US2414809A

US2414809A - Antenna loading apparatus

Info

Publication number: US2414809A
Application number: US483031A
Authority: US
Inventors: John W Hammond
Original assignee: Bendix Aviation Corp
Current assignee: Bendix Aviation Corp
Priority date: 1943-04-14
Filing date: 1943-04-14
Publication date: 1947-01-28
Anticipated expiration: 1964-01-28

Description

jme 11%? J. w. HAMMOND 9 9 6 ANTENNA LOADING APPARATUS Filed April 14, 1943 3 STIeetS-Sheet l I'M/Hammond.

Jan. 28, 1947. M ND 2,414,809

ANTENNA LOADING APPARATUS Filed April 14. 1943 V s Sheets-Sheet 2 Jan. 28, HAMMOND ANTENNA LOADING APPARATUS 3 Sheets-Sheet 3 Filqd April 14, 1943 -uunqgfn Patented Jan. 28, 1947 UNITED STATES PATENT OFF-ICE ANTENNA LOADING APPARATUS Application April 14, 1943, Serial No. 483,031

14 Claims.

This invention relates to antenna tuning apparatus and more particularly to antenna loading devices for securing maximum radiation of low frequency energy from aircraft antennas at high altitudes. The antennas used by aircraft are limited in size by the requirements of aerodynamics and manueverability so that when radio frequency energy at frequencies below 500 kilocycles per second is to be radiated, the antennas used are characterized by very high capacitive reactance. For maximum radiation of power, it is necessary that the high negative reactance of the antenna be cancelled by an equally high ositive reactance (inductance) in the circuits between the output stage of the transmitter supplying the energy and the antenna. So long as transmitters were designed to work over only one frequency band, it was most convenient to provide all the necessary circuit elements within the transmitter housing, and when the frequency band over which the transmitter operated was sufficiently high to eliminate the need for the reactance neutralizing, or loading provisions as they are called, these were omitted with a consequent decrease in the size and weight of the transmitter.

Antenna loading circuits in which the amount of negative reactan e to be neutralized is large are characterized by the appearance of very high voltage across the loading reactor and the antenna as is customary in resonant series circuits, and the presence of these voltages requires that the equipment be designed to provide very large clearance between all parts of the antenna circuit at h gh voltage to prevent corona and arc-over. When radiating modulated continuous waves with a power of 100 watts at 300 kilocycles, it is not unusual to find peak potentials of 20.000 volts at the terminals of the antenna and the loading inductor with some of the frequently employed types of antennas.

The large spacings to prevent corona and arcover are necessary only at low frequencies, and t is obviously wasteful of space and material to make any such provisions in high frequency trans mitters. Therefore, with the advent of multiple channel transmitters in which the individual channels may be set to operate at any frequency between 300 kilocycles and 10 megacycles per second, the antenna loading equipment was eliminated from the transmitter itself and made available in a separate unit, termed an antenna loading unit. With the equipment split up in this manner, it is possible for those individuals requiring only the use of high frequency channels to install only the transmitter unit in the aircraft, eliminating the weight of the antenna loading unit which is superfluous for their purposes, while in. installations in which low frequency operation is required, both the transmitter itself and the antenna loading unit are installed. The apparatus described herein is an improved antenna loading unit and is designed to be connected between the output of a radio transmitter and an antenna.

It is customary to control multiple channel transmitters remotely; that is, the operation of a remote control box located conveniently to the operator switches the transmitter, which may be located in an entirely different part of the aircraft, into operation on a preset channel frequency and the antenna loading units now in use are also adapted for remote control, automati ally inserting a coil of preset inductance between the transmitter and antenna on the low frequency channels, a different coil for each channel, and connecting the transmitter output directly to the antenna on all the high frequency channels. In the antenna loading unit, it has been customary to use a diiferent coil for operation on each low frequency channel with the various coils selected by means of a large rotary tap switch and the high voltages encountered have for ed the use of very great spacing for the taps to prevent arc-over when operating under the low air pressures characteristic of very high altitudes. The resultant switch design has been large. bulky, fragile, and d fficult to manufacture, and the large number of coils required to provide for operation on a number of channels has been such as to impart excessive weight and bulk to the antenna loading unit.

One of the rin ipal obiects of this invention is to provide an improved remotely controlled multiple channel antenna loading unit of lesser bulk and weight than the equipment hitherto available.

