Modulated Radio Waves:

Principles, Applications, and IoT Wireless Solutions

Introduction: Why Modulation Makes Wireless Communication Possible

Radio waves, by themselves, are nothing more than high‑frequency sine waves oscillating at a single carrier frequency. Without modulation, they carry no information. Modulation is the essential process of encoding an information signal — whether it is human voice, digital data, sensor readings, or video — onto a carrier wave for transmission through the air. The device that performs this encoding is a radio frequency modulator, while the receiver counterpart that recovers the original information is a demodulator.

Modulation is not merely an optional enhancement; it is a fundamental necessity. An audio signal at 3 kHz has a wavelength of 100 km, requiring an impractically large antenna. By modulating that audio onto a carrier at 433 MHz, the wavelength shrinks to just 69 cm, making a handheld antenna perfectly feasible. Modulation also enables frequency‑division multiplexing — multiple radio stations, each on a different carrier frequency, can share the same geographic area without interfering with each other.

This article explores the two major families of radio wave modulation — analog and digital — and explains how Coral RF‘s Sub‑1GHz wireless modules implement these techniques for IoT, industrial telemetry, smart metering, and remote control applications.

Part 1: Analog Modulation – The Foundation

Analog modulation techniques modify a carrier wave continuously in response to an analog information signal. They form the basis of traditional broadcast radio and remain widely used for voice communication.

Amplitude Modulation (AM)

AM varies the amplitude (strength) of the carrier wave in direct proportion to the instantaneous amplitude of the audio signal. The carrier frequency and phase remain constant. The modulated signal consists of three components: the carrier itself (which carries no information) and two identical sidebands that contain the information.

Key characteristics:

• Bandwidth: Approximately 10 kHz per station (double the highest modulating frequency)

• Noise immunity: Poor — amplitude interference (lightning, motors) directly corrupts the signal

• Receiver complexity: Very low — a simple diode envelope detector can demodulate AM

• Transmitter efficiency: Low — up to two‑thirds of transmitted power is wasted on the carrier

AM remains in use for long‑range broadcast radio, aviation communication, and certain industrial telemetry applications where simplicity outweighs noise performance.

Frequency Modulation (FM)

FM encodes information by varying the carrier frequency in proportion to the audio signal while keeping the carrier amplitude constant. Because information resides in frequency rather than amplitude, FM is inherently resistant to amplitude‑based interference.

Key characteristics:

• Bandwidth: Approximately 180 kHz per station (much wider than AM)

• Noise immunity: Excellent — amplitude interference is rejected by limiter/discriminator circuits

• Audio fidelity: Superior — supports full‑bandwidth stereo audio

• Receiver complexity: Moderate — requires frequency‑discriminating circuitry

FM is the standard for high‑quality music broadcasting, two‑way analog radios (walkie‑talkies), and analog wireless microphones. Its digital descendant, FSK, forms the basis of many modern IoT wireless systems.

Phase Modulation (PM)

Phase modulation varies the phase angle of the carrier wave in response to the information signal. In practice, PM is closely related to FM — a PM signal can be viewed as an FM signal with a different modulation index. PM is used in certain satellite and navigation systems where phase stability is critical.

Part 2: Digital Modulation – The IoT Revolution

Digital modulation techniques represent binary data (0s and 1s) by switching the carrier wave between discrete states. They are the foundation of virtually all modern wireless communication, from Wi‑Fi and Bluetooth to LoRaWAN and cellular networks.

Amplitude Shift Keying (ASK) and On‑Off Keying (OOK)

ASK is the digital equivalent of AM. A binary 1 is represented by a high‑amplitude carrier; a binary 0 is represented by a low (but non‑zero) amplitude. OOK is a special case of ASK where the “low” level is literally zero — the transmitter‘s power amplifier is completely off during a binary 0. ASK modulation is simple, but prone to interference.

Key characteristics:

• Implementation: Extremely simple — a transistor oscillator, battery, and switch suffice for OOK

• Power consumption: Very low — the PA draws zero current during “0” bits

• Noise immunity: Poor — amplitude interference corrupts the signal

• Bandwidth efficiency: Good — narrow bandwidth for low data rates

ASK and OOK are widely used in garage door openers, remote keyless entry systems, wireless doorbells, and other low‑cost, unidirectional remote controls.

