Just thought I would pass this along... I am working on an application that doesn't like the 60Hz that is inevitable all around us. Just wanted to show some unloaded scope views of the effects of what a simple filter can accomplish. This filter is often referred to as a twin "T" notch filter, and as far as passive filters are concerned twin "T's" are pretty darn good.
Note: values are given in the schematic that would provide similar results for a 50Hz grid.
Schematic: (Note: in this case, the antenna was my finger)
Image capture with the Filter ground (Vss) removed. Notice the 62 Volt Pk-Pk voltage
Image capture with the Filter ground (Vss) applied. Pk-Pk has been dramatically reduced to 2V
Image capture with the Filter ground (Vss) applied. Same as above but zoomed in. Pk-Pk value is even lower (slight more loading from the scope? ... Perhaps?) ... but you can see the "other noise" much better without being swamped with 60Hz.
Image capture with the Filter ground (Vss) removed. Same zoom in as above. Notice the 60Hz taking over the ground slope. If I kept zooming out I would eventually have the same view as the first scope image.