MICROWAVE TRANSMITTER AND COMMUNICATIONS SYSTEM

摘要

In multiple-channel microwave transmitters (Tx) and communications systems, such as multi-point video distribution systems operating at frequencies of around 29GHz or 40GHz, good frequency stability for each of the channel frequencies (Fa, Fb,...) is achieved with a feed-back loop (20, 40) including an error detector circuit (39, 29). The error detector circuit (39, 29) is coupled between a sampler (41) and an input circuit (13, 24) of the source (12). This detector circuit (39, 29) detects any drift or other error in the carrier frequency (Fa, Fb,...) of the sample from the desired microwave frequency for that channel signal and provides a corrective signal (AFC) to the input circuit (13, 24). The part of the feed-back loop (20, 40) comprising at least a part of the detector circuit (39, 29) is common to a group of the channels. Switch means (28, 38) couple the common part of the feed-back loop between the sampler (41) and the source input circuit (13, 24) of each channel, and so permit this common part to be time multiplexed between the respective feed-back loops of the group of channels. The input circuit (13a, 24a, 13b, 24b,...) for each source (12a, 12b...) applies an up-datable bias signal (Vb) for regulating the frequency (Fa, Fb...) of the source (12a, 12b...) in accordance with the last corrective signal (AFC) generated by the detector circuit (39, 29) for that source. By adopting such a stabilisation arrangement in accordance with the present invention, expensive component parts (23, 39, 40) of the feed-back loop (20, 40) can be common to a group of the channels, so reducing the assembly cost of the multiple-channel transmitter. Good long-term frequency stability for all the channels can be obtained, including a reliably constant frequency relationship between the channels.