In a recording apparatus frequency modulators (25-28) are provided for carriers having different frequencies with an information signal. The different frequency carriers are sequentially combined by a switch (12) and applied to a recording head in response to the head being shifted from one track to...http://www.google.com.tw/patents/US4724494?utm_source=gb-gplus-share專利 US4724494 - Tracking apparatus responsive to multiple frequency-modulated carriers on different tracks