Another object of the invention is to provide a new and novel remotely controlled mult ple channel antenna loading unit operating safely into antennas having high capa itive reactance at higher altitudes than possible with equipment previously available.

A further object of the invention is to provide a new and novel remotely controlled multiple channel antenna loading unit in which unused elements do not absorb power from the transmitter output.

The above objects and advantages are accomplished by the use of three serially connected variometers carried on a common rotatable shaft with taps brought out from each of the variometers, a vacuum relay alternatively connecting the transmitter output directly to the antenna and to the antenna in series with one or more of said variometers, and a cooperating sector and contact for disconnecting the variometer assembly from the antenna upon the rotation of the variometer shaft to a predetermined position.

Other objects and advantages of the invention will in part be disclosed and in part be obvious when the following specification is read in conjunction with the drawings in which:

Figure 1 is a right side view of the tuning unit with the case removed.

Figure 2 is a top view of the tuning unit variometer assembly removed from the apparatus.

Figure 3 is a sectional view of a variometer rotor.

Figure 4 is a front view of a slip ring and flexible drive coupling assembly.

Figure 5 is a side view of the slip ring and flexible drive coupling assembly.

Figure 6 is an end view of the variometer assembly showing the shaft operated disconnect mechanism.

Figure 7 is a schematic diagram of the electrical circuits utilized in the tuning unit.

In the drawings, like parts are designated by like reference characters.

Referring to Figure 1, the radio frequency input terminal is connected to a terminal stud on the indicating meter 2 by the connecting lead 3. The meter 2 is mounted on the tuning unit front panel 4 and its two terminals are shunted by the coil 5, which insures continued energy transfer to the antenna circuits in the event of meter burnout. The inductance of coil 5 is such that 90% or more, of the input current flows through meter 2. The other terminal stud of the meter'Z is connected by the lead 8 to the movable element of a single-pole-doub-le-throw vacuum relay 6 actuated by the operating coil 1. In the tie-energized position of relay 6, the lead 8 is connected to the rear relay contact and to the radio frequency output terminal 9 by the lead l provided with the anti-corona terminals I2 and !3. In the present design, a radius of one-half inch has been found very satisfactory on terminals !2 and !3. With the relay 6 in the energized position, the lead 8 is connected to the front contact of the relay, through the flexible lead H to the quick detachable connector M which may be attached to the contact as shown, or alternatively connected to the contact !8 or !'l. Contact I? is provided with a corona shield i8 which remains in place at all times except when the connector M is attached thereto. The contacts [5, it, I! are carried on the variometer support rod iii of insulating'material such as that known to the trade as Bakelite, and the support rod !9 in turn is supported from the base of the unit by the standoif support rods 28. A'second variometer support rod is less the terminals !5, !t, l! is similarly located on the other side of the tuning unit base and the two variometer support rods 19 between them support the three'variometer assemblies 2!, 22, 23. In Figure 1, only the fixed variometer coils may be seen. The rear 'winding terminal of the winding 2 3 is connected to the metallic series connector 2f bridging the gap between the structures of variometers 2! and 22, and the front winding terminal of the winding 25 is'also connected to the metallic series connector 21, thus connecting the windings of these two variometers in series. The series connector 21 also serves to support the contact brush 28 engaging the slip ring 29 which is connected to the rear winding terminal of the variometer rotor winding of variometer 2! and to the front winding terminal of the variometer rotor winding of'variometer 22. Brush 28 is in electrical contact with connector 2'! and the connecting link 39 completes the connection between the connector 27 and the terminal !6 which is thus connected to the junction between the series connected variometers 2! and 22. The slip ring 23 is so constructed that it also serves as a flexible driving member as will be detailed in a later figure. The front winding terminal of the rotor winding of variometer 2i is connected to the front winding terminal of winding 24 through a sliding connection and thence to the terminal 15 by the lead 3!. Similarly to connector 21, connector 32 connects the terminals of windings 25 and 26 and serves as a support for the brush 33 engaging the slip ring 34 which serves as a flexible driving connection and is connected electrically to the rotor windings of variometers 22 and 23. Connector 32 is connected to the terminal l! by the lead 35.

