US3659204A

US3659204A - Short range microwave system

Info

Publication number: US3659204A
Application number: US856685A
Authority: US
Inventors: Wayne T Hufford
Original assignee: Cherokee Electronics Co Inc
Current assignee: Cherokee Electronics Co Inc
Priority date: 1969-09-10
Filing date: 1969-09-10
Publication date: 1972-04-25
Anticipated expiration: 1989-04-25

Abstract

A short range, low power, microwave system for transmitting single channel data (video, audio, computer pulses, etc.) over distances up to approximately one mile at a frequency range of about 12.2 to 12.7 GHZ. The system includes a microwave transmitter wherein the carrier is amplitude modulated by the desired intelligence and a microwave receiver which includes a reflector feed horn, crystal detector assembly, a bias system for the detector and video amplification; the receiver circuit operates to convert the intelligence from the carrier directly into a usable signal without heterodyning.

Description

United States Patent Hufford 1451 Apr. 25, 1972 [54] SHORT RANGE MICROWAVE SYSTEM [21] Appl. No.: 856,685

[52] US. Cl ..325/373, 325/26, 325/67, 329/205 R [51] Int. Cl ..H03d l/l0, H04b 1/22 [58] Field of Search ..325/1l3, 343, 373, 449, 363, 325/67, 26, 445; 329/203, 205 R, 179

[56] References Cited UNITED STATES PATENTS 2,468,655 4/1949 Cole et a1 ..325/445 X 1,624,185 4/1927 Round ..325/373 2,074,887 3/1937 Beshore ..329/205 X OTHER PUBLICATIONS Bronwell & Bean, Theory and Application of Microwaves 1947pp.213-2lS,233-234 Welch Laboratory Apparatus-Catalog page 307 copyright 1954 Primary Exarixiner-Robert L. Richardson Att0rne \'William S. Dorman [57] ABSTRACT A short range, low power, microwave system for transmitting single channel data (video, audio, computer pulses, etc.) over distances up to approximately one mile at a frequency range of about 12.2 to 12.7 01-12, The system includes a microwave transmitter wherein the carrier is amplitude modulated by the desired intelligence and a microwave receiver which includes a reflector feed horn, crystal detector assembly, a bias system for the detector and video amplification; the receiver circuit operates to convert the intelligence from the carrier directly into a usable signal without heterodyning.

4 Claims, 4 Drawing Figures PATENTEDAPRZS 1972 3,659,204 SHEET 1 OF 2 .WAYA/E 7. HUFFORD //VVEN7'0R PATENTEDAPR 25 m2 WWWWWW\\ WAYNE THurrana ATTORNEY SHORT RANGE MICROWAVE SYSTEM The present invention relates to a short range microwave system for transmitting and receiving single channel data over distances up to one mile at frequencies in the range of 12.2 to 12.7 GI-IZ. More particularly, the present invention relates to the receiver portion of this microwave system wherein the intelligence is detected from the carrier by means of a novel circuit including a crystal detector without any heterodyning and wherein the crystal detector itself is of novel design.

In most microwave systems operating at or near the frequencies involved herein, it is generally necessary to employ a klystron or other expensive beat frequency equipment to extract the intelligence from the incoming signal using the well known heterodyne principle. Not only is the particular frequency oscillator expensive in and of itself, but the power supply circuit therefor is also generally quite expensive. On the other hand, the receiver of the present invention utilizes a crystal detector, a biassing network and a high-gain solid state amplifier (without any beat frequency oscillator) so as to result in a. low cost with high reliability. A camera can be connected to the transmitter and a monitor can be connected to the output of the receiver; no additional equipment is required.

It is understood, of course, that cables or other conduits have also been used to transmit intelligence over relatively short distances; however, where the intelligence represents a wide spectrum of different frequencies, the attenuation is generally non-uniform for the different frequencies such that compensation therefor is required at the remote end of the cable or conduit. Also, where it is desired to transmit across busy streets, .over rough terrain or through hazardous areas, the present system is feasible where the cable or conduit is not.

Therefore, it is a principal object of the present invention to provide a short range microwave system capable of transmitting and receiving single channel data over relatively short distances with relatively simple and inexpensive equipment.

It is a further object of the present invention to provide a short range microwave system which is capable of transmitting information over relatively short distances where it is not feasible or possible to transmit this information by cable or other conduit.

It is a further object of the present invention to provide a short range microwave system wherein the receiver is adapted to convert the intelligence from the carrier into a usable signal without using the heterodyne principle or the necessary equipment which is generally required when utilizing this principle.

