Audio frequency-shift keying (AFSK) is a frequency modulation method sometimes used when transmitting radioteletype (RTTY) signals.

Lower sideband (LSB) is normally used for RTTY signals throughout the amateur radio bands when using this method with an SSB transmitter.

There is no technical reason to use LSB instead of USB, however, LSB is used by convention.

LSMFT = Lower Sideband Means Fine Teletype.

Silly Hint: The "A" in "AFSK" is the lowest letter in the alphabet, hinting you towards the lower sideband.

Frequency-shift keying

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(A). PSK31 is a data transmission method that uses Phase-Shift Keying, with a symbol rate of 31 baud. PSK31 uses characters based on a system called Varicode, which uses shorter character bit sequences for common phases and longer ones for less common phases. As the Varicode name indicates, the number of data bits varies.

For more info see Wikipedia: PSK31

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Tags: digital modes

When forming a packet for transmission the information is organized into a specific order so that the message segments may be properly reassembled and decoded after all parts are received.

Each data packet contain several fields, including the Header, which contains routing and handling information.

The packet also includes an address field indicating where the message is going; a control field, indicating the type of data; a frame number which indicates the section order; the data field; and the frame check or cyclic redundancy check field.

For more info see Wikipedia: Packet Radio

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Band plans are organized so that each transmission type uses its own portion of the band frequency. On bands where the FCC designates areas for data versus phone transmissions, data transmission frequencies are located in the lower frequency portion of the band. The 20 meter band allows a General Class licensee to use the range from 14.025 - 14.150 MHz for CW and data communications. The section set aside WITHIN that segment for use by RTTY/Data transmissions is the portion of that segment from 14.070 - 14.100 MHz.

Note: Only 14.070 - 14.100 MHz falls within the CW/data section of the whole 20 meter band. 14.000 - 14.050 MHz falls below the frequency privileges, 14.150 - 14.225 MHz is the frequency gap between the data and voice segments, and 14.275 - 14.350 MHz is the range for the voice segment of the band. If you look at the frequencies from the bottom to the top of the range, data is located in the allowed lower section of the range, it is fairly easy to pick out 14.070 - 14.100 MHz as the correct segment.

For more info go to: ARRL Band Plan for RTTY/Data Frequencies

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Silly Hint: Remember "2" and "0" (as in 20 meter band), and that only one of the answers ends in "0" (14.070) and "2" (14.112).

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The Baudot code is a character set used with some radioteletype (RTTY) transmissions. This code assigns each letter of the alphabet with a 5 bit code, with stop and start bits for each character.

Hint: Baudot has 5 letters plus an additional letter (6 total)

For more info see Wikipedia: Baudot code

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Amateur radio transmissions of radioteletype (RTTY) signals use methods of frequency-shift keying (FSK). Two frequencies, known as the mark and space tones are used. The difference between these two frequencies is known as the frequency shift. The amount of shift most frequently used on the HF bands for amateur operators is a 170 Hz difference.

For more info see Wikipedia: RTTY

Silly hint: The letter "R" (in RTTY) is the 18th letter of the alphabet. The first two digits of the correct answer (17) is the closest number to 18.

Major System 170 = ticks, the sound an old teletype makes.

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(B). The abbreviation "RTTY" represents the method of data transmission known as RadioTeleTYpe.

For more info see Wikipedia: Radioteletype

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The FCC allows General Class license privileges on the 80 meter CW/data band from the range of 3525 to 3600 kHz. The band plans set aside portions within each band to indicate specific types of transmissions within each band segment. The portion of the 80 meter band set aside for data transmissions, such as RTTY, is from 3570 to 3600 kHz.

Note: Answer "3500-3525" is below the frequencies allowed, and both "3700-3750" and "3775-3825" fall at least partially within the gap between the 80 meter data segment and the 75 meter voice segment of the band. Therefore 3570 to 3600 kHz is the only valid answer.

Silly hint: When calculating the frequency for 80 meters, you get 300 / 80 = 3.75MHz. Only one answer includes the numbers 3, 7, and 5, and a zero in the first position, which is "3570 to ..."

For more info see: ARRL Band Plan for RTTY/Data Frequencies

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Tags: digital modes 75/80 meters best practices

PSK31, or Phase-Shift Keying at 31 baud, is a data transmission method. On bands where the FCC has indicated specific areas for CW/data versus phone operations, the data modes are allocated to the lower frequency end of the range. PSK31 is most similar to RTTY, and so on the 20 meter band is assigned to the area below the RTTY segment, near 14.070 MHz.

Notes: Slow scan TV is in the image/voice section at the upper end of the band, just above the SSB phone segment. The CW range is contiguous, not having anything stuck in the middle like one (incorrect) distracter suggests.

Probably the best way to remember this is to know that RTTY (Radio Teletype) is also a "digital mode" and is the most similar to PSK31 of all the options listed; PSK31 is just below the RTTY segment, putting the two digital modes together.

For more info see: ARRL Band Plan for RTTY/Data Frequencies.

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Tags: digital modes frequencies 20 meters

(D). MFSK16 is an abbreviation for Multi-Frequency Shift Keying which uses a system of transmission using 16 different tones. This digital mode shapes the tones being turned on and off into a narrow bandwidth. This type of modulation is very good for offering good performance in weak signal environments without error correction.

For more info see Wikipedia: Multi-Frequency Shift Keying

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(B). MFSK is an abbreviation that stands for Multi (or Multiple) Frequency Shift Keying, such as MFSK16 which uses a modulation mode of 16 different tones for efficient data transmission with little distortion.

For more info see Wikipedia: Multi-Frequency Shift Keying.

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Hint ARQ = Automatic Repeat Request

When transmitting using the packet system for data transmissions, a mode of operation for automatic error control is ARQ which stands for Automatic Repeat ReQuest.

If the receiving station gets a message containing errors the operator will request that the packet be retransmitted. The packet message will re-transmit automatically until the receiver sends a message confirming that the message was received correctly, or the system times out.

For more info see Wikipedia: Automatic Repeat Request.

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Hint: NACK = Not ACKnowledges so “retransmit”

PACTOR protocol is a modulated packet data mode that uses an ARQ, or Automatic Repeat Request, system for error controls. The receiving station will send a message letting the transmitter know that either ACK, the message received corrrectly and is ACKnowledged, or NAK, that the message has errors or is NOT ACKnowledged. In which case, the receiver is requesting that the packet be re-transmitted.

For more info see Wikipedia: PACTOR

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