This decoder features a sine wave recovery channel and uses a PIN diode attenuator driven by the sine wave recovery system to cancel out the sine wave sync suppression signal.
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Click para ampliarSecond Audio Program Adapter
The baseband-audio input comes from the pole of switch Sl in the stereo decoder, and is coupled to C9 IC1 (a CA3089) via a 78.6 kHz bandpass filter that consists of capacitors Cl and C2, and inductor Ll. IC1 is a combination i-f amplifier and quadrature detector normally used for FM radio systems operating within an i-f of 10.7 MHz. The device works equally well at 78.6 kHz. Capacitors C6 and C7, and inductor L2 tune the detector section to 78.6 kHz, while C5 provides the necessary 90-degree phase shift for proper quadrature detector operation. The output voltage at pin 13 of IC 1 is proportional to the level of the incoming signal. When the voltage at the wiper of potentiometer R3 reaches a predetermined threshold level, Ql conducts, grounding pin 5 of IC1, enabling lCl's mute function.
Detected audio output from pin 6 of IC1 goes to IC2a, which is configured as a 12-kHz, - 12 dB per octave, low-pass filter. The output of IC2a appears across potentiometer R10, which provides a means of adjusting the drive level into IC3b, the 2:1 compander.
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Detected audio output from pin 6 of IC1 goes to IC2a, which is configured as a 12-kHz, - 12 dB per octave, low-pass filter. The output of IC2a appears across potentiometer R10, which provides a means of adjusting the drive level into IC3b, the 2:1 compander.
Click para ampliarOutband Descrambler
This circuit consists of an amplifier for the synch channel and a video detector which controls an attenuator so that the gain of the systems is increased during synch intervals. For the outband decoder to work, the cable company must provide at least a 1 millivolt signal. Values for C1-C5 and L1-L4 are found in Table 1.
Table 1
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Table 1
| 50Mhz | 90-114Mhz | |
| C1 | 5pf | 5pf |
| C2 | 47pf | 12pf |
| C3 | 200pf | 82pf |
| C4 | 56pf | 12pf |
| C5 | 56pf | 10pf |
| L1 | 0.2mH | 0.2mH |
| L2 | 0.05mH | 0.03mH |
| L3 | 0.175mH | 0.2mH |
| L4 | 0.175mH | 0.24mH |
Click para ampliarGated Pulse Descrambler
This circuit consists of an amplifier and video detector with a second subcarrier detector for synch recovery purposes. A pulse-former circuit modulates the gain of the main channel increasing it during synch intervals. Provision for subcarrier audio descrambling is also provided.
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Click para ampliarDirection Detector Decoder
This circuit, which was developed to monitor the traffic of bumblebees in and out of the hive, differentiates a -to-b motion from b-to-a motion. When used with an optical decoder, the circuit distinguishes clockwise from counterclockwise rotation and provides a resolution of one output pulse per quadrature cycle.
Q1 and Q2 are mounted so that a moving object first blocks one phototransistor, then both, then the other. Depending on the direction in which the object is moving, either IC1B or IC1D emits a negative pulse when the moving object blocks the second sensor. An object can get as far as condition 3 and retreat without producing an output pulse; that is, the circuit ignores any probing or jittery motion. If an object gets as far as condition 4, however, a retreat will produce an opposite-direction pulse.
The time constants R3C1 and R4C2 set the output pulse width. A 100 Kohm/100pF combination, for example, produces 10-us pulses. Select a value for pullup resistors R1 and R2 from the 10 K to 100 Kohm range, according to the sensitivity your application requires.
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Q1 and Q2 are mounted so that a moving object first blocks one phototransistor, then both, then the other. Depending on the direction in which the object is moving, either IC1B or IC1D emits a negative pulse when the moving object blocks the second sensor. An object can get as far as condition 3 and retreat without producing an output pulse; that is, the circuit ignores any probing or jittery motion. If an object gets as far as condition 4, however, a retreat will produce an opposite-direction pulse.
The time constants R3C1 and R4C2 set the output pulse width. A 100 Kohm/100pF combination, for example, produces 10-us pulses. Select a value for pullup resistors R1 and R2 from the 10 K to 100 Kohm range, according to the sensitivity your application requires.
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