General License Class

General License Class Chapter 5 Radio Signals & Equipment (Part 1)

Signal Review • Continuous Wave (CW) • A signal at one frequency whose amplitude never varies. • Normally used to refer to turning the signal on & off in a specific pattern to convey information. • Morse Code.

Signal Review • Modulation • Changing a signal in some manner to convey information. • Can change amplitude (AM). • Can change frequency (FM). • Can change phase (PM). • A signal with no information is “unmodulated”.

Signal Review • Modulation • Changing a signal in some manner to convey information. • Voice mode or phone. • Information is voice. • Analog. • Digital. • Data mode or digital mode. • Information is data.

Signal Review • Amplitude Modulated Modes • Amplitude Modulation (AM). • Carrier plus two sidebands are transmitted. • Higher fidelity. • Single-Sideband (SSB). • Carrier & one sideband are suppressed. • Lower Sideband (LSB). • Only lower sideband is transmitted. • Upper sideband (USB). • Only upper sideband is transmitted. • Higher efficiency. • Less bandwidth.

Signal Review • Angle Modulated Modes • Frequency Modulation (FM). • Deviation = amount of frequency change. • Phase Modulation (PM). • Constant power whether modulated or not.

Signal Review • Bandwidth Definition • All modulated signals have sidebands. • FCC defines bandwidth as: • §97.3(a)(8) -- Bandwidth. The width of a frequency band outside of which the mean power of the transmitted signal is attenuated at least 26 dB below the mean power of the transmitted signal within the band.

Signal Review • Bandwidth Definition

G8A01 -- What is the name of the process that changes the envelope of an RF wave to carry information? A. Phase modulation B. Frequency modulation C. Spread spectrum modulation D. Amplitude modulation

G8A02 -- What is the name of the process that changes the phase angle of an RF wave to convey information? A. Phase convolution B. Phase modulation C. Angle convolution D. Radian inversion

G8A03 -- What is the name of the process which changes the frequency of an RF wave to convey information? A. Frequency convolution B. Frequency transformation C. Frequency conversion D. Frequency modulation

G8A05 -- What type of modulation varies the instantaneous power level of the RF signal? A. Frequency shift keying B. Pulse position modulation C. Frequency modulation D. Amplitude modulation

G8A07 -- Which of the following phone emissions uses the narrowest frequency bandwidth? A. Single sideband B. Double sideband C. Phase modulation D. Frequency modulation

G8A11 -- What happens to the RF carrier signal when a modulating audio signal is applied to an FM transmitter? A. The carrier frequency changes proportionally to the instantaneous amplitude of the modulating signal B. The carrier frequency changes proportionally to the amplitude and frequency of the modulating signal C. The carrier amplitude changes proportionally to the instantaneous frequency of the modulating signal D. The carrier phase changes proportionally to the instantaneous amplitude of the modulating signal

Digital Modes • Overview • Data speeds. (Clear as mud?) • Data rate = Bits per second (bps). • Symbol rate = Symbols per second (baud). • Data rate = symbol rate only if 1 symbol = 1 bit. • Duty cycle considerations. • Most digital modes are 100% duty cycle. • Most modern transmitters must reduce output power to avoid exceeding maximum average power output.

Digital Modes • Bandwidth • Required bandwidth increases as symbol rate increases. • BW = B x K • B = Symbol rate in bauds. • K = Factor relating to shape of keying envelope.

Digital Modes • Frequency Shift Keying (FSK) Modes. • Radioteletype (RTTY). • Oldest digital mode. • Still very popular. • Normal shift = 170 Hz. • Baudot code. • Characters = combinations of 5 bits each. • Each element = 1 data bit. • Maximum of 32 (25) characters. • LTRS & FIGS (shift codes). • Start & stop bits frame each character.

Digital Modes • Frequency Shift Keying (FSK) Modes. • Multiple Frequency Shift Keying • MFSK16. • 16 tones, 15.625 Hz apart. • Data rate = 63 bps (42 wpm). • Bandwidth = 316 Hz (approx). • Good weak signal performance even though does not use error correction. (ERROR: MFSK16 uses FEC.) • MT63. • Uses 64 tones to modulate signal. • Bandwidth = 1 kHz. • Includes extensive error correction.