It is still a further object of the present invention to provide a microwave receiver of the type referred to above which includes a novel crystal detector, biassing network and high-gain amplifier. 7

Other and further objects and advantageous features of the present invention will hereinafter more fully appear in connection with a detailed description of the drawings in which:

FIG. 1 is a semi-diagrammatic representation ofa portion of the receiver showing the antenna, detector and pre-amplifier sections; v

FIG. 2 is a circuit diagram of the video amplifier section of the receiver which connects with the output from FIG. 1;

FIG. 3 is a side elevation of the crystal detector diagrammatically shown in FIG. 1; and

FIG. 4 is a longitudinal sectional view of the crystal detector of FIG. 3 showing the internal details thereof.

Referring to the drawings in detail, FIG. 1 shows a parabolic reflector mounted on a wave guide 22 so as to comprise an antenna feed horn. The left hand end of the wave guide 22 is properly positioned with respect to the focal point of the reflector 22 so as to maximize signal reception. It should be understood that the above described antenna feed horn is properly directed towards a signal antenna feed horn (not shown) located at the transmitter (not shown). The transmitter feed horn in turn will be properly directed towards the receiver antenna feed horn. The transmitter will be provided with a modulator-power supply (not shown) including a klystron (not shown), or similar device. The transmitter will be capable of producing an output carrier wave of the frequency referred to herein which carrier is preferably amplitude modulated by the intelligence which the operator desired to send from the point of transmission to the point of reception. The details of the transmitter are not shown herein since any suitable means for providing an amplitude modulated carrier of the frequency range desired would be suitable for the purposes of the present invention.

In turning to the description of FIG. 1, the wave guide section 22 is suitably aligned with and properly electrically mated with the internal wave guide section 24 at one end of which is mounted the detector assembly 26 which will be described hereinafter in greater detail. The lower end of the detector assembly 26 is connected to a fixed bias resistor R, which, in turn, connects with variable bias resistor R the other end of the bias resistor R connects with a fixed bias voltage of approximately 1.5 volts, the negative terminal of this voltage source being connected to ground as shown.

The signal developed at the upper end of the bias resistor R, is fed into terminal No. 3 of an integrated circuit, which, in this instance, is CA3018, the internal details of which are well known and, hence, not described. The input terminal No. 3 is also connected to ground through a filter circuit consisting of R and C Terminal No. 4 is grounded as shown and terminal No. 2 connects with terminal No. 3 through resistor R to ground through resistor R Terminal No. l connects to ground through resistor R and capacitor C connected in parallel. A bias voltage of six volts is applied directly to terminal No. 8 and through resistor R to terminals No. 5 and 9 in common. An intermediate bias voltage is applied to terminal No. 12 at the junction of resistors R and R which connect in series between the six volt source and terminal No. 9.

For the purposes of this description, terminal No. 7 will be considered as the output terminal of the integrated circuit and the output signal is developed across resistor R The output signal is fed through capacitor C and the potentiometer R The output from FIG. 1 appears on lead 28 which connects with the center arm of the potentiometer R Turning now to FIG. 2, lead 28 connects through capacitor C to the base of transistor 0,. In FIG. 2 transistor Q together with transistors 0 and Q constitute a video amplifier. The negative side of a twelve volt d.c. source is applied directly to the collector of 0;. This same negative voltage is applied to the bases of transistors Q Q and Q through resistors R R and R respectively. The collector of Q, connects with the negative side of the twelve volt source through resistor R The positive side of the twelve volt source connects with the base of transistor Q through resistor R to the emitter of Q through resistor R to the base of Q through resistor R to the emitter of 0 through resistor R and to the emitter of Q through resistor R The signal coming through the lead 28 is developed across resistor R before being fed into the transistor Q through the capacitor C The collector of Q connects to the base of Q through capacitor C The outputfrom the emitter of Q, is taken off through capacitor C at 30 and should represent a 1.4 AC. signal corresponding in frequency to the input intelligence received. Feed back from the emitter of O to the emitter of Q, is provided through the capacitor C Referring to FIGS. 3 and 4, the detector assembly 26, briefly described in FIG. 1, will now be set forth in detail. The upper end of the detector assembly is comprised of an RF plug 32 which, by way-of example, could be a standard UG-58A/A U plug. The plug 32 has a flange 34 as shown, is provided with a lower threaded portion 36, is further provided with a central pin 38 which is supported internally within the plug 32 by means of the Teflon body 40. The lower, inner end of the pin 38 is provided with a small, circular hole 42 for a purpose which will be hereinafter described. The outer concave portion of the Teflon member 40 is covered with a radial, or circular, resistor which is made by grinding up carbon, mixing the carbon with glue and applying it as a layer 44 as shown.