Frequency Shift Keying (FSK) and Gaussian Frequency Shift Keying (GFSK)

FSK is the digital equivalent of FM. The carrier switches between two distinct frequencies: one frequency represents a binary 1, another represents a binary 0. Because FSK relies on frequency changes rather than amplitude changes, it is much less susceptible to interference than ASK. The trade‑off is that FSK requires more bandwidth for the same data rate.

GFSK (Gaussian Frequency Shift Keying) improves upon basic FSK by passing the baseband data through a Gaussian low‑pass filter before modulation. This smooths the frequency transitions, reducing out‑of‑band spectral emissions and minimizing adjacent‑channel interference. GFSK maintains a constant amplitude envelope while keeping the power spectrum concentrated and narrow.

Key characteristics:

• Noise immunity: Good — frequency‑based, rejects amplitude interference

• Data rate: 0.6 kbps to 500 kbps

• Bandwidth efficiency: Moderate

• Implementation complexity: Moderate

GFSK is the modulation used in Bluetooth, many Zigbee devices, and the majority of Sub‑1GHz ISM band transceivers. When you use a wireless mouse, Bluetooth speaker, or garage door opener, you are relying on GFSK modulation — the digital descendant of classic FM.

Phase Shift Keying (PSK) and Quadrature Amplitude Modulation (QAM)

PSK encodes information by shifting the phase of the carrier wave. Binary PSK (BPSK) uses two phase states (0° and 180°). Quadrature PSK (QPSK) uses four phase states, encoding two bits per symbol. Higher‑order PSK schemes (8‑PSK, 16‑PSK) increase data rate but become more susceptible to noise.

QAM (Quadrature Amplitude Modulation) combines both amplitude and phase variations, encoding multiple bits per symbol by simultaneously modulating both the amplitude and phase of the carrier. 16‑QAM encodes four bits per symbol; 64‑QAM encodes six bits; 256‑QAM encodes eight bits. The trade‑off is severe: BPSK achieves a bit error rate of 10⁻⁵ at 9 dB SNR, while 16‑QAM requires 16 dB SNR to reach the same error threshold.

QAM is the foundation of Wi‑Fi (802.11ac/ax), 4G/5G cellular, digital television broadcasting, and cable modems — applications where high data rate is more important than extreme range or ultra‑low power.

Spread Spectrum and LoRa

Spread spectrum techniques spread the signal across a wide bandwidth, making it resistant to narrowband interference and difficult to intercept. Direct Sequence Spread Spectrum (DSSS) is used in GPS and older Wi‑Fi. LoRa (Long Range) uses a proprietary chirp spread spectrum (CSS) technique developed by Semtech. Unlike traditional modulation, LoRa spreads a narrowband signal across a wide bandwidth using frequency chirps, achieving extraordinary receiver sensitivity at the cost of very low data rates.

Compared with FSK and GFSK modulation, LoRa offers three key advantages: its communication distance is approximately 10 times longer; it consumes very low power, extending battery life; and it provides approximately 30 dB improvement in co‑channel rejection. LoRa combines digital spread spectrum, digital signal processing, and forward error correction coding — technologies previously found only in military communication systems.

LoRa is the dominant modulation for LPWAN (Low‑Power Wide‑Area Network) applications including LoRaWAN sensors, agricultural IoT, asset tracking, and smart metering in remote or obstructed locations.

Part 3: Modulation Comparison at a Glance

The key trade‑off across all modulation types is between spectral efficiency (bits per second per Hertz) and noise immunity. Higher‑order modulations like 64‑QAM pack more bits into each symbol, dramatically increasing data rate, but require significantly higher signal‑to‑noise ratio for reliable reception. Lower‑order modulations like BPSK and LoRa are far more robust in noisy or weak‑signal conditions but transmit data much more slowly.

Part 4: Coral RF Modules – Practical Implementation of Modern Modulation

Coral RF offers a comprehensive portfolio of Sub‑1GHz and 2.4 GHz wireless modules that implement the modulation techniques described above. Their products are based on industry‑leading Texas Instruments wireless MCUs and Semtech LoRa transceivers, covering frequency bands from 169 MHz to 1250 MHz and 2.4 GHz.

