HIGH POWER SYSTEMS

Abstract: A method of automatically tuning a high power system by measuring the gradient of component value against efficiency for each component (3,9,l0,l4) in turn and, for each component, finding two points (l7,l9) of equal and opposite gradient and setting the component (3,9,l0,l4) to a value (2l) half-way between these points (l7,l9).

Description: This invention relates to a method for automatically setting up a high power variable frequency electrical system. For a high power system even relatively minor power losses can represent significant amounts of power in absolute terms. For maximum efficiency in a high power system the impedance of one stage should be properly matched to that of a following stage. This cannot be arranged simply by choice of component values because the impedance of certain components in a variable frequency system will be highly frequency sensitive, so the system must be re-tuned every time the operating frequency is changed. It has been proposed in Japanese Patent No. 59-50619, which can be found in Patent Abstracts of Japan Volume 8 number 139, 28th June 1984 that pre-set values for some of the components in a transmitter for each frequency used can be stored in a RAM and accessed when the transmitter frequency is altered, these values are then used to control servo motors to set the component values. However altering the values of some components in the system to pre-set values for each different frequency is unsatisfactory in practice, because changes in reactive components may occur over a period of time due, for example, to ageing or temperature variations, and the impedance of a highly frequency sensitive component such as an antenna, may change with the weather. In French Patent No. 2,129,001 a system is proposed in which a mechanically tuned component has its value altered while the power reflected by the component is measured. The component value is varied from one extreme of its range of values until it passes through a set level of reflected power twice, it is then set to a value midway between the values where it passes through the set reflected power levels. It has been proposed in US Patent No. 3,271,684 to automatically tune a transmitter by firstly coarse tuning by setting component values to pre-set values in dependence on the selected transmission frequency and then secondly fine tuning by measuring the relative phases of source and load signals. Such a phase based adjustment is complex and it is not always possible to adjust for maximum efficiency using this approach. The present invention seeks to provide an improved method of setting up a frequency dependent high power system. According to a first aspect of this invention a method of setting up a high power system including the steps of: monitoring the efficiency of the system at the appropriate points in the system; adjusting the value of a component in such a sense as to vary the monitored efficiency through a point of maximum efficiency until it reaches a reference value having a predetermined gradient of component value against efficiency; re-adjusting the value of the component in the reverse sense to vary the monitored efficiency back through said maximum efficiency until a reference value having a gradient of equal magnitude but opposite sign is obtained; resetting the component to a value mid-way between those two values which produced said reference values; and repeating said steps for a plurality of components in said system. The maximum value in the monitored signal level which results from the adjustment of a particular component is arranged to represent the maximum efficiency at which that stage of the system can operate having regard to the states of other stages in the system. In a high frequency high power electrical system, it may be that the highest possible efficiency for a particular stage cannot be achieved until preceding or following stages have themselves been brought to a more efficient state of adjustment. Thus a number of reactive components may be adjusted in turn to progressively raise the efficiency of the system as a whole. Then some or all of the reactive components are adjusted again to produce a new and higher state of efficiency which is higher than that which could have been achieved on the first round of adjustments. In a practical system, the adjustment of a reactive component alters the impedance of the circuit of which it forms a part at the operating frequency. It is found that for relatively small tuning errors, the variation in monitored signal level which occurs as it passes through a maximum or minimum value which is indicative of peak efficiency is substantially symmetrical about the tune point. As a consequence, the selection of the mid-point between two reference values on opposite sides of the maximum or minimum points gives a component value which is remarkably close to that needed for peak efficiency. As this method does not require a detailed knowledge of the internal operation of the various stages of a system, it is much more versatile than a method which relies on setting up optimum signal phase conditions. For this reason the method can be applied to many different points in a large system, and the method performed under the control of a common controller circuit. The invention is particularly applicable to the setting up of a high power radio transmitter which is required to operate over a wide frequency band. The invention is further described by way of example, with reference to the accompanying drawings, in which: Figure 1 shows the output stage of a high power radio transmitter, Figure 2 is an explanatory diagram, and Figure 3 shows part of a control circuit for setting up the transmitter. Figure 1 shows the output stage of a high power radio transmitter where the output of a previous low power stage is applied at terminal 1 and is amplified by an input amplifier 2. The amplified signal goes through the variable inductor 3 which, with capacitor 4, matches the output impedance of amplifier 2 with the input impedance of a tetrode power tube 5. Tetrode power tubes 5 and 6 are supplied with current by current sources 7 and 8 respectively. The tetrode power tubes 5 and 6 are linked by a tuned circuit formed by variable capacitors 9 and 10 and inductor 11. This tuned circuit is used to impedance match the tetrode power tubes 5 and 6. Tetrode power tube 6 is linked to a remote antenna 12 by a matched transmission line made up of a plurality of inductances 13 and variable capacitances 14. If efficiency of a transmission is defined as the ratio of output power to input power, it is possible to measure the efficiency of a radio transmitter directly by comparing the cathode current in the tetrodes with the forward RF voltage into the load. If a curve of component value is plotted against transmitter efficiency for a reactive component in the transmitter, a curve that is highly symmetrical about its maximum, for component values close to the maximum, is obtained. In order to tune the transmitter to maximum efficiency, the values of the variable components 3, 9, 10 and 14 will need to be adjusted, the way in which this is done will be described with reference to Figures 2. Figures 2a to 2d show the variation of efficiency which occurs whilst a component is being adjusted to its best value. Referring to Figure 2a, an arbitrary initial component value 15 is shown. The gradient of the component value against efficiency curve, is measured by altering the component's value slightly. From this gradient, the direction of the peak of the efficiency curve is deduced. The value of the component is then adjusted towards and through the peak 16 of the efficiency curve, see figure 2b, until the gradient reaches some predetermined reference value at a point 17. The adjustment stops at this point 17 and the component value 18 is noted. Instead of using gradient as a reference value, a predetermined value of the monitored signal level could be used instead. This adjustment is carried out by means of a stepping motor connected to the component. A stepping motor is used because its position can be easily calculated by counting the number of steps it has taken. The value of the component is then adjusted back in the opposite direction, and it travels through the peak 16 of the efficiency curve, see figure 2c, until the gradient is equal to but opposite in sense to the reference value used to decide on point 17; this is point 19. The component value 20 at this point is noted. The mid-point of values 18 and 20 is then interpolated by resetting the stepping motor by exactly half the total number of steps moved between points 17 and 19. Thus the component is adjusted to this point 21, thereby putting it at the best point 16 of the efficiency curve. As the value of each reactive component is frequency dependent, the point 16 generally represents the tune point of a circuit section of which the component forms a part. Referring to Figure 3 there is shown therein the computer control system, in block diagram form so as to indicate the functions performed by its constituent parts. When the transmitter is set to a new frequency most of the variable components will need to be re-set. When such a change is made, all variable components are simultaneously set to appropriate approximate values by the component value adjuster 24. This operation is carried out using the information in the initial value store 25. When these initial approximate values have been set, one variable component (e.g. inductor 3) is selected by the controller 26. The controller 26 instructs the component selector 22 and monitor point selector 27 which of the plurality of stepping motor control lines 23 and which of the plurality of monitoring lines 28, to use. Each monitoring line 28 is connected to a different one of the monitor points 33, 34, 35, 36 and 37 which are shown in Figure 1. The controller 26 also selects from data store 29 the information which is needed by the evaluator 30. The evaluator 30 then adjusts the component to its best value using information obtained via the monitor point selector 27 and data from data store 29 and altering component values by means of component value adjuster 24 in accordance with the process described with reference to Figure 2. When adjustment of component 3 is finished, the controller 26 selects the next component 9 and monitor point 34 in sequence and repeats until all components have been adjusted for maximum efficiency. The sequence can then be repeated to further optimise the setting of each component, as each monitored value could well be influenced by the adjustment of more than a single component.

