History of radio § Broadcasting

               

                             One way voice communication

One way, unidirectional radio transmission is called simplex

Baby Monitor: this is a crib side appliance for mothers of infants that transmits the baby's sounds to a receiver carried by the mother, so she can monitor the baby while she is in other parts of the house. These transmit in FM on 49.300, 49.830, 49.845, 49.860, or 49.875 MHz with low power. Many baby monitors have duplex channels so the mother can talk to the baby, and video cameras to show a picture of the baby, this is called a baby cam.

Wireless Microphone: a battery powered microphone with a short range with a short-range transmitter which is handheld or worn on a person's body which transmits its sound by radio to a nearby receiver unit connected to a sound system. Wireless microphones are used by public speakers, performers, and television personalities so they can move freely without trailing a microphone cord. Analog models transmit in FM on Some models transmit on two frequency channels for diversity reception to prevent  nulls from interrupting transmission as the performer moves around. Some models use digital modulation to prevent unauthorized reception by scanner radio receivers; these operate in the 900 MHz, 2.4 GHz or 6 GHz ISM bands.