US 3419869 A
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Description (OCR text may contain errors)
Dec. 31, 1968 J. ALTMAYER REMOTELY TUNED RADIO ANTENNA Sheet Filed Oct. 2, 1967 INVENTOR. JOH N ALTMAYER Ob mm @9505! E6 \Ov zwtiwzgi H mm V J N w. 6528 move: .2 I o o 0 .V.V(\- \O mm)- mm J a? 0m O mum U w w N H mm J m. 3 E Q f EVE mm mm m BY T 4e A TORNEYS Dec. 31, 1968 J. ALTMAYER HEMOTELY TUNED RADIO ANTENNA Filed Oct. 2, 1967 Sheet III Dec. 31, 1968 J. ALTMAYER REMOTELY TUNED RADIO ANTENNA fiiled Oct. 2, 1967 Sheet United States Patent 3,419,869 REMOTELY TUNED RADIO ANTENNA John Altmayer, Euclid, Ohio, assignor, by mesne assignments, to New-Tronics Corporation, Brook Park, Ohio, a corporation of Ohio Continuation-impart of application Ser. No. 327,713, Dec. 3, 1963. This application Oct. 2, 1967, Ser. No. 676,003
11 Claims. (Cl. 343-703) ABSTRACT OF THE DISCLOSURE A dipole antenna having a feed point approximately midway between its ends wherein: each element can have its electrical length simultaneously increased or decreased whereby the resonant frequency of the antenna can be changed at will to the frequency of the transmitter; or the electrical length of one element can be increased or decreased relative to the electrical length of the other element whereby the impedance of the feed point may be varied to match the impedance of the feed line.
Application This application is a continuation-in-part of my copending application Ser. No. 327,713, now abandoned, filed Dec. 3, 1963, and entitled, Remotely Tuned Radio Antenna.
This invention pertains to the art of radio antennas and more particularly to a radio transmitting antenna which may be adjusted from a position remote from the antenna.
The invention is particularly applicable to a radio antenna of the type generally referred to as a dipole which is electrically energized at a point intermediate its ends and will be described with particular reference thereto although it will be appreciated that the invention has broader applications and may be used in some instances with end-fed quarter wave antennas.
The invention is also applicable to the field of ama teur radio where the frequency of transmission may be varied at will within given bands of frequencies.
Radio antennas of the dipole type generally consist of a pair of colinear electrical elements insulated from each other at the center and energized through a two conductor feed line connected at the other end to a radio frequency power source in the form of a transmitter through suitable coupling or impedance matching arrangements. In amateur radio work, the output frequency 0f the transmitter is usually variable continuously or in steps throughout a given band of frequencies, e.g., 35004000 kc. or 7000-7300 kc.
The electrical elements have a single resonant frequency determined, mostly, by their electrical length and, to a lesser degree by their proximity to the ground or surrounding objects such as buildings or trees. If the transmitter supplies energy at this resonant frequency, the maximum amount of energy supplied to the antenna will be radiated into space. As the frequency of the transmitter shifts from this resonant frequency, either up or down, the radiating efiiciency drops and in rapidly increasing amounts as the frequency difference increases.
It is known to make the electrical length of each element of a dipole adjustable and to provide remotely energized power means for adjusting the electrical length and resonating the antenna to the transmitter frequency. This resonating is done by adjusting the antenna length until a minimum reflected power or standing wave ratio is indicated on the feed line.
The electrical power input to the transmitter in almost all radio work is limited, either by law or by limitations 3,419,869 Patented Dec. 31, 1968 ice of the equipment. It is therefore desirable to have as much of the electrical energy supplied by the transmitter to the feed line to be supplied to the antenna so that it can be radiated. This requires accurate matching of the electrical impedances. The transmitters ordinarily have means for adjusting the impedance of the transmitter to match that of the feed line. However, heretofore, matching the impedance of the feed point of the antenna to that of the feed line has always been a very serious problem. If a mismatch exists at the feed point of the antenna, electrical power supplied to the antenna from the feed line is reflected back into the feed line resulting in excessive power losses in the feed line and in general, inefliciencies. Also damage to the transmitter can result.
At frequencies other than the resonant frequency, the impedances along the antenna change from the above stated values and also become complex, being either capacitive 0r inductive depending upon whether the elements are shorter or longer than the actual resonant length. In either event, when the antenna is not resonant to the transmitter frequency, it is impossible to secure an effective impedance match between the feed line and the feed point of the antenna. As the invention contemplates an antenna which is always resonant to the transmitter frequency, feed point impedance as used hereinafter, means feed point impedance at the resonant frequency.
There are generally two types of feed lines available. One is balanced and consists of a pair of parallel conductors with some form of electrical insulation therebetween. The other is unbalanced and consists of a center conductor and a surrounding coaxial conductor with electrical insulation therebetween. The parallel conductors, depending upon the diameter of the conductors, the physical spacing and the type of electrical insulation therebetween will normally have fixed impedance in the range from to 1200 ohms.
