Watching different types of radio waves

There was also a spectrometer to see a concrete representation of radio waves depending on their wavelength (FM - TV - GSM 900 - DAB - GSM 1800 - UMTS): It reminded me this "Tuneable city" project where people could see a concrete representation of the radio waves in a certain are (here in the exhibit it' just the spectrum at a certain location) but I though it could be nice to have a device to see colored forms (depending on their type (= wavelength). Like for instance red forms for WiFi and blue for UMTS. This might be useful for not so common waves (I don't care to have a representation of FM or GSM which are everywhere).