opt301 laser receiver


Posted on Feb 5, 2014

The OPT301 is in a TO-99 8 lead package and has good sensitivity but a reduced bandwidth of 4kHz. The peak response is just into the Infra Red region at 750nm but its sensitivity in the visible red spectrum at 670nm is only a few percent down. The circuit is almost identical to the original receiver. Changes are the new detector / PCB layout and i


opt301 laser receiver
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mproved op-amps. It uses a single supply at 12 - 13. 8V. The detector has a a 10M Ohm feedback resistor soldered directly betw1een pins 2 and 5. The detector output is followed by a NE5534 low noise op-amp (3. 4nV/Hz) which is configured as a bandpass filter. The final NE5534 is an inverting buffer amplifier with a gain of 20. The complete detector assembly is designed to be mounted in a small metal box at the focal point of a lens. The track is viewed from the top or component side. The detector is fitted to the other side of the board where a groundplane in unetched copper has holes countersunk for the TO-99 package. With a single supply line the body of the detector is held at the zener voltage. Therefore it should be isolated from the groundplane and from any metal enclosure. To evaluate the op-amp section I connected a 600 Ohm sig gen to the input of the bandpass filter and measured the response at the output of the buffer. The Input was adjusted from 50Hz to 3kHz with a constant level of 200mV Peak to Peak. As you can see from the results below, the 6dB bandwidth is just 200Hz. This makes the detector ideal for transmitters using modulated CW on a fixed frequency. My TX uses a 4MHz crystal and a CMOS 4060 oscillator / divider to generate 488Hz. This degree of accuracy gives the option of using a lap top and modern DSP softw1are (e. g. ARGO or Spectran by IK2PHD) to receive signals 20dB below normal noise level.




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