The coaxial conductor, depending upon the dimensions and the dielectric employed will have fixed impedance of from approximately 25 to 200 ohms. 52 and 72 ohm coaxial cables are of reasonable dimensions and are commercially available.
The electrical impedance of a dipole antenna at its resonant frequency is resistive and varies from a maximum at its ends to a minimum at the electrical center, located approximately midway between the ends. The minimum may vary from two to several hundred ohms, depending upon many factors, e.g. the dimensions of the conductors making up the elements; the electrical height of the antenna above the ground; whether the antenna elements are full length or shortened with loading coils placed intermediate their ends; or the proximity of other objects to the elements, such as trees, houses, or directing or reflecting elements. When directing or reflecting elements or loading coils are used, the minimum impedance is usually always below 50 ohms.
Heretofore it has been conventional to select an appropriate feed line, connect it to the feed point of the antenna and accept any mismatches in the impedance of the feed line and the impedance at the feed point as inevitable. Thus, heretofore standing wave ratios so long as they were below two to one were considered satisfactory.
Alternatively it has been conventional to provide impedance matching devices and adjust them when the antenna is on the ground to obtain a minimum standing wave ratio. However, when the antenna is hoisted into position (because of the change in the minimum impedance of the antenna due to the change in some of the factors above discussed and particularly the height of the antenna above the ground) usually the standing wave ratio also increases, necessitating lowering the antenna and making a readjustment. oftentimes the antenna had to be raised and lowered several times to achieve the optimum condition with the antenna in its ultimate position.
It has also been known to hoist the antenna into position and then climb a tower or mast and adjust the impedance matching devices with the antenna in place. This is not only dangerous but if the weather is incumbent can be quite uncomfortable.
Both of these previous known ways of adjusting the input impedance were all complicated by the fact that even though the matching device was once adjusted to obtain a standing wave ratio of unity, it did not always remain so. Thus, the impedance of the antenna at the feed point can change due to numerous factors e.g. the antenna being rotated about a vertical axis so that one element is brought into closer proximity with another object than the other element, or the antenna is tilted about a horizontal axis such that one element is brought closer to the ground than the other element; or a tree grows or loses its leaves as winter approaches; or weather conditions may change. While remotely powered adjustable impedance matching devices are known, they have heretofore been unduly complicated and diflicult to operate. In the alternative they have been separate from the power means for adjusting the resonant frequency of the antenna.
The present invention provides a radio antenna comprised of a pair of elongated antenna elements with their adjacent ends insulated to form a feed point for a twin conductor feed line which elements include means for adjusting their electrical length, which antenna overcomes all of the above-referred objections and enables the resonant frequency of the antenna to be readily adjusted to the transmitter frequency and also enables the impedance of the feed point at the resonant frequency to be adjusted so as to match exactly the impedance of the feed line.
In accordance with the present invention, power means are provided for operating each adjusting means in combination with remote energizing means for the power means and control means so arranged as to either: simultaneously increase or decrease the electrical length of each element; or, to increase or decrease the electrical length of one element relative to the other.
By simultaneously increasing or decreasing the electrical length of each element, the resonant frequency of the antenna can be readily varied.
By increasing or decreasing the electrical length of one element relative to the other element, the feed point of the antenna is shifted relative to the point of minimum impedance or the electrical center of the antenna. Because the impedance of an antenna increases from a minimum at its electrical center, by oifsetting the feed point from the electrical center of the antenna, the impedance of the feed point can be varied to almost any desired value and in particular can be varied to match the impedance of any known .feed line so long as the minimum antenna impedance is equal to or less than the feed line impedance.
Thus a single dipole antenna can be used readily with either parallel wire or coaxial wire type feed lines with absolute matching of the impedances,
The energizing means for the power means when increasing or decreasing the electrical length of one element relative to the other may be arranged to, increase or de crease the electrical length of one element only; or may be arranged to increase the electrical length of one elernent while at the same time decreasing the electrical length of the other element.
The electrical length of the elements may be varied in any one of a number of different ways e.g. by providing an extensible member at the end of each element; by making each element itself extensible, by varying the number of turns in a loading coil placed intermediate the ends of each element; or by moving various loading members along the outside of an element in a manner such as to effectively change the electrical length.
Electrical length as used herein is one-half the wave length of the resonant frequency of the antenna taking into account all of the various factors which determine the resonant frequency such as the dimensions of the elements, various lumped impedances thereon or the proximity of adjacent objects. Because of the unbalance of these factors, the electrical center of the antenna need not necessarily be at the mechanical center.
It is believed that I am the first to ever have provided a dipole antenna which can be both readily tuned by a remote control and to have its feed point impedance matched to the feed line impedance by remote control.