Claims: A method of setting up a high power system including the steps of: monitoring the efficiency of the system at the appropriate points (33,34,35,36) in the system; adjusting the value of a component (3,9,10,14) in such a sense as to vary the monitored efficiency through a point (16) of maximum efficiency until it reaches a reference value (17) having a predetermined gradient of component value against efficiency; re-adjusting the value of the component in the reverse sense to vary the monitored efficiency back through said maximum efficiency (16) until a reference value (19) having a gradient of equal magnitude but opposite sign is obtained; resetting the component to a value (21) mid-way between those two values (18,20) which produced said reference values; (17,19) and repeating said steps for a plurality of components (3,9,10,14) in said system. A method of setting up a high power system as claimed in claim 1 and further characterised by including the step of making an initial adjustment to the value of a reactive component (3,9,10,14) to determine whether the monitored signal level alters in a required sense in response thereto and using this information to determine in which sense the value of the component must be adjusted in order to vary the monitored signal level through a point of maximum value. A method of setting up a high power system as claimed in claim 1 or 2 and wherein the value of the component being adjusted is changed in discrete steps. A method of setting up a high power system as claimed in claim 3 and wherein said action of resetting the component to a value mid-way between two values which produced said reference value is carried out by altering the component value by half the number of discrete steps made between the two values that produced the reference value. A method of setting up a high power system as claimed in claims 1 to 4 and wherein components to be adjusted, appropriate points to monitor the effect of adjustment and appropriate reference values, are selected in a predetermined series. A method of setting up a high power system as claimed in claim 5 and wherein said predetermined series is repeated to progressively optimise the adjustment of each component. A high power system which is capable of being set up by the method claimed in claim 1 and which comprises: means for monitoring the efficiency of the system at appropriate points (33,34,35,36) in the system; means for adjusting the value of a component (3,9,10,14) in such a sense as to vary the monitored efficiency through a point (16) of maximum efficiency until it reaches a reference value (17) having a predetermined gradient of component value against efficiency; means for re-adjusting the value of the component in the reverse sense to vary the monitored efficiency back through said maximum efficiency (16) until a reference value (19) having a gradient of equal magnitude but opposite sign is obtained; means for resetting the component to a value (21) mid-way between those two values; (17,19) which produced said reference values (17,19) and means for repeating said steps for a plurality of components (3,9,10,14) in said system. A high power system as claimed in claim 7 and wherein the adjusted components include a plurality of tuned stages associated with a wideband antenna. A high power system as claimed in claim 8 and wherein said wideband antenna is linked to said plurality of tuned stages by a transmission line and said plurality of tuned stages are also linked to a tetrode valve. A high power system as claimed in claims 7 to 9 and wherein components are adjusted by stepping motors. A high power system as claimed in claim 10 and wherein said stepping motors are controlled in turn by a common control circuit.

Inventors: PIKE, TUDOR DAVID
Applicants: GEC-MARCONI LIMITED
Application year: 1987
Main classification: H03J7
IPC codes: H03J7