Title:
Ultra high frequency receiving system
United States Patent 2428300


Abstract:
This invention relates generally to ultra-highfrequency apparatus and more particularly to an improved ultra-high-frequency receiving system including means for improving the signal-to-noise magnitude ratio. For ultra-high-frequency reception, it is usually desirable to install the antenna...



Inventors:
Stott, Harold B.
Application Number:
US52039544A
Publication Date:
09/30/1947
Filing Date:
01/31/1944
Assignee:
RCA CORP
Primary Class:
Other Classes:
455/283, 455/291
International Classes:
H04B1/26
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Description:

This invention relates generally to ultra-highfrequency apparatus and more particularly to an improved ultra-high-frequency receiving system including means for improving the signal-to-noise magnitude ratio.

For ultra-high-frequency reception, it is usually desirable to install the antenna in a location as high above ground and as free of obstructions as possible in order to obtain maximum signal pickup with a minimum of signal reflections.

Such an installation requires a long antenna feeder system with the result that considerable signal attenuation is encountered before the received signals reach the receiver. Also, interference picked up by the feeder system is amplified in the receiver to the same extent as the signal intelligence.

In the instant invention several modifications of an improved circuit are provided whereby the received ultra-high-frequency signals are converted in the immediate vicinity of the receiving antenna to corresponding signals of a considerably lower intermediate frequency which are transmitted from the remotely located converter over the feeder line to a local conventional intermediate frequency amplifier forming a part of a superheterodyne radio receiver in which the converter is omitted. An adjustable local heterodyne oscillator, forming a part of the local receiver system remote from the converter and the antenna, furnishes heterodyne signals over the same feeder line to beat with the received signals in the remote converter thereby to provide the desired intermediate frequency signals.

If the signal converter comprises a conventional thermionic tube modulator, energizing potentials for the cathode and other electrodes thereof may be supplied from the local receiver power supply over the same feeder line which transmits the intermediate frequency signals and local oscillator signals. Similarly, tuning of the antenna circuit of the remote converter may be accomplished over the same transmission line or a separate feeder line by means of direct current or low frequency alternating currents controlled at the local receiver network.

Since signal attenuation, or feeder line loss is proportional to the signal frequency, it will be seen that the transmission of intermediate frequency signals which are usually of the order of * of the signal frequency will permit improved transmission of the received signals to the local receiver circuits for a given transmission line, while noise signals induced in the transmission line will not be amplified in the remote converter stage. Incidental attenuation of the local oscillator signals transmitted to the converter is not a serious disadvantage since sufficient local oscillator power may be provided readily to compensate for any such losses. The heterodyne oscillator is located at the local receiver network to minimize the apparatus necessarily located adjacent the remote antenna, and to facilitate accurate tuning of the oscillator frequency. Among the objects of the invention are to provide an improved method of and means for coupling an ultra-high-frequency antenna, to an ultra-high-frequency receiver. Another object of the invention is to provide an improved method of and means for improving the signal-to-noise ratio in an ultra-high-frequency system. A further object of the invention is to provide an Improved method of and means for converting ultra-high-frequency signals to lower intermediate frequency signals for transmission between a remotely located ultra-high-frequency antenna and converter to the local circuits of an ultrahigh-frequency receiver.

Further objects of the invention include improved means for converting received ultra-highfrequency signals to lower intermediate frequency signals, transmitting said intermediate frequency signals over a feeder line to the remaining circuits of a radio receiver, transmitting local oscillations from said remaining receiver circuits to said remote converting means to provide said beat frequency intermediate frequency signals and synchronously tuning said converting means and predetermined ones of said remaining receiver circuits.

The invention will be described in further detail by reference to the accompanying drawings of which Figure 1 is a schematic circuit diagram of one embodiment thereof, Figure 2 is a schematic circuit diagram of a second embodiment thereof, Figure 3 is a schematic circuit diagram of a third embodiment and Figure 4 is a fragmentary schematic circuit diagram of a remote control tuning means which may be incorporated in any of the circuits shown in Figures 1, 2 and 3.

Similar reference characters are applied to similar elements throughout the drawings.