The radial or circular resistor 44 results uponthe drying of the glue. The resulting resistor 44 is symmetrical with respect to any wave received in the wave guide assembly previously described.

A crystal assembly 46, which preferably is a 1N78 is attached to the lower inner end of the RF plug in the following manner. The crystal assembly 46 is provided with a Teflon coating or cylinder 48. A thin RF sleeve 50, made of suitable metal such as aluminum or brass is inserted into the lower end of the plug 32 in a snug fitting relationship. Thereafter, the crystal assembly 46, with the Teflon insulation thereon is inserted inside the RF sleeve 50 until the small internal pin 52 (which is part of the crystal assembly 46) is received within the small hole 42. The crystal assembly 46 is a standard purchased item and, therefore, will not be described in detail except to note that a crystal is mounted within the interior in a suitable encapsulating material, is electrically connected to the pin 52 and is grounded to the case 46.

After the crystal assembly and RF sleeve have been inserted in the plug 32 in the manner described above, a cylindrical RF shield 54 is screwed onto the lower end of the plug 32. The lower end of the RF shield 54 is provided with a threaded opening 56 which is adapted to receive the upper threaded end of a plug 58'. The latter plug, for example, can be a standard UGlO94/U plug or equivalent. A springcontactor 60 having an upper pointed end is secured at its lower end in a suitable opening provided in the upper end of the plug 58. The connector 60 is provided a complete turn 62 to provide the desired resiliency. When the plug 58 is screwed into the opening 56 the upper pointed end of the contactor 60engages the lower surface of the crystal assembly 46; upon screwing the plug 58 all the way into the hole 56, the resiliency of the spring contactor 60 will insure that the crystal assembly is held securely in the position shown in H6. 4. For the purpose of permitting electrical contact with the lower end of the detector assembly, the plug 58 is provided with a lower hollow contactor 64 to accommodate a pin, for example, which will connect with R,.

The lower end of the contactor. 60 connects with hollow connector 64 by means of wire 66, and these last three-mentioned elements are surrounded by a layer of Teflon 68 to electrically insulate them from the plug 58'.

OPERATION The incoming signal is received by the parabolic reflector from any suitable transmitter (not shown) operating in the preferred range of [2.2 to 12.7 GHZ. The

wave guide sections

22 and 24 are standard A-inch by l-inch wave guides and, therefore, the transmitter could operate anywhere in the frequency range from 9 GHZ up to 13 GHZ and beyond. However, it should be understood that this invention is not limited to any particular frequency or frequency range. By selecting a different size of wave guide and a different transmitter, the invention is capable of operation over a wide range of frequencies. The details of the transmitter have not been shown, but it should be understood that any suitable transmitter which is capable of operating in the frequency ranges referred to above with amplitude modulation would be acceptable for the purposes of the invention.

The signal received by the parabolic reflector 20 is introduced to the wave guide section 22 at the approximate focal point of the antenna as is well known to those skilled in this art. The signal is transmitted from the wave guide section 22 to the wave guide section 24 also using those principles which are well known in this art. A suitable choke is provided on either wave guide 22 or 24 to permit proper conduction from one wave guide section into the other. Within the wave guide section 24, the pin 38 is properly positioned with respect to the end of the wave guide to, maximize the signal received.

The radial resistor 44 will produce the proper impedance,

match required and also presents a symmetrical termination for the bias network later to be described. It should be noted that the point where .the radial resistor 44 contacts the flange 34 is at ground potential.

The signal received by the pin 38 represents the carrier plus the intelligence. The intelligence is detected from the carrier by the crystal which is shown in the interior of the crystal case 46. The crystal will also detect the carrier itself but this is bled off or shorted out through the capacitor which is created by the physical space between the outside cylindrical portion of the case 46 and the RF sleeve 50, the dielectric in this case being the Teflon coating 48. Obviously, any other suitable dielectric might be employed. The detected intelligence is developed across the top of resistor R,; a bias system is created from the 1.5 volt source through resistors R R,, the

crystal itself and radial resistor 44. The bias across the crystal can be varied by adjusting the resistance of R When making this adjustment, R is adjusted for maximum output at point 28, point 30, or the terminal No. 3 on the integrated circuit.

