Chapter 3: Radio Frequency Components, Measurements, and Mathematics

2.14

A standard dipole antenna has a dBi value of _____. In order to convert dBd to dBi, you simply add this value to the dBd value.

+20

A transmission amplitude of 100 mW is equal to _____ dBm.

Rule of 10s and 3s

According to the _____, for every 3 dB gain, double the power. For every 3 dB loss, halve the power. For every 10 dB gain, times the power by 10. For every 10 dB loss, divide the power by 10.

-23 dB

An AP delivers 100 mW of power to its antenna. If the receiver detects a signal power level of 0.5 mW, what is the received power level relative to the power delivered to the transmitting antenna?

isotropic radiator

An _____ is a point source that radiates signal equally in all directions.

intentional radiator (IR)

An _____ is something that is specifically designed to generate RF, as opposed to something that generates RF as a by-product of its main function, such as a motor that incidentally generates RF noise.

*dBm = 10 × log10(PmW)*

As 0 dBm is equal to 1 mW, using the formula _____, you can determine that 100 mW of power is equal to +20 dBm.

FSPL

Because of _____, received signals will always measure below 1 mW. A very strong received signal is -40 dBm.

15

If a radio receives a signal of -85 dBm and the noise floor is measured at -100 dBm, the difference between the received signal and the background noise is _____ dB (The SNR is 15 dB). An SNR of 25 dB or greater is considered good signal quality, and an SNR of 10 dB or lower is considered very poor signal quality.

*PmW = 10(dBm ÷ 10)*

If you happen to have the dBm value of a device and want to calculate the corresponding milliwatt value, the formula is _____.

noise floor

The _____ is the ambient or background level of radio energy on a specific channel.

signal-to-noise ratio (SNR)

The _____ is the difference in decibels between the received signal and the background noise level (noise floor), not actually a ratio.

*dB = 10log(P1/P2)*

The formula _____, where P1 is the reference power and P2 is the power level of interest, allows the power level in dB to be calculated. P1 is commonly an "initial power level" or the input power being applied to a device/circuit. P2 is commonly a "final power level" or the output power of a device/circuit.

decibels isotropic (dBi)

The gain, or increase, of power from an antenna when compared to what an isotropic radiator would generate is known as _____.

decibels dipole (dBd)

The other scale used to describe antenna gain is _____, or decibel gain relative to a dipole antenna.

Multiplying 1 by 10 twice will give you 100. So the bridge is generating 100 mW, or +20 dBm, of power. After you calculate the effect of the -3 dB loss, you know the value of the IR. You can represent the IR as either +17 dBm or 50 mW. Because the gain is 10 dBi, you add 10 to the dBm column and multiply the mW column by 10. This gives you an EIRP of +27 dBm, or 500 mW.

You have a wireless bridge that generates a 100 mW signal. The bridge is connected to an antenna via a cable that creates -3 dB of signal loss. The antenna provides 10 dBi of signal gain. In this example, calculate the IR and EIRP values using the Rule of 10s and 3s.

Equivalent isotropically radiated power (EIRP)

_____ is the highest RF signal strength that is transmitted from a particular antenna.

dBm

_____ means decibels relative to 1 milliwatt.

Receive sensitivity

_____ refers to the power level of an RF signal required to be successfully received by the receiver radio.