The rear winding terminal of winding 26 and the rear winding terminal of the rotor of variometer 23 are connected to the semi-circular contact sector So which engages the contact 3'! during approximately one-half the rotation of the shaft to which sector 36 is connected. The contact 3'! is mounted on the support plate 38 attached to the structure of the variometer 23 and is connected to the radio frequency output terminal 9 by the lead 39 secured to the anticorona connector to. The rod 4! merely serves as a stiffener for the support plate 33. The variometers 2!, 22, 23 are mounted so that the rotation centers of the variometer rotors lie on a single line and the rotors may be driven to a number of predetermined positions by the motor and preselector assembly 42 driving the rotor of variometer 2! through the flexible driving connection 43.

The structure of the variometer assembly is more clearly seen in the top view of Figure 2 showing the variometers 2!, 22, 23 secured in place between the variometer support rods l9 by the screws 44 and the connection of the windings 2 3 and 25 to the series connector 2! and tothe terminal it by the connection 39 between connector 2'! and the terminal l5. Also shown in this View are the flexible drive coupling :3 connecting the rotor of variometer 2! to the controlled drive shaft of the motor and preselector t2, and the connections between adjacent variometer rotors including the rotor shafts t5, the shaft stub inserts 46 and the flexible drive coupling hubs 47!. I

In the cross sectional view of the rotor in Figure 3, there is seen the rotor hub 48 pinned to the rotor shaft 45 by the pin 50 and to the rotor coil form M by the pin 52. Iron'cores 53 are held in place against the rotor hub 48 by the sleeves 54 secured to the rotor shaft 45 by the.

pins 55 and serve to materially increase the'induotance range of the variometer. The shaft stub inserts 46 are forced into the ends of the rotor shaft 45 and may be secured in place by cementing or using some other suitable adhesive. The rotor coil 51 is wound over the outside of the rotor coil form 5! and the two ends of the winding are connected individually to the two shaft stub inserts in the manner shown, the

winding leads being brought through apertures in the rotor shaft 45 and then soldered in place in the central aperture of the shaft stud in serts 46.

The rotors are mechanically and electrically connected to one another by the slip ring assembly of Figures 4 and 5 with the slip ring 29 provided with the mounting ears 5% along the inner periphery to which the spring steel arms 59 are riveted. Atv their inner end, the arms 59 carry the coupling hubs 41 which are provided with set screws for attaching to the shaft stubs of the shaft stub inserts 46. A slip ring assembly of this type is employed in making the electrical and mechanical connection between the successive variometers 2!, 22 of Figure 2. Slip ring 34 issimilarly constructed. Equipment of the nature of this antenna tuning unit is called upon to operate over wide ranges of temperature which may cause considerable distortion of the variometer support rod is. This distortion is of such magnitude as to cause binding of the variometer rotors in their bearings if a solid drive shaft and mounting are employed for the variometer rotors. This defect is overcome by the use of the combined slip ring and flexible drive coupling assembly just described to connect the rotors of the variometers mechanically and electrically so that each variometer rotor shaft rotates freely and independently in its own bearings located in the stationary frame of the variometer.

The disconnect mechanism at the rear end of the rotor shaft of the last variometer 23 is clearly seen in the end view of Figure 6 showing the variometer 23 located between the variometer support rods 59 and the contact sector 36 afiixed to and driven by the rotor shaft of variometer 23 and connected to one terminal of the rotor winding and one terminal of the stator winding 25 of this variometer. So long as the arcuately shaped portion of the sector 35 is opposite the contact 31', these two points are connected electrically, but upon rotation of the shaft to place the flat side of the sector 36 opposite the contact 31, the circuit is broken. The relation of sector 35 and contact 31 to each other is such that they are in contact during approximately the 180 degrees of rotation required for the inductance of the variometers to pass from maximum to minimum.

The operation of the antenna unit described in the foregoing figures in its intended position in a radio transmitting system is most readily understood by consultation of the schematic diagram of Figure '7. The variometers 2!, 22, 23 have their rotor and stator windings connected in parallel, and the three variometers are then connected in series, with the intermediate connections brought out to the contacts l5 and I l.

The ends of the series circuit including the variometers 2!, 22, 23 are connected to the contact '15 and to the semicircular contact sector 3'5 re- 'to the radio frequency output terminal 9 by the lead Ill and the central movable contact is connected to the radio frequency input terminal I through the antenna current indicating ammeter 2. The rotors of the variometers are driven by the control shaft 5i! extending from the motor and preselector assembly 42, as is also the semi- "circular contact sector 36 which engages the fixed contact 31 connected to the radio frequency output terminal during approximately 180 degrees of shaft rotation in which the inductance of the variometers varies from minimum to maximum. In the de-energized position of relay 6, the input terminal I is connected directly to the output terminal 9 while in the energized position, the input terminal I is connected to the output terminal 9 in series with a number of variometer sections determined by the position of the connector I4 and with the contact sector 36 and con tact 31.

