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) NOT These Time or Distance Voltage or Current “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 BW FM = 5 to 15 KHz Single Audio Tone

Sidebands 28 MHz Note break in axis 3 KHz AM SSB USB LSB DSB

SSB (BW = 3 KHz) Long Distance or Weak Signal Photo: 1. Two Tone Test Waveform Compression “Splatter” 3. This is how SSB speech sounds (tuned, AM detection, untuned) Sound clip: 2. Single Tone Test Waveform: Just a pure RF sinewave offset from carrier by audio tone frequency!!

Amateur TV Analog fast-scan NTSC Widest BW (6 MHz) 440 MHz, 75 cm

Modulation Video Demos

Digital / Data Modes TNC/Sound Card Audio IN/OUT USB FSK PSK Fldigi WinPack

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

MFSK Shifts Audio Frequency between a number of different tones Low data rate 64 bps Sounds like a crazy bird Sound files from

Packet “High” Data Rate Checksum Header (Destination Call Sign) Automatic Repeat if error detected How it sounds: Sound files from

Satellites AO-27 Mode V/U (J) FM Voice Uplink: MHz FM (2 m) Downlink: 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 up few hundred miles up Drawing

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

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 Product Detector Single-conversion superheterodyne receiver for CW/SSB 28 MHz CW/SSB RF signals 455 KHz BP filtering for selectivity KHz MHz 500 Hz

FM Receiver (VHF/UHF) Discriminator RF preamplifier Increases sensitivity 146 MHz FM RF signals 10.7 MHz MHz FM to Audio 1 KHz Limiter Eliminates Any 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 Z load = Z o (Feedline characteristic impedance) ? If Z load = Z line, 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 Ratio Between Z load and design Z = 50 Ohms “SWR =1:1” means Z load = 50 Ohms Note that “SWR Meter”, when used with Antenna Tuner, Doesn’t actually measure SWR on feedline High SWR on feedline is still present and is usually OK Low SWR Here Transmitter is Happy, because it can deliver power to antenna system!

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 an 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 Hazards P=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

Bad Solder Joint (Cold Joint) Photo: Wikipedia

Broken and Good Joints Photo: Wikipedia