US2299059A

US2299059A - Frequency modulation system

Info

Publication number: US2299059A
Application number: US330718A
Authority: US
Inventors: Louis K Sandor
Original assignee: RAY C STOTTS
Current assignee: RAY C STOTTS
Priority date: 1940-04-20
Filing date: 1940-04-20
Publication date: 1942-10-13
Anticipated expiration: 1959-10-13

Description

L. K. SANDOR Filed April 2o,

FREQUENCY MODULATION SYSTEM OOUIIOQ oct. 13, 1942.

l l" INVENToR l g BY Q KTTREY k PSU f wk Patented v Oct. 13, 1942 2,299,059 FREQUENCY MODULATIQN SYSTEM Louis K. Sandor, Piqua,

Ohio, assignor of seventeen and one-half per cent to Ray C. Stotts and seventeen and one-half per cent -to Harry Friedman, both of Dayton, Ohio Appiication Api-i1 zo, 1940, serial No. 330,718

4 5 claims. (01.250-20) This invention relates to a frequency modulation broadcasting system and more particularly to a radio receiver for use with frequency modulated broadcasting systems.

In order to produce the wide band width, which virtually is the same as amplitudeamplication, it is necessary to expand or multiply the signal a great number of times. These signals are received by radio receivers adapted to discriminate the frequency modulated signal so as to produce an intermediate or audio frequency signal.

An object of the system disclosed herein is to eliminate some of the multiplication of the signal at the broadcasting station and instead, multiply or expand the band width of the signal at the receiving station or in the radio receiver.

Another object of this invention is to provide a radio receiver provided with means for expanding or multiplying the frequency of the incoming signal.

Another object of this invention is to amplify the incoming signal, followed by one or more stages for expanding or multiplying the amplified signal and then passing the expanded signal through a detector circuit.

Another object of this invention is to provide a broadcasting system of modulated4 frequencies wherein comparatively narrow band Widths are transmitted, the band width being broadened or expanded at the radio receiver.

Other objects and advantages reside in the construction of parts, the combination thereof and the mode of operation, as will become more apparent from the following description.

In the drawing, Figure 1 is a schematic showing illustrating the principle incorporated into a radio receiver.

Figure 2 is a Wiring diagram of a circuit that has been shown for the purpose of illustration, carrying out the system shown schematically in Figure 1.

Figure 3 discloses another schematic system wherein the same radio receiver may be used for receiving amplitude modulated signals when using one channel and frequency modulated signals when using the other channel.

- All successful systems of frequency modulation used up to the present time, so far as known to applicant, have been those which utilize a wide carrier band. The volume or amplitude of the signal is contained in the band width. With a given carrier signal input, the greater the band width, the greater will be the volume output of the detector of the frequency modulation receiver. Frequency modulation system also has less noise from the tubes of the receiver itself, for the reason that the detector is designed to respond to changes in frequency of constant amplitude and not to changes in amplitude. For example, it hasy been found that for satisfactory reception., the band Width should be equal to ve times the highest audio frequency. This width gives a satisfactory ratio of signal to noise level. This Wide band width limits the number of broadcasting channels that are available.

If it were possible to transmit frequency modulated signals with a smaller band width without sacrificing' the advantages obtained from frequency modulated signals of the broad band width now used, the smaller band Width would be very beneficial to our radio broadcasting systems. With that thought in mind, experiments have been conducted to determine the results obtained by using the smaller band width than is now generally used. It has been found that a frequency modulated signal that swings over a band width of ten kilocycles. has advantages over amplitude modulated signals, as far as the noise level is concerned. This ten kilocycle band width was received on a conventional frequency modulated receiver, having the output from the modulated receiver amplified, as in the conventional radio receivers now in use. However, instead of receiving the ten kilocycle band Width frequency modulated signals on ordinary frequency modulated receivers now in use, it has been found that very satisfactory results have been obtained by passing this ten kilocycle band width frequency modulated signal through a receiver provided with several stages of band expanders or frequency multipliers, such as frequency doublers or frequency quadruplers, connected in series. By this system, the band width is expanded to any desired width, so as to provide satisfactory amplitude in the form of band Width for satisfactory detection. For each time' that the frequency modulated signal is doubled, the band width is doubled, and consequently, the volumeA of the detector output is automatically increased proportionately.