Referring to Figure 1, an ultra-high-frequency antenna such, for example, as a dipole 1, 2 is connected to the terminals of an antenna coupling coil 3 located within an adjacently disposed unit enclosure 5 which may or may not be shielded.

The antenna coupling coil 3 is coupled inductively to a tapped secondary inductor 7. One end terminal of the secondary Inductor 7 is serially connected through a resistor 9 to one terminal of an adjustable tuning capacitor 11. The remaining terminal of the tuning capacitor I I is connected to an adjustable contact 13 which may be selectively connected to each of the taps on the secondary inductor 1. The common terminal of the series resistor 9 and the tuning capacitor II is connected to the control electrode of a thermionic mixer tube 15 which, for example, is of the indirectly - heated - cathode, screen - grid type.

The anode of the thermionic mixer tube 15 is connected through a parallel-connected tuning capacitor 17 and the primary winding 19 of an intermediate frequency transformer- 2 to the tube screen electrode. A secondary winding 23 of the intermediate frequency transformer 21 is connected through D.-C. blocking capacitors 25, 21 to a conventional high frequency transmission line 29 which passes through a suitable aperture in the remote unit enclosure 5. The transmission line 29 extends to the remaining circuits of a local radio receiver circuit which includes a second intermediate frequency transformer 31 having its primary winding 33 terminating the transmission line 29 through third and fourth D.-C. blocking condensers 35, 37, respectively. The secondary winding 39 of the second intermediate frequency. transformer 31 is tuned to the desired intermediate frequency by a third tuning capacitor 41 and is connected across the control electrode circuit of a first intermediate frequency amplifier tube 43. The output of the first intermediate frequency tube 43 may be applied to successive intermediate frequency amplifier tubes, a second detector and an audio amplifier, all not shown, in accordance with conventional superheterodyne practice. The local receiving circuits may- comprise a conventional superheterodyne circuit in which the converter is omitted.

A source of direct voltage connected to terminals 45 is applied, through first and second radio frequency chokes 47, 48, to the local receiver end of the high frequency transmission line 29. The positive terminal of the high frequency transmission line 29 within the remote unit enclosure is connected through a third radio frequency choke 49 to the common terminal of the screen electrode and the primary winding 19 of the first intermediate frequency transformer 21, to provide operating voltages for the screen and anode electrodes of the remote thermionic mixer tube 15.

This common terminal is connected through a voltage dropping resistor 51 to one terminal of the heater element of the thermionic mixer tube 15. The remaining terminal of the heater element of the mixer tube 15 is connected through a fourth radio frequency choke 53 to the negativelybiased terminal of a high frequency transmission line 29.

The superheterodyne local oscillator 55, located at the local receiver network, includes a parallelresonant circuit comprising a tapped oscillator inductor 57 and an adjustable oscillator tuning capacitor 59. A coupling coil 61, inductively coupled to the oscillator inductor 57, is connected through a balanced "H" high-pass filter 63 to the local receiver terminals of the high frequency transmission line 29 to supply the local oscillator frequency to the remotely located thermionic mixer tube 15. The terminals of the high frequency transmission line 29 within the remote enclosure 5 are connected through a second balanced "H" high-pass filter 65 to the primary winding 67 of a high frequency coupling transformer 69. The secondary winding 71 of the high frequency coupling transformer 69 is connected between the negative terminal of the heater element and the cathode of the thermionic mixer tube 15 to apply to the cathode the currents of oscillator frequency. Thus the oscillator frequency currents are applied to the mixer circuit to beat with the received signals to provide in the output circuit of the remote mixer tube the desired intermediate frequency signals for transmission over the high frequency transmission line 29 to the input of the intermediate frequency amplifier tube 43 at the local receiver. The grid return from the adjustable contact 13 on the antenna secondary reactor 7 is connected to the low voltage terminal of the primary winding 67 of the high frequency coupling transformer 69.