It is also believed that the mechanism for accomplishing this is novel and thus further in accordance with the present invention there is provided a radio antenna comprised of a housing and a pair of elongated coaxially aligned conductive antenna elements extending in opposite directions from the housing, each element having at its remote ends an elongated extensible conductive antenna member movably secured thereto for purposes of varying the overall length of each element so as to vary the electrical length of the elements. Further power means are provided in the housing for simultaneously extending and retracting each antenna member so as to vary the electrical length of the antenna thus vary its resonant frequency as well as extending and retracting one of the antenna members so as to vary the electrical length of one element only or for extending and retracting one antenna member while retracting and extending the other antenna member so as to simultaneously vary the electrical length of the two elements but in opposite directions.
The primary object of the present invention is to provide a radio antenna in which the resonant frequency may be readily varied to the frequency of the transmitter and the impedance of the feed point may be readily varied to match the feed point of the feed line.
Another object of the present invention is to provide a radio antenna in which a standing wave ratio of unity can be obtained at all frequencies and with all conventional feed lines.
A further object of the present invention is to provide a radio antenna in which the impedance of the feed point may be readily varied.
Another object of the present invention is to provide an antenna which is electrically energized at a point intermediate its ends and its length is remotely adjustable so as to resonate at a desired operating frequency, as well as match its impedance at its feed point to the feed line.
A still further object of the present invention is the provision of an antenna having reversible motor means and motor control means for controlling same to vary the length of the antenna so as to resonate it at a desired operating frequency, as well as obtain impedance matching of the antenna at its feed point with the feed line.
These and other objects and advantages of the invention will become apparent from the following description used to illustrate the preferred embodiment of the invention, as read in connection with the accompanying drawings in which:
FIGURE 1 is a schematic elevational view illustrating the preferred embodiment of the invention;
FIGURE 2 is an enlarged sectional view taken along line 22 of FIGURE 1;
FIGURES 3, 3A, 3B and 3C constitute a longitudinal section of one-half of the antenna shown in FIGURE 1;
FIGURES 4 and 4A constitute a fragmentary plan view of FIGURE 3; and
FIGURE 5 is a schematic circuit diagram of a motor control circuit in accordance with the invention.
Referring now the drawings and more particularly FIG- URE 1, there is shown a center fed, half wave dipole antenna comprising an aluminum housing 12 having a pair of hollow coaxially aligned antenna elements 14 and 16, extending therefrom in opposing directions. Antenna element 14 is of fixed length and includes an aluminum cylindrical sleeve 18, a hollow resonator coil assembly 22 and another aluminum cylindrical sleeve 26. Similarly, antenna element 16 is of fixed length, equal to that of element 14, and includes an aluminum cylindrical sleeve 20, a hollow resonator coil assembly 24 and another aluminum cylindrical sleeve 28.
Extending coaxially from antenna elements 14 and 16 are extendable aluminum antenna members 30 and 32 respectively, shown in their fully extended positions in FIGURE 1. As is more fully described hereinafter, antenna members 30 and 32 retract into and extend from the antenna elements so as to vary the length of the antenna 10.
Radio frequency power is applied to the antenna 10 at spaced feed points or antenna terminals 34 and 36 from a transmitter 38 via an SWR (Standing Wave Ratio) indicator or meter 40. Any suitable feed line may be used to connect terminals 34 and 36 with the transmitter 38, although, as shown in FIGURE 1, a coaxial cable 42 is provided having a characteristic impedance of approximately 52 ohms.
Each extendable antenna member 30 and 32 is connected to a reversible motor located within the housing (not shown in FIGURE 1) for purposes of varying the length of the antenna 10 to tune same. In tuning the antenna 10, utilization is made of a motor control console 44 connected to the two reversible motors via lead pairs 46 and 48 to control the operation of the motors. The control console 44 includes a switch lever 47, selectively actuable to L0 and Hi positions for simultaneously energizing both motors to extend or retract the extendable antenna members 30 and 32. A spring biased, normally closed, push button switch 50 is provided on the top of console 44 for purposes of de-energizing one of the reversible motors so that fine tuning of the antenna 10 may be accomplished by extending or retracting only one of the extendable antenna members 30 and 32. Lastly, the console 44 is provided with an indicator lamp 52, which in accordance with the invention is energized and glows brightly only when one or both of the reversible motors in housing 12 is energized.
Referring now to FIGURES 1 2 and 3, the housing 12 comprises a left half portion 54 and a right half portion 56 separated by a suitable gasket 58 to provide a weather tight seal. Housing portions 54 and 56 are secured together by any suitable means, such as nut and bolt assemblies 60. The housing 12 rests in a cradle -62 and is secured thereto by means of a pair of straps 64. The cradle 62 is mounted to the top of a post or pipe 66, as by screw-threading 68 and lock screw 70, in such a manner that antenna elements 14 and 16 are horizontally aligned with respect to ground level so as to thereby insure relatively constant capacitance to ground along the length of the antenna.
Having briefly described the general arrangement of the invention with particular reference to FIGURE 1, attention is now directed to the various structural and operative features of the invention, as enumerated in FIGURES 2 through 5. Since the structural features of both halves of the antenna 10, i.e. including the left and right half portions 54 and 56 of housing 12 and extending outwardly therefrom to the antenna members 30 and 32, are the same, only the right half of antenna 10 will be described in detail. It is to be understood that the following detailed description applies equally to the left half of antenna 10.
