Complete Radio and Telecommunications: From Crystal Set to Transmitter
⟁ cover painted for this edition — the source module carried no illustrations
Complete Radio and Telecommunications: From Crystal Set to Transmitter
Radio enables communication beyond line of sight without wires. This campaign covers electromagnetic theory, receiver construction, transmitter basics, antenna design, and communication protocols.
Chapter 1: Electromagnetic Fundamentals
Concept
Definition
Relevance
Unit
Frequency
Oscillations per second
Determines radio band
Hertz (Hz)
Wavelength
Distance of one complete wave
Antenna sizing
Meters
Amplitude
Wave height/strength
Signal power
Volts or watts
Modulation
Encoding information on carrier
How voice/data rides the wave
AM, FM, CW
Bandwidth
Range of frequencies used
Channel capacity
Hz
Propagation
How waves travel
Range and coverage
Ground/sky/line-of-sight
Frequency-wavelength relationship: wavelength (meters) = 300 / frequency (MHz). Example: 7 MHz signal → wavelength = 300/7 = 42.8 meters. This matters because antenna length is typically 1/4 or 1/2 wavelength. So a 7 MHz antenna is approximately 10-21 meters long.
Band
Frequency
Wavelength
Propagation
Range
Use
LF (Low)
30-300 kHz
1-10 km
Ground wave
100s of miles
Navigation, time signals
MF (Medium)
300-3000 kHz
100-1000 m
Ground + sky wave
100s of miles (night)
AM broadcast
HF (High)
3-30 MHz
10-100 m
Sky wave (ionosphere)
Worldwide
Shortwave, amateur
VHF (Very High)
30-300 MHz
1-10 m
Line of sight
30-100 miles
FM broadcast, TV, 2-way
UHF (Ultra High)
300-3000 MHz
10-100 cm
Line of sight
10-50 miles
TV, cell phones, WiFi
Chapter 2: Crystal Radio (Simplest Receiver)
Component
Function
Materials
Substitute
Antenna
Captures radio waves
50-100 ft wire, high as possible
Any long wire
Coil (inductor)
Tunes to frequency
60-80 turns wire on cardboard tube
Any insulated wire on form
Capacitor (variable)
Fine tuning
Variable capacitor (salvaged)
Sliding coil tap
Detector (diode)
Rectifies signal
Germanium diode or galena crystal + cat whisker
Razor blade + pencil lead
Earphone
Converts signal to sound
High-impedance earphone (2000+ ohm)
Piezoelectric element
Ground
Completes circuit
Wire to water pipe or ground rod
Metal stake in moist earth
Crystal radio construction: 1) Wind coil: 60-80 turns of insulated wire on toilet paper tube (4-inch diameter). 2) Tap coil at every 10 turns (for tuning). 3) Connect antenna to one end of coil. 4) Connect ground to other end. 5) Connect detector (diode) from coil tap to earphone. 6) Connect earphone other lead to ground. 7) Move coil tap to tune different stations. 8) NO BATTERIES NEEDED — powered entirely by radio waves from transmitter. 9) Range: 10-50 miles from AM broadcast station.
Dipole antenna construction: 1) Calculate length: 468 / frequency (MHz) = total length in feet. 2) Cut two equal wires (each half the total length). 3) Connect feed line (coax cable) to center: one wire to center conductor, other to shield. 4) Hang horizontally, as high as possible. 5) Ends can slope down (inverted-V shape — easier to support). 6) Example: 7 MHz dipole = 468/7 = 66.8 feet total (33.4 feet each side). 7) Height matters: higher = better (minimum 1/4 wavelength above ground).
Chapter 5: Communication Protocols
Protocol
Purpose
Format
Example
Call sign
Identify station
Assigned or improvised
"W1ABC" or "Base Camp"
CQ (calling)
General call to any station
"CQ CQ CQ de [call sign]"
"CQ CQ CQ de Base Camp"
QSO (contact)
Two-way communication
Exchange call signs, signal report
Standard conversation
Signal report
Quality assessment
RST (Readability, Strength, Tone)
"Your signal is 5-9"
Emergency
Distress call
"MAYDAY" (voice) or SOS (CW)
"MAYDAY MAYDAY MAYDAY"
Net (scheduled)
Group communication
Net control directs traffic
Daily check-in schedule
Reference Card
Crystal radio needs no power (powered by radio waves themselves — build one as emergency receiver). 2. Antenna height matters most (doubling antenna height dramatically improves range — get it up high). 3. HF bounces off ionosphere (shortwave signals reflect off upper atmosphere — worldwide range possible). 4. Morse code is simplest (CW requires least power and simplest equipment — learn it). 5. Ground wave for local (AM/MF signals follow earth's surface — reliable local coverage). 6. Dipole is the standard (half-wave dipole is the reference antenna — simple, effective, proven). 7. SOS is universal (... --- ... — every person on Earth should know this signal). 8. Scheduled nets maintain contact (daily check-in times ensure communities stay connected — establish routine).
