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# Iuwne10 S01 L03

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### Iuwne10 S01 L03

1. 1. Wireless Fundamentals Understanding Radio Frequency Mathematics
2. 2. Watts, Milliwatts, and Decibels
3. 3. Decibels <ul><ul><li>Compares powers, originally sounds </li></ul></ul><ul><ul><li>0 dB = same power </li></ul></ul><ul><ul><li>3 dB = twice the power </li></ul></ul><ul><ul><li>-3 dB = half the power </li></ul></ul><ul><ul><li>10 dB = 10 x the power </li></ul></ul><ul><ul><li>-10 dB = 1 tenth of the power </li></ul></ul>
4. 4. dBm <ul><ul><li>Used for AP transmitters </li></ul></ul><ul><ul><li>Same scale as the other dB </li></ul></ul><ul><ul><li>0 dBm = 1 mW </li></ul></ul><ul><ul><li>30 dBm = 1 W </li></ul></ul><ul><ul><li>- 20 dBm = 0.01 mW </li></ul></ul>
5. 5. Decibel Referenced to Isotropic Antenna <ul><ul><li>dBi refers to an isotropic antenna. </li></ul></ul><ul><ul><li>This antenna is theoretical and does not exist in reality </li></ul></ul><ul><ul><li>dBi is used as a reference point to compare antennae. </li></ul></ul><ul><ul><li>The same logarithm progression applies to dBi as to the other decibel scales. </li></ul></ul>
6. 6. Decibel Referenced to Dipole Antenna <ul><ul><li>Refers to dipole </li></ul></ul><ul><ul><li>Is simplest antenna </li></ul></ul><ul><ul><li>Also called rubber duck </li></ul></ul><ul><ul><li>0 dBd = 2.14 dBi </li></ul></ul><ul><ul><li>Logarithm scale same as the other dB scales </li></ul></ul>
7. 7. Effective Isotropic Radiated Power EIRP: Effective Isotropic Radiated Power
8. 8. Summary <ul><ul><li>1 W represents 1 J of energy per second; 1000 mW = 1 W. Decibels are used to compare relative powers. </li></ul></ul><ul><ul><li>dBm compares milliwatts. </li></ul></ul><ul><ul><li>dBi compares antennae to a theoretical isotropic antenna. dBd compares them to a basic 2.14 dBi dipole antenna. </li></ul></ul><ul><ul><li>The EIRP (dBm) is the power of the transmitter (dBm), minus the loss of the cable (dBm), plus the gain (dBi) of the antenna. </li></ul></ul>