What is the most common method of generating...

🔍 Key Concepts

• SITOR (Simplex Teletype Over Radio) is a narrow-band direct-printing mode used in GMDSS for HF/MF data communications • SITOR/NBDP uses a specific type of frequency shift keying (FSK) tone pair for mark and space signals • The common ITU-standard tone spacing and audio tones for NBDP telex over HF radio

💭 Think About

• Think about how digital information (mark and space) is represented in HF radioteletype systems: is the carrier itself shifted, or are audio tones used with a suppressed carrier SSB transmitter? • Compare which choices describe a realistic and common audio tone pair used with SSB transmitters versus unusual or overly complex descriptions. • Consider standard NBDP/RTTY tone frequencies you may have memorized (commonly used mark and space audio tones and their separation).

✅ Before You Answer

• Identify which option most clearly describes two distinct audio tones (mark and space) used with an SSB transmitter and suppressed carrier. • Check which frequency separation between the tones (and/or from the carrier) matches the standard NBDP (SITOR) shift you learned in GMDSS theory (typically around a 170 Hz shift). • Eliminate any options that describe tone arrangements or offsets that are not consistent with standard FSK audio tone pairs used in HF telex services.

What is the most common method of generating a SITOR (NBDP) signal on shipboard GMDSS equipment?

Two alternating sidebands of 1615 Hz and 1785 Hz are offset from the carrier frequency by 1700 Hz.

The carrier frequency is alternately shifted from + 85 Hz to - 85 Hz while suppressing the sidebands.

There is one 1500 Hz sideband which is shifted from +170 Hz to - 170 Hz with a suppressed carrier.

Two alternating sidebands of 1500 Hz and 2300 Hz are offset from the carrier frequency by 1900 Hz.

🔍 Key Concepts

💭 Think About

✅ Before You Answer