SUMMARY

3-44 MULTICOUPLERS patch several receivers or transmitters to one antenna. They also filter out harmonics and spurious responses, and provide impedance matching. MARKING is when a circuit is closed and current flows in teletypewriter operation. SPACING is when a circuit is open and no current flows in teletypewriter operation. INTELLIGENCE is any signal that conveys information (voice, teletypewriter, facsimile). A START unit is the first unit of a teletypewriter signal. It is always a space. A STOP unit is the last unit of a teletypewriter signal. It is always a mark. A TRANSITION is the time it takes to shift from a mark to a space condition or from a space to a mark condition. A CODE in teletypewriter operation is a combination of mark and space conditions representing symbols, figures, or letters. NONSYNCHRONOUS teletypewriter operation is when both transmitter and receiver do not operate continuously. SYNCHRONOUS teletypewriter operation is when both transmitter and receiver operate continuously. WORDS-PER-MINUTE is an approximate rate of speed. It means the number of five letter words with a space between them that can be transmitted or received in a one-minute period. BAUD is a measurement of speed based on the number of code elements or units per second. BITS-PER-SECOND is an acronym of the words binary digit. One bit is equal to one signal unit or element. NEUTRAL teletypewriter operation is where current flow represents a mark and no flow represents a space. POLAR teletypewriter operation is where current flow of one polarity represents a mark and current of the opposite polarity is a space. RUNNING OPEN is the teletypewriter condition where the type hammer constantly strikes the type box but does not print or move across the page. A KEYER is a device that changes dc pulses to mark and space modulation for teletypewriter transmissions. A CONVERTER changes an audio signal back to dc pulses during teletypewriter reception. AUDIO FREQUENCY TONE SHIFT systems use amplitude modulation to change dc mark and space impulses into audio impulses. RADIO FREQUENCY CARRIER SHIFT systems use a keyer to shift a radio frequency signal above or below an assigned frequency. These shifts correspond to marks and spaces. A TELETYPEWRITER is a machine that can transmit and or receive letters, numbers, or symbols. It may have a keyboard similar to a typewriter.