Frequency conversion of an RF signal transmitted for color-television receivers

US4782385A · kind A · utility

Assignee

• Deutsche ITT Industries, GmbH · DE

Inventors

• Gerhard Gunter · Ettlingen, DE
• Hermannus Schat · Glückstadt, DE
• Herbert Elmis · Denzlingen, DE
• Bernd Novotny · Gundelfingen, DE
• Otmar Kappeler · Denzlingen, DE
• Dietmar Ehrhardt · Glückstadt, DE

Key dates

• Filing date: Aug 25, 1986
• Grant date: Nov 1, 1988
• Expiry date: Aug 25, 2006

Classification

• Technology area (CPC H): Electricity
• CPC primary: H04N9/64
• WIPO field: Audio-visual technology
• WIPO sector: Electrical engineering

Abstract

The frequency conversion of an RF signal is performed by the "third method" using a suitable frequency reversal which makes the frequencies of the picture carrier, the chrominance subcarrier, and at least one sound carrier appear transformed into the baseband, such that the frequencies of the transformed picture carrier and the transformed chrominance subcarrier coincide. Unavoidable differences in the signal paths of the frequency reversal result in a spurious signal which produces a temporally/locally varying moire on the screen. By means of a frequency offset, this spurious signal is transformed into a frequency range which is not found annoying by the observer, so that the moire becomes invisible. This frequency range is preferably the exact center region between two spectral lines of the horizontal frequency of the composite color signal in the baseband.