The right half housing portion 56 includes an outwardly extending cylindrical sleeve 72, see FIGURE 3, coaxially surrounding an antenna sleeve 20 for a portion of its length adjacent one end, and is insulated therefrom by means of a cylindrical insulator 74. A pair of set screws 76 extend through the sleeve 72 for purposes of applying forces directed radially inward to the insulator 74 and sleeve 20 to secure same in place.
The housing 12 defines a chamber 78 containing a pair of reversible AC. motors 80 and 80a in the right and left half portions 56 and 54, respectively. Motor 80 is secured to the walls of housing portion 56 as by bolts 82, and is provided with an output shaft 84 connected to a nylon shaft cOupling 86 via a gear train 87.
Coupling 86 serves to transmit rotational forces developed by motor 80 to a threaded shaft 88 keyed at one end to coupling 86 as by a pin 90. The threaded shaft 88 is rotatably supported in coaxial relationship within antenna sleeve 20 by a bearing 92 positioned within an aluminum separator block 94. The block 94 is of circular crosssection and is located within sleeve 20 as shown in FIGURE 3 and includes an O-ring 96 seated in an annular groove 97 in the block in fluid sealing engagement with sleeve 20. The block 94 also receives and supports one end of an elongated cylindrical steel tube 98 which coaxially surrounds the threaded shaft 88.
The terminal 36 includes a threaded cadmium plated terminal stud 100 which extends through insulator 74, antenna sleeve 20 is threaded to a threaded passage 101 in the separator block 94. In this manner, a good electrical circuit is obtained between terminal stud 100 and the antenna sleeve 20. An insulator 102 is received by stud 100 for purposes of electrically insulating a conductor lead 104 of coaxial cable 42, as well as stud 100 from the housing 12. Further, insulators 74 and 102 insure electrical insulation of terminal 36 from terminal 34 as well as antenna sleeve 20 from antenna sleeve 18. Conductor lead 104 is provided with a suitable terminal end 106 for attachment to stud 100 and is held in place thereto by a nut 108.
Referring now to FIGURE 3A, there is shown a portion of the antenna adjacent that illustrated in FIGURE 3. A second aluminum separator block 110, similar to block 94, is also located within sleeve 20 and receives and supports the other end of tube 98. Tube 98 is fixed to block 110 by means of a set screw 112, threaded through block 110 into tight engagement with tube 98. An O-ring 114 is seated in an annular slot 116 of block 110 in fluid sealing engagement with antenna sleeve 20.
Intermediate separator blocks 94 and 110, an annular nut 118 is threaded to the threaded shaft 88. Nut 118 is provided with an annular flange 120 which is press fitted to a brass push rod tube 122, which coaxially surrounds the remaining length of shaft 88. Tube 122 is supported by and extends through block 110 by means of an annular bearing 124 seated in block 110 intermediate tube 9 8 and tube 122.
Nut 118 is provided with an annular channel 126 in its exterior surface to which a steel strap 128 is secured as by spot welding. Strap 128 includes a depending relatively fiat flange 130, which extends radially outward of nut 118. In assembly nut 118 is positioned relative to tube 98 so that flange 130 extends through a slot 132 (see FIGURES 4 and 4A) extending longitudinally throughout the length of tube 98. Flange 130 serves, when rotational forces are applied to the threaded shaft 88 from the motor 80, to engage the longitudinal walls of tube 9 8 defining the slot 132. In this manner, nut 1'18 resists rotational displacement and the rotational forces transmitted to screw shaft 88 are converted by means of the threadings on the shaft and the nut into forces directed axially of shaft 88, so as to thereby provide axial motion of push rod tube 122.
Referring now to FIGURE 3B, there is shown another portion of the antenna immediately adjacent and extending outwardly from the portion illustrated in FIGURE 3A. The hollow resonator coil assembly 24 is secured to the outward extending end of antenna sleeve 20 and comprises a cylindrical insulator sleeve 134, which is preferably constructed of laminated phenolic material. An inductor coil 136 is helically wound on the exterior surface of insulator 134 and is connected at each end to cadmium plated brass end caps 133 and 140 by means of terminals 142 and 144 respectively. End cap 138 coaxially surrounds a portion of the length of insulator 134 adjacent one end thereof, and is secured thereto by means of a screw 146. Also, the end cap 138 includes 2. depending cylindrical portion 148 which is received within the outwardly directed end of antenna sleeve 20. Sleeve 28 is provided with a compression slot 150 extending longitudinally of the sleeve for a portion of its length adjacent tis outward end. In this manner, after portion 148 of end cap 138 is received by the outward end of sleeve 20, a clamp 152 may be wrapped tightly about the exterior surface of sleeve 20 and by virtue of compression slot 15 9 secured end cap 138 in place. End cap 148 coaxially surrounds insulator 134 for a portion of its length adjacent its other end and is secured thereto by means of a screw 154 or a press fit. End cap 140 is provided with a cylindrical sleeve portion 156 of smaller diameter than insulator 134, which serves to receive therein an aluminum elongated cylindrical antenna sleeve 158 in a tightly press fitted relationship so as to obtain a good electrical contact between end cap 148 and sleeve 158.
