(C). Channel spacing values are a function of bandwidth values.

Channel width, or band width is the range of frequencies assigned for a specific purpose. Then, channel spacing is the allocation of channel widths for specific purposes.

In US, FCC created a "road map" of channels (channel widths) and where on the overall all radio spectrum the channels are located. See FCC Frequency and Channel Maps

Wide channels of large number of assigned frequencies produces better sound quality, but you end up with fewer channels. Narrow band width channels allow a lot more channels (and types of user) but the sound quality is not as good.

For more details, well explained, please see
Radio Academy: Introduction to Channel Spacing

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(D). To minimize the possibility of interference from adjacent channels.

Any arrangement of channel spacing for dedicated use will assist in preventing unintended use, reducing interference by the user who should be on other channels.

Channel width, or band width is the range of frequencies assigned for a specific purpose. Then, channel spacing is the allocation of channel widths for specific purposes.

In US, FCC created a "road map" of channels (channel widths) and where on the overall all radio spectrum the channels are located. See FCC Frequency and Channel Maps

Wide channels of large number of assigned frequencies produces better sound quality, but you end up with fewer channels. Narrow band width channels allow a lot more channels (and types of user) but the sound quality is not as good.

For more details, well explained, please see
Radio Academy: Introduction to Channel Spacing

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(A). Both TELEX bandwidth and channel spacing values are less than voice bandwidth and channel spacing values.

For TELEX bandwidth map in pdf please see
World Wide Telex Band Chart

You can have narrower channels for texting of lower sound quality, but you need greater width channels for better voice sound quality.

Wide channels of large number of assigned frequencies produces better sound quality, but you end up with fewer channels. Narrow band width channels allow a lot more channels (and types of user) but the sound quality is not as good.

For more details, well explained, please see
Radio Academy: Introduction to Channel Spacing

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(B). SITOR (NBDP), SSB-voice, VHF-FM voice.

SITOR, or sImplex teletype over radio was designed to send text messages, like SMS texting. To modulate radio waves, it uses FSK, or frequency-shift keying, and it contains functions for error detection, and retransmission, so it is more reliable than the RTTY system it improved on. Because it is texting use, it needs only a narrow band, as voice quality is not as big issue as in SSB-voice, or VHF-FM voice.

Wide channels of large number of assigned frequencies produces better sound quality, but you end up with fewer channels. Narrow band width channels allow a lot more channels (and types of user) but the sound quality is not as good.

In US, FCC created a "road map" of channels (channel widths) and where on the overall all radio spectrum the channels are located. See FCC Frequency and Channel Maps

For more details, well explained, please see
Radio Academy: Introduction to Channel Spacing

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Communications with an emission of F1B/J2B would typically have a channel spacing of 0.5 kHz

Class of Emission Authorized bandwidth (kHz)
  F1B         0.5
  J2B        0.5

Radiotelegraphy (4000-27500 kHz) bandwidth is for: Manual A1A, J2A, J2B, J2D
DSC F1B, J2B
Facsimile F1C, F3C, J2C, J3C

For an excellent document of channel frequency assignments, please see:

Coast and Ship Station Equipment Operating in the Maritime Service in the Frequency Range

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Communications with an emission of J3E would typically have a channel spacing of 3.0 kHz

Although not specified by name in the table in the document listed below, the table states that "For all other emission types" the range is 3.0 kHz.

Radiotelegraphy (4000-27500 kHz) bandwidth is for: Manual A1A, J2A, J2B, J2D
DSC F1B, J2B
Facsimile F1C, F3C, J2C, J3C

For an excellent document of channel frequency assignments, please see:

Coast and Ship Station Equipment Operating in the Maritime Service in the Frequency Range

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