| 摘要 |
A down converter, such as a low noise block (LNB) converter, of the outdoor unit of a terrestrial microwave or satellite receiving system includes apparatus for automatically controlling the conversion gain of the down converter. In one embodiment the automatic gain control apparatus, including a gain controllable RF stage and a gain control signal generator for generating a gain control signal in response to the output signal of the down converter, are both included within the outdoor unit. In another embodiment, the gain controllable RF stage is included in the outdoor unit, but the gain control signal generator is included in the indoor unit of the receiving system and the gain control signal is coupled to the outdoor unit in direct or in encoded form. In the latter case, the encoded gain control signal can be coupled to the down converter via the coaxial cable connected between the outdoor and indoor units. In a receiving system which processes digitally encoded information, the error rate of the information which is decoded in the indoor unit can be utilized to generate the gain control signal for the gain controllable stage of the outdoor unit.
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