A radio frequency (RF) signal refers to a wireless electromagnetic signal used as a form of communication, if one is discussing wireless electronics. Radio waves are a form of electromagnetic radiation with identified radio frequencies that range from 3Hz to 300 GHz. Frequency refers to the rate of oscillation (of the radio waves.) RF propagation occurs at the speed of light and does not need a medium like air in order to travel. RF waves occur naturally from sun flares, lightning, and from stars in space that radiate RF waves as they age. Humankind communicates with artificially created radio waves that oscillate at various chosen frequencies. RF communication is used in many industries including television broadcasting, radar systems, computer and mobile platform networks, remote control, remote metering/monitoring, and many more.
While individual radio components such as mixers, filters, and power amplifiers can be classified according to operating frequency range, they cannot be strictly categorized by wireless standard (e.g. Wi-Fi, Bluetooth, etc.) because these devices only provide physical layer (PHY) support. In contrast, RF modules, transceivers, and SoCs often include data link layer support for one or more wireless communication protocols. These products are organized by wireless technology and can be browsed under the “Solutions” tab.
Although wireless communication is often associated with the 2.4 GHz frequency range, many devices and technologies use radio frequencies below 1 GHz (1000 MHz). The 900 MHz band, or 33-centimeter band, is a well-known ISM (industrial, scientific and medical) frequency range used for cordless phones, walkie-talkies, amateur radio and even amateur television. ZigBee, a specification for low-power communication in wireless personal area networks (WPANs), as well as the IEEE 802.15.4 standard it is based on, can use the 900 MHz ISM band in the Americas.
Also in the sub- GHz range is Citizens’ Band (CB) radio, a popular two-way amateur radio service occupying the 26.79 MHz to 27.4 MHz range in the United States. Both AM broadcast radio (535 KHz – 1.7 MHz) and FM broadcast radio (87 MHz – 108 MHz) are in this lower range of frequencies as well, and over-the-air television in the U.S. spans a wide (54 MHz to 806 MHz) range of carrier frequencies. Recent near field communication technology (NFC), found today in many of the newest smartphones, operates at 13.56 MHz.
The 2.4 GHz ISM (industrial, scientific and medical) band is perhaps the most common in this frequency range. Its unlicensed nature has made the ISM bands a popular choice for many wireless technologies, such as ZigBee (IEEE 802.15.4), Bluetooth (IEEE 802.15.1), and Wi-Fi (802.11).
Many other 2.4GHz technologies exist as well; WiMAX, GPS, cordless phones, car alarms, and even microwave ovens operate in this frequency range.
Wireless signals in the upper end of the super high frequency (SHF) band and higher (5 GHz+) are often referred to as microwaves. At these frequencies water is more or less “opaque”, so a microwave signal will experience significant attenuation and scattering issues due to moisture in the air. For this reason, extremely high frequency communications are either severely limited in range or always require line of sight.
Still, these types of signals can be made highly directional, and are seeing increasing use in modern technology. The ISM (industrial, scientific and medical) bands include several frequencies in the high GHz range such as Wi-Fi based on IEEE 802.11a and 802.11n wireless standards, which both 5 GHz capable. IEEE 802.11ac is the latest standard standard for emerging WiFi technology, operating exclusively in the 5 GHz band and offering significant improvements in speed, range, power consumption, and reliability. Other new technologies are designed to opearate on frequency bands much higher still; WirelessHD is a wireless specification based and frequencies as high as 60 GHz and features an impressive maximum nominal data rate of 25 gigabits per second – rivaling that of HDMI.
Based on the IEEE 802.15.1 standard for wireless personal area networks (WPANs), Bluetooth technology is designed to provide reliable, low-power wireless communications over short distances.
Bluetooth is best known as the primary technology for wirelessly connecting mobile phones with peripheral devices such as wireless headsets. However, Bluetooth radios can be an ideal choice for a wide range of designs. Bluetooth may be a good fit if your product:
Bluetooth 4.0 is the latest version of this technology, being adopted in June 2010. It incorporates Classic Bluetooth as well as Bluetooth high speed – a feature introduced in v3.0 which uses a separate 802.11 link to achieve nominal data transfer rates up to 24 Mbits/s.
Yet, perhaps most importantly, Bluetooth 4.0 features a new protocol called Bluetooth low energy (BLE). Also known as “Bluetooth Smart Ready”, BLE offers many significant changes and improvements over other Bluetooth protocols, including low cost, reduced size, and ultra-low power consumption. Compared to Classic Bluetooth, BLE devices are designed to operate using a much lower duty cycle, resulting in significantly lower current consumption – typically in the microamp range. Although BLE is not compatible with Classic Bluetooth, many Bluetooth 4.0 “dual-mode” devices exist which integrate the architecture and protocol stacks of both.
