January 13, 2014

FCC Technician Exam Question Of The Day (T3A04)

Q) What can happen if the antennas at opposite ends of a VHF or UHF line of sight radio link are not using the same polarization?

A) Signals could be significantly weaker

NJ2X Notes:
Both receive and transmit antennas must have the same spatial orientation, the same polarization sense and the same axial ratio in order to maximize reception.  Antennas that are not aligned or do not have the same polarization will have reduced power transfer.  The reduction in power transfer equates to a loss in overall efficiency and performance.

It is very difficult to receive a horizontally transmitted wave with a receive antenna that is vertically polarized due to the polarization mismatch which can cause a 20dB loss.

This question is from the FCC Element 2 Technician Class Question Pool
Effective July 1, 2010 for examinations and is valid until June 30, 2014
Written by: NJ2X, Michael Maher