As indicated previously, the signal developed across the top of R is introduced to the integrated circuit at terminal No. 3. Further description of the internal details of the integrated circuit and the transistors Q Q and Q, is believed to be unnecessary except insofar as to state that thisv circuitry has been designed to amplify whatever intelligence is imposed upon the carrier received whether this intelligence is video, audio or computer pulses. Accordingly, the output from point 30 is fed to a suitable monitor which is capable of reproducing the type of signal superimposed on the carrier by the audio, video (black and white or color) or computer information.

Whereas the present invention has been described in particular relation to the drawings attached hereto, it should be understood that other and further modifications, apart from those shown or suggested herein, may be made within the spirit and scope of this invention.

What is claimed is:

1. A short range, low power, microwave system for transmitting and receiving. single channel data which includes a microwave receiver capable of receiving an amplitude-modulated microwave .carrier, said microwave receiver including a receiving antenna, a crystal detector connected directly to the receiving antenna, a first symmetrical resistor connected from said antenna to ground, a second resistor connected to said crystal detector, a bias means connected in series with said crystal detector and said resistors for biasing said crystal, high frequency capacitance means surrounding said crystal and means for amplifying the signal produced at the point of connection between said crystal detector and said second resistor.

2. A microwave system as set forth in claim 1 including an RF shield surrounding said high frequency capacitor and crystal detector.

3. A microwave system as set forth in claim 1 wherein said antenna comprises a pin which projects upwardly into and is properly positioned within a wave guide which receives the microwave signal. 1 t

4. A crystal detector for a microwave receiver comprising a substantially cylindrical crystal assembly containing a crystal therein, a support means for said crystal assembly, a centrally disposed and upwardly projecting pin located within said support means and electrically insulated therefrom, said pin being adapted to project upwardly into a wave guide at a position for the optimum reception of a microwave signal, the other end of said pin being electrically connected to said crystal, a radial resistor positioned on said support means symmetrically disposed about said pin, said symmetrical resistor being connected at one end to said pin and at the other end to said support means, a radio frequency sleeve positioned within said support means between said support means and said crystal assembly, a non-conductive sleeve positioned between said radio frequency sleeve and said crystal assembly, said crystal assembly, non-conductive sleeve and radio frequency sleeve constituting a microwave condenser, a radio frequency shield connected to said support and surrounding said crystal as sembly and said sleeves, a spring contactor mounted within said radio frequency shield and insulated therefrom, one end of said spring contactor engaging said crystal assembly and urging the same into contact with said pin, the other end of said spring contactor being electrically connected to an electrical connection external of said radio frequency shield.

Claims

1. A short range, low power, microwave system for transmitting and receiving single channel data which includes a microwave receiver capable of receiving an amplitude-modulated microwave carrier, said microwave receiver including a receiving antenna, a crystal detector connected directly to the receiving antenna, a first symmetrical resistor connected from said antenna to ground, a second resistor connected to said crystal detector, a bias means connected in series with said crystal detector and said resistors for biasing said crystal, high frequency capacitance means surrounding said crystal and means for amplifying the signal produced at the point of connection between said crystal detector and said second resistor.

3. A microwave system as set forth in claim 1 wherein said antenna comprises a pin which projects upwardly into and is properly positioned within a wave guide which receives the microwave signal.

4. A crystal detector for a microwave receiver comprising a substantially cylindrical crystal assembly containing a crystal therein, a support means for said crystal assembly, a centrally disposed and upwardly projecting pin located within said support means and electrically insulated therefrom, said pin being adapted to project upwardly into a wave guide at a position for the optimum reception of a microwave signal, the other end of said pin being electrically connected to said crystal, a radial resistor positioned on said support means symmetrically disposed about said pin, said symmetrical resistor being connected at one end to said pin and at the other end to said support means, a radio frequency sleeve positioned within said support means between said support means and said crystal assembly, a non-conductive sleeve positioned between said radio frequency sleeve and said crystal assembly, said crystal assembly, non-conductive sleeve and radio frequency sleeve constituting a microwave condenser, a radio frequency shield connected to said support and surrounding said crystal assembly and said sleeves, a spring contactor mounted within said radio frequency shield and insulated therefrom, one end of said spring contactor engaging said crystal assembly and urging the same into contact with said pin, the other end of said spring contactor being electrically connected to an electrical connection external of said radio frequency shield.