ABSTRACT
INTRODUCTION The Federal Communications Commission (FCC) has always encouraged performing field strength measurements in the VHF and UHF portion of the television band. The design of television systems, whether National Television System Committee (NTSC) or digital television (DTV), depends on the field strength at the receive location. The FCC, through its rulemaking process, determines the signal strength required for the receiver input, incorporates the losses and gain from the transmission line and antenna, and specifies a minimum field strength that the receiver requires for a predictable viewer result. The value required for the receiver input is based on a number of viewing tests performed under controlled laboratory conditions. As stated in the FCC Rules, the signal strength is determined with the receive antenna at 9.1 m (30 ft) in height above ground. The ability to predict the signal level is dependent on many variables. These variables are factors that are present from the transmitter antenna to the receive antenna on what can be described as the receive path. For a comprehensive review of the characteristics and propagation of signals, see Chapter 1.8, “Propagation Characteristics of Radio Waves.” Further, when performing field strength measurements using a vehicle with an elevated mast, it is important for field personnel to be familiar with all necessary safety practices (see Chapter 2.6, “Electrical Shock”).
