It is hard to imagine a culprit radiator that emits fields of 20v/m (or even 30v/m) into a hospital ward or a local clinic from 3m or more away. It is true enough that the airwaves are full of signals from WLAN, wifi, bluetooth, etc. But these are all low power emitters.
The real culprit and hence the real threat is the ubiquitous cell phone in close proximity (placed on top of the medical equipment). Being at such a short distance away, this means by definition the medical equipment is within the near field of the threat emitter. So why test against this threat with a source 3m away?
By the way, when does a cell phone emit the greatest field?
Answer – at switch on. The power is at maximum while the phone identifies all available base stations in its vicinity. The power is then turned down to a level conducive with the distance to the selected base station.
In the next posting we will do the engineering calculations permitting a valid comparison between testing at 3m and 1m.