>> Website Resources
.. >> Library: TechXchange
.. .. >> TechXchange: Radio Design 101
Wireless, or radio if you prefer, is a strange and wonderful phenomenon. Voice, music, video, and data miraculously move almost instantaneously from one place to another invisibly through the air. How could that be? Our entire environment is an invisible fog of thousands of electromagnetic waves. The whole phenomenon has been amazing to me since I was a kid. Even though I understand it I am still in awe of the technology.
That said, wireless technology is a complex subject. It has taken me most of my life time to learn it. And I still don’t know it all. But to non-wireless engineers, radio must seem an enigma. There’s much to get accustomed to and understand. What follows are 11 myths about wireless you may not know but should.
1. Wireless was invented by Marconi.
No, it was not. I would give my vote to Heinrich Hertz, who should get more recognition for his earliest demonstