You've seen plots of the RF field from antennas. How would you like to take a photograph of them? Browsing Hack A Day I saw a way to do it. BERG, the design consultancy firm whose clients include the BBC, Nokia, Ofcom, and Unilever, has a Web page with a photograph and video of the readable “volume” of a radio field from an RFID reader.
The technique is surprising simple and probably one you can duplicate with your own RF emitter, provided it’s small enough. Rather than use a special camera that “sees” RF fields, BERG attached an LED to an RFID tag. The RFID tag was moved around the RF field generated by the RFID reader. Whenever the field was strong enough to turn on the LED, the camera, using a time exposure, picked up the glow. If the RF source was strong enough, it seems that a small antenna attached to an LED could be sufficient to get some indication of the near field from that RF emitter, although by using a neon bulb (if the power was high enough) or having a circuit that didn't trigger the LED until the RF was at a certain level might work better—safety first.
