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LoRaLoRaWAN tutorial 5 Decibel dBm dBi dBd
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If you like this video and want to support me, go this page for my donation Paypal or crypto addresses: • / mobilefish • This is part 5 of the LoRa/LoRaWAN tutorial. • In this video series different topics will be explained which will help you to understand LoRa/LoRaWAN. • It is recommended to watch each video sequentially as I may refer to certain LoRa/LoRaWAN topics explained earlier. • In this video I will explain what the decibel is and what the purposes are of the units dBm, dBi and dBd. • A deciBel (dB) is a unit of measurement used to express the ratio of powers, sound pressures or others things on a logarithmic scale. • The deciBel was invented by Bell Labs and named after Alexander Graham Bell. • In this tutorial the deciBel is used to express the ratio of electrical powers (meaning Watts). • A = 10 x log10(Po / Pi) dB • Where Pi is the input power and Po the output power. • Convert deciBel to power ratio: • Po/Pi = 10^(A/10) • The logarithmic scale is used to avoid very big or very small numbers, meaning the ratios. Using decibels is easier to work with. • For example: A power ratio of 1,000,000 (1 million) can be expressed by 60 dB. • A power ratio of 0,000001 can be expressed by -60 dB. • A power ratio of 1,000,000,000,000,000 (1 quadrillion) can be expressed by 150 dB. • A power ratio of 0,000000000000001 can be expressed by -150 dB. • A power ratio of 1,000,000,000,000,000,000,000,000 (1 septillion) can be expressed by 240 dB. • A power ratio of 0,000000000000000000000001 can be expressed by -240 dB. • dB is a ratio it does not represent an absolute value. • If we use a reference input power of 1mW (Pi=1 mW) the unit is expressed as dBm. • A = 10 x log10(Po / 1) dBm • Po/Pi = 10^(A/10) • P = 10^(A/10) mW • Unit dBm represents an absolute value because it uses a fixed reference value 1mW. • Rule of 10s and 3s: • 10 dB = x10 • -10 dB = ÷10 • 3 dB = x2 • -3 dB = ÷2 • Prefixes can be used with SI units. • SI is French for Systeme Internationale which means International System of Units. • Fore example: • -138dBm = 16 aW • -14dBm = 0.04 mW • Other notable deciBel notations are: dBi and dBd (these also represents ratios) • Antenna manufacturers are using these units to measure antenna performance and is useful for comparison purpose. • Manufacturer A has an 868MHz antenna, its gain is 3 dBi • Manufacturer B has an 868MHz antenna, its gain is 2.5 dBi • dBi refers to the antenna gain with respect to an isotropic antenna. • This is an hypothetic point source antenna, that radiates its power uniformly in all directions. • Radiation or antenna pattern reflects the strength of the radio waves from the antenna in different directions. • dBd refers to the antenna gain with respect to a reference dipole antenna. • The radiation pattern of a dipole antenna looks like a donut. • The relationship between dBd and dBi: • dBi = dBd + 2.15 • Check out all my other LoRa/LoRaWAN tutorial videos: • • LoRa/LoRaWAN tutorials • Subscribe to my YouTube channel: • / @mobilefish • The presentation used in this video tutorial can be found at: • https://www.mobilefish.com/developer/... • #mobilefish #lora #lorawan
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