general license class

General License Class

Chapter 5Radio Signals &

Equipment(Part 1)

• 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:

Signal Review

§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.

• Bandwidth Definition

Signal Review

Type of Signal Typical Bandwidth

AM Voice 6 kHz

Amateur Television 6 MHz

SSB Voice 2 khz to 3 kHz

Digital using SSB 50 Hz to 3 kHz

CW 100 Hz to 300 Hz

FM Voice 10 kHz to 15 kHz

G8A01 -- What is the name of the process that changes the envelope of an RF wave to carry information?

A. Phase modulationB. Frequency modulationC. Spread spectrum modulationD. Amplitude modulation

G8A02 -- What is the name of the process that changes the phase angle of an RF wave to convey information?

A. Phase convolutionB. Phase modulationC. Angle convolutionD. Radian inversion

G8A03 -- What is the name of the process which changes the frequency of an RF wave to convey information?

A. Frequency convolutionB. Frequency transformationC. Frequency conversionD. Frequency modulation

G8A05 -- What type of modulation varies the instantaneous power level of the RF signal?

A. Frequency shift keyingB. Pulse position modulationC. Frequency modulationD. Amplitude modulation

G8A07 -- Which of the following phone emissions uses the narrowest frequency bandwidth?

A. Single sidebandB. Double sidebandC. Phase modulationD. 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

• 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.

Digital Modes

G2E01 -- Which mode is normally used when sending an RTTY signal via AFSK with an SSB transmitter?

A. USBB. DSBC. CWD. LSB

G2E02 -- How many data bits are sent in a single PSK31 character?

A. The number variesB. 5C. 7D. 8

G2E03 -- What part of a data packet contains the routing and handling information?

A. DirectoryB. PreambleC. HeaderD. Footer

G2E05 -- Which of the following describes Baudot code?

A. A 7-bit code with start, stop and parity bitsB. A code using error detection and correction C. A 5-bit code with additional start and stop

bitsD. A code using SELCAL and LISTEN

G2E06 -- What is the most common frequency shift for RTTY emissions in the amateur HF bands?

A. 85 HzB. 170 HzC. 425 HzD. 850 Hz

G2E10 -- What is a major advantage of MFSK16 compared to other digital modes?

A. It is much higher speed than RTTYB. It is much narrower bandwidth than most

digital modesC. It has built-in error correctionD. 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 contactB. Requests the packet be retransmittedC. Sends the packet back to the transmitting

stationD. 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 packetD. 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 transmitterB. 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

G8B11 -- How does forward error correction allow the receiver to correct errors in received data packets?

A. By controlling transmitter output power for optimum signal strength

B. By using the varicode character setC. By transmitting redundant information with

the dataD. By using a parity bit with each character

G8B12 -- What is the relationship between transmitted symbol rate and bandwidth?

A. Symbol rate and bandwidth are not relatedB. Higher symbol rates require higher

bandwidthC. Lower symbol rates require higher

bandwidthD. Bandwidth is constant for data mode signals

• Oscillators• Generates sine wave.• Amplifier with positive feedback.

• AV = Amplifier gain.

• β = Feedback ratio.• Loop Gain = AV x β

• If loop gain > 1 and in phase, circuit will oscillate.

Radio’s Building Blocks

• Oscillators• Colpitts oscillator.

• Hartley oscillator.


Frequency determined by values of L & C.

Frequency determined by values of L & C.

• Oscillators• Pierce oscillator.

• Crystals.• Usually small wafer of quartz with precise dimensions.• Piezoelectric effect.

• Crystal deforms mechanically when voltage applied.• Voltage generated when crystal deformed.


Frequency determined by crystal.

• Oscillators• Variable-frequency oscillator (VFO).

• Make either L or C adjustable (usually C).• Not as stable.• Used to tune radio to different frequencies.


• Oscillators• Variable-frequency oscillator (VFO).

• “Crystal-controlled” VFO’s.• Phase-Lock-Loop (PLL).• Direct Digital Synthesis (DDS)

• Stability of crystal oscillator.• Can be controlled by software.


• Mixers• Mixing is also known as heterodyning.• Used to change the frequency of a signal.• Mathematically multiplies 2 frequencies together,

generating 4 output frequencies.• f1 x f2 f1, f2, f1+f2, f1–f2

• Operation of a mixer is similar to operation of detectors & modulators.


• Mixers


• Mixers• Single-balanced mixer.

• Local oscillator or input signal is suppressed, but not both.


• Mixers• Double-balanced mixer.

• fRF & fLO are suppressed leaving only sum & difference frequencies.

• Multipliers• A multiplier stage creates a multiple of the input

frequency.• An amplifier stage designed to have a lot of

distortion (harmonics) & output circuit is tuned to the desired harmonic.

• Class C amplifier.

• Used in VHF/UHF transmitters to generate FM/PM modulated signal at a low frequency & then multiplied to the desired frequency.


• Modulators• Amplitude Modulators.

• Plate modulation.• Originally, AM was produced by varying the DC plate voltage

to the final stage of a CW transmitter.• If solid-state transmitter, substitute collector or drain for

plate.• Requires a LOT of audio power.

• 1 kW transmitter needs 1 kW of audio!

• Screen modulation.• Applied AF to screen voltage of final stage.

• Less AF power required, but worse quality.



