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A TV tuner have only syntetizable sinusoidal frequency starting from about 40-50MHz and up to 900Mhz (satelite tuners goes upper). The amplitude is not constant over the entire frequency range. So I quess it's the most complicated way to do it (even if getting the square from sinusoidal is feasable).
Up to 12.5Mhz there are single chip digital frequency sintesizers (sinus, triangle and square) based on DDS. Also there are DDS running up to 100Mhz but only sinus.
Search for DDS at https://www.analog.com.