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Deflection Yoke Shield

IP.com Disclosure Number: IPCOM000093938D
Original Publication Date: 1966-Apr-01
Included in the Prior Art Database: 2005-Mar-06
Document File: 2 page(s) / 54K

Publishing Venue

IBM

Related People

Tech, DD: AUTHOR [+2]

Abstract

When using certain deflection yokes in a magnetically deflected cathode ray tube display, the fringe field flux leakage of the deflection yoke causes the cathode ray beam to manifest different degrees of focus for various scanning positions. If the beam is deflected to a large angle, particularly with short-necked cathode ray tubes, it passes in close proximity to the fringe flux created by the end turns. The normal circular shape of the CRT beam is distorted to produce defocusing.

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Deflection Yoke Shield

When using certain deflection yokes in a magnetically deflected cathode ray tube display, the fringe field flux leakage of the deflection yoke causes the cathode ray beam to manifest different degrees of focus for various scanning positions. If the beam is deflected to a large angle, particularly with short-necked cathode ray tubes, it passes in close proximity to the fringe flux created by the end turns. The normal circular shape of the CRT beam is distorted to produce defocusing.

Magnetic yoke 1 has a dual set of yoke windings 3 and 5 fastened by bindings 7 and 9 mounted in a yoke frame about the neck of a cathode ray tube. The yoke windings emerge to form loops in the front and rear, the front being visible in the drawing, to generate cross fields oriented at an angle to the deflection field. To prevent or substantially reduce the adverse effects produced by the end turns of electromagnetic deflection coils, a pair of small magnetic shields 11-13 is inserted within the front loops of the deflection coil to provide low reluctance paths for the fringe flux. Thus the cross fields generated are effectively shunted from the deflection path.

Shields 11-13 merely comprise thin strips of low reluctance material which are secured to the yoke frame. The shields permit the use of inexpensive yokes and provides improved focus with a nominal increase in material cost of the deflection yoke assembly.

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