Generating subcarrier signals for transmission in white space between adjacent television broadcast channels

摘要

Multiple RF subcarrier signals for transmission between two adjacent UHF broadcast channels are generated from a plurality of local oscillator LO signals using a plurality of mixers each arranged to mix one of the LO signals with one of a plurality of input signals. A TCXO 302 produces a reference frequency which is connected to a signal generating circuit 304a, which may comprise a VCO and PLL. Circuit 304a produces a first local oscillator signal LO1 which is mixed with a first input signal i1 in mixer 306. A second signal generating circuit comprises divider 304b and mixer 304c. The second signal generating circuit receives the reference frequency from the TCXO and receives the first local oscillator frequency LO1 and mixes these to produce a second local oscillator frequency LO2. Further stages may be added (fig.4). The generation of additional LO signals by means of counter and mixer combinations (e.g. divider 304b and a mixer 304c) reduces the cost of the circuit in comparison with the prior art (fig.2) which uses additional VCOs and PLLs. Variable gain amplifiers (516, fig.5) may provide independent amplification of the RF subcarrier signals before they are combined.