# TELECOMMUNICATION SCIENCE… A look at some antenna concepts in TCS301(wireless communications and antenna concepts).

Some Selected Calculation Questions and Solutions

On TCS301 by A.A Otuoze

1. Given a wireless access point with 150mW of output power connected through a 100 foot cable with 6dB of loss with a gain of 9dBi. A, calculate the transmit power. B, if 30dBm is given as a transmit power and 4dB loss. Find the Gain. C, what is the Equivalent Isotropically Radiated Power (EIRP) of the antenna?

Solutions

A, Power output (Po) =150mW, Loss=6dB, Gain=9dBi

Transmit power (Pt) = 10×log (Po)

Pt=10×log(150mW) = 21.76dBm.

B, to find the Gain at 30dBm transmit power we must first calculate the EIRP of the antenna because EIRP=transmit power-Loss+Gain=Pt-L+G

Therefore we have to find EIRP which is on question C

C, EIRP=Pt-L+G

EIRP= 21.76dBm-6dB+9dBi

EIRP=24.76dBm

B, if Pt=30dBm, Loss=4dB, Gain=?

From EIRP=Pt-L+G, we can express G=EIRP-Pt+L

G=24.76dBm-30dBm+4dB

G= -1.24dBi

1. Given an access point with an output power of 100mW connected through a cable with a loss of 2dB to an antenna with gain of 11dBi. What is the EIRP in mW.

Soln

Power output (Po)=100mW, Loss (L)=2dBi, Gain (G)=11dBi, EIRP=?

EIRP=Pt-L+G where Pt=10×log (Po)

Pt=10×log (100mW) =20dBm

EIRP=20dBm-2dB+11dBi

EIRP=29dBm

EIRP in mW=10ˆ2.9mW

1. An antenna receives 60mW from a transmitted power of 100mW of a wireless AP. Find the loss.

Pt=100mW, Po=60mW, Loss=Pt-Po

Pt=10*log(100mW)=20dBm

Po=10*log(60mW)=17.78dBm

Loss=20dBm-17.78dBm=2.22dBm

Loss in dB= 2.22-30=-27.78dB