The outward extending end of push rod tube 122 coaxially surrounds a portion of the length of an aluminum rod 160 adjacent one end thereof, and is secured thereto as by press fitting. Rod 160 extends through and is slid ably supported by an insulator bushing 162, and is secured at its other end to an insulator rod 164 by means of a coupling 166. Coupling 166 is press fitted to rod 164 at one end and fastened to rod 160 at the other end by means of a set screw 168. Rod 164 may be constructed of fiber glass and is of a suificient length that it extends completely through the length of the resonator assembly 24 when the antenna is extended between fully retracted and fully extended positions so as to provide a minimum of electrical interference with the resonator assembly.
Reference is now made to FIGURE 3C which illustrates the outermost portion of the antenna adjacent that illustrated in FIGURE 3B. Rod 164, in addition to extending through resonator coil assembly 24, extends for a portion of its length coaxially through antenna sleeve 158, and is secured at its outer end to the extendable antenna member 32, as by a press fit. Antenna member 32 is coaxially received within antenna sleeve 158 and is in frictional sliding engagement therewith at inward end portion 170 of member 32 and at a recessed portion 172 of sleeve 158. Recessed portion 172 is provided with a longitudinally extending inwardly flanged slot 183, which serves to apply a frictional drag force of approximately pounds on antenna member 32 which insures a good electrical contact between antenna sleeve 158 and antenna member 32. A short length of plastic tubing 174 is heat shrunk fitted to sleeve 158 about recessed portion 172 to provide a weather tight seal over slot 183. Tubing 174 also includes an annular flange portion 176 which is maintained in frictional contact with antenna member 32, providing a weather tight seal therewith. To reduce and minimize effects of corona discharge, a metal ball 178 is press fitted to the outer end of antenna member 32. Sleeve 15-8 is also provided with a longitudinally extending slot 181 which serves as a breather slot for purposes of emitting air to the interior of the antenna to evaporate any water trapped therein. Preferably during assembly of the antenna care should be taken to align breather slot 181 and compression slot 150 in antenna sleeve 20 on the under side of the antenna, i.e., facing ground to prevent rain water and the like from being passed to the interior of the antenna.
Referring now to FIGURE 4, there is shown within chamber 78 of housing 12, a pair of limit switches 180 and 182. Limit switch 180 comprises a pair of contact reeds 184 and 186 mounted in spaced relationship to the housing 12 by means of an insulator block 188. Similarly,
limit switch 182 comprises a pair of contact reeds 190 and 192 mounted in spaced relationship to each other by means of insulator block 188. Contact reeds 184 and 190 extend beyond reeds 186 and 192, and are respectively secured at their extended ends to opposite sides of a limit switch actuator 194. An elongated rod 196 is secured at one end to the actuator 194- as by providing a right angle bend at the end of the rod 196 and passing it through a transverse passage 1% in actuator 194, as shown in FIGURE 3. Rod 1% extends longitudinally through antenna sleeve 28 and is received and slidably guided by a slot 188 extending longitudinally through separator block 94 and by a slot 200 extending longitudinally through separator block 110. Intermediate the ends of rod 196 there is provided a U-shaped bend portion 202 defined by right angle legs 2G4 and 2% of rod 1%. Legs 204 and 206 are located in the travel path of flange and are spaced from each other by a distance relative to the axial length of flange 130 so that just before antenna member 32 is fully retracted, flange 130 will engage leg 204 and thereby push rod 1% to the left, as viewed in FIGURE 4. With the antenna member 32 in its fully retracted position, as shown in FIGURE 4, switch is open. Similarly, just before antenna member 32 is in its fully extended position, flange 130 will engage leg 206 pushing rod 196 to the right, as viewed in FIGURE 4, to open the limit switch 182. Contact reeds 184 and 1% are spring biased toward each other so that when the antenna member 32 is between its fully retracted and fully extended positions the limit switches 188 and 182 will be closed.
Referring now to FIGURE 5, there is illustrated a schematic circuit diagram of the motor control circuit housed within control console 44 and a schematic circuit diagram of the connections between the reversible capacitor-split phase motors 80 and 80a located within housing 12. The circuit of motor 88 includes a pair of stator field windings 208 and 210 connected together in series across a capacitor 212. Similarly, the circuit of motor 80a includes a pair of stator field windings 214 and 216 connected together in series across a capacitor 218. Limit switches 180 and 182 within the right half portion 56 of housing 12 are respectively directly connected in series with field windings 210 and 208. Also, included Within the left half portion 54 of housing 12 is a pair of limit switches 180 and 18211 respectively identical in structure and operation to limit switches 18 0 and 182. Limit switch 188a is directly connected in series with field winding 216 and to one side of limit switch 180, and limit switch 182a is directly connected in series with field winding 214 and to one side of limit switch 182 so that the two motor control circuits are electrically connected in parallel.
