We all know communication is key but talking into a handheld or headset isn't the only way we find communication useful. This series, "Digital Comms Explained," aims to break down the complexities of digital communication systems and builds up to showing you the equipment, software, and processes required for you to take advantage of digital. In Part 1, we will explore the fundamental differences between analog and digital communication, starting with how we naturally communicate and progressing to how these concepts apply to modern radio communication.
Face-to-Face Communication
When we communicate face-to-face, our vocal cords produce sound waves that travel through the air. These sound waves are variations in air pressure that our ears detect and our brains interpret as speech. This is a continuous, analog process.
Technical Breakdown of Sound Waves
Generation of Sound Waves:
- Vocal Cords: When we speak, our vocal cords vibrate, creating sound waves.
- Frequency: The pitch of our voice corresponds to the frequency of the sound waves, measured in Hertz (Hz). Human speech typically ranges from 85 Hz to 255 Hz.
- Amplitude: The loudness of our voice is related to the amplitude of the sound waves, which represents the energy or pressure of the wave.
Propagation of Sound Waves:
- Medium: Sound waves travel through the air, a medium made up of molecules that vibrate to carry the wave.
- Waveform: The waveform of sound is a continuous sine wave that oscillates with varying frequency and amplitude, representing the nuances of our speech.
Reception of Sound Waves:
- Ear Drum: Our ears detect these variations in air pressure. The eardrum vibrates in response to the incoming sound waves.
- Inner Ear: These vibrations are transmitted through the bones of the middle ear to the cochlea in the inner ear, where they are converted into electrical signals.
- Brain: The brain interprets these electrical signals as meaningful sounds and speech.
Analog Communication with Radios
Analog radio communication mimics this natural process of sound wave transmission.
Technical Breakdown of Analog Radio Communication
Transmitting Voice:
- Microphone: When we speak into a radio microphone, it converts our voice (sound waves) into an electrical signal. The varying pressure of the sound waves creates a corresponding varying electrical signal.
- Modulation: This electrical signal is then used to modulate a carrier wave, typically a high-frequency sine wave. There are different methods of modulation.
- Amplitude Modulation (AM): The amplitude of the carrier wave is varied in proportion to the voice signal.
- Frequency Modulation (FM): The frequency of the carrier wave is varied in accordance with the voice signal.
- Antenna: The modulated carrier wave is transmitted through the air via an antenna. The antenna radiates the signal as electromagnetic waves.
- Reception: The receiver’s antenna captures the transmitted electromagnetic waves.
- Demodulation: The receiver demodulates the carrier wave, extracting the original voice signal (electrical signal).
- Speaker: This electrical signal is then converted back into sound waves by the speaker, allowing us to hear the transmitted message
The Need for Digital Communication
While analog communication is effective, it has limitations, especially when it comes to transmitting text or data. Analog signals are more susceptible to noise and degradation over long distances. Additionally, transmitting data in analog form is inefficient and prone to errors.
Digital Communication
Digital communication involves encoding information into a digital format that can be transmitted and decoded by radios. This process converts the continuous analog signal into a series of discrete binary values (0s and 1s). Digital signals are less susceptible to noise and can be corrected for errors, making them more reliable for transmitting data.
How Digital Signals Work
- Encoding: Information (voice, text, data) is converted into a digital signal using a specific protocol.
- Transmission: The digital signal modulates a carrier wave and is transmitted via an antenna. This is accomplished by using a terminal node controller or TNC (software) as well as a sound card (internal or external hardware depending on the radio equipment being used).
- Reception: The receiver’s antenna captures the modulated signal.
- Decoding: The receiver decodes the digital signal back into its original form and software is often used to display the decoded information (wether it's text, photos, or files) using a graphical user interface (GUI).
If you were born in the 1900s, you've already witnessed (and heard) this process happening real time when you connected to the internet over your home phone line using a dial-up modem. That sound you hear is your computer transmitting an encoded message in the form of sound waves for a server on the other end to decode and fulfill the request. The GUI is the internet browser displaying the data of the webpage in a form you can comprehend.
Digital communication has revolutionized the way we transmit information, offering greater clarity, efficiency, and reliability compared to analog methods. This especially holds true for long distance communication over HF to include successfully transmitting information when conditions are well below suitable for normal voice communication. Computers can hear much better down in the noise than our ears can.
In the next part of our series, Digital Comms Explained: Part 2 - A Closer Look at Protocols, we'll dive deeper into the different protocols used in digital communication such as DMR, VARA, JS8, etc. and their specific attributes and applications.