The position of the adjustable contact 13 on the taps of the tapped antenna secondary inductor 7 may be adjusted simultaneously with the adjustment of the position of the adjustable contact 73 on the tapped local oscillator inductor 57 by any convenient remote control means known in the art. Two control devices for adjusting the contact 13 in synchronism with the contact 73 on the oscillator inductor are described hereinafter and are illustrated in Figures 3 and 4. It should be understood that the tuning of the remote input and local oscillator circuits by means of tapped inductors in combination with preset adjustable capacitors provides a convenient method of tuning such a receiving system to various fixed frequency bands such, for example, as are employed in the television spectrum. The series resistor 9 connected between the input tapped secondary inductor 7 and the tuning capacitor 11 provides the required broad frequency response necessary for the reception of television signals or other signals which cover a relatively wide frequency band.

Basically, the circuit of Figure 2 is similar to the circuit of Figure 1 described heretofore with the exception that the thermionic mixer tube 15 is of the type employing a directly-heated cathode. The cathode of the tube 15 is heated by radio frequency energy derived from the local receiver heterodyne oscillator tube 55 through the transmission line 29. The high frequency energy derived from the heterodyne oscillator is applied to the cathode of the remote mixer tube 15 through a coupling capacitor 75 thereby providing a shunt connection from the mixer tube cathode to the high frequency transmission line 29. A tapped series resistor 77, connected between one side of the mixer tube filament and the grounded conductor of the transmission line provides suitable grid bias for the mixer tube 15 through a grid leak 79 connected between the grid of the tube 15 and the resistor tap. A grid condenser 81 is inserted between the mixer tube control electrode and the common terminal of the input circuit series resistor 9 and tuning capacitor II. A radio frequency choke coil 49 is connected between the positive terminal of the transmission line and the common terminals of the mixer tube screen electrode and the first intermediate frequency transformer primary winding 19 as described in the circuit of Figure 1.

Single D.-C. blocking capacitors 37, 83 are inserted between the high frequency transmission line 29 and the inductors 33, 61 coupled respectively to the input of the local intermediate frequency amplifier tube 43 and the local oscillator inductor 57. The second radio frequency choke coil 47 is inserted in the local connection between the positive terminal of the power supply and the positive conductor of the high frequency transmission line 29.

The currents of heterodyne oscillator frequency are injected into the input circuit of the remote mixer tube 15 by means of their direct application to the tube cathode circuit. As in the circuit of Figure 1, the transmission line 29 transmits intermediate frequency signals from the output of the remote mixer tube 15 to the input of the local intermediate frequency amplifier tube 43, while simultaneously transmitting the heterodyne oscillator frequency and the anode and screen energizing potentials from the local receiver circuits to the remote mixer tube 15. The adjustment of the movable contact 13 on the remote input inductor 7 and the movable contact 73 on the local oscillator inductor 57 may be accomplished simultaneously in the same manner as will be described hereinafter in the circuits-of Figures 3 and 4.

Figure 3 is similar to the circuits of Figures 1 and 2 with the exception that the remote mixer tube 15 employs a directly-heated cathode which is series energized at the oscillator frequency through a series coupling capacitor 75 connected to the low voltage terminal of the first intermediate frequency transformer secondary winding 23. A shunt capacitor 85, connected across the secondary winding 23 of the first intermediate frequency transformer 2 1, effectively bypasses the oscillator frequency across the transformer winding, thereby providing a low impedance path for oscillator energy applied to the cathode circuit.

The remaining terminal of the mixer tube cathode is connected, through a voltage dropping resistor 77, to the adjustable tap 13 on the tapped input inductor 7 and to the remaining grounded terminal of the high frequency transmission line 29.

The anode return circuit and the screen grid are connected to the junction of a series-connected radio frequency choke 87 and blocking capacitor 89 connected between the low voltage terminal of the secondary winding 23 of the first intermediate frequency transformer 21 and the ground terminal of the ultra-high-frequency transmission line 29. Another radio frequency choke coil 91 connected between the high potential side of the cathode of the mixer tube 15 and the ground terminal of the high frequency transmission line 29 completes, with the choke coil 87 and the capacitor 75, a first high pass filter 92 in the energizing circuit to the mixer tube cathode.

