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Chapter 8 Radio Modes and Equipment

Chapter 8 Radio Modes and Equipment. Modulation Systems. FCC Emission Designations and Terms Specified by ITU. Either 3 or 7 characters. If 3 characters: 1 st Character - type of modulation of the main carrier. 2 nd Character - nature of signal(s) modulating the main carrier.

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Chapter 8 Radio Modes and Equipment

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  1. Chapter 8Radio Modes and Equipment

  2. Modulation Systems • FCC Emission Designations and Terms • Specified by ITU. • Either 3 or 7 characters. • If 3 characters: • 1st Character - type of modulation of the main carrier. • 2nd Character - nature of signal(s) modulating the main carrier. • 3rd Character - type of information to be transmitted. • If 7 characters, add 4-character bandwidth designator in front of 3-character designator.

  3. Modulation Systems • FCC Emission Designations and Terms • Type of Modulation.

  4. Modulation Systems • FCC Emission Designations and Terms • Type of Modulating Signal.

  5. Modulation Systems • FCC Emission Designations and Terms • Type of Transmitted Information.

  6. Modulation Systems • FCC Emission Designations and Terms • 3-character designator examples: • A1A = CW. • A3E = Amplitude-modulated phone. • J3E = Single-sideband phone. • F3E = Frequency-modulated phone. • F1B = Radioteletype (RTTY) using FSK. • F2B = Radioteletype (RTTY) using AFSK.

  7. Modulation Systems • FCC Emission Designations and Terms • Emission Types. • Part 97 refers to emission types rather than emission designators. • Continuous Wave (CW) • Phone (AM, FM, SSB) • Radiotetetype (RTTY) • Data (Packet, PSK-31, etc.) • Image (SSTV, Fascimile, etc.) • Modulated CW (MCW) • Spread Spectrum (SS) • Pulse • Test

  8. Modulation Systems • FM/PM Modulation and Modulators • Amount of frequency change is proportional to amplitude of modulating signal. • Deviation. • Speed of frequency change is equal to frequency of modulating signal. • Need to understand 2 terms to fully describe an FM or PM signal. • Deviation Ratio. • Modulation Index.

  9. Modulation Systems • FM/PM Modulation and Modulators • Deviation ratio. • Deviation Ratio = fDev / fMod • fDev = Maximum frequency deviation. • fMod = Maximum modulating frequency. • Deviation ratio is constant in both an FM modulator and in a PM modulator.

  10. Modulation Systems • FM/PM Modulation and Modulators • Modulation index. • Modulation Index = fDev / fm • fDev = Maximum frequency deviation. • fm = Instantaneous modulating frequency. • Modulation index is continuously changing with modulating frequency in an FM modulator. • Modulation index is constant in a PM modulator. • The FCC Rules limit the modulation index at the highest modulating frequency to 1.0. [§97.307(f)(1)]

  11. E1B07 -- What is the highest modulation index permitted at the highest modulation frequency for angle modulation below 29.0 MHz? .5 1.0 2.0 3.0

  12. E8B01 -- What is the term for the ratio between the frequency deviation of an RF carrier wave, and the modulating frequency of its corresponding FM-phone signal? FM compressibility Quieting index Percentage of modulation Modulation index

  13. E8B02 -- How does the modulation index of a phase-modulated emission vary with RF carrier frequency (the modulated frequency)? It increases as the RF carrier frequency increases It decreases as the RF carrier frequency increases It varies with the square root of the RF carrier frequency It does not depend on the RF carrier frequency

  14. E8B03 -- What is the modulation index of an FM-phone signal having a maximum frequency deviation of 3000 Hz either side of the carrier frequency, when the modulating frequency is 1000 Hz? 3 0.3 3000 1000

  15. E8B04 -- What is the modulation index of an FM-phone signal having a maximum carrier deviation of plus or minus 6 kHz when modulated with a 2-kHz modulating frequency? 6000 3 2000 1/3

  16. E8B05 -- What is the deviation ratio of an FM-phone signal having a maximum frequency swing of plus-or-minus 5 kHz when the maximum modulation frequency is 3 kHz? 60 0.167 0.6 1.67

  17. E8B06 -- What is the deviation ratio of an FM-phone signal having a maximum frequency swing of plus or minus 7.5 kHz when the maximum modulation frequency is 3.5 kHz? 2.14 0.214 0.47 47

  18. E8B09 -- What is meant by deviation ratio? The ratio of the audio modulating frequency to the center carrier frequency The ratio of the maximum carrier frequency deviation to the highest audio modulating frequency The ratio of the carrier center frequency to the audio modulating frequency The ratio of the highest audio modulating frequency to the average audio modulating frequency

  19. Modulation Systems • Multiplexing. • Transmitting multiple, independent signals on one carrier. • Two different types: • Frequency division multiplexing (FDM). • Time division multiplexing (TDM).