This system has been exemplified schematically in Figure 1, where the antenna I0 supplies a signal to a receiver circuit I2, which may include a tuning circuit and one or more stages of radio frequency amplification. It may also include an oscillator detector circuit, having an intermediate frequency output, which may be supplied directly to band expanders or, frequency multipliers or first amplified and then supplied to band expanders or frequency multipliers |4. The number of frequency multipliers is purely a matter of choice, depending upon the desired output. 'Ihe number of stages of band expanding devices I4 depends in part upon the width of the received band and the desired amplitude of the current output.

Band expanding or frequency multiplication corresponds to amplitude amplification used in conventional radio receivers for receiving an amplitude modulated signal. However, the frequency modulated signal, upon being multiplied, does not suffer from tube distortion and is not aiected by tube noises. Furthermore, extraneous disturbances do not have as great a detrimental eifect upon frequency multiplication as they do upon amplitude amplification. That being the case, frequency multiplication has substantially all of the advantages of amplitude amplification without the disadvantages caused by extraneous disturbances and defective amplification, tube distortion, tube noises and the like. The signal output from the frequency multipliers or band expanders |4 is supplied to a current limiting device I6 and possibly current filters. This current limiting device is used to energize a detector supplying power to an audio frequency interpreting device 20.

The details of a circuit arrangement shown for the purpose of illustration have been shown in Figure 2, wherein the receiver circuit includes one stage of radio frequency amplification, a detectoroscillator stage having an intermediate frequency output and one stage of intermediate frequency amplification. The multipliers or band expanding devices include a stage of quadruple multiplication, followed by a doubler. If, for example, the intermediate frequency is selected at 240 kilocycles, the resulting output frequency from the doubler stage would be 1920 kilocycles, resulting in expanding the band eight times. The expanded signal is supplied to a current limiting device that energizes the frequency modulated detector circuit having its output connected to an audio signal perceptible device, such as a loud speaker.

'Ihe several stages referred to above will now be more fully described. 'I'he antenna is connected in series to ground through a primary winding 30 coupled to a resonant circuit including a secondary winding or coil 32 arranged in parallel with a variable condenser 34 used in tuning the circuit to the desired incoming signal. One terminal of the resonant circuit is connected to -the grid of the radio frequency amplifying tube 36, which may be of any suitable type, as for eX- ample a GSK? tube. The cathode is connected through a resistance 38 to the other terminal of the coil 32. A suitable by-pass condenser 40 grounds the circuit.

The anode or plate circuit of the tube 36 contains the primary coil 50 coupled to a resonant circuit including the secondary winding or coil 52, connected in parallel with a variable condenser 54. The output of this resonant circuit is connected to the oscillator-detector tube 56, which may be any suitable tube, as for example, a tube known in the trade as 6A8. The cathode of this tube is connected through a resistance 58 to ground. This resistance 58 is shunted bv a bypass condenser 60. 'I'he cathode of the tube 56 is also connected through a resistance 62 to an electrode of the tube 56 and grounded through a condenser 64 connected in series with the reso- 75 nant circuit including the elements E6, 60 and the variable condenser 10. The oscillating anode of the tube 56 is coupled to the coil 66 through inductance windings 12, connected in series to ground by a, series of

resistances

14, 16 and 13. A suitable. by-pass condenser connects one terminal of the inductance 12' to ground.

