By Jeremy Cook
The radio frequency (RF) spectrum is all around us, unseen, transmitting natural and man-made signals at a mind-boggling…frequency. This article answers the question, “What is RF?” and explores how regulators work to ensure proper access to this limited resource. We will also touch on how 5G fits into the picture.
Radio Frequency Physics
At its most basic, a varying electrical signal on an antenna can produce electromagnetic oscillations (i.e., RF waves). These can be unintentional (potentially causing interference with other devices) or intentional, carefully modulated signals that can be received by other antennas and interpreted as usable information. AM (amplitude modulation), for instance, uses a series of fixed frequency waves as a so-called carrier wave, while changing the amplitude of these waves in series as a modulated signal.
The RF spectrum can be defined as electromagnetic waves cycling between 3 Hz and 3,000 GHz, giving it a wide range of characteristics and use cases. Consider that a 3 Hz carrier produces three full electromagnetic waves per second and that the modulated signal that “rides” on this carrier is typically of a slower frequency.
While several factors are at play, a modulated signal data rate using a 3 Hz carrier will be extremely slow, likely expressed in the bits/second range or even less. At the other end of the spectrum, a 3,000 GHz carrier wave will allow for a much faster-modulated signal, and there is a wide range of (more practical) values in-between. This range allows for the high-speed data rates that we now take for granted in WiFi and cellular communications, as well as traditional AM and FM radio.
Radio frequencies are related to the speed of light and inversely proportional to wavelength, expressed via the equation:
speed of light = wavelength x frequency
The speed of light (approximately 3 x 10^8 m/s) never changes, so as an RF signal’s wavelength increases, the frequency decreases proportionally, and vice versa. A relatively high-frequency RF signal has a short wavelength, and a lower-frequency RF signal has a higher wavelength.
The tradeoff for high-frequency signals and data rates is that while they can transmit a lot of information over a short distance, these signals are quickly absorbed by the atmosphere and surrounding objects. As an everyday example, consider how 2.4 GHz WiFi data rates are somewhat slower than their 5 GHz counterparts, but they can be received at a further distance.
At the extreme end of low-data-long-distance transmissions, signals in the sub-hundred-hertz range are used to communicate with submarines, penetrating the ocean’s depths. The main tradeoff is a very low data rate. The other consideration is that working with longer RF wavelengths requires correspondingly long antennas.
RF signals and regulation to prevent interference
Since there is a fixed frequency range at which RF communications can reasonably take place, the world’s airwaves are, by definition, a limited resource. Finite bandwidth must have seemed academic (if considered at all) by RF pioneers at the turn of the 20th century, but today RF is used for an incredible array of technologies and must be carefully allocated. When signals do necessarily overlap (e.g., the 97.1 MHz radio channel in New York City vs. the same frequency in Austin, or the billions of Bluetooth devices worldwide), power limits are enforced to keep interference to a minimum.
Consider how many devices around you intentionally transmit and receive RF signals. Typical smartphones have at least four RF modes: WiFi, Bluetooth, cellular, and GPS. On top of that, there is a wide range of unintentional RF transmitters, including everything from lightbulbs to electric motors to wiring.
Fortunately, the world’s RF signals typically get along due to the guidance of groups like the International Telecommunication Union (ITU), Federal Communications Commission (FCC), and the National Telecommunications and Information Administration (NTIA). These organizations divide the spectrum into usable chunks. While the spectrum is limited due to our massive utilization of this resource, remember that this range stretches from 3 Hz to 3000 GHz (3,000,000,000,000 Hz, written out). The official FCC Online Table of Frequency Allocations is a correspondingly massive 181 pages of text.
How does 5G work with frequency bands?
The public simply expects RF devices to work, rarely engaging with its intricacies, similar to how we expect electrical power when plugging into a socket. However, perhaps due to 5G’s heavy touting in carrier advertisements, RF—and specifically 5G—is part of our collective consciousness. 5G does promise better data rates and lower latency for cellular data transfer, but it’s also been the subject of controversy, including fears that it could interfere with radar altimeters used in airplanes.
Concerns aside, 5G is now implemented in much of the U.S. without major issues. 5G doesn’t use a single frequency band, but, as discussed here, it operates on three distinct frequency ranges. Higher frequencies are used for high data rates at short distances from a transmitter, and lower frequencies transmit longer distances at lower data rates.
5G is also not the same as 5 GHz WiFi, a largely unrelated RF technology with a similar name. Adding more confusion, WiFi 5 uses 5 GHz for transmission, but the 5 actually stands for fifth-generation wireless. And new WiFi standards keep coming: WiFi 6E extends signaling into the newly available 6 GHz range, while WiFi 7 uses the same bands as 6E, but allows for multi-link operation and speeds of up to 46 Gbps. Learn more about the differences between 5G and 5GHz technology.
RF Range: A Limited Resource That Must Be Carefully Allocated
While the RF frequency will never “run out” in the same way as oil or rare earth metals, the 3 Hz to 3,000 GHz band is what we have to work with. This range was the same at the dawn of radio communication in the late 1800s, and unless there is a dramatic shift in how we understand physics, it will be the same in the future.
To properly utilize this resource, we need careful frequency allocation with proper power limits and technological innovation (such as QPSK signaling) that lets us transfer more data without occupying more frequency space.
Arrow stocks a wide range of radio frequency products and devices from industry-leading manufacturers for your next project. For example, the DFR0868 ESP32-C3 development board lets you get started with both WiFi and Bluetooth in the same module.
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