  20. Modulation Systems • Multiplexing. • Frequency-division multiplexing. • One or more “sub-carriers”, each carrying a different signal. • Commercial FM broadcast SCA. • VHF Omni-Range (VOR). • Fiber optics.

  21. Modulation Systems • Multiplexing. • Time-division multiplexing. • Signals are sampled & samples from each signal are interleaved in sequential time slots. • D-Star. • DMR. • a.k.a. - MOTOTRBO • Normally digital transmission. • Telemetry.

  22. E8B10 -- What describes frequency division multiplexing? The transmitted signal jumps from band to band at a predetermined rate Two or more information streams are merged into a baseband, which then modulates the transmitter The transmitted signal is divided into packets of information Two or more information streams are merged into a digital combiner, which then pulse position modulates the transmitter

  23. E8B11 -- What is digital time division multiplexing? Two or more data streams are assigned to discrete sub-carriers on an FM transmitter Two or more signals are arranged to share discrete time slots of a data transmission Two or more data streams share the same channel by transmitting time of transmission as the sub-carrier Two or more signals are quadrature modulated to increase bandwidth efficiency

  24. Digital Protocols and Modes • Digital Modes • Digital mode consists of a protocol plus a modulation method. • Can be used to transmit voice, video, or data. • Different FCC emission designators for each type of information. • Digital signals can be regenerated several times without error.

  25. Digital Protocols and Modes • Symbol Rate and Data Rate • Data speeds • Air link. • Speed that data is transmitted over the air. • Data stream. • Speed that data is transferred between modem & PC. • Data throughput. • Overall data transfer speed.

  26. Digital Protocols and Modes • Symbol Rate and Data Rate • Data rate = Bits per second (bps). • Symbol rate = Symbols per second (baud).

  27. Digital Protocols and Modes • Symbol Rate and Data Rate • Data rate may or may not equal symbol rate. • Symbol = A change in the waveform to convey information. • Each symbol may encode more than one bit at a time. • RTTY or 1200 baud packet • 1 symbol = 1 bit. • Data Rate = Symbol Rate. • bps = baud • 9600 baud packet • 1 symbol = 2 bits. • Data Rate = 2 x Symbol Rate. • Bps = 2x baud

  28. E8C02 -- What is the definition of symbol rate in a digital transmission? The number of control characters in a message packet The duration of each bit in a message sent over the air The rate at which the waveform of a transmitted signal changes to convey information The number of characters carried per second by the station-to-station link

  29. E8A15 -- What is the relationship between symbol rate and baud? They are the same Baud is twice the symbol rate Symbol rate is only used for packet-based modes Baud is only used for RTTY

  30. Digital Protocols and Modes • Protocols and Codes • Protocol . • Set of rules controlling the exchange of digital data. • e.g. – Packet radio uses the AX.25 protocol. • Protocol does not specify method of modulation. • e.g. – Packet uses FSK or AFSK on HF & FM on VHF. • Transmitter & receiver are under control of the computer. • Automatic Link Enable (ALE) protocol uses automatic control of the station.

  31. Digital Protocols and Modes • Protocols and Codes • Code. • Method of changing information to digital data & back. • Elements are the individual symbols that make up the code. • Code does not specify how data is transmitted. • e.g. – Morse code can be sent by radio, flashing light, sound, or vibration.

  32. Digital Protocols and Modes • Protocols and Codes • Code. • There are 3 types of codes commonly used in amateur radio: • Varicode. • Baudot. • ASCII.

  33. Digital Protocols and Modes • Protocols and Codes • Morse and varicode. • Most codes use the same number of elements (bits) in each character. • Baudot & ASCII are examples. • Some codes have a variable number of elements (bits) per character. • This is called Varicode. • Morse & PSK31 are examples.

  34. Digital Protocols and Modes • Protocols and Codes • Morse and varicode. • Morse. • 2 Symbols. • ❶ = Signal on. • ⓪ = Signal off. • 5 Elements. • Dit = ❶. • Dah = ❶ ❶ ❶. • Inter-element space = ⓪. • Inter-character space = ⓪⓪⓪. • Inter-word space = ⓪⓪⓪⓪⓪⓪⓪.

