What’s a dB? How is it useful?

Steve Taranovich
Apr 20, 2020 · 4 min read
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(Image from Keysight)

I want to share some of my design experiences regarding the usefulness of the dB in engineering designs. It’s obvious that engineers work with numbers daily; some of these numbers may be quite large. In many of these cases we are able to use ratios of two numbers.

The dB

α = 10 x log10(P1/P2) dB where log10 is the base 10 logarithm

Well, it’s so much more compact and convenient to use logarithms when dealing with extremely small or large numbers.

A small number

A large number

The dBm

Power = 10 x log10 (P1/1mW) dBm

The decibel scale in audio

dBi: How far can 5G Waves travel? (Reference 1)

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(Image from Sanny Telecom)

dBi is used to calculate the directional gain of an antenna as compared to an isotropic radiator, an ideal antenna that radiates its power uniformly in all directions. The last letter ‘i’ in the word ‘dBi’ denotes isotropic.

dBi is a value calculated against the antenna input power to determine the directional output power of the antenna.

My friend, Ted Rappaport, is a David Lee/Ernst Weber Chaired Professor of Electrical and Computer Engineering at NYU Tandon School of Engineering and a Professor of Computer Science at New York University’s Courant Institute of Mathematical Sciences. He is also a Professor of Radiology at the NYU School of Medicine. Mr. Rappaport also serves as the founding director of NYU WIRELESS.

In the summer of 2016, a group of New York University students took it upon themselves to investigate just how far 5G millimeter waves could travel in rural southwest Virginia, near the town of Riner.

These students, under the direction of Professor Rappaport, ran a two-day test after erecting a transmitter on the front porch of Professor Rappaport’s mountain home. Next, they selected 36 locations from which to measure any 5G millimeter waves being received from the 5G equipment on the Professor’s front porch. They broadcast at the 73 GHz frequency band with A narrowband CW tone transmitted at a center frequency of 73.5 GHz with a maximum transmit power of 14.7 dBm (28 mW)

The result was that the waves could travel greater than 10 km in that rural area with trees and hills present.

Written for @SupplyFrame

Reference

1 Millimeter Wave Wireless Communications: New Results for Rural Connectivity, George R. MacCartney, Jr., Shu Sun, Theodore S. Rappaport, Yunchou Xing, Hangsong Yan, Jeton Koka, Ruichen Wang, and Dian Yu, NYU WIRELESS New York University, Tandon School of Engineering, Oct. 7, 2016

Supplyframe

Discussing the business of hardware and hardware…

Steve Taranovich

Written by

BEEE NYU, MSEE Brooklyn Polytech, Eta Kappa Nu Honor Society, IEEE Educational Activities Chairman, Electronics Design Engineer 40 years, Tech writer 9 years

Supplyframe

Discussing the business of hardware and hardware manufacturing.

Steve Taranovich

Written by

BEEE NYU, MSEE Brooklyn Polytech, Eta Kappa Nu Honor Society, IEEE Educational Activities Chairman, Electronics Design Engineer 40 years, Tech writer 9 years

Supplyframe

Discussing the business of hardware and hardware manufacturing.

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