The performance of radio telemetry receiving systems can be affected by numerous factors, thus it is important for researchers to understand these factors when designing a radio telemetry study. One approach that has been used to describe these factors is the radio system equation which defines six variables that affect radio receiving systems (Sisak and Lotimer 1998; Section 5.1). This equation is:

P_r = P_t – L_w – L_awi –L_air + G_r – L_rtl

where P_r is the received power level, P_t is the transmitted power level, L_w is the signal loss in water, L_awi is the loss at the air-water interface, L_air is the loss in air, G_r is the gain of the receive antenna, and L_rtl is the loss of the receive transmission line (Figure 1). Three of these variables (L_w, L_air, and L_awi) are affected by factors that researchers have little control over (i.e., distance traveled by a given radio signal, water conductivity and temperature, angle of refraction of the signal as it exits the water). However, P_t, G_r, and L_rtl can be influenced by the user and planning for the effects of each is an essential first step towards designing a radio receiving system that operates at the highest level possible. The first of these factors P_t, is addressed while choosing which transmitter to purchase, a topic which was covered in a previous Section. Much of the information that we present will focus on maximizing the strength of the signal that is received by the radio receiver which is affected by G_r and L_rtl. Additionally, we will cover techniques to minimize the effects of ambient (or background) noise which is also an important aspect of radio receiving systems. Ambient noise is important because low signal-to-noise ratios will result in signals that cannot be detected by the receiving system. In other words, tagged fish within range of the receiving system are not detected because ambient noise levels exceed the received signal at the receiver.