| 摘要 |
P/8472/MCSL Circuit for Adding r.f. Signals (Figure 6) The circuit is capable of selectively adding r.f. inputs at A, B, dependent on the bias voltage applied to varactor diodes D1, D2. In one bias condition of the diodes and hence one value of capacitance, the reactance between A and B and between the output and point D is equal to the reactance of transmission lines 10, 11 formed by co-axial cables, and quadrature inputs at A and B are combined at output O/p. At another value of capacitance of the varactor diodes, corresponding to another bias voltage, the capacitance of the diodes and the series capacitances C1, C2 resonate with the inductances L1, L2 and input A is effectively isolated from input B. The circuit can be used to produce a power amplified composite video r.f. signal, input A being connected to a power amplifier for the video signal only and input B being connected to a pulse amplifier for the sync pulses only. This permits more efficient use of the amplifiers compared to a single amplifier for amplifying the composite video signal.
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