| 摘要 |
A video carrier, which is amplitude modulated with a fixed video pattern signal, and sync and blanking signals, is combined with an amplitude modulated I.F. trap frequency signal and supplied to the input of the I.F. stages of a television receiver to cause the video pattern to be displayed on the screen of the receiver, which pattern will exhibit interference until the I.F. trap corresponding to the applied I.F. frequency is set precisely at the applied I.F. frequency.
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