The primary winding 33 of the local second intermediate frequency transformer 31 coupled to the input circuit of the first intermediate frequency amplifier tube 43 is bypassed by a capacitor 93 and is serially connected through a second high pass filter 95 and a capacitor 97 to the local grounded terminal of the ultra-high-frequency transmission line 29. The local receiver heterodyne oscillator inductor 57 is coupled through an oscillator coupling capacitor 99 to the input of the second high pass filter 95. The anode and screen operating potentials for the mixer tube 15 are applied to the local end of the transmission line 29 across the series capacitor 97. In this manner the two operating potentials, the heterodyne oscillator frequency currents and the intermediate frequency input signals are applied in series to the local receiver terminals of the high frequency transmission line 29.

In addition to the signal coupling circuits described heretofore in the embodiments of the invention disclosed in Figures 1, 2, and 3, the high frequency transmission line 29 also may be employed as a tuning line for adjusting the adjustable tap 13 on the remote input secondary inductor 7 simultaneously with the adjustment of the adjustable tap 73 on the local oscillator inductor 57. The adjustment of the adjustable contact 13 on the input secondary inductor 7 may be accomplished by an A.-C. operated solenoid actuating mechanism of the type described in detail hereinafter in Figure 4.

The solenoid winding 101 may be connected through series D.-C. blocking capacitors 103, 105 and radio frequency chokes 107, 109 connected for example, across the blocking capacitor 89 within the remote unit enclosure 5 as shown in Figure 3. Low voltage, for example of line frequency, applied to the line terminals 11 at the local receiver network, may be coupled through a low frequency transformer 113 to provide low frequency potentials on the transmission line 29 for energizing the solenoid winding 101 whenever the contacts 115, 117 in series with the low frequency transformer 113 are closed.

The contacts 115, I17 may be synchronized with the positioning of the adjustable contact 73 on the local oscillator 57 in a manner to provide a pulse of low frequency energy on the transmission line 29 during the interval between contacts on the oscillator inductor 57. Under these conditions, while low frequency energy will be transmitted by the high frequency transmission line 29 in successive pulses as the oscillator inductor contact is adjusted, the pulse intervals will correspond to intervals in which no oscillator frequency is existent on the line and hence will be ineffective in the high frequency local receiving system circuits including the intermediate frequency amplifier tube 43.

Figure 4 discloses an optional circuit for actuating the remote mixer tube input secondary inductor adjustable contact 13 synchronously with the adjustment of the local heterodyne oscillator inductor adjustable contact 73. A solenoid winding 101, as described in the circuit of Figure 3, actuates a solenoid plunger 119 which steps a ratchet gear 127 counterclockwise an angle of 60° for each actuation of the solenoid plunger against the tension of the spring 129. The ratchet gear 127 is mechanically coupled, as indicated by the dash line 128, to the adjustable contact 13 which connects one terminal of the input tuning capacitor II to any one of the taps 121, 122, 123, 124, 125, 126 on the tapped inductor 7 to tune the input circuit of the remote mixer tube 15.

A similar second switch 131, actuated by a band tuning knob 133 at the local receiver network, has fixed contacts 121', 122', 123', 124', 125', 126' connected to corresponding taps on the local oscillator inductor 57. A movable contact 73 may be arranged to tap the oscillator inductor as the input inductor 7 connected to the remote mixer tube 15 is adjusted. The various positions of the oscillator inductor switch 131 may be indicated by means of the knob 133 as positions I, II, III, IV, V, VI. A third switch 135 having all of its fixed contacts connected together and arranged at angular positions intermediate the angular positions of the contacts on the second switch 131, is serially connected with terminals 137 to apply either low voltage, low frequency alternating current or direct current through the high frequency transmission line or a separate transmission line 139 to energize the remote solenoid winding 101 each time the movable contact 141 of the third switch 135 touches one of the switch fixed contacts. Since the contacts of the solenoid actuating third switch 135 are closed intermediate each step on the oscillator inductor second switch 131, the remote solenoid winding 101 will be intermittently energized and actuate the input inductor switch at the mixer unit.

The oscillator inductor second switch 131 and the solenoid actuating third switch 135 may be ganged to a ratchet gear 143 which, in conjunction with a pawl 145, permits rotation of the switches in definite steps and in only one direction. If the local oscillator and remote mixer input inductor switches get out of step, the solenoid may be actuated independently of the oscillator inductor switch by means of a pair of local auxiliary contacts 141, 148 which may be successively closed until signals are obtained, at which time the switches will be in synchronism.

