Frequency: Electronic Products Word of the Week

Over the years, frequency changed its unit of measure. Oldtimers will remember cycles per second, a unit that was supplanted some 50 years ago by hertz, named for the 19th century physicist Heinrich Hertz (1857 —1894).

In its simplest terms, frequency is fairly straightforward: Calculating the frequency of a repeating event is accomplished by counting the number of times that event occurs within a specific time period, then dividing the count by the length of the time period. For example, if 75 events occur within 15 seconds the frequency is:

F= 75/15=5 hertz.

This answer could also be written as 5 Hz. This number is far too small to mean anything in this day and age, because we routinely speak of kilohertz (thousands of cycles per second, kHz), megahertz (millions of cycles per second, MHz), gigahertz (billions of cycles per second, GHz), and terahertz (trillions of cycles per second). And the speeds (this is a speed, after all, a rate) go up from there (they also go down, of course). Here is a chart of hertz measurements from the Systeme Internationale, the modern form of the metric system:

Source: Wikipedia

Accurate frequency owes a lot to the quartz crystal. As Ming Hoong Chong of Pericom Semiconductor noted in Electronic Products Magazine in 2012, “The stability of vibration that an excited quartz crystal is capable of maintaining is what makes quartz such a good timing source.”

Everyday uses of frequency include a what’s what list of devices we all use (the hyperlinks below point to further information on specific frequencies):

• cellphone
• cordless phone
• garage door opener
• car key remote control
• broadcast television and audio
• Standard time broadcast
• vehicle-speed radar, air traffic radar, weather radar
• mobile radio
• Global Positioning System (GPS) navigation
• satellite TV broadcast reception; also backend signal dissemination
• Microwave oven
• Bluetooth
• Wi-Fi
• ZigBee
• RFID devices such as active badges, passports, wireless gasoline token, no-contact credit-cards, and product tags
• toll-road payment vehicle transponders
• Citizen’s band radio and Family Radio Service
• Radio control, including radio-controlled model aircraft and vehicles
• wireless microphones and musical instrument links

Everything on this list needs upgrades, which means each device will have increased frequencies, if it has not been assigned a frequency band already.

One article in Electronic Products Magazine, by Keng Chen and Kimmo Koskiniemi of the Pulse Engineering Antenna Division, made the point in February 2008 that that “operating frequency is determined by the type of application. For example, Wi-Fi 802.11 b/g, ZigBee, and Bluetooth use the same 2.4-GHz ISM band that has a bandwidth of about 80 MHz (2.4 to 2.48 GHz). A commercial GPS system uses the L1 1.575-GHz band with a bandwidth of 2 MHz (1,575.42 MHz ±1 MHz).”

This discussion is built on the role of the Federal Communication Commission, which was created by an act of Congress in 1934 to regulate the U.S. airwaves. The FCC’s Office of Engineering and Technology is charged with the responsibility to manage the electromagnetic spectrum, specifically frequency allocation and spectrum usage. OET conducts technical studies of advanced phases of terrestrial and space communications and administers FCC rules regarding radio devices, experimental radio services, and industrial, scientific, and medical equipment.

As technology changes, the discussion of frequency changes to keep up. That’s why Electronic Products Magazine has no shortage of articles mentioning “frequency.”