In its most basic form, radio does not need a modulation: OOK (on-off-keying) works like ancient morse transmitters and turns a radio emitter either on or off.
OOK cannot transport much information at high speeds which is why modulations where added that can be imposed on a continuous transmission. So rather than turning the transmitter completely on and off all the time, modern radios slightly vary the output power (affecting the amplitude, AM) or vary the frequency (within a predefined bandwidth, FM).
There are many more sophisticated modulations, including phase-modulation which is a third way of modulating information onto a radio wave. Digital communications uses PSK (Phase-shift keying) and combinations with other encodings.
Overview
Transmitting large amounts of information over radio waves requires using the same modulation at both sender and receiver, and also to encode and decode the information so that it can be imposed onto the modulation.
In the context of this website, I am looking at digital data transmissions only. Transmitting analog data via AM or FM is much simpler: the audio NF itself is modulating either the amplitude or frequency of the radio wave.
With digital information, consisting of binary on and off information only, various modulations and encodings are used:
| Modulation Type | Typical Use in ISM Bands | Modulation Characteristics | Use Cases | When to Use | Digital DIY Examples |
|---|---|---|---|---|---|
| AM (Amplitude Modulation) | 433 MHz, 315 MHz, 868 MHz (Low power) | The amplitude of the carrier is varied by the signal | AM Radio, OOK (On-Off Keying), Simple Analog Communication | When simplicity and low power are required, or when long-range communication is not critical | OOK (e.g., simple on/off signals), AM Radio (low-fi communication), Home automation (simple, long-range, low-data-rate links) |
| FM (Frequency Modulation) | 433 MHz, 868 MHz, 2.4 GHz, 5.8 GHz | The frequency of the carrier is varied by the signal | FM Radio, Wi-Fi, LoRa, Bluetooth | When higher noise immunity, better signal quality, and higher data rates are needed | Wi-Fi (using OFDM modulation), LoRa (for long-range, low-power, wide-area networks), Bluetooth |
| OOK (On-Off Keying) | 433 MHz, 315 MHz, 868 MHz | A form of AM modulation where the presence or absence of a signal represents data | Simple remote controls, basic sensor networks | When very low power is needed and simple binary data transmission is sufficient | Simple RF modules like nRF24L01, RFID tags, keyfob remotes |
| ASK (Amplitude Shift Keying) | 433 MHz, 315 MHz | A form of AM where the amplitude of the carrier is modulated to represent data | Basic digital communication over short distances | When minimal complexity and low data rates are sufficient | RF modules (e.g., 433 MHz ASK modules for simple communication) |
| LoRa (Long Range) | 433 MHz, 868 MHz, 915 MHz | FM with spread-spectrum modulation, using Chirp Spread Spectrum (CSS) | Long-range, low-power IoT communication networks | When long-range, low-data-rate, and low-power communication is needed in areas with potential interference | LoRaWAN (for IoT networks, agriculture, and smart cities) |
| Wi-Fi (OFDM) | 2.4 GHz, 5 GHz | AM (using Orthogonal Frequency Division Multiplexing) with Frequency Modulation | High-speed data transmission in local area networks | When high bandwidth, reliable communication, and moderate range are needed | Wi-Fi routers, IoT devices, Smart home systems |
| Bluetooth | 2.4 GHz | FM with FHSS (Frequency-Hopping Spread Spectrum) | Short-range wireless communication for devices | When low-power, short-range communication is needed with robust interference resistance | Bluetooth Low Energy (BLE) devices, Wireless peripherals (e.g., keyboards, headphones) |
| Zigbee | 2.4 GHz | FM (with DSSS) | Low-power, low-data-rate networks for home automation, smart devices | When very low power consumption is critical and short-range, reliable communication is needed | Smart home devices, Home automation networks |
AM (Amplitude Modulation)
For digital transmissions on AM, ASK (Amplitude-Shift keying) is used: in its simplest form (OOK, On-Off keying), bit 1 is represented by full amplitude, and bit 0 is represented by absence of signal.
AM is typically used for low-power and long-range communication but has lower noise immunity and limited data rate capabilities.
Here are popular use cases that utilize AM:
EV1527 - Remote Controls
One coding format used on ASK is EV1527, a 24bit code with roughly a million different ID codes and four bits of payload. EV1527 is often used with simple remote controls, especially those with learning codes.
