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Typical Mistake

Typical Mistake. When working with dB and dBm (or why you should not convert the dB Gain or Attenuation of a device or medium to dBm). Bagel Slicer. You cut any bagel by half all the time with this device. If the bagel is plain, you get two halves of plain bagel.

winifred-cohen
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Typical Mistake

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  1. Typical Mistake When working with dB and dBm (or why you should not convert the dB Gain or Attenuation of a device or medium to dBm)

  2. Bagel Slicer • You cut any bagel by half all the time with this device. • If the bagel is plain, you get two halves of plain bagel. • If the bagel is sesame, you get two halves of sesame bagel. • If the bagel is whole wheat, you get two halves of whole wheat bagel. • The input is the type of bagel, the slicer always does the same job, the output is two halves of whatever goes in. Transfer function is 1/2 output Input

  3. Example • A box increases magnitude by two times • Any input is increased by twice its magnitude 2 times output Input

  4. “Box” with a 2 times gain 2 Times gain equivalent to 3 dB 2 times output Input

  5. “Box” with a 2 times gain A signal with 1 Watt of power enters the box 2 times Or 3 dB output 1 Watt

  6. Correct Result 1 Watt is 0 dB 2 Watts is 3 dB 2 times is 3 dB 2 times 2 Watts 1 Watt = +

  7. Same Result but referred as dBm (Correctly) 1 Watt is 30 dB 2 Watts is 33 dB 2 times is 3 dB 2 times 2 Watts 1 Watt = +

  8. The Mistake 2 times Converting the box gain to dBm is incorrect 2 Watts 1 Watt = + Wrong result Wrong! 2,000 Watts is not 2 Watts Big mistake!

  9. Correct -vs.- Mistake • One Watt is 1,000 milli-watt (1,000 x 0.001 W) • One Watt is represented by 0 dB. • 1000 milli-watts is represented by 30 dBm. • Both 0 dB and 30 dBm represent the same quantity. • Twice One Watt is 2 Watts. • 2 Watts is represented by 3 dB. • 2 Watts is 2,000 milliwatts. • 2 Watts is also represented by 33 dBm • But 2 Watts is not 2,000 Watts. That is super wrong.

  10. Conclusions • SignalLevels can be converted to dB and dBm • Devices/mediumcharacteristic Gain or Attenuation must be left as dB. Do not convert it to dBm. NO!

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