Abstract: A local communication system comprises a first cluster (10) of devices interconnected for the communication of messages via a first data bus (18) and in accordance with a first set of communication protocols, a second cluster (20) interconnected via a second data bus (28) and following the first set of communication protocols; and a data channel (41) linking a device (19) of the first cluster (10) and a device (29) of the second cluster (20). The data channel (41) suitably comprises an RF link supporting communication of messages in accordance with a second set of communications protocols. A device (19) of the first cluster (10) holds a stored software representation of operational features of a selected device (DVHS-2) of the second cluster (20) and any device (11) of the first cluster wishing to interact with said selected device (DVHS-2; 22) instead interacts with said stored representation.

Abstract: A method of estimating the loop phase error in a negative feedback amplifier is disclosed which comprises applying a test signal to the input of the amplifier, modulating the phase of the feedback signal to be summed to the test signal input to the amplifier, measuring the amplitude of the forward signal of the amplifier at two harmonics of the frequency of the phase modulation, and estimating the loop phase error on the basis of said two amplitude measurements. Apparatus for carrying out such a method is also disclosed.