The output frequency of the tube 56 is an 1ntermediate frequency. This intermediate frequencymay be selected at will. For the purpose of illustration, 240 kilocycles have been used. The anode of the tube 56 is connected to the resonant circuit including the primary winding connected in parallel with a condenser 02. The primary winding 90 is coupled to a resonant circuit including the secondary coil or winding 96 connected in parallel with the adjustable condenser 98. The output of the resonant circuit including the coil 96 and the condenser 08 is connected to the grid of an amplifying tube |00, which may be a GSK? tube, for amplifying the intermediate frequency. The cathode .of the tube |00 is conected to. ground through a suitable resistance |02 connected in parallel with the bypass condenser |04.

The output circuit of the tube |00 is connected in series with an adjustable condenser ||0 connected in parallel with the prmary winding or coil ||2, coupled to a resonaml circuit including the secondary winding or coil ||4 and the adjustable condenser H8. A suitable resistance ||6 is connected in parallel with the variable condenser l0 and the primary windingl 2, so as to broaden the band width of the resonant circuit, as is well known to those skilled in the art. 'I'he output of the resonant circuit including the coil |4 andthe condenser ||8 is connected to a grid of the tube |20 having an output frequency four times the frequency of the original intermediate frequency. Assuming the intermediate frequency is 240 kilocycles, the output of the tube |20 will then have a frequency of 960 kilocycles. anode circuit is connected to a resonant circuit including the adjustable condenser |22 and the coil |24. 'I'he resonant circuit is connected between the anode and the screen grid of the tube I 20. Furthermore, the output circuit of this tube |20 is connected through a condenser |26 to the control electrode of a tube |28, which may be of the 6SJ7 type. The control electrode is grounded through a suitable grid leak |30.

The output of the tube |23 has a frequency twice that of the input, that is, 1920 kilocycles. 'Ihis output is connected through a pair of condensers |32 and |34 to ground. An inductance |36 is connected in parallel with the adjustable condenser, |32, so as to form a resonant circuit, connected by a suitable condenser |40 to the current limiting tube |42. This tube may also be of the 6SJ7 type. A suitable resistance |44 is also connected in parallel with the adjustable condenser |32 and the inductance |36, so as to broaden the band width of this circuit. The cathode of the tube |42 is grounded and the control electrode is connected to ground through a suitable grid leak resistance |46. The output of the tube |42 is connected to a resonant circuit including the adjustable condenser |48 and the primary winding or coil |50.

. Theoutput of the current limiting tube |42 is supplied to the detector by the coil |50 being inductively coupled to the secondary windings |52 and |54. 'I'he terminal of one Winding is connected to one anode of the detector tube |60 and the terminal of the other winding is connected to The' the other anode of the detector tube |60. This detector tube may be of the type known as 6I-I6. The center tap of the secondary windings |52 and |54 is connected through a suitable inductance |62' to the circuits of the cathodes of the tube |60. One of these circuits includes the resistance |10 shunted by a by-pass condenser |12. The cathode in this circuit is grounded. The other of these circuits includes the resistance |14 shunted by a by-pass condenser |16. The cathode in this other circuit is grounded through the resistance |64 and variable resistance |66 connected in series with a condenser |68. The resistance |66 is provided with an adjustable tap for supplying audio signal current' to any suitable audio perceptible signal device. The inductance |62 is connected by a condenser |80 back to the anode of the tube |42.

Frequency expanding device or frequency expanding stages have been used to describe a system for expanding the band width in a receiver, which in some respects isthe equivalent of frequency multipliers in transmitting devices. However, the final signal supplied to the detector need not necessarily be higher than the signal input of the receiver. ultimate signal supplied to the detector may not be as high, and if so, is not a multiple of the signal input into the receiver. Therefore, band width expanding device, or frequency expanding device, has been used herein to designate any suitable device for widening the band width, whether or not the ultimate signal supplied to the detector is a multiple of, lower than or higher than the input signal that is picked up at the antenna.

