Transcript Modulation

Modulation
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Amplitude: “Size”
Frequency: “Rate of occurrence”
Phase: “Position or interval within a cycle”
Modulation: “To vary amplitude, frequency,
or phase”
“Carrier”
Pure Sine Wave (146 MHz, no info)
Voltage or Current
“Magical”
NOT
These
Time or Distance
HF and VHF Carriers
Voltage or Current
Slow (HF, 80 m, 3 MHz)
Fast (VHF, 2 m, 144 MHz)
Time or Distance
Carrier/CW/AM
“Carrier”
Modulator
or speech
CW or OOK (BW=150 Hz)
AM
AM vs. FM
Single Audio Tone
BWFM = 5 to 15 KHz
Sidebands
AM
SSB
USB
LSB
DSB
Note break in axis
3 KHz
28 MHz
SSB (BW = 3 KHz)
Long Distance or Weak Signal
1. Two Tone Test Waveform
2. Compression
Single Tone Test Waveform:
“Splatter”
Just a pure RF sinewave offset from
carrier by audio tone frequency!!
3. This is how SSB speech sounds (tuned, AM detection, untuned)
Sound clip: http://www.hamuniverse.com/ssbinformation.html
Photo: http://users.tpg.com.au/users/ldbutler/Intermodulation.htm
Amateur TV
• Analog fast-scan NTSC
• Widest BW (6 MHz)
• 440 MHz , 75 cm
Modulation Video Demos
http://hamelmer.com/Videos.html
Digital / Data Modes
Fldigi
WinPack
FSK
PSK
Audio IN/OUT
USB
TNC/Sound Card
Digital / Data Modes
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219 to 220 MHz, also others
Many different “flavors”
“parity bit” extra bit detects errors
BER = Bit Error Rate
GPS can provide APRS
PSK31
• Low Data Rate (Keyboard)
• continuous whistle with a slight warble
Sound files from http://www.kb9ukd.com/digital/
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/
Packet
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“High” Data Rate
Checksum
Header (Destination Call Sign)
Automatic Repeat if error detected
How it sounds:
Sound files from http://www.kb9ukd.com/digital/
Satellites
AO-27
Mode V/U (J) FM Voice
Uplink: 145.8500 MHz FM (2 m)
Downlink: 436.7950 MHz FM (75 cm)
SO-50
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
Satellite Orbits
few hundred miles up
Drawing http://www.gma.org/surfing/sats.html
22,237 miles up
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
Satellite Location
•Get Pass Info from satellite tracking program, or
•Get Pass Info from web (see screenshot above)
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
Radio Transceiver (and Amplifier)
Transceiver Block Diagram
CW/SSB Receiver
Single-conversion superheterodyne receiver for CW/SSB
28 MHz CW/SSB RF signals
Product
Detector
455 KHz BP filtering
for selectivity
500 Hz
455.5 KHz
28.455 MHz
FM Receiver (VHF/UHF)
146 MHz FM RF signals
RF preamplifier
Increases sensitivity
Limiter
Eliminates
Any trace
of AM
10.7 MHz
135.3 MHz
Discriminator
FM to Audio
1 KHz
CW Transmitter
Oscillator
Other Equipment
• Transverter – Transmitter frequency converter
– Example: 28 MHz up to 222 MHz
• RF Power Amplifier – 5W up to 25 Watts (see
satellite setup)
Antenna Measurements
Feedline and Load
SWR
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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”
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
Antenna Tuner and SWR Meter
Measures Impedance
Ratio
Impedance
Transformer
SWR Meter
1. Forward, adjust Sensitivity to “SET” (Transmitting)
2. Reverse, read SWR (Transmitting)
Antenna Tuner Action
Note that “SWR Meter”, when used with Antenna Tuner,
Doesn’t actually measure SWR on feedline
Measures Impedance Ratio
Between Zload and design Z = 50 Ohms
“SWR =1:1” means Zload = 50 Ohms
Transmitter
is Happy, because
it can deliver power
to antenna system!
Low SWR
Here
“Impedance
Transformer”
High SWR
on feedline is still
present and is
usually OK
Dummy Load
Use to prevent
Radiation when
Testing Transmitter
(instead of using
Antenna)
Safety
Handheld Radios (HTs)
Generally safe as is
–Low Battery Voltage, Enclosed
–Low Power gives low RF exposure
–Low Power gives low antenna voltage
(16Vrms)
RF Exposure
• Non-Ionizing radiation
• Hazard is said to be Tissue Heating
• Microwaves – eyes most vulnerable
Maximum Permissible Exposure
(MPE)
RF Exposure Duty Cycle
Thresholds for RF Evaluation
Re-evaluate the station whenever
an item of equipment is changed
To Reduce RF exposure:
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Relocate antennas
Reduce Power
Change frequency band
Change antenna radiation pattern
Change antenna heading
Electrical Hazards
Electrical Hazards
P=IV=IE
1. High V, Low I
2. Low V, High I
3. High V, High I
Human Body Model
Human Body Model
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!
Current in the Body
Shock Protection
• 3-wire cords with safety ground pin
• Common ground for all equipment
• GFI
• Check voltage on large capacitors,
discharge if necessary
Lightning
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
Fusing
• Interrupts circuit in case of overload
• Prevents fires
• Place in series with AC “hot” conductor
Consequences of Improper
Fusing
Large Batteries
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Vent explosive gas
Don’t charge or discharge too quickly
Can charge 12V batteries from car
Use a fuse!
Antenna Safety
• >10’ from power lines
• Mount out of reach (rf burns)
• Climbing harness, safety glasses, gin pole
Troubleshooting & Repair
RFI Causes
Radio Frequency Interference
• Fundamental overload – clean, but very
strong signals
• Harmonics
• Spurious Emissions
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
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
“Distorted or Noisy Audio”
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Off frequency
Low batteries
Bad location
Hold radio “straight up”
“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
Multimeter or DMM
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Voltage: Voltmeter - connect in parallel
Current: Ammeter – connect in series
Resistance: Ohmmeter – unpowered target
Capacitor with Ohmmeter – reads low, then high
Soldering
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Use Rosin-core solder
Use correct size iron and tip
Be able to see joint clearly
Apply heat to terminal, apply solder to terminal
Soldering tools
Bad Solder Joint (Cold Joint)
Photo http://www.aaroncake.net/
Bad Solder Joint (Cold Joint)
Photo: Wikipedia
Broken and Good Joints
Photo: Wikipedia