Circuit for detecting free frequency channel has local oscillator inputs, complex channel filter, level detection and arrangement for varying phase of signal on frequency converter output(s)

摘要

The circuit arrangement has first and second frequency conversion devices (M), each with an input and output, a local oscillator input (1) receiving signals of equal frequency and 90 degree different phase, a complex channel filter arrangement (PF) with a polyphase filter whose inputs are connected to the frequency converter outputs and an arrangement (D) for detecting a signal level connected to the complex channel filter outputs. It also has an arrangement for varying the phase position of a signal on at least one output of a frequency conversion device. An independent claim is also included for the following: (a) a method of detecting a free frequency channel.