The calculation of the noise figure of a cascade of N unity gain sections is based on the formula NF where F is the amplifier noise figure. A more detailed analysis indicates that this formula is only an approximation. A more exact representation includes the noise figure of the passive elements (coax, taps, etc.), as well as that of the active components. The noise figure of a coax cable is shown to be equal to 1/L where L is the attenuation of the passive/component. The calculation of the thermal noise for forward and reverse transmission of a cable network is made more precise through the consideration of the noise figure of a matched passive element. In addition to providing a more complete understanding of system noise figure for nonunity gain configurations, the resulting formulation also provides an opportunity for introducing additional parameters in the design of cable networks.