| 摘要 |
In a SECAM-PAL transcoder, color-difference signals, sequentially recovered from received SECAM signals by a single FM discriminator, are supplied via a first emitter-follower to a first modulating signal input terminal of a balanced modulator, which develops a quasi-PAL signal output using PAL subcarrier frequency oscillations. A DC potential, supplied to a second modulating signal input terminal of the modulator via a second emitter-follower, matches discriminator output level under no-color signal conditions. A third emitter-follower, responsive to a blanking waveform, effects cutoff of the first emitter-follower during blanking periods and delivers elevated blanking pedestal to the first terminal. A fourth emitter-follower, responsive to the same blanking waveform, effects cutoff of the second emitter-follower during blanking periods and delivers matching blanking pedestal to the second terminal. During a portion of the blanking period, a burst gating pulse supplied via the third emitter-follower causes departure from the blanking pedestal level at the first terminal without disturbing the blanking pedestal level at the second terminal, to develop a burst component of controlled magnitude in quasi-PAL signal output.
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