modulation
DESCRIPTION
Modulation. Definitions. Amplitude: “Size” Frequency: “Rate of occurrence” Phase: “Position or interval within a cycle” Modulation: “To vary amplitude, frequency, or phase”. “Magical”. “Carrier”. Voltage or Current. Pure Sine Wave (146 MHz, no info). NOT These. Time or Distance. - PowerPoint PPT PresentationTRANSCRIPT
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Modulation
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Definitions
• Amplitude: “Size”
• Frequency: “Rate of occurrence”
• Phase: “Position or interval within a cycle”
• Modulation: “To vary amplitude, frequency, or phase”
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“Carrier”Pure Sine Wave (146 MHz, no info)
NOTThese
Time or Distance
Vol
tage
or
Cur
rent
“Magical”
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HF and VHF Carriers
Slow (HF, 80 m, 3 MHz)
Fast (VHF, 2 m, 144 MHz)
Time or Distance
Voltage or Current
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Carrier/CW/AM
CW or OOK (BW=150 Hz)
“Carrier”
AM
Modulator
or speech
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AM vs. FM
BWFM = 5 to 15 KHz
Single Audio Tone
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Sidebands
28 MH
z
Note break in axis 3 KHz
AMSSBUSBLSBDSB
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SSB (BW = 3 KHz)Long Distance or Weak Signal
Photo: http://users.tpg.com.au/users/ldbutler/Intermodulation.htm
1. Two Tone Test Waveform Compression “Splatter”
3. This is how SSB speech sounds (tuned, AM detection, untuned)
Sound clip: http://www.hamuniverse.com/ssbinformation.html
2. Single Tone Test Waveform:Just a pure RF sinewave offset fromcarrier by audio tone frequency!!
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Amateur TV
• Analog fast-scan NTSC
• Widest BW (6 MHz)
• 440 MHz , 75 cm
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Digital / Data Modes
TNC/Sound Card
Audio IN/OUT
USB
FSKPSK
FldigiWinPack
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Digital / Data Modes
• 219 to 220 MHz, also others
• Many different “flavors”
• “parity bit” extra bit detects errors
• BER = Bit Error Rate
• GPS can provide APRS
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PSK31• Low Data Rate (Keyboard)• continuous whistle with a slight warble
Sound files from http://www.kb9ukd.com/digital/
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MFSK
• Shifts Audio Frequency between a number of different tones
• Low data rate 64 bps• Sounds like a crazy bird
Sound files from http://www.kb9ukd.com/digital/
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Packet
• “High” Data Rate
• Checksum
• Header (Destination Call Sign)
• Automatic Repeat if error detected
• How it sounds:
Sound files from http://www.kb9ukd.com/digital/
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Satellites
AO-27
Mode V/U (J) FM VoiceUplink: 145.8500 MHz FM (2 m)Downlink: 436.7950 MHz FM (75 cm)
SO-50
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Satellite Info
• 30+ operating satellites, including ISS
• Any ham with privileges that allow transmitting on uplink frequency
• Use minimum power necessary (as always)
• Member contacted ham in England
• U/V means UHF uplink, VHF downlink
• V/U VHF up, UHF down
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Satellite Orbits
22,237 miles upfew hundred miles up
Drawing http://www.gma.org/surfing/sats.html
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Doppler Shift
• LEO – Low Earth Orbit – Vs. Geostationary
• 17,000 mph!
• Start by tuning receive freq HIGH by 15 KHz
• End by tuning receive freq LOW by 15 KHz
Sound file http://www.exploratorium.com
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Satellite Location
•Get Pass Info from satellite tracking program, or•Get Pass Info from web (see screenshot above)
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Satellite operation
• Show up at correct time!• Steer beam antennas, tune radios for
Doppler• Spin Fading due to rotation of satellite and
antennas• Very short voice contacts
– Callsign and GridSquare (WA1QKT FN32)
• FM Packet commonly used digital mode
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Radio Transceiver (and Amplifier)
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Transceiver Block Diagram
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CW/SSB Receiver
ProductDetector
Single-conversion superheterodyne receiver for CW/SSB
28 MHz CW/SSB RF signals
455 KHz BP filtering for selectivity
455.5 KHz
28.455 MHz
500 Hz
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FM Receiver (VHF/UHF)
Discriminator
RF preamplifierIncreases sensitivity
146 MHz FM RF signals
10.7 MHz
135.3 MHz
FM to Audio
1 KHz
LimiterEliminatesAny trace of AM
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CW Transmitter
Oscillator
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Other Equipment
• Transverter – Transmitter frequency converter– Example: 28 MHz up to 222 MHz
• RF Power Amplifier – 5W up to 25 Watts (see satellite setup)
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Antenna Measurements
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Feedline and Load
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SWR• Standing Wave Ratio
• Zload = Zo (Feedline characteristic impedance) ?
