Figure 7.10 Phasor Diagrams of Discriminator Transformer Voltages.

Part A, tuned to center frequency.

Part A shows the phasor diagram of the voltages in the circuit. There are a total of 5 voltage phasors radiating out from a common point that is known as the origin. The voltage across the top half of the secondary is represented by a phasor which begins at the origin and is horizontal and pointing to the left, zero degrees. The voltage at the center tap, voltage across the tertiary winding, is represented by a phasor that starts at the origin and is pointing straight up, 90 degrees. The voltage across the bottom half of the secondary is represented by a phasor that starts at the origin and is pointing to the right, 180 degrees. The origin is half way between the tips of the top half and bottom half phasors. All three phasors are the same length. These are shown in solid black lines. The parallelogram which is used to construct the sums of phasors is shown in dashed lines that are parallel to each of the phasors just described. The dashed line starts at the tip of the top half voltage phasor and goes straight up until it becomes even with the tip of the tertiary winding voltage phasor. This segment of the dashed line is parallel to the tertiary winding voltage phasor. Then it turns to go horizontally to the left until it is even with the tip of the secondary bottom half voltage. This segment is parallel to both secondary winding voltage phasors. Then it turns to go straight down and continues until it meets the tip of the bottom half phasor. This line segment is once again parallel to the tertiary winding voltage phasor. The sum of the top half voltage and the tertiary voltage is shown in red. It begins at the origin and goes up to the right at an angle of 45 degrees until it meets the corner of the parallelogram. It's length is 1.414 times the length of the top half voltage phasor and the tertiary voltage phasor. The sum of the bottom half voltage and the tertiary voltage is also shown in red. It starts at the origin and goes up to the left at an angle of 135 degrees until it meets the corner of the parallelogram. Its length is the same as that of the sum of the top half voltage and the tertiary voltage.

Part B, tuned above center frequency.

The two phasors for the voltage across the two halves of the secondary have been rotated 45 degrees clockwise. The phasor representing the voltage across the tertiary winding has not changed. The parallelogram has been readjusted so that the longest side is parallel to the two secondary voltage phasors. The two red lines radiate out from the origin to the corners of the parallelogram. The total voltage at the top of the secondary is now 7.653 volts at an angle of 22.5 degrees, while the total voltage at the bottom is 18.478 volts at an angle of 112.5 degrees.

Part C, tuned below center frequency.

The two phasors for the two halves of the secondary have been rotated 45 degrees counterclockwise from the center frequency position. The phasor representing the voltage across the tertiary winding has not changed. The parallelogram has been readjusted so that the longest side is parallel to the two secondary voltage phasors. The two red lines radiate out from the origin to the corners of the parallelogram. The total voltage at the top of the secondary is now 18.478 volts at an angle of 112.5 degrees, while the total voltage at the bottom is 7.653 volts at an angle of 22.5 degrees. End verbal description.
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