TV tuner for incorporation in car navigation system using e.g. GPS

摘要

The TV tuner has local oscillators (5, 8) respectively to heterodyne with VHF and UHF TV signals. Between an input terminal (18) and the input tuning circuits (12, 15) there is located an attenuator (2) for a signal with a frequency higher than the max. frequency of a received TV signal. Preferably the attenuator comprises a low pass filter for blocking passage of signals of frequency above that of the highest UHF TV channel. The blocking circuit thus attenuates harmonics of the local oscillator signal with a frequency near to that used by the car navigation system receiver. In particular, the circuit may reduce the level of the second harmonic of the UHF tuner oscillator when Japanese channel 56 is being received (788 MHz), which falls at 1576 MHz, i.e. close to GPS satellite frequencies.