د "راډيو" د بڼو تر مېنځ توپير

[[Mobile phone]]s transmit to a local [[cell site]] (transmitter/receiver) that ultimately connects to the public switched telephone network ([[Public switched telephone network|PSTN]]) through an optic fiber or microwave radio and other network elements. When the mobile phone nears the edge of the cell site's radio coverage area, the central computer switches the phone to a new cell. Cell phones originally used FM, but now most use various digital modulation schemes. Satellite phones use satellites rather than cell towers to communicate. They come in two types: [[Inmarsat|INMARSAT]] and [[Iridium (satellite)|Iridium]]. Both types provide world-wide coverage. INMARSAT uses geosynchronous satellites, with aimed high-gain antennas on the vehicles. Iridium uses 66 Low Earth Orbit satellites as the cells.

 

[[Television]] sends the picture as AM and the sound as FM, with the sound carrier a fixed frequency (4.5 MHz in the [[NTSC]] system) away from the video carrier. Analog television also uses a [[vestigial sideband]] on the video carrier to reduce the bandwidth required.