CC1101‑Based Modules – ASK/OOK and GFSK at Ultra‑Low Cost

The Texas Instruments CC1101 is one of the most widely deployed Sub‑1GHz transceivers globally. It supports 2‑FSK, 4‑FSK, GFSK, MSK, ASK, and OOK modulation formats — all configurable via SPI commands.

Coral RF‘s N503AS module (based on CC1101) delivers:

• Output power: +12 dBm (programmable)

• Receiver sensitivity: -116 dBm at 0.6 kBaud (433 MHz), -112 dBm at 1.2 kBaud (868 MHz)

• Data rate: 0.6–500 kBaud, fully programmable

• Sleep current: 0.2 μA — enabling multi‑year battery life

• Modulation: GFSK, FSK, MSK, ASK, OOK, 4‑FSK

• Frequency bands: 315/433/868/915 MHz

The N503AS is ideal for low‑cost OOK remote controls, ASK‑based wireless sensors, and GFSK‑modulated telemetry links. Its ultra‑low sleep current makes it particularly suited for battery‑powered devices that wake up briefly to transmit and return to deep sleep. When paired with the CC1190 range extender, output power can be boosted to +27 dBm for significantly extended range.

CC1310‑Based Wireless MCU Modules – Software‑Defined RF

The CC1310 is a highly integrated wireless MCU that combines an ARM Cortex‑M3 application processor with a flexible Sub‑1GHz RF transceiver. The RF section is implemented as a dedicated ARM Cortex‑M0 processor — a true software‑defined radio architecture that handles modulation, demodulation, packet assembly, and timing synchronization under software control. It supports GFSK, MSK, and OOK modulation for multiple physical layers.

Coral RF offers multiple CC1310‑based modules with different output power levels:

The CC1310‘s receiver sensitivity reaches -124 dBm in long‑range mode, with excellent selectivity (±100 kHz): 56 dB and blocking performance (±10 MHz): 90 dB. Transmit current at +10 dBm is only 13.4 mA, while standby current with RTC running and RAM retained is just 0.7 μA.

The N530AS module is specifically optimised for the 433 MHz, 868 MHz, and 915 MHz ISM bands, delivering +14 dBm output power and -110 dBm sensitivity at 50 kbps. It is controlled via simple UART AT commands and includes native support for Wireless M‑Bus (WMBus) protocols, making it an ideal solution for smart metering, home automation, and IoT sensor applications.

SX1262‑Based LoRa Modules – Extreme Range and Deep Penetration

For applications requiring maximum range — covering farms, ports, or entire cities — Coral RF offers LoRa modules based on Semtech‘s SX1262 transceiver. The SX1262 achieves a receiver sensitivity of -148 dBm in LoRa mode, while drawing only 4.2 mA in active receive.

Coral RF‘s N401AS module (based on SX1262) delivers:

• Output power: +22 dBm (≈150 mW)

• Receiver sensitivity: -148 dBm (LoRa mode)

• Data rate: 0.3–62.5 kbps (LoRa mode, software‑programmable)

• Sleep current: 0.1 μA

• Modulation: LoRa (chirp spread spectrum) and (G)FSK modes

• Frequency bands: 169/433/868/915 MHz

• Measured range: 3000 meters in open field (3 dBi antenna, 1.2 kbps)

The module uses a 2‑layer PCB design with excellent impedance matching and anti‑interference performance, making it suitable for IoT, smart home, wireless meter reading, water/gas/electricity meters, coal mine monitoring, research, medical devices, and medium‑to‑long‑range wireless communication equipment.

For higher power requirements, Coral RF offers additional SX1262‑based variants:

• N425AS: +27 dBm (≈500 mW) output, LoRaWAN‑ready

• N426AS: +30 dBm (1 W) output

• N427AS: +33 dBm (2 W) output, designed for LoRaWAN gateways

• N428AS: +37 dBm (5 W) output, achieving link budgets exceeding 185 dB for tens of kilometres in non‑line‑of‑sight conditions

USB Dongles – Plug‑and‑Play Development Tools

Coral RF also provides USB dongles that function as portable spectrum sniffers, gateway adapters, and development tools. These dongles appear as serial devices on a PC or Raspberry Pi and can be controlled via AT commands — no SPI driver development or soldering required. Sub‑1GHz dongles are available based on LoRa SX1262, CC1120, CC1125, CC1312, and CC1314, with output power ranging from +14 dBm to +27 dBm. Zigbee and BLE dongles based on CC2538, CC2650, CC2651, CC2652, and CC2674 (with optional CC2592 PA) are also available, with output power up to +20 dBm.