The control console 44 contains a motor control circuit including a transformer core 220 having a primary winding 222 wound thereon and connected across an alternating voltage source 224 via armature 225 and contacts 227 and 229 of a double pole, double throw switch S. Transformer core 221! has a secondary winding 226 wound thereon having terminals 228 and 230 at opposite ends of the winding. Terminal 228 is directly connected with a junction point 238 of field windings 214 and 216, and is connected with a junction point 232 of field windings 208 and 210 via normally closed push button switch 50. Switch lever 47, on the face of control console 44 (see FIGURE 1), is connected to and operates an armature 234 of double pole, double throw switch S, provided for reversing the operation of the field windings of motors 80 and 88a. Switch S includes a Lo position contact 236 corresponding to the L0 position of switch lever 47 and a Hi position contact 238 corresponding with the Hi position of switch lever 47. Lo contact 236 is connected to a junction point 240 intermediate limit switches 182 and 182a. Similarly, the Hi contact 238 is connected to a junction point 242 intermediate limit switches 180 and 9 182a. The armature 234 of switch S is connected to the terminal 230 of the secondardy winding 226 via motor energized indicating lamp 52 connected in parallel with a resistor 244.
The motor control circuits of motors 80 and 800: are arranged so that when armature 234 of switch S is in contact with Lo contact 236, the motors operate to drive the extendable antenna members toward their fully extended positions. The reverse is true when armature 234 is in contact with Hi contact 238.
It will be observed from FIGURE that when armature 234 of switch S in in contact with Lo contact 236, lamp 52 will be in the motor energizing circuit of the field windings of motors 80* and 8011, respectively. Thus, lamp 52 will glow brightly until both antenna members 30 and 32 reach their fully extended positions, causing limit switches 182 and 182a to open. Similarly, when armature 234 is in contact with Hi contact 238, lamp 52 will be in the motor energizing circuit of field windings and will glow brightly until both antenna members 30* and 32 reach their fully retracted positions, opening limit switches 180 and 180a. In this manner, an operator stationed at the control console 44 is informed by lamp 52 whether or not either of the motors 80 and 80a is energized.
In the operation of antenna 10, as with most antennas, greatest radiation efliciency is obtained when the antenna is tuned to resonate at a desired frequency of operation within the frequency band of the antenna. Thus, for example, a 40 meter band includes operating frequencies from 7.0 to 7.3 mc. (megacycles, and a 75 to 80 meter band includes operating frequencies from 3.5 to 4.0 me. The length of antenna 10 determines whether it is tuned to resonate at the operating frequency during which the radiation efficiency of the antenna is maximum. Also, in the operation of antenna 10 the transfer of power from coaxial cable 42 to the antenna 10 is greatest When impedance matching is obtained, i.e., when the characteristic impedance of coaxial cable 42 is equal to that of the antenna 10 at the feed point, terminals 34 and 36, If the two impedances are equal no reflected power is present. In this condition no standing waves will appear on the feed line (coaxial cable 42) and, hence, the standing wave ratio will be equal to unity. The standing wave ratio (SWR) may be defined as:
Reflected power Forward power Hence, it is seen in view of the above equation that as reflected power increases (due to impedance mismatching) the SWR increases and the radiation efliciency of antenna 10 decreases.
SWR indicator 40 connected in the feed line (coaxial cable 42) between antenna 10 and transmitter 38 provides the operator with knowledge as to the SWR, which for best operation should be unity. With the extendable antenna members 30 and 32 fully retracted the antenna will be outside of the high frequency end of the operating frequency band of the antenna by a length approximately corresponding to 50 to 100 kc. (kilocycles). At this point, the operator should excite the antenna with radio frequency power at a frequency within and near the high frequency end of the operating frequency band of the antenna. The excitation should be with just enough power to obtain an indication on SWR indicator 40 of the presence of reflected power, i.e., any SWR reading greater than unity. The operator should now turn the motor control switch lever 47 to its Lo position. By doing so, armature 234 of switch S will engage the L0 contact 236, thereby energizing the field windings of reversible motors 80 and 80a via limit switches 182 and 182a respectively whereby the motors will operate to drive the extendable antenna members 30 and 32 toward their fully extended positions. Since lamp 52 is in the electrical circuit of the motor windings it will glow brightly due to current flow therethrough and thereby inform the operator stationed at the control console 44 that the antenna motors and 80a are energized.
While antenna members 30 and 32 are being driven toward their fully extended positions to increase the length of the antenna 10, the operator should monitor the SWR indicator 40. When a reading on the SWR indicator 40 is at a minimum SWR level, minimum power is being reflected indicating that the antenna 10 is tuned to resonate at the chosen excitation frequency. At this point switch lever 47 may be turned to disconnect armature 234 from L0 contact 236, thereby deenergizing motors 80 and 80a and the indicator lamp 52.
