less than the intermediate frequency.

In Fig. 2 there is illustrated a tuned radio frequency or selecting circuit which may be substituted for the circuits I3 and 29 shown in Fig. 1.

Referring to Fig. 2, where parts similar to those in Fig. 1 are indicated by like reference numerals, the secondary I9 of the radio frequency coupling transformer I5 is provided with the variable condenser 23 for tuning over the broadcast band and with a small adjustable condenser I 2| for tuning over the higher frequency or police band.

An inspection of Figs. 1 and 2 will show that a feature common to the two circuits is that of having fixed tuning for the police band while permitting the broadcast tuning condensers to be varied during the adjustment of the oscillator frequency. In both circuits, the stations in the police band are selected by causing the oscillator to produce arsecond harmonic frequency of the proper value.

By employing my invention, a small receiver of the so-called midget type may be made tunable over a plurality-of frequency ranges without adding materially to its production cost. Specifically, my invention permits a low production cost because only a few small parts need to be added to the usual single range receiver and also because it permits lining-up the tuned radio frequency circuits and the oscillator in the usual way. The last feature is of special importance because any design which makes a lineup for uni-control difficult necessarily adds to the cost of assembly.

Various other modifications may be made in my invention without departing from the spirit and scope thereof, and I desire, therefore, that only such limitations shall be placed thereon as are necessitated by the prior art and set forth in the appended claims.

I claim as my invention:

1. In a receiver of the superheterodyne type, a detector, an oscillator including means for producing oscillations having a selected frequency and a harmonic frequency thereof, said oscillator being coupled to said detector, a selecting circuit coupled to said detector, said circuit comprising an inductance coil, a variable tuning condenser and a second condenser of relatively low capacity value connected in series across said coil, and means for short-circuiting said second condenser, said selecting circuit being so adjusted with respect to said oscillator that the signal selected when said second condenser is short-circuited combines in said detector with said selected frequency oscillation to produce a signal at a predetermined intermediate frequency, and that the signal selected when said smaller condenser is in circuit combines in said detector with said harmonic frequency oscillation to produce a signal at said same intermediate frequency.

2. A receiver according to claim 1 characterized in that said selecting circuit is broadly tuned when said second condenser is in circuit and is comparatively sharply tuned when said second condenser is short circuited.

3. A receiver according to claim 1 characterized in that said second condenser has a capacity value which is less than the minimum capacity of said variable condenser.

4. A receiver according to claim 1 characterized in that the inductance coil provides distributed capacity to tune said coil substantially to the frequency to which it is tuned when said second condenser is not short-circuited.

5. A receiver according to claim 1 characterized in that when said second condenser is effectively .in circuit, the selecting circuit has an inductance to capacity ratio which is relatively high, thereby to provide a broad tuning characteristic.

6. In a radio receiver of the superheterodyne type, the combination with a first detector and an oscillator including means for varying the frequency thereof, of an inductance coil, a variable condenser and a second condenser of relatively low capacity connected in series therewith, said series condenser combination being connected with said coil to provide a tuned circuit preceding said first detector, a switch for shorting said second condenser, and unitary control means for operatingsaid frequency varying means and said variable condenser simultaneously,'said coil and said variable condenser having respective inductance and capacity values such that when-said switch is closed said circuit is tuned to pass a sigdenser having a capacity value such that when said switch is open the radio frequency selecting circuit is tuned within a band of frequencies which beat with a harmonic frequency of said oscillator to produce a signal at said intermediate frequency. 1

7. In a superheterodyne receiver, a radio frequency selecting circuit tunable within two differing frequency ranges, a tunable oscillator including means for producing fundamental frequency oscillations and harmonic oscillations therof, a detector electrically coupled with said selecting circuit and said oscillator, said selecting circuit and said oscillator being simultaneously tunable for selecting signals in one of said frequency ranges, whereby over said one frequency range the signal passed by the selecting circuit beats with the fundamental frequency oscillations of said oscillator to produce a signal at a predetermined intermediate frequency, and means for independently adjusting the tuning ofthe,

selecting circuit whereby the selecting circuit is rendered ineffective for tuning control over the other frequency range and a signal passed thereby beats with a selected harmonic oscillation of said oscillator to produce a signal at said same predetermined frequency.