  35. Digital Protocols and Modes • Protocols and Codes • Morse and varicode. • PSK31. • 2 elements. • 0. • 1. • Number of elements per character varies from 1 to 10. • Requires less bandwidth. • Two 0’s in a row  Space between characters.

  36. Digital Protocols and Modes • Protocols and Codes • Baudot. • a.k.a. – International Telegraph Alphabet Nr 2 (ITA2) • Elements • Mark. • Space. • Characters. • Combinations of 5 elements each. • Each element = 1 data bit.

  37. Digital Protocols and Modes • Protocols and Codes • Baudot. • Maximum of 32 (25) characters. • Special characters LTRS & FIGS (shift codes) switch between 2 sets of characters. • Maximum of 60 different characters can be represented. • Upper-case letters only. • Start & stop bits frame each character.

  38. Digital Protocols and Modes • Protocols and Codes • ASCII. • 2 Elements • 1. • 0. • Characters  Combinations of 7 elements each. • An 8th bit called a parity bit may be added. • Parity bit used to detect some types of transmission errors. • Or the 8th bit could be an additional data bit. • Each element = 1 data bit.

  39. Digital Protocols and Modes • Protocols and Codes • ASCII. • Maximum of 128 (27) characters. • Both upper & lower case letters can be encoded. • 256 (28) maximum characters (if 8 data bits). • Start bit at beginning of each character. • Stop bit(s) at end of each character. • 1, 1.5, or 2 stop bits can be used.

  40. Digital Protocols and Modes • Protocols and Codes • Gray code. • Code arranged so that only one bit changes between consecutive characters. • Often used in rotary encoders. • Less likelihood of errors occurring. • Easier to detect errors when they do occur.

  41. E2E09 -- Which of the following HF digital modes uses variable-length coding for bandwidth efficiency? RTTY PACTOR MT63 PSK31

  42. E2E12 -- Which type of control is used by stations using the Automatic Link Enable (ALE) protocol? Local Remote Automatic ALE can use any type of control

  43. E8C09 -- Which is the name of a digital code where each preceding or following character changes by only one bit? Binary Coded Decimal Code Extended Binary Coded Decimal Interchange Code Excess 3 code Gray code

  44. E8C10 -- What is an advantage of Gray code in digital communications where symbols are transmitted as multiple bits It increases security It has more possible states than simple binary It has more resolution than simple binary It facilitates error detection

  45. E8D10 -- What are some of the differences between the Baudot digital code and ASCII? Baudot uses 4 data bits per character, ASCII uses 7 or 8; Baudot uses 1 character as a letters/figures shift code, ASCII has no letters/figures code Baudot uses 5 data bits per character, ASCII uses 7 or 8; Baudot uses 2 characters as letters/figures shift codes, ASCII has no letters/figures shift code Baudot uses 6 data bits per character, ASCII uses 7 or 8; Baudot has no letters/figures shift code, ASCII uses 2 letters/figures shift codes Baudot uses 7 data bits per character, ASCII uses 8; Baudot has no letters/figures shift code, ASCII uses 2 letters/figures shift codes

  46. E8D11 -- What is one advantage of using ASCII code for data communications? It includes built in error correction features It contains fewer information bits per character than any other code It is possible to transmit both upper and lower case text It uses one character as a shift code to send numeric and special characters

  47. E8D12 -- What is the advantage of including a parity bit with an ASCII character stream? Faster transmission rate The signal can overpower interfering signals Foreign language characters can be sent Some types of errors can be detected

  48. Digital Protocols and Modes • Digital Mode Characteristics • Digital Mode Bandwidth. • The bandwidth required by a digital signal depends on the symbol rate & the shape of the transmitted waveform. • BW = B x K • B = Symbol rate in bauds. • K = Factor relating to shape of keying envelope.

  49. Digital Protocols and Modes • Digital Mode Characteristics • CW. • ITU designator = A1A. • Speed usually expressed in words per minute (wpm). • Use standard word PARIS. • PARIS contains 50 elements. • 50 elements in 60 seconds = 0.83 baud. • Baud = 0.83 x wpm = wpm / 1.2 • Typical shape factor (K) for CW is 4.8. • BW = (wpm / 1.2) x 4.8 = wpm x 4.

  50. Digital Protocols and Modes • Digital Mode Characteristics • CW. • Keying envelope  Shape of the leading edge and the trailing edge of each element. • Changing keying envelope changes K and consequently changes bandwidth. • The faster the rise & fall times of the signal, the wider the bandwidth. • Key clicks.

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