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Proper Termination for ASIs Autofocus Card

The Input Video IN of the Autofocus Card is terminated with a 10KΩ resister, as it expected to share the video signal coming from the camera with other devices like a monitor or video capture card, which usually have 50Ω or 75Ω termination in them.

If the Autofocus card is the sole recipient of the video signal then proper termination has to be provided to avoid noise due to reflections and to maximize the power transfer.

1) BNC Tee and BNC terminator

Figure 1: BNC Tee and BNC terminator

For temporary experimentation a BNC Tee and a BNC 50Ω / 75Ω terminator could be used to see if the systems performance improves.

2) SMD Components replacement

If the above BNC tee setup works out, carry out the following modifications of the autofocus board to make the change permanent.

  • Replace R12 series 75Ω resistor with a short
  • Replace R26 10KΩ resistor with 75Ω
Figure 2: Positions of the SMD resistors on the Autofocus board
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autofocus_termination.txt · Last modified: 2019/04/18 23:34 (external edit)