The preselector 42 is provided with a number of notched discs til, 62, 63, E4, and 55 mounted on the shaft ED whose individual peripheries are engaged by followers on the

switches

66, 61, 68, 69, and it which are closed except when the notch in the associated disc lies directly under the follower on the movable switch arm. Switch It also operates the switch H from the disc 65. The fixed contacts of switches 66, B1, 68, 69, and '1!) are connected in parallel and to one of the input terminals of the ratchet motor 12 which actuates a pawl driving a ratchet wheel on the shaft 68. The other power input terminal of the ratchet motor 12 is connected to ground and the operating winding is shunted by the spark-suppressing condenser E3. The ungrounded input terminal of the ratchet motor is also connected to the indicator lamp 56 located in the remote channel selector which serves as a reminder when the equipment is changing channels so that the operator will not attempt to transmit during this period. The movable arms on the

switches

65, 61, 68, 69, and 10 are individually connected to the fixed contacts on the local antenna. tuning selector switch 14 and the remote channel selector switch section 15. The wiper arms on switch 14 and on remote channel selector switch sections 15 and Hi are connected together and to t e pos tive terminal of the direct current source 17 havi g the negative terminal grounded. The positive terminal of source l"! is also connected to the movable arm of switch H whose fixed contact arm is connected to one terminal of the operating winding 1' of the vacuum re ay 6. The other terminal of winding 1 is grounded and when switch 1! s closed. the relay 6 is actuated by virtue of the current flowing through the above circuit, connecting the input terminal I to the variometers through the lead H.

The remote channel selector switch section 16 is utilized to control the channel selector located in the transmitter 18. The radio frequency output terminal '19 of the transmitter 18 is connected to the terminal l of the antenna loading unit, and the output energy is fed through a circuit controlled by the position of the remote channel selector switch section '15 to the antenna loading unit output terminal 3 and antenna 8!). With the switch sections '55 and 16 in the extreme counterclockwise position, the channel selector of the transmitter 18 may be manually set to any desired channel and the antenna loading controlled by the local antenna loading selector 14 located at the antenna loading unit. In the second position of switch the positive terminal of the source Ti is connected to the ungrounded terminal. of the ratchet motor 12 through the switch causing the motor to rotate the control shaft to and the attached discs until the notch in the disc 85 lies under the follower attached to the movable arm of the switch 66, when the switch opens'a'nd interrupts the power supply to the motor 72 bringing the shaft 60 and the driven variometer to a, halt in the desired position as shown in Figure '7. The position of the disc 6! on the shaft 66 is adjustable so that it may be set to bring the variometers to any desired position. As the switch H3 successively connects the ungrounded terminal of the source 17 to different disc operated switches, the .variometers are similarly rotated by the control shaft 66 until the notch in the disc actuating the selected switch lies under the follower thereby inserting a number of different predetermined values of inductance between the input and output terminals of the antenna loading unit. So long as the follower controlling switches iii and II do not engage the notch, in the control disc 65, switch H is closed, energizing relay 6 and connecting the antenna input terminal I to the connector l4 so that the selected number of variometer sections is connected between the input and output terminals in series with the

contact members

36 and 31 which present a closed connection for all the shaft positions defined by the controlling discs 6!, 62, 63, and 6 3. The position of the notch in the control disc 6-5 bears such a relation to the contact sector 36 that th flat side of this sector is presented to the contact 31, breaking the connection between them, when this notch is engaged by the follower controlling the switches 18 and H. Therefore, when the source 11 is connected to the movable contact of switch '10, the ratchet motor 12 drives the control shaft 60 to a position where the follower of switches and H engages the notch of control disc 65, opening the power supply circuit to the motor 72 and to the operating winding 7 of the relay 6 so that the input terminal l is connected directly to the output terminal 9 through the central movable and the fixed rear contact of relay 8. At the same time, the positioning of the shaft 66 disengages the contact 37 from the sector 36, disconnecting the variometers from the output terminal 9. The corresponding position of the selector switch "M is termed the HP or high frequency position, as it is used when the frequency to be radiated is sufficiently high to eliminate the need for antenna loading.