WiFi
WiFi also uses AM although in reality, it is a mixture that contains both AM and FM components. To encode information and achieve high transmission speeds, much more sophisticated encodings are used (i.e. QAM, Quadrature Amplitude Modulation).
QAD is a combination of PSK (Phase-shift keying) and ASK (Amplitude-shift keying). Using both phase and amplitude shifts can encode more information and is one of the reasons why modern WiFi standards were able to increase the maximum data transmission speed.
| Standard | Year | Speed | Encoding |
|---|---|---|---|
| 802.11 | 1997 | 1MBit | DBPSK (Differential-binary Phase-shift keying) |
| 802.11 | 1997 | 2MBit | DQPSK (Differential-quadrature Phase-shift keying) |
| 802.11b | 1999 | 5.5/11MBit | CCK (Complementary-code keying) |
FM (Frequency Modulation)
FM is used in applications that require better noise immunity and higher data rates, such as Wi-Fi, LoRa, and Bluetooth. It is basically used in most modern radio applications.
FM works by varying the frequency of the carrier signal, making it resistant to noise and suitable for longer-range communications with better signal quality.
For digital transmissions on FM, FSK (Frequency-Shift keying) or one of its successors is often used: bits (or symbols) are encoded in shifts of frequency.
Spread Spectrum
Aside from modulation (like AM and FM), another technology is used in modern digital data transmissions: spread spectrum.
FHSS
FHSS (Frequency Hopping Spread Spectrum) is a method of transmitting radio signals by rapidly switching the carrier frequency among many different frequency channels, in a pseudo-random sequence. The frequency hops are done in a way that both the transmitter and receiver are synchronized to hop to the same frequencies at the same time.
FHSS is part of many modern wireless technologies:
- Bluetooth: Uses FHSS to reduce interference from other devices in the 2.4 GHz ISM band, making it more reliable in crowded environments.
- Zigbee: Also uses FHSS for robust, short-range, low-power wireless communication.
- Military and Secure Communications: Because of its security features, FHSS is often used in military applications to avoid detection or interception.
FHSS improves the reliability of wireless communication, especially in environments with a lot of interference, by constantly changing the frequency the signal uses.
WiFi is not using FHSS. It uses OFDM (Orthogonal Frequency Division Multiplexing), which is not based on frequency hopping. OFDM divides the available bandwidth into several subcarriers that are orthogonal to each other. These subcarriers are used to transmit data simultaneously, increasing the data rate and efficiency of the communication.
Rapidly changing frequencies has a number of advantages:
- Distance: strong interference and noise signals on one particular frequency cannot distort the signal as only a very small fraction of it is affected.
- Security: the spread-out signal is almost impossible to detect and intercept without knowing the parameters in which it was spread out
- Field Strength: the field strength for a particular frequency is lower
LoRa - Chirp Spread Spectrum
LoRa (Long Range) is a modern modulation that builds on FHSS but adds chirp. It is a proprietary modulation intended for long range transmissions at very low radio power (10mW LoRa radio signals can travel 2km within cities and up to 40km in rural areas).
To achieve this, it is using the proprietary, patented LoRa (LongRange) wireless protocol based on the Chirp-Spread-Spectrum modulation technique.
Slow Website?
This website is very fast, and pages should appear instantly. If this site is slow for you, then your routing may be messed up, and this issue does not only affect done.land, but potentially a few other websites and downloads as well. Here are simple steps to speed up your Internet experience and fix issues with slow websites and downloads..
Comments
Please do leave comments below. I am using utteran.ce, an open-source and ad-free light-weight commenting system.
Here is how your comments are stored
Whenever you leave a comment, a new github issue is created on your behalf.
-
All comments become trackable issues in the Github Issues section, and I (and you) can follow up on them.
-
There is no third-party provider, no disrupting ads, and everything remains transparent inside github.
Github Users Yes, Spammers No
To keep spammers out and comments attributable, all you do is log in using your (free) github account and grant utteranc.es the permission to submit issues on your behalf.
If you don’t have a github account yet, go get yourself one - it’s free and simple.
If for any reason you do not feel comfortable with letting the commenting system submit issues for you, then visit Github Issues directly, i.e. by clicking the red button Submit Issue at the bottom of each page, and submit your issue manually. You control everything.
Discussions
For chit-chat and quick questions, feel free to visit and participate in Discussions. They work much like classic forums or bulletin boards. Just keep in mind: your valued input isn’t equally well trackable there.
(content created Mar 13, 2025 - last updated Mar 15, 2025)