Typical Mistake

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!