The disconnection of the variometers from the antenna circuit, except when they are required for optimum transmitter loading, has been found to produce a large increase in the radiated energy in those portions of the spectrum in which the loading may be deleted. When even one terminal of the variometer circuit is permanently connected to the antenna circuit, there are many frequencies in which the major portion of the transmitter output power is dissipated in parasitic resonances within the variometer structure. Because of the high voltages found in this service during low frequency transmission, the in-line arrangement of the variometers imparts the best performance characteristics due to the lower potential gradients encountered.

When simultaneous remote control of both the transmitter 18 and the antenna tuning unit is desired, the local antenna tuning selector M is placed in the extreme counterclockwise position and the. remote channel selector incorporating the switch sections and i5 is utilized, Switch section 76 selects eight different preselected transmitter channel frequencies produced by the transmitter 18, four of which must lie at such a part of the frequency spectrum that antenna loading is not required when the antenna loading unit, which has been described, is used. Channel 7 loading.

selector switch section 7-5, whose wiper arm is mechanically coupled to the wiper arm of section it by the mechanical connection 8|, simultaneously energizes the preselector switch which will index the control shaft carrying the variometers 2|, 22, and 23 in the antenna loading unit to the position providing the proper antenna ,In the four extreme clockwise positions of the switch arm in section, 75, the high frequency switch 79 is energized, indexing the control shaft to a position disconnecting the variometers from the antenna circuit by the action of sector 36, contact 37, and the operation of the relay 6. The connections of the trans mitter channel selector to the switch section 16 are such that the highest frequency operating channels are selected in the four extreme clockwise positions of this selector switch.

The set up procedure followed after the installation of this equipment in an aircraft is as follows: The transmitter is set in operation with the remote channel selector in the desired position and adjusted to provide the lowest desired output frequency, the screw securing the control discs to the shaft 59 is loosened, control shaft 60 operating the variometer rotors is rotated to the setting giving the maximum indication on the radio frequency current meter 2, and with shaft 69 in this position, the control disc associated with the control switch now energized by the channel selector switch section 15 is rotated so that the notch engages the switch follower. This process is repeated for each of the remaining three low frequency channels, but on the high frequency channels only the transmitter need be adjusted, as switch EB engaging the control disc is energized on all the high frequency channels. On the high frequency channels, therefore, the control shaft SE! is rotated by the motor 72 to a position disengaging sector 36 and contact 31 and disconnecting terminal 9 from the variometers. After all the above adjustments have been completed, the screw securing the control discs to the shaft 59 is retightened and, henceforth, setting the channel selector to any one of the low frequency channels simultaneously places the transmitter in operation on the desired channel and loads or tunes the antenna circuit to provide maximum radiation. When making the initial adjustment on the lowest frequency channel, the connector i it is positioned to resonate the antenna circuit at the selected frequency with the smallest number of variometers in the circuit. When a very small antenna is used, it is generally necessary to place the connector It on the terminal l5, thereby inserting all three variometers in the antenna circuit on the low frequency channels, while the use of a large antenna enables the attachment of the connector is to the terminal I! eliminatin all but variometer 23 from the circuit.

It will be noted in the drawings that all parts operating at high radio frequency potentials are provided with anti-corona, terminals or connectors having rounded surfaces. The following radii of curvature have been found satisfactory: For terminals 9, l2, and I3, one-half inch; for terminal 4t and brush 3?, three-eighths inch; for sector 35, one-fourth inch; and for the corona shield 88, seven-thirty-seconds of an inch.

In evaluating the performance of antenna loading units, it is to be remembered that the voltage developed at the antenna terminals is inversely proportional 'to the antenna reactance; thus,

halving the antenna capacity doubles the antenna potentials existing within the loading unit for the same radiated power. The factor determining the minimum size of antenna which may be successfully loaded, exclusive of inductance limitations, is the potential at which arc-over occurs within the antenna loading unit, the greater this potential, the greater the range of antennas which may be accommodated. The following characteristics serve to indicate the improvement in performance and reduction in size and weight which have been realized by the use of the antenna loading unit design described above. The antenna capacity indicated is the minimum which ma be resonated at 300 Kc and 31,000 ft.

altitude.

Switched coil In line varidesign ometcr design Minimum antenna capacity. 250 mmfd. 125 mmfd. Space occupied 3,415 on. in 1,552 on. in.

Percent reduction n volum 54.4.

