"Demodulator" and "Detector" are probably the most often misused and misunderstood words in the language of electronic countermeasures.    A very basic discussion of each of these terms follows. The final conversion stage in a receiver is the demodulator.   It converts an incoming signal into a desired end product such as audio or video.   The type of modulation determines the design of the demodulator.  "Amplitude Modulation" (AM) means the receiver contains an AM demodulator.   "Frequency Modulation" (FM) means the receiver contains an FM demodulator. Standard television (TV) signals contain both AM and FM components thus requiring two demodulators. One for the picture, which is usually AM, and one for the sound, which is FM. A detector converts a signal from one form into a more recognizable form.   It may not demodulate the information on a signal but it clearly shows the presence of the signal.  To more clearly define the dividing line between demodulators and detectors consider an example of the FM stereo radio.   The radio or receiver picks up the airborne FM signal and demodulates the FM component so beautiful stereo music comes out of the speakers.   Note the frequency on the dial and adjust the tuning so the music is no longer heard.   Turn the volume down or disconnect the speakers.   Tune the radio back to the original frequency and note that the small red or green stereo lamp or word "STEREO" lights thus indicating the detection of a stereo signal. Using these terms correctly becomes increasingly important as new modulation schemes develop.  The probability of demodulating spread-spectrum or frequency hopping transmitters is virtually impossible without first knowing the spreading or hopping code.  Detecting these signals, however, is a relatively simple process. In reality, the wider a signal is spread, the easier it is to detect with a good broadband or nearfield field signal strength meter.

12/06