Digital Modes • Phase-Shift Keying (PSK) Modes. • PSK31. • G3PLX developed PSK31 for keyboard-to-keyboard communications. • 31 = data rate (31.25 baud). • Uses variable-length code (Varicode). • Number of bits per character varies. • Most common characters have shortest code. • Uses 00 as separator between characters. • Bandwidth = 37.5 Hz. • Narrowest of all HF digital modes, including CW.

Digital Modes • Packet Modes. • Packet basics. • Data to be sent is divided into “chunks”, control/status information is added before & after each "chunk” forming a “packet”. • Header -- Control & routing information and sometimes error correction information. • Data -- Typically 128 or 256 characters. • Trailer -- Check sum & possibly additional control & status information.

Digital Modes • Packet Modes. • Packet basics. • Error detection. • Cyclic Redundancy Check (CRC). • A number calculated from all of the other bytes in the packet which is appended to the end o the packet. • Receiving system can calculate the CRC of the incoming packet, & if they don’t match ask the packet to be sent again. • Forward Error Correction (FEC). • Additional information is added to each packet to help receiving system reconstruct the packet if CRC fails.

Digital Modes • Packet Modes. • Packet radio. • American Standard Code for Information Interchange (ASCII). • Characters = combinations of 7 elements each. • An 8th bit called a parity bit may be added. • Or the 8th bit could be an additional data bit. • Each element = 1 data bits. • Maximum of 128 (27) characters • 256 (28) maximum characters if 8 data bits. • Start bit & 1, 1.5, or 2 stop bits frame each character. • AX.25 Protocol.

Digital Modes • Packet Modes. • Packet radio. • HF packet. • Limited to 300 baud. • Not well suited for HF propagation conditions. • VHF/UHF packet. • AFSK using FM transmitters at 1200 or 9600 baud. • Basis of APRS.

Digital Modes • PACTOR & WINMOR • Teletype-Over-Radio (TOR). • TOR modes developed to improve reliability over RTTY. • Data sent in short bursts with error detection & error correction information. • AMTOR. • G-MOR. • More reliable, but slow.

Digital Modes • PACTOR & WINMOR • PACTOR. • PACTOR-I developed by DL6MAA & DK4FV. • Uses FSK modulation. • Overcomes shortcomings of AMTOR & HF packet. • Works well in weak-signal & high-noise conditions.

Digital Modes • PACTOR & WINMOR • PACTOR. • PACTOR-II & PACTOR-III used today. • Uses PSK modulation. • Automatic repeat request (ARQ) used to eliminate errors. • Adjusts speed (“trains”) to match conditions. • 5 kbps data rates possible. • Most popular modes for transferring large amounts of data. • WINMOR. • Like PACTOR but can use either FSK or PSK modulation.

G2E01 -- Which mode is normally used when sending an RTTY signal via AFSK with an SSB transmitter? A. USB B. DSB C. CW D. LSB

G2E02 -- How many data bits are sent in a single PSK31 character? A. The number varies B. 5 C. 7 D. 8

G2E03 -- What part of a data packet contains the routing and handling information? A. Directory B. Preamble C. Header D. Footer

G2E05 -- Which of the following describes Baudot code? A. A 7-bit code with start, stop and parity bits B. A code using error detection and correction C. A 5-bit code with additional start and stop bits D. A code using SELCAL and LISTEN

G2E06 -- What is the most common frequency shift for RTTY emissions in the amateur HF bands? A. 85 Hz B. 170 Hz C. 425 Hz D. 850 Hz

G2E10 -- What is a major advantage of MFSK16 compared to other digital modes? A. It is much higher speed than RTTY B. It is much narrower bandwidth than most digital modes C. It has built-in error correction D. It offers good performance in weak signal environments without error correction

G2E12 -- How does the receiving station respond to an ARQ data mode packet containing errors? A. Terminates the contact B. Requests the packet be retransmitted C. Sends the packet back to the transmitting station D. Requests a change in transmitting protocol

G2E13 -- In the PACTOR protocol, what is meant by an NAK response to a transmitted packet? A. The receiver is requesting the packet be re-transmitted B. The receiver is reporting the packet was received without error C. The receiver is busy decoding the packet D. The entire file has been received correctly

G8B08 -- Why is it important to know the duty cycle of the data mode you are using when transmitting? A. To aid in tuning your transmitter B. Some modes have high duty cycles which could exceed the transmitter's average power rating. C. To allow time for the other station to break in during a transmission D. All of these choices are correct

General License Class