Weight 28 lbs 16 lbs, '7 oz. Percent reduction in weight 41.2.

An inspection of the above table indicates that the range of antennas which may be accommodated has been doubled while at the same time halving the volume occupied and almost halving the weight of the unit.

It will be obvious that many changes and modifications may be made in the invention without departing from the spirit thereof as expressed in the foregoing description and in the appended claims:

1. In radio apparatus, an ntenna loading unit, comprising a control shaft, motor and preselector means for driving said control shaft to a plurality of predetermined positions, a radio frequenc input terminal, a radio frequency output terminal, a plurality of variometers having a rotatable winding connected in parallel with a fixed winding, means for mounting said variometers in spaced relation with the axes of rotation of said rotatable windings collinearly located, means electrically connecting said variometers in series,

a driving connection between said control shaft fixed winding, insulating means for mounting said variometers in spaced relation with the axes of rotation of said rotatable windings collinearly located, means electrically connecting said variometers in series, a flexible drive coupling connecting said control shaft and the rotor of one of said variometers, flexible drive couplings connecting the rotors of the remainder of said variometer rotors with each other and with the rotor of the driven variometer, means for connecting said radio frequency output terminal with an end terminal of the series circuit in-- cluding said variometers, and means for selectively connecting said radio frequency input terminal with said series connecting means.

3. In an antenna loading unit, a radio frequency input terminal, a radio frequency output terminal, a variable impedance element controlled by a continuously rotatable shaft and controllable between the maximum and minimum limits of impedance upon rotation of said shaft through a control rotation sector of less than 360 degrees, disconnect means operated by the rotation of said control shaft connecting one terminal of said impedance to said output terminal for control shaft positions lying within said control sector and disconnecting said terminal of said impedance from said output terminal for control shaft positions lying without said control sector, and switching means connecting said radio frequency input terminal to the "other terminal of said impedance when the circuit through said shaft controlled disconnect device is closed and connecting said radio frequency input terminal to said radio frequency output terminal when the circuit through said shaft controlled disconnect device is open.

4. In an antenna loading unit, a radio frequency input terminal, a radio froquency output terminal, a variable impedance controlled by a continuously rotatable shaft and controllable between the maximum and minimum limits of impedance .upon rotation of said shaft through a control rotation sector of less than 360 degrees, a circular conducting sector actuated by said control shaft and subtending an angle at least equal to said control sector, means connecting said circular sector to one terminal of said impedance element, a contact member intermittently engaging said circular sector, means connecting said contact member to said radio frequency output terminal, and means connecting said radio frequency input terminal to the other terminal of said impedance element and to said radio frequency output terminal.

5. In an antenna loading unit, a radio frequency input terminal,' a radio frequency output terminal, a variable impedance controlled by a continuously rotatable shaft and controllable between the maximum and minimum limits of impedance upon rotation of said shaft through a control rotation sector of less than 360 degrees, a circular conducting sector connected to said impedance actuated by said control shaft and subtending an angle at least equal to said control sector, motor and preselector means for driving said control shaft to a plurality of predetermined positions, a contact member intermittently engaging said circular sector, means connecting said contact member to said radio frequency output terminal, and switching means connecting said radio frequency input terminal to the other terminal of said impedance element when said contact member is in engagement with said circular sector and connecting said radio frequency input terminal to said radio frequency output terminal when said contact member is disengaged from said circular sector.

6. In an antenna loading unit, a radio frequency input terminal, a radio frequency output terminal, a variable impedance controlled by a continuously rotatable shaft and controllable between the maximum and minimum limits of impedance upon rotation of said shaft through a control rotation sector of less than 360 degrees, a circular conducting sector actuated by said control shaft and subtending an angle at least equal to said control sector, means connecting said sector to one terminal of said impedance, a contact member intermittently engaging said circular sector, motor and preselector means for driving said control shaft to a pluir-rat rality of predetermined positions, one of said positions disengaging said contact member from said circular sector, means connecting said contact member and said radio frequency output terminal, and switching means for selectively connecting said radio frequency input terminal to the other terminal of said impedance element and to said radio frequency output terminal.

7. In an antenna loading unit, a radio frequency input terminal, a radio frequency output terminal, a control shaft, a plurality of variometers'driven by said control shaft, means elec trically connecting said variometers in series, a substantially semicircular conducting sector rotatably driven by said control shaft, means connecting said conducting sector to one terminal of the series circuit including said variometers, a contact member intermittently engaging said conducting sector, means connecting. said contact member to said radio frequency output terminal, and means for selectively connecting said radio frequency input terminal to the windings of said variometers and to said radio frequency output terminal.

