Patent GB-1362154-A (GB)
Title: Automatic tuner
IPC: H03H7/40
Filed: 1973-05-08
Abstract: 1362154 RF couplings HUGHES AIRCRAFT CO 8 May 1973 [8 May 1972] 21982/73 Heading H4A An aerial tuner for matching the impedance of an aerial to a load resistance comprises a plurality of reactance elements of incremented values, switching means for connecting said elements to the aerial, and digital control means. Said digital control means includes impedance-sensing means which detects the impedance of the aerial together with such reactance elements as are connected thereto, and which provides a digital output to logical control circuit means. The switching means is coupled to the logical control circuit means, and is actuated thereby to selectively connect reactance elements to the aerial to obtain matching with the load. As described, transceiver circuits 60, Fig. 3, operable in the range 2 to 80 MHz., are coupled to a selected aerial of a group 64 through either an HF (2 to 50 MHz) matching network or through a VHF (50 to 80 MHz) matching network. Output from the transmitter is coupled by a line 10 through three sensors, respectively concerned with voltage standing wave ratio (VSWR), phase, and load, to a first pole SKl-1 of a two-pole relay K1. This relay is controlled by a frequency detector 62, and the pole SKl-1 connects the line 10 either to the HF network or to the VHF network. Each network comprises a plurality of inductance elements having values in binary sequence and connectible in series by digitally controlled latching relays, followed by a plurality of capacitance elements having values in binary sequence and connectible in parallel by digitally controlled latching relays. The HF matching network is followed by a switch 74, driven by a motor 66, and having 32 positions associated with different pre-load inductance elements and matching transformers. The said pre-load network may be by-passed, during the initial stage of a tuning cycle, by means of a two-pole relay K2. The VHF matching network is isolated from the aerial during HF operation by means of the second pole SKl-2 of the relay K1. Separate control logics 68, 70 are provided for operating the latching relays associated respectively with the HF and VHF matching networks, and pre-load control circuits 72 are provided for the pre-load switch motor 66. The VSWR sensor has one output which is coupled back to the transmitter power amplifier to reduce the output to 2 watts (from 50 watts) during a tuning cycle. As shown in Fig. 1, it has two current/voltage taps 16/17, 18/19 on the transmission line 10. The coupling transformers 16, 18 are of opposite polarities, and combining networks and diodes associated with the taps produce positive detected voltages on respective lines 22, 23 corresponding to the forward and reflected signal samples. The said lines are respectively connected to the positive and negative inputs of dual operational amplifiers 12, 14. Each positive input of said amplifiers includes a respective threshold level adjusting voltage divider 27, 28. The operational amplifier 12 provides a control signal at lower logical level (e.g. zero volts) whenever the VSWR exceeds 3 : 1 for initiating a tuning cycle. The operational amplifier 14 provides a control signal at higher logical level (e.g. +5 volts) whenever the VSWR is 1À5 or less, for terminating the tuning cycle. As is shown in Fig. 3, the VSWR sensor is coupled to both the HF and the VHF control logics. The phase sensor and the load sensor together form the impedance-sensing means, and they are coupled to the HF control logic and to the pre-load control circuits. A common current/voltage tap on the transmission line 10 is used for both sensors. In the case of the phase sensor (Fig. 1a), not shown) current and voltage samples are coupled through respective circuits to the inputs of a sampling gate, a fixed delay being introduced in the voltage sample. The gate provides a pulse output from detection of a positive phase angle, corresponding to an inductive condition. Output from the summing gate is coupled through a flip-flop circuit and a driver circuit to the + input of an operational amplifier having a - input input which is coupled to a threshold adjustment. The operational amplifier provides a high logical level output (e.g., + 5 volts) for a capacitive aerial load, and a low logical level output (e.g., zero volts) for an inductive aerial load. In the case of the load sensor (Fig. 1b, not shown) the current and voltage samples are rectified in opposite senses by diodes and are summed in a common load. An adjustable tap on the common load is connected to opposite inputs of two operational amplifiers, one of which provides an output at high logical level when the load is under 50 ohms, and at low logical level when it is over 50 ohms, and the other of which provides an output of high logical level when the load is over 100 ohms, and at low logical level when it is under 100 ohms. In operation, within the HF range, the preloading is first adjusted until the load sensor indicates a value of 100 ohms or more. The tuning sequence is then begun, with no inductive elements in circuit, but all capacitive elements in circuit. Insertion and removal of reactive elements continues until the sensors indicate substantially 0 degree phase angle and 50 ohms impedance. If tuning is not effected within a predetermined maximum time interval, the sequence is stopped (Fig. 5, not shown).