The original version of Bluetooth used Gaussian frequency shift keying (GFSK). Bluetooth 2.0 introduced the Enhanced Data Rate (EDR) feature. EDR-capable devices are capable of data rates up to three times faster using phase shift keying (PSK) modulation techniques instead of GFSK.
Although they operate in the widely used and often “crowded” 2.4GHz ISM frequency band, devices using later versions of Bluetooth (1.2 and higher) offer robust links even in very noisy environments by employing a frequency-hopping technique called adaptive frequency-hopping spread spectrum (AFH). Bluetooth devices avoid interference by rapidly changing between 79 evenly spaced frequency channels – from 2402MHz to 2480MHz. This hopping occurs 1600 times every second, and any data lost due to interference is resent later over a different channel.
ZigBee, like Bluetooth, is a specification for communication in wireless personal area networks (WPANs). Designed to be low cost, low power and low duty cycle, ZigBee technology is ideal for wireless sensor networks (WSNs) and other low power networks that span potentially large distances. ZigBee builds upon the IEEE 802.15.4 standard, but adds mesh networking capability with multi-hop functionality and a routing protocol. Star networks as well as peer-to-peer (e.g., mesh and cluster tree) are supported, making ZigBee networks dynamic, scalable, and decentralized.
ZigBee technology is not meant to compete with technologies such as Wi-Fi (IEEE 802.11) or Bluetooth (IEEE 802.15.1). Rather, ZigBee is designed for applications where data transfer rate is much less important than power efficiency, network size, and the capacity for ad hoc routing.
ZigBee PRO is currently the latest and most feature rich ZigBee stack available. In addition to a higher maximum number of devices (up to 65,560 in a single network), ZigBee PRO supports three times as many hops as standard ZigBee 2007 and features advanced routing techniques, multicast functionality, and better network security.
Virtually all wireless local area networks (WLANs) are based upon the IEEE 802.11 standard for WLANs, called “Wi-Fi”. Nearly all of today's smartphones, laptops, tablets, and eBook readers are Wi-Fi capable – with very few exceptions. WLANs allow computer networks to be established for often a fraction of the cost of installing wired Ethernet, and can be used for temporary Wi-Fi connection “hotspots” in hotels, coffee shops, airports, libraries, and more. There are a range of standards within IEEE 802.11, each denoted by a letter suffix:
802.11b – This was the first Wi-Fi standard to be widely used for creating wireless computer networks. It operates in the unlicensed 2.4GHz ISM frequency band and supports a maximum (nominal) data rate of 11 Mbit/s. 802.11b supports two modulation techniques: complementary code keying (CCK) and direct-sequence spread spectrum (DSSS).
802.11a – This standard, which is alphabetically first but developed slight later than 802.11b, operates in the less “crowded” 5GHz frequency band. It includes support for a more advanced modulation scheme called orthogonal frequency division multiplexing (OFDM) resulting in faster data transfer rates than 802.11b – up to 54 Mbit/s.
802.11g – For now, this is still the most common Wi-Fi technology in use today. Operating in the 2.4GHz band with OFDM support, 802.11g offers the higher data rates of 802.11a but without the greater costs associated with 5GHz chips. 802.11g is also backwards compatible with 802.11b.
802.11n Featuring greatly extended range and improved data rates of up to 600Mbit/s, this standard is quickly overtaking 802.11g. These improvements are thanks in large part to wider channel bandwidth and the addition of multiple-input multiple-output (MIMO) technology. Because 802.11n can operate in both the 2.4GHz and 5GHz bands, it can provide backward compatibility with previous standard at the cost of network speed.
802.11ac – This is the newest 802.11 standard, which is currently in the final stages of approval by the 802.11 Working Group. 802.11ac will offer channel bandwidth four times wider than previous standards, multi-user MIMO (MU-MIMO), highly sophisticated error correction, and data throughput rates in the Gbit/s range.
While Bluetooth, ZigBee, and Wi-Fi are some of the most prominent wireless standards, there are certainly many other important wireless technologies.
The Global Positioning System (GPS) is a satellite-based global navigation system that provides accurate location and time information anywhere on the planet. GPS is an important and ubiquitous technology used in applications ranging from commercial car-based navigation to advanced military target tracking and missile guidance systems. Most GPS satellites broadcast at the same two frequencies: 1575.42MHz, called the “L1” band, and the 1227.60MHz “L2” band. The signals are encoded using a CDMA spread-spectrum technique, allowing individual satellites to be distinguished from each other without co channel interference.
Radio frequency identification (RFID) is a wireless technology analogous to UPC barcodes. It is used worldwide for tracking and identifying consumer products. RFID transponders, or tags, are placed on portable objects to be tracked or identified, whether it is vehicles, livestock, baggage, or even people. RFID readers entail greater cost and complexity, so are typically stationary – installed in locations where the RFID data exchange is to take place. RFID is used in many applications including employee access control, asset tracking, electronic toll collection, and supply chain control.
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