It should be understood that any of the three embodiments of the invention described in Figures 1, 2 and 3 may be employed in combination with either of the remote control circuits described in Figures 3 and 4, or that any other known type of remote control circuit or device may be substituted therefor. Also it should be understood that any other type of non-linear rectifying device may be substituted for the thermionic mixer tube in the remote antenna mixer stage. For example, a crystal detector may be thus employed in a manner well known in the art.

As described, the invention comprises several embodiments of an improved circuit for receiving high frequency signals wherein the mixer circuit of a superheterodyne system is disposed within a unit enclosure immediately adjacent a remote high frequency antenna. Signals derived from the heterodyne oscillator located at the local receiver, (in which the mixer is omitted), are transmitted through a conventional high frequency transmission line to beat with the received signals in the remote mixer stage. Similarly, biasing potentials for the mixer tube electrodes are supplied through the transmission line. Intermediate frequency signals derived from the mixer are transmitted in the opposite direction through the transmission line to a conventional intermediate frequency amplifier forming a local portion of an otherwise conventional superheterodyne receiver system. Tuning of the local oscillator frequency and of the input circuit of the remote mixer stage may be accomplished either through the same high frequency transmission line or through an auxiliary line.

Due to the fact that received signals picked up by the antennae are amplified and are converted to a lower intermediate frequency before any line attenuation, and since the amount of attenuation per unit length of the transmission line is considerably less at the lower frequency being transmitted, and the noise picked up by the transmission line does not receive amplification by the remote mixer stage preceding the line, the resultant signal-to-noise ratio in the complete receiver system is greater than in conventional systems wherein the noise as well as the desired signal receive like amplification and the ultrahigh-frequency signal is greatly attenuated in the transmission line.

I claim as my invention: 1. A noise reduction circuit for an ultra-highfrequency antenna including a modulator situated adjacent to and responsive to signals from said antenna, an intermediate frequency amplifier and a heterodyne oscillator located at a point remote from said modulator, a transmission line interconnecting said modulator and said amplifier, and means for coupling said oscillator through said line to said modulator to provide intermediate frequency signals in said modulator for transmission in the opposite direction through said line to said amplifier.

2. A noise reduction circuit for an ultra-highfrequency antenna including a modulator situated adjacent to said antenna and having input and output circuits, said input circuit being responsive to signals from said antenna, a fixed tuned intermediate frequency amplifier and an adjustably tunable heterodyne oscillator both located at a point remote from said modulator, a transmission line interconnecting said modulator output circuit and said amplifier, and means for coupling said oscillator through said line to said modulator input circuit to provide intermediate frequency signals in said modulator output circuit for transmission in the opposite direction through said line to said amplifier.

3. A noise reduction circuit for an ultra-highfrequency antenna including a modulator situated adjacent to said antenna and having an adjustably tunable input circuit and an output circuit, said input circuit being responsive to signals from said antenna, a fixed tuned intermediate frequency amplifier and an adjustably tunable heterodyne oscillator located at a point remote from said modulator, a transmission line interconnecting said modulator output circuit and said amplifier, means for coupling said oscillator through said line to said modulator input circuit to provide intermediate frequency signals in said modulator output circuit for transmission in the opposite direction through said line to said amplifier, and means operable at said remote point for simultaneously adjusting the tuning .reactances of said oscillator and said modulator input circuit.

4. A noise reduction circuit for an ultra-highfrequency antenna including a modulator situated adjacent to said antenna and having an adjustably tunable input circuit and an output circuit, said input circuit being responsive to signals from said antenna, an intermediate frequency amplifier, a source of operating potentials and an adjustably tunable heterodyne oscillator located at a point remote from said modulator, a transmission line interconnecting said modulator output circuit and said amplifier, means for coupling said oscillator through said line to said modulator input circuit to provide intermediate frequency signals in said modulator output circuit for transmission in the opposite direction through said line to said amplifier, means for connecting said potential source through said line to provide operating potentials for said modulator, and means operable adjacent said oscillator for simultaneously adjusting the tuning reactances of said oscillator and said modulator input circuit. 5. A circuit as described in claim 4 wherein said tunable input and oscillator circuits include adjustably tunable capacitors responsive to said simultaneous adjusting means.

