Modulation

Definitions

• 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)

NOTThese

Time or Distance

Vol

tage

or

Cur

rent

“Magical”

HF and VHF Carriers

Slow (HF, 80 m, 3 MHz)

Fast (VHF, 2 m, 144 MHz)

Time or Distance

Voltage or Current

Carrier/CW/AM

CW or OOK (BW=150 Hz)

“Carrier”

AM

Modulator

or speech

AM vs. FM

BWFM = 5 to 15 KHz

Single Audio Tone

Sidebands

28 MH

z

Note break in axis 3 KHz

AMSSBUSBLSBDSB

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!!

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

TNC/Sound Card

Audio IN/OUT

USB

FSKPSK

FldigiWinPack

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

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

• “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 VoiceUplink: 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

22,237 miles upfew hundred miles up

Drawing http://www.gma.org/surfing/sats.html

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

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

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

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• 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

Impedance Transformer

Measures Impedance Ratio

SWR Meter

1. Forward, adjust Sensitivity to “SET” (Transmitting)2. Reverse, read SWR (Transmitting)

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!

Dummy Load

Use to prevent Radiation whenTesting 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 wheneverRe-evaluate the station whenever an item of equipment is changedan item of equipment is changed

To Reduce RF exposure:

• Relocate antennas

• Reduce Power

• Change frequency band

• Change antenna radiation pattern

• Change antenna heading

Electrical Hazards

Electrical HazardsP=IV=IE

1. High V, Low I

2. Low V, High I

3. High V, High I

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!

Human Body Model

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

• 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

• Fundamental overload – clean, but very strong signals

• Harmonics

• Spurious Emissions

Radio Frequency Interference

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”

• 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

• Voltage: Voltmeter - connect in parallel• Current: Ammeter – connect in series• Resistance: Ohmmeter – unpowered target• Capacitor with Ohmmeter – reads low, then high

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

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