Callaghan et al. have discussed the calculation of the signal to noise ratio expected from their device in detail[10], and the calculation for the present device is similar. The details are discussed in Appendix A. The magnitude of the signal observed is in excellent agree-ment with that expected, while the noise measured in an indoor urban environment is some 2.2 times larger than calculated. We find a typical time-domain signal to noise ratio (SNR) of 24 for a single shot experiment in an in-door, urban environment, with much of this noise arising from isolated power-line harmonics. The most important differences between Callaghan’s device and the present in terms of sensitivity is that the polarization field used here is about a factor of three less strong, and additional shielding is used here. As can be seen by comparing fig-ure 4a to Callaghan’s figure 7b, which shows the average of four times as many transients with a polarization field three times larger, the present device compares very well. Despite the six-fold disadvantage from the reduced polar-ization field and smaller number of transients, the SNR here appears to be similar or better. This difference how-ever, is entirely due to the increased shielding provided by the aluminum tubing. In both cases the receiver con-tributes negligibly to the noise.