8. A receiver according to claim 7 characterized in that the tuning adjusting means causes the selecting circuit to be substantially fixedly tuned and responsive to signals over a frequency range which is less in width than the value of the intermediate frequency.

9. In a radio receiving system, the combination of a tunable oscillator circuit having fundamental and harmonic frequencies, a tunable signal receiving circuit, means common to each circuit providing electrical coupling therebetween, unitary means for simultaneously varying the tuning of said circuits to provide a predetermined intermediate frequency signal in response to received signals, and additional tuning means in said signal receiving circuit for simultaneously adjusting the tuning of said circuit for broad response within a differing predetermined signal frequency range wherein signals beat with harmonic frequency oscillations in the oscillator circuit to provide the said intermediate frequency signals, and rendering said first named variable tuning means substantially inefiective to vary the tuning of said signal receiving circuit within the last named frequency range.

10. In a radio receiving system,.the combination of a tunable oscillator circuit, a tunable signal receiving circuit, means common to each circuit providing electrical coupling therebetween, said last named means being substantially independent of frequency change, unitary means for simultaneously varying the tuning .of said circuits to provide a predetermined intermediate frequency signal in response to received signals, said tuning means in the receiving circuit including an inductance, a variable condenser therefor and a second condenser in series with said variable condenser, said second condenser having a capacity lower than the minimum capacity of said variable condenser whereby oper\ ation of said variable condenser is ineffective to substantially vary the tuning of said receiving circuit, and means for short circuiting said second condenser to render said variable condenser effective as cuit.

11. In a radio receiving system, a tunable oscillator circuit having fundamental and harmonic frequencies, a tunable signal receiving circuit, an electric discharge device having grid electrodes connected with each of said circuits and having a common output circuit whereby said circuits are electrically coupled with said output circuit,- unitary means for simultaneously varying the tuning of said oscillator and signal receiving circuits to provide a predetermined frequency signal in response to received signals, and additional tuning means in said signal receiving circuit for simultaneously adjusting the tuning of said signal receiving circuit for broad response within a differing predetermined signal frequency range wherein signals beat with harmonic frequency oscillations in the oscillator circuit to provide the said intermediate frequency signals and rendering said first named variable tuning means substantially'ineifective to vary the tuning of said signal receiving circuit within the last named frequency range.

12. In-a superheterodyne receiver, the combination of a signal receiving circuit comprising an inductance, a variable tuning condenser therefor and'a second condenser in series with said variable condenser, an oscillator, an electron discharge device providing a common coupling means between said oscillator and said receiving circuit, said oscillator and receiving circuit being simultaneously tunable, said second condenser having a capacity value lower than the minimum capacity of said variable tuning condenser, and means for selectively short circuiting said second condenser thereby to tune said receiving circuit within a differing signal frequency range, and said second condenser and inductance having respective capacity and inductance values such that when said second condenser is in circuit, the signal receiving circuit is tuned within a frequency range of signals adapted to beat with the oscillator frequency to produce the predetermined intermediate frequency of the receiver.

; 13. A receiver'according to claim 7 characterized in that the tuning adjusting means causes the selecting circuit to be tuned to substantially a fixed frequency within the other frequency range independently of the tuning of the oscillator.

14. A receiver according to claim '7 characterized in that the tuning adjusting means causes the selecting circuit to be broadly tuned to substantially a fixed frequency in the middle of the other frequency range independently of the tuning of the oscillator.

15. In a superheterodyne receiver, an oscillator, including variable tuning means for producing oscillations having a selected frequency and a harmonic frequency thereof within a predetermined tuning range, variable tuning means for selecting a radio signal within a predetermined tuning range, means for combining said oscillations with a selected signal to produce a signal at a predetermined intermediate frequency, common means for simultaneously operating said first and second named variable tuning means, and means for rendering said second named variable tuning means ineffective to select signals and responsive to signals in a differing predetermined range effective to beat with said harmonic frequency oscillations to produce a signal at said same intermediate frequency,

a'tuning-means inxsaid receiving cirwhereby the oscillator tuning determines the signal selection.

16. In a radio receiving system, the combination with a combined detector-oscillator electric discharge device, of a signal selecting circuit, an oscillator circuit, said circuits being connected with said device, uni-control means for tuning said circuits through predetermined related frequency ranges to provide a predetermined beat

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