A Note on Coupling Transformers for Loop Antennas

The function that determines signal-to-noise ratio is calculated for loop-coupling transformers. It is shown that the optimum signal-to-noise ratio obtains when the loop inductance equals the primary inductance. General expressions are derived for calculating the sensitivity for a 6-decibel signal-to-noise ratio, gain, and selectivity in loop-coupling transformers, when the condition of optimum signal-to-noise obtains. This expression for the sensitivity for a 6-decibel signal-to-noise ratio is also shown in a graph to facilitate the computations. The discussion is limited to the case in which circuit noise is the limiting factor for the sensitivity.