8. In an antenna loading unit, a radio frequency input terminal, a radio frequency output terminal, a control shaft, a plurality of variometers driven by said control shaft, means electrically connecting said variometers in series, a substantially semicircular conducting sector rotatably-driven by said control shaft, means connecting said conducting sector to one terminal of the series circuit including said variometers, a contact member intermittently engaging said conducting sector, means connecting said contactmember to said radio frequency output terminal, motor and preselector means for driving said control shaft to a plurality of predetermined positions, one of said positions disengaging said contact member from said sector, and means for selectively connecting said radio frequency input terminal to the windings of said variometers and to said radio frequency output terminal.

9. In antenna loading unit, a radio frequency input terminal, a radio frequency output terminal, a control shaft, a plurality of variometers driven by said control shaft, means electrically connecting said variometers in series, a substantially semicircular conducting sector rotatably driven by said control shaft, means connecting said conducting sector to one terminal of the series circuit including said variometers, a contact member intermittently engaging said conducting sector, means connecting said contact member to said radio frequency output terminal, motor and preselector means for driving said control shaft to a plurality of predetermined positions, one of said positions disengaging said contact member from said sector, and means for selectively connecting said radio frequency input terminal to the windings of said variometers during the engagement of said sector by said contact member and connecting said radio frequency input terminal to said radio frequency output terminal when said contact member is disengaged from said sector.

10. In radio apparatus, an antenna loading unit comprising a control shaft, motor and preselector means for driving said control shaft to a plurality of predetermined positions, a radio frequency input terminal, a radio frequency output terminal, a plurality of variometers driven by said control shaft, means connecting said variometers in series, relay means alternatively feeding energy from said: radio frequency input a rotatable winding whose terminals are directly electrically connected to the terminals ofthe fixed winding most closely coupled thereto, means for mounting said variometers in spaced relation with the axes of rotation of said rotatable windings collinearly located, means electrically connecting said variometers in series, a driving connection between said control shaft and said variometers, means alternatively feeding energy from said input terminal directly to said output terminal and to said output terminal through at least a portion of said plurality of variometers, and means for controlling the number of variometers traversed by said energy.

12. In radio apparatus, an antenna loading unit comprising a control shaft, motor and preselector means for driving. said control shaft to a plurality of predetermined positions, a radio frequency input terminal, a radio frequency output terminal, a plurality of .variometers each having a rotatable winding electrically connected to a fixed winding, means for mounting said variometers in spaced relation with the axes of rotation of said rotatable windings collinearly located, means electrically connecting said variometers in series, a driving connection between said control shaft and said variometers, disengageable connecting means between one of said radio frequency terminals and an end terminal of the series circuit including said variometers, and relay means alternatively connecting said radio frequency terminals together when said disengageable connector is disengaged and con- 7 nesting the other radio frequency terminal to another point on the series circuit including said variometers when said disengageable connector is engaged.

13. In an antenna loading unit, a radio frequency input terminal, a radio frequency output terminal, a variable reactor having a plurality of terminals controlled by a rotatable shaft, and controllable between predetermined limits of reactance upon. rotation of said shaft through a control rotation sector of less than 360 degrees, means connecting one terminal of said reactor to one of said radio frequency terminals when said control shaft is positioned within said control sector and disconnecting said reactor terminal from said one terminal when said control shaft is positioned without said control sector, and means for connecting the other of said radio frequency terminals alternatively to another terminal of said reactor when said control shaft is positioned within said control sector and to said one radio frequency terminal when said control shaft is positioned without said control sector.

14. In an antenna loading unit, a first terminal, a second terminal, a variable impedance element having a plurality of. terminals controlled by a rotatable shaft. and controllable between predetermined limits of. impedance upon; rotation of said shaft through. a. control. sector of less than 360 degrees, means connecting one terminal of said impedance element to said first terminal when said shaft is positioned within said control sector and disconnecting said one terminal of said impedance from said first terminal when said shaft is positioned without said control sector, and means alternatively connect- 14 ing said second terminal alternatively to another terminal of said impedance element when said shaft is positioned within said control sector and to said first terminal when said shaft is posi- 5 tioned without said control sector.

JOHN W. HAm/IQND.