• If Zload = Zline , SWR = 1, else SWR > 1
• SWR > 1:1 Due to Reflections from load, and Constructive and Destructive interference
“Standing Waves”
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Acceptable “SWR”?
• 1:1 is perfect match
• 2:1 is fairly good, but transmitter may start to reduce power output
• 4:1 is poor, may stress parts, some power lost as HEAT in feedline, and transmitter will reduce power output
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Antenna Tuner and SWR Meter
Impedance Transformer
Measures Impedance Ratio
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SWR Meter
1. Forward, adjust Sensitivity to “SET” (Transmitting)2. Reverse, read SWR (Transmitting)
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Antenna Tuner Action
“Impedance Transformer”
Measures Impedance RatioBetween Zload and design Z = 50 Ohms“SWR =1:1” means Zload = 50 Ohms
Note that “SWR Meter”, when used with Antenna Tuner,Doesn’t actually measure SWR on feedline
High SWRon feedline is stillpresent and is usually OK
Low SWRHere
Transmitteris Happy, because it can deliver powerto antenna system!
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Dummy Load
Use to prevent Radiation whenTesting Transmitter(instead of using Antenna)
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Safety
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Handheld Radios (HTs)
Generally safe as is–Low Battery Voltage, Enclosed–Low Power gives low RF exposure–Low Power gives low antenna voltage (16Vrms)
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RF Exposure
• Non-Ionizing radiation
• Hazard is said to be Tissue Heating
• Microwaves – eyes most vulnerable
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Maximum Permissible Exposure (MPE)
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RF Exposure Duty Cycle
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Thresholds for RF Evaluation
Re-evaluate the station wheneverRe-evaluate the station whenever an item of equipment is changedan item of equipment is changed
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To Reduce RF exposure:
• Relocate antennas
• Reduce Power
• Change frequency band
• Change antenna radiation pattern
• Change antenna heading
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Electrical Hazards
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Electrical HazardsP=IV=IE
1. High V, Low I
2. Low V, High I
3. High V, High I
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Human Body Model
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A pair of copper wires was connected to a 120V wall plug. The extreme danger of this was explained and then a hotdog was used to short-circuit the wires. The hotdog was cooked and then later eaten by a participant.
DO NOT TRY THIS AT HOME!
Human Body Model
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Current in the Body
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Shock Protection
• 3-wire cords with safety ground pin
• Common ground for all equipment
• GFI
• Check voltage on large capacitors, discharge if necessary
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Lightning
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Lightning Protection•Disconnect Antennas
•Ground Antennas
•Do NOT operate with external antennas during thunderstorms
•8’ ground rods for each tower leg, short and direct connections to tower and each other, no sharp bends
•Lightning protectors all to common plate
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Fusing
• Interrupts circuit in case of overload
• Prevents fires
• Place in series with AC “hot” conductor
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Consequences of Improper Fusing
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Large Batteries
• Vent explosive gas
• Don’t charge or discharge too quickly
• Can charge 12V batteries from car
• Use a fuse!
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Antenna Safety
• >10’ from power lines
• Mount out of reach (rf burns)
• Climbing harness, safety glasses, gin pole
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Troubleshooting & Repair
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RFI Causes
• Fundamental overload – clean, but very strong signals
• Harmonics
• Spurious Emissions
Radio Frequency Interference
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Curing your neighbor’s RFI
• First, make sure your station is operating properly– If TVI – is your own TV receiving interference?
• Ideal next step is to identify nature of “aggressor” and “victim” – f, location, etc.
• Telephone – acts as radio receiver –add RF filter at telephone
• RF filters – Snap-on ferrite chokes; Lowpass, Highpass, Bandpass, &Band-reject filters
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If your neighbor’s Part 15 devices interfere with you
• Work to identify offending device
• Politely inform him that rules require him to stop usage if RFI occurs
• Apply fixes at your station if practical
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“Distorted or Noisy Audio”
• Off frequency
• Low batteries
• Bad location
• Hold radio “straight up”
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“Garbled or Unintellegible Transmissions”
• RF Feedback
• FM: Over-deviation – talk farther away
or, Under-deviation – speak up!
• Noise or whine on mobile unit: interference from vehicle’s electrical system
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Multimeter or DMM
• Voltage: Voltmeter - connect in parallel• Current: Ammeter – connect in series• Resistance: Ohmmeter – unpowered target• Capacitor with Ohmmeter – reads low, then high
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Soldering• Use Rosin-core solder• Use correct size iron and tip• Be able to see joint clearly• Apply heat to terminal, apply solder to terminal
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Soldering tools
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Bad Solder Joint (Cold Joint)
Photo http://www.aaroncake.net/
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Bad Solder Joint (Cold Joint)
Photo: Wikipedia
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Broken and Good Joints
Photo: Wikipedia