| 摘要 |
<p>1,101,752. Recording and playback. AMPEX CORPORATION. 28 April, 1965 [26 June, 1964], No. 17847/65. Heading G5R. [Also in Division H3] A gating system, particularly for switching outputs from the playback heads of a rotating drum magnetic tape recorder, comprises a plurality of gates coupled between respective input channels and an output terminal and a bi-stable circuit for producing control signals for the gates in response to the presence of R.F. signals in the appropriate input channel. In Fig. 1B, modulated R.F. signals from diametrically opposed playback heads on a rotating drum are fed via terminal 10, an emitter follower T1 and a gate comprising diodes 40, 42 and transistor T2 to a common output terminal 18. Signals at the other heads are fed via terminal 11, emitter follower T3 and gate 86, 87, T4 to the common output terminal 18. When transistor T2 is off, diodes 40, 42 are biased on, so that signals at terminal 10 are transmitted to output 18. This path, however, is broken whenever T2 is made conductive by voltage El supplied to its base. Transistor T4 is arranged to be made conductive by signals E2 whenever T2 is non-conductive so as to block signals A2 from the output 18. Derivation of gate control signals.-In Fig. 1A, R.F. signals from one pair of playback heads are fed via terminal 10 and an amplifier T9 to voltage-doubling rectifiers 166, 168, the output of which is smoothed at 174. The D.C. output is passed by an emitter follower T10, a differentiating capacitor 188 and a pulse shaping transistor T11 to line D1 where a negativegoing pulse is provided in response to the onset of each R.F. signal at 10. A further negativegoing pulse is provided at D2 in response to the onset of each R.F. signal at 11. Each pulse D1 or D2 sets or resets a bi-stable multivibrator 420 signals E1, E2 from which respectively open or close the gates (Fig. 1B) comprising transistors T2, T4 in such a way that the appearance of a signal at 10 causes gate 40, 42 to pass that signal to the output 18 whilst the subsequent appearance of a signal at 11 results in gate 86, 87, T4 passing such signal to the output 18. In the rotary head tape recorder, playback signals at 10 or 11 are thus steered by the appropriate gate to output 18 without the need for any separate gate control signals synchronized with the rotating drum. The D.C. levels of signals from 10 and 11 are equalized by adjustment of variable resistor 22.</p> |