Although by the above procedure, the antenna 10 may be tuned to resonate at the excitation or operating frequency of transmitter 38, the characteristic impedance of coaxial cable 42 may not be matched to the impedance of antenna 10 at the feed point, i.e., at terminals 34 and 36. To achieve impedance matching the operator depresses push button switch 50, as indicated by the arrow in FIGURE 5, to open same and thereby disconnect motor windings 208 and 210 from the transformer secondary winding 226. While the operator maintains switch 50 opened, he should alternately position switch lever 47 to its Hi and Lo positions so as to respectively energize windings 214 and 216 of motor 80a in opposite senses relative to each other. In this manner, antenna member 30 is alternately extended and retracted. While alternating the position of switch lever 47 the operator monitors the SWR indicator 40 until it is established in which direction the antenna member 30 must be driven to decrease the value of the SWR. With this knowledge the operator will next turn the switch lever 47 to the appropriate position for driving the antenna member 30 in the direction which results in a lower SWR reading until the reading has past slightly through its minimum value. The operator should now release switch 50, permitting it to close, and once again position switch lever 47 to its Hi or L0 position to drive both antenna members 30 and 32 until resonant antenna length is obtained, i.e., when the reading on the SWR indicator 40 is at a minimum SWR level. At this point the operator should again depress and maintain switch 50 opened and alternate the position of switch lever 47 and repeat the previous procedures for impedance matching. It has been found in practice that in tuning antenna 10 by repeating the foregoing impedance matching procedure, a reflected power of almost zero, i.e., a SWR reading of unity, may be obtained with 500 watts directed forward. .Under these circumstances if the operator measured the right and left halves of antenna 10, as viewed in FIGURE 1, he might note a differential in length ranging from /2 inch to 6 inches, or more depending upon the operating frequency band, type of installation and antenna environment.
In practicing the invention it has been found that normally to vary the operating frequency up and down the frequency band of operation, it is necessary only to position switch lever 47 to the Hi or L0 position to turn the antenna 10 to resonate at the desired operating frequency. Under such conditions the SWR will remain substantially constant across the frequency band. Further, it has been found that the antenna 10 has exceptional Q and, therefore, it has been found desirable to locate control console 44 in a readily accessible position for the operator so that the antenna can be tuned to resonance as frequency excursions are made. This will keep the SWR at a low value at all times, as well as maintaining the received signal at a maximum level. It has been found that it is permissible to deviate from the resonant frequency by approximately plus or minus 10 kc. and still maintain an SWR of less than 2 to 1.
While the preferred embodiment energizes one motor only for impedance matching, it will be appreciated that if only one of the members 30, 32 is moved to change the impedance of the feed point, the resonant frequency of the antenna will be changed slightly requiring a readjustment of both members. Thus alternatively the switch 50 in accordance with the invention can 'be so arranged as to reverse the direction of rotation of one motor 80 relative to the other motor 80a so that when the switch lever 47 is placed in either the high or low position, the two motors will rotate in opposite senses relative to each other so as to extend one antenna member 30 or 32 while at the same time retracting the other in an equal amount such that the resonant frequency of the antenna will not change during adjustment of the impedance of the feed point. Still further alternatively, the switch 50 can be arranged so that all three types of adjustments may be made. As the circuit changes are within the abilities of those skilled in the art, the circuits to accomplish this type of control are not shown. Instead of using two motors, only one may be employed with a selectively actuated reversing gear between the motor and one member only.
It will also be appreciated that rather than use the extensible members 30, 32 the tubular elements 14, 16 could be made extensible or means be provided for changing the number of turns on the coils.
In all events the invention contemplates either: simultaneously increasing or decreasing the electrical length of the two elements to tune the antenna to the frequency of the transmitter; or changing the electrical length of one element relative to the other element to change the impedance of the feed point.
The invention has been described in connection with a particular preferred embodiment, but is not to be limited to the same. Various modifications may be made without departing from the scope and spirit of the present invention as defined by the appended claims.
Having thus described my invention, I claim:
1. A remotely adjustable radio antenna comprised of a pair of elongated elements having adjacent ends in insulated relationship to form a feed point, each of said elements including means for changing its electrical length power means for actuating said changing means, energizing means for said power means located remote from said antenna, said energizing means including control means for energizing said power means to simultaneously increase or decrease the electrical length of each element whereby the resonant frequency of the antenna may be changed; or for increasing or decreasing the electrical length of one element relative to the electrical length of the other element whereby the impedance of the feed point may be changed.
2. The combination of claim 1 wherein said changing means include an antenna member slidably extending from the end of each antenna element and in electrical contact therewith.
3. The combination of claim 2 wherein said power means include an electric motor associated with each element and operatively connected to its extendable member.
4. The combination of claim 3 wherein said control means is arranged to simultaneously energize both motors for rotation in one direction and the other to simultaneously extend or retract said antenna members or for energizing one of said motors only in either direction to extend or retract one of said members only.