Part 5: Application‑Specific Modulation Selection

The choice of modulation technique determines the fundamental performance characteristics of a wireless system. The following table provides a rapid selection guide based on application requirements:

Part 6: GFSK vs. LoRa – Understanding the Trade‑off

A common question among engineers is whether to choose GFSK or LoRa modulation. The answer depends entirely on the application requirements.

When to Choose GFSK

GFSK is the superior choice when:

• Data rate matters: GFSK supports up to 500 kbps, versus LoRa‘s 0.3–37.5 kbps

• Low latency is required: GFSK‘s latency is measured in microseconds; LoRa at SF12 introduces seconds of delay

• Bidirectional real‑time control is needed

• The deployment is moderate range (2‑5 km in line‑of‑sight conditions)

• Cost is a primary constraint: GFSK transceivers (e.g., CC1101) are significantly less expensive than LoRa equivalents

When to Choose LoRa

LoRa is the superior choice when:

• Maximum range is the primary requirement: LoRa achieves approximately 10× the range of GFSK for the same transmit power

• Deep penetration through buildings, basements, or foliage is required

• Devices are battery‑powered and transmit infrequently: LoRa‘s -148 dBm sensitivity allows reception far below the noise floor

• The deployment is in a noisy RF environment: LoRa‘s spread spectrum provides excellent co‑channel rejection and interference immunity

• LoRaWAN network compatibility is required

The practical trade‑off is fundamental: GFSK trades sensitivity for data rate and latency; LoRa trades data rate and latency for sensitivity and range. Both are valuable; the correct choice depends on whether your application prioritises speed or distance.

Part 7: From Modulation Theory to Practice

Understanding modulated radio waves — how information is encoded onto a carrier — is not merely an academic exercise. It directly determines the cost, range, power consumption, and data rate of every wireless product.

Coral RF‘s portfolio spans the full spectrum of modulation techniques relevant to IoT and industrial wireless:

• ASK/OOK on the CC1101 provides the simplest, lowest‑cost path for unidirectional remote controls

• GFSK on the CC1310 delivers reliable medium‑range telemetry with ultra‑low power consumption (0.7 μA standby, 5.4 mA RX) and integrated ARM Cortex‑M3 processing

• LoRa on the SX1262 achieves extreme range and deep penetration for LPWAN applications, with sensitivity down to -148 dBm and output power up to +37 dBm (5 W)

• Zigbee (O‑QPSK) on CC2538 enables mesh networking for smart home and building automation

Each product family is designed for a specific set of modulation‑related trade‑offs. The CC1101‑based N503AS excels at low‑cost, low‑data‑rate applications where simplicity and battery life are paramount. The CC1310‑based N530AS provides a software‑defined RF core with UART AT commands, dramatically reducing development time for smart metering and industrial IoT. The SX1262‑based LoRa modules deliver unparalleled sensitivity and range for LPWAN gateways and remote sensors.

Conclusion

Modulated radio waves are the invisible backbone of wireless communication. From the earliest AM broadcasts to today‘s sophisticated LoRaWAN networks, the fundamental principle remains unchanged: encode information onto a carrier wave, transmit it through the air, and recover it at the destination.

For engineers building modern wireless systems, understanding the trade‑offs between modulation techniques — analog vs. digital, amplitude vs. frequency, narrowband vs. spread spectrum — is essential for selecting the right radio for each application. Coral RF‘s Sub‑1GHz modules and USB dongles provide practical, production‑ready implementations of ASK, OOK, GFSK, and LoRa modulation, spanning output power from +12 dBm to +37 dBm, frequencies from 169 MHz to 1250 MHz, and sleep currents as low as 0.1 μA.

Whether you are building a simple garage door opener or a city‑wide LoRaWAN gateway, the same physics of modulated radio waves govern your design — and Coral RF provides the hardware to turn that physics into a working product.

This article is intended for embedded systems engineers, IoT developers, and RF product designers evaluating modulation techniques for Sub‑1GHz wireless applications.