6. A circuit as described in claim 4 including a second line interconnecting said oscillator and said modulator and wherein said simultaneous adjustment of said modulator and said oscillator tuning reactances is operable through said second line.

7. A noise reduction circuit for an ultra-highfrequency antenna including a modulator tube situated adjacent to said antenna and having anode, cathode and control electrode circuits, an adjustably tuned network responsive to signals from said antenna and connected to said control electrode circuit, an intermediate frequency amplifier, a source of operating potentials and an adjustably tunable heterodyne oscillator located at a point remote from said modulator, a transmission line interconnecting said modulator tube anode circuit and said amplifier, means for coupling said oscillator through said line to said modulator tube cathode circuit to provide intermediate frequency signals in said modulator tube anode circuit for transmission in the opposite direction through said line to said amplifier, means for connecting said potential source through said line to provide operating potentials for said modulator tube, a second line interconnecting said oscillator and said modulator, and means situated adjacent said oscillator and operable through said second line for simultaneously adjusting the tuning reactances of said oscillator and said modulator tuned network.

8. A noise reduction circuit for an ultra-highfrequency antenna including a modulator tube situated adjacent to said antenna and having anode, cathode and control electrode circuits, an adjustably tuned network responsive to signals from said antenna and connected to said control electrode circuit, an intermediate frequency amplifier, a source of operating potentials and an adjustably tunable heterodyne oscillator located at a point remote from said modulator, a transmission line interconnecting said modulator tube anode circuit and said amplifier, means for coupling said oscillator through said line to said modulator tube cathode circuit to provide intermediate frequency signals in said modulator tube anode circuit for transmission in the opposite direction through said line to said amplifier, isolating filter means for connecting said potential source through said line to provide operating potentials for said modulator tube, a second line interconnecting said oscillator and said modulator, and means situated adjacent said oscillator and operable through said second line for simultaneously adjusting the tuning reactances of said oscillator and said modulator tuned network.

9. A noise reduction circuit for an ultra-highfrequency antenna including a modulator tube situated adjacent to said antenna and having anode, cathode and control electrode circuits, an adjustably tuned network responsive to signals from said antenna and connected to said control electroae circuit, an intermediate frequency amplifier, a source of operating potentials and an adjustably tunable heterodyne oscillator located at a point remote from said modulator, a transmission line interconnecting said modulator tube anode circuit and said amplifier, means including a high-pass filter connected between said line and said modulator cathode circuit for coupling said oscillator through said line to said modulator to provide intermediate frequency signals in said modulator tube anode circuit for transmission in the opposite direction through said line to said amplifier, isolating filter means for connecting said potential source through said line to provide operating potentials for said modulator tube, a second line interconnecting said oscillator and said modulator, and means situated adjacent said oscillator and operable through said second line for simultaneously adjusting the tuning reactances of said oscillator and said modulator tuned network.

10. A circuit of the type described in claim 6 including means for energizing said modulator tube cathode by radio frequency energy transmitted by said transmission line from said local oscillator.

11. A circuit of the type described in claim 1 including a source of low frequency alternating current, and means selectively responsive to 10 said current and operable through said transmission line for selectively tuning said modulator input circuit to signals derived from said antenna.

12. A circuit of the type described in claim 1 5 including a source of low frequency alternating current, and means selectively responsive to said current and operable through said transmission line for selectively tuning said modulator input circuit to signals derived from said antenna, the 0 intervals of said tuning corresponding to intervals during which no intermediate frequency signals are derived from said modulator.

HAROLD B. STOTT.

5 REFERENCES CITED The following references are of record in the file of this patent: SNumber 2,056,011 2,103,079 2,189,287 1,922,623 2,114,031 UNITED STATES PATENTS Name Date Lowell --.----- Sept. 29, 1936 Johnson -- ___.--- Dec. 21, 1937 Hershey --_ __---- _ Feb. 6, 1940 Hotopp _--------- Aug. 15, 1933 Rust et al. -------- Apr. 12, 1938