In the modification disclosed in Figure 3, a dual purpose radio receiver has been shown. When the input signal is a frequency modulated signal, it passes through the upper branch of the circuit through the frequency expanding devices, through the detector to the output. If the incoming signal is an amplitude modulated signal, it is passed through the lower branch -of the receiver, which may be a conventional 'superheterodyne or a tunedradio frequency receiver, or any other suitable receiver for receiving amplitude modulated signal, amplifying the same and converting this signal either directly or indirectly into an audio perceptible signal through any suitable medium. The upper branch may consist of a circuit similar to that described in connection with Figure 2, or any other circuit for expanding the band widths of the frequency modulated incoming signal. may function as the receiver for frequency modulated incoming signals converted into audio perceptible signals through the band'expandin'g device, or for converting the incoming amplitude modulated signal into an audio perceptible signal through the use of a conventional amplitude modulated signal receiving circuit.

Although the preferred modification of the device has been described, it will be understood that within the purview of this invention various changes may be made in the form, details, proportion and arrangement of parts, the combination thereof and mode of operation, which generally stated consist in a device capable of carrying out the objects set forth, as disclosed and defined in the appended claims.

Having thus described my invention, I claim:

1. A super-heterodyne radio receiver including means for selecting a radio frequency signal,

Thus, the same receiver That being the case, the

means including an oscillator-detector circuit for converting the selected signal into an intermediate frequency signal, a selected circuit selected from a pair of parallel circuits, one for expanding the band width of a frequency modulated signal and the other for amplifying an amplitude modulated signal, and means for converting the signal output of the selected circuit into perceptible signals.

2. In a radio receiver for use either with a frequency modulated signal or an amplitude modulated signal, said receiver having a pair of pa'rallel circuits, one for use with a frequency modulated signal and the other for use with the amplitude modulated'signal, said radio receiver including a circuit network including a by-pass band filter for selecting a broadcast signal, means including an oscillator-detector circuit for converting the selected signal into an intermediate frequency signal, a circuit selected from a pair of circuits, one for expanding the band width of the frequency modulated signal, the other for amplifying an amplitude modulated signal, and a detector circuit for converting the current output of the selected circuit into perceptible signals.

3. A super-heterodyne radio` receiver including means for selecting a radio frequency signal, which signal may be either a frequency modulated signal or an amplitude modulated signal, means including an oscillator-detector circuit for converting the selected signal into an intermediate frequency signal, a selected circuit selected from a pair of parallel circuits, one of which circuits includes means for expanding the band width of the selected signal, and current limiting circuit means having a substantially constant amplitude current output and the other circuit. for amplifying an amplitude modulated signal, and means:O for converting the signal output of the selecteu'circuit into perceptible signals.

4. A super-heterodyne radio receiver including means for selecting a radio frequency signal, which signal may be either a frequency modulated signal or an amplitude modulated signal, said means including a resonant circuit for selecting the signal, means including an oscillatordetector circuit for converting the selected signal into an intermediate frequency signal, a selected circuit selected from a pair of parallel circuits, one of which circuits includes means for expanding the band width of the intermediate frequency signal, current limiting means having a substantially constant amplitude signal current output, and a detector for translating the intermediate frequency expanded band Width into perceptible signals. y

5. In a radio receiver for use either with a frequency modulated signal or an amplitude modulated signal, said receiver having a pair of parallel circuits, one for use with .a frequency modulated signal and the other f'or use with the amplitude modulated signal, said radio receiver including a circuit network including a by-pass band filter for selecting a broadcast signal, means including an oscillator-detector circuit for converting the selected signal into an intermediate frequency signal, a circuit selected from a pair of circuits, one for expanding the band width of the frequency modulated signal, said one including current limiting means having a substantially constant amplitude signal current output, the other for amplifying an amplitude modulated signal, and a detector circuit for converting the current output of the selected circuit into perceptible signals.

LOUIS K. SANDOR.