5. The combination of claim 3 wherein said energizing means include switch means for: energizing said motors for rotation in one direction or the other for simultaneously extending or retracting said antenna members; or energizing said motors for rotation in both directions so as to retract one member and extend the other member.
6. A method of tuning a half-wave dipole antenna having extendable and retractable end members extending in opposing directions comprising the steps of applying radio frequency power to the antenna via a feed line connected to a feed point on the antenna, continuously measuring the reflected power from the antenna at the feed point thereof, varying the length of the antenna by simultaneously extending and retracting both said antenna members until a minimum value of reflected power is measured, and matching the impedance of said feed line to that of the antenna at said feed point by extending or retracting one of said antenna members relative to the other to change the relative length of each pole of the antenna until a further minimum value of reflected power is obtained.
7. A method of tuning a half-wave dipole antenna having extendable and retractable end members extending in opposing directions and reversible motor means for independently extending and retracting said members so as to tune said antenna to resonate at an operating frequency within the frequency band of said antenna, and comprising the steps of applying radio frequency power to said antenna via a feed line connected to a feed point on said antenna at a desired frequency of operation, continuously measuring the standing wave ratio of said antenna and feed line, energizing said motor means to simultaneously extend or retract said antenna members until a minimum value of standing wave ratio is obtained, and matching the impedance of said feed line to that of said antenna at said feed point by energizing said motor means in a manner to change the relative length of one pole relative to the other pole of said antenna until said standing wave ratio is at a further minimum.
8. A method of tuning of half-wave dipole antenna having extendable and retractable end members extending in opposing directions and reversible motor means for independently extending and retracting said members so as to tune said antenna to resonate at an opening frequency within the frequency band of the antenna, and comprising the steps of applying radio frequency power of the antenna via a feed line connected to a feed point on the antenna, continuously measuring an indication of the value of the reflected power from the antenna at the feed point thereof, varying the length of the antenna by energizing said motor means to simultaneously drive both said antenna members in opposing directions until a minimum value of reflected power is measured, and matching the impedance of said feed line to that of the antenna at said feed point by energizing said motor means in a manner to alternately drive only one said antenna member is opposing directions until it is established in which direction said antenna member must be given to obtain an even smaller measurement of reflected power and then energizing said motor means to drive said one antenna member in that direction until a measurement of minimum reflected power is obtained.
9. A method of tuning a half-wave dipole antenna having extendable and retractable end members extending in opposing directions and reversible motor means for independently extending and retracting said members so as to tune said antenna to resonate at an operating frequency within the frequency band of said antenna, and comprising the steps of energizing said motor means to fully retract said antenna members so as to define an antenna length corresponding to a resonant frequency outside the high frequecy end of the frequency band of said antenna, applying radio frequency power to said antenna via a feed line connected to a feed point on said antenna at a frequency near the high frequency end and Within said frequency band, continuously measuring the standing wave ratio of said antenna and feed line, energizing said motor means to simultaneously extend said antenna members until a minimum value of said measurement of standing wave ratio is obtained, and matching the impedance of said feed line to that of said antenna at said feed point by energizing said motor means in a manner to alternately drive only one of said antenna members in opposing directions until it is established in Which direction said member must be driven to obtain an even smaller measurement of standing wave ratio and then driving said member in the direction until said measure- 13 ment of the value of the standing wave ratio is at a minimum.
10. The method as claimed in claim 8, including an additional step after said one antenna member has been driven in the direction to obtain a measurement of minimum reflected power, said additional Steps including energizing said motor means to again simultaneously drive both said antenna members in opposing directions until a minimum value of reflected power is measured so as to obtain a resonant length of said antenna, corresponding to said operating frequency.
11. In combination a dipole antenna having a feed point intermediate its ends connected with an unbalanced electrical feed line for supplying radio frequency power to said antenna;
first and second coaxially aligned elongated conductive antenna elements extending in opposing directions from said housing;
first and second elongated extendable conductive an tenna members movably secured to said first and second antenna elements, respectively, for varying the length of said antenna;
first and second reversible motor means for extending and retracting said first and second antenna members, respectively;
motor control circuit means for selectively energizing both said first and second motor means whereby the antenna length may be varied to obtain a resonant antenna length for a selected excitation frequency of the applied power or only one of said motor means for unbalancing said feed point relative to the opposing ends of said antenna members so as to match the impedance of said antenna to that of said unbalanced feed line; said motor control means includfirst switching means having a first condition for energizing both said motor means to extend both said antenna members and a second condition for energizing both said motor means to retract both said antenna members; and
second switching means for disabling only a selected one of said motor means, whereby the other of said motor means may be energized by said first switching means so that only one of said antenna members is extendable and retractable for impedance matching.
References Cited UNITED STATES PATENTS 1,911,234 5/1933 Meyer 343823 2,069,513 2/1937 Wolff 343-823 2,644,089 6/1953 Bliss 343-724 2,861,267 11/1958 Arrasmith 343823 ELI LIEBERMAN, Primary Examiner.
US. Cl. X.R. 343--749, 823