• AM can be generated by mixing the modulating signal (fM) with a carrier (fC).

• fC x fM fC, fM, fC+fM, fC–fM

• Using a single-balanced mixer, an AM signal is generated & you don’t have to filter out the modulating signal.

• fC x fM fC, fC+fM, fC–fM

• Using a double-balanced mixer, a double-sideband (DSB) signal is produced.

• fC x fM fC+fM, fC–fM



• AM can be generated by mixing the modulating signal (fM) with a carrier (fC).

• fC x fM fC, fM, fC+fM, fC–fM



• Using a double-balanced mixer, a double-sideband (DSB) signal is produced.

• fC x fM fC+fM, fC–fM



• The double-sideband signal is then converted to a SSB signal by filtering out the unwanted sideband.

• Filter method of SSB generation.


OR


• Phase method of SSB generation.• 2 double-balanced mixers.• 2 carrier signals 90° out-of-phase• 2 modulating signals 90° out-of-phase

• REALLY difficult to create in hardware.• Easy to create in software.



• Advantages of SSB.• Transmitter power used more effectively.

• In AM signal, 1/2 of power is in carrier.• In AM signal, 1/2 of remaining power is in each sideband.• Sidebands carry same information.• In AM, only 25% of available power is used to transmit

the information.• In SSB, 100% of transmitter power is used.

• 1/2 the bandwidth of AM.


• Modulators• Frequency & Phase Modulators.

• Frequency modulation (FM).• Carrier frequency deviates in proportion to amplitude of the

modulating signal.

• Phase modulation (PM).• Carrier frequency deviates in proportion to both the

amplitude and the frequency of the modulating signal.

• By changing the audio frequency response of the modulator, an FM modulator can be used to generate PM and vice versa.


• Modulators• Frequency & Phase Modulators.

• Both FM & PM sound the same on the air (almost).• Only difference is in frequency response of the audio.

• Both FM & PM can be demodulated with the same circuitry.

• Design of modulator circuit determines whether FM or PM.

• FM = modulation applied to oscillator circuit.• PM = modulation applied to amplifier stage following the

oscillator.


G4D08 -- What frequency range is occupied by a 3 kHz LSB signal when the displayed carrier frequency is set to 7.178 MHz?

A. 7.178 to 7.181 MHzB. 7.178 to 7.184 MHzC. 7.175 to 7.178 MHzD. 7.1765 to 7.1795 MHz

G4D09 -- What frequency range is occupied by a 3 kHz USB signal with the displayed carrier frequency set to 14.347 MHz?

A. 14.347 to 14.647 MHzB. 14.347 to 14.350 MHzC. 14.344 to 14.347 MHzD. 14.3455 to 14.3485 MHz

G4D10 -- How close to the lower edge of the 40 meter General Class phone segment should your displayed carrier frequency be when using 3 kHz wide LSB?

A. 3 kHz above the edge of the segmentB. 3 kHz below the edge of the segmentC. Your displayed carrier frequency may be set

at the edge of the segmentD. Center your signal on the edge of the

segment

G4D11 -- How close to the upper edge of the 20 meter General Class band should your displayed carrier frequency be when using 3 kHz wide USB?

A. 3 kHz above the edge of the bandB. 3 kHz below the edge of the bandC. Your displayed carrier frequency may be set

at the edge of the bandD. Center your signal on the edge of the band

G7B07 -- What are the basic components of virtually all sine wave oscillators?

A. An amplifier and a dividerB. A frequency multiplier and a mixerC. A circulator and a filter operating in a feed-

forward loopD. A filter and an amplifier operating in a

feedback loop

G7B09 -- What determines the frequency of an LC oscillator?

A. The number of stages in the counterB. The number of stages in the dividerC. The inductance and capacitance in the tank

circuitD. The time delay of the lag circuit

G7C05 -- Which of the following is an advantage of a transceiver controlled by a direct digital synthesizer (DDS)?

A. Wide tuning range and no need for band switching

B. Relatively high power outputC. Relatively low power consumptionD. Variable frequency with the stability of a

crystal oscillator

G8A04 -- What emission is produced by a reactance modulator connected to an RF power amplifier?

A. Multiplex modulationB. Phase modulationC. Amplitude modulationD. Pulse modulation

G8A06 -- What is one advantage of carrier suppression in a single-sideband phone transmission?

A. Audio fidelity is improvedB. Greater modulation percentage is obtainable

with lower distortionC. The available transmitter power can be used

more effectivelyD. Simpler receiving equipment can be used

G8A12 -- What signal(s) would be found at the output of a properly adjusted balanced modulator?

A. Both upper and lower sidebandsB. Either upper or lower sideband, but not bothC. Both upper and lower sidebands and the

carrierD. The modulating signal and the unmodulated

carrier

G8B01 -- What receiver stage combines a 14.250 MHz input signal with a 13.795 MHz oscillator signal to produce a 455 kHz intermediate frequency (IF) signal?

A. MixerB. BFOC. VFOD. Discriminator

G8B03 -- What is another term for the mixing of two RF signals?

A. HeterodyningB. SynthesizingC. CancellationD. Phase inverting

G8B04 -- What is the name of the stage in a VHF FM transmitter that generates a harmonic of a lower frequency signal to reach the desired operating frequency?

A. MixerB. Reactance modulatorC. Pre-emphasis networkD. Multiplier

Questions?

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