Attenuate/remove "Ethernet over Power line" signal

I have a lab which is testing wireless systems which use the 5 to 85  MHz signal for return data, much like cable TV systems. Someone nearby is using “Ethernet over power wiring” communication which use about the same spectrum. We can see the Ethernet system modulation on our AC power system. Since we are making sensitive measurements, we would like to remove the Ethernet signal by blocking the signal at the input or our single phase power, or by blocking at individual outlets. Are there existing units that will attenuate the Ethernet signal, hopefully by about 60 dB or more?  If not, can you suggest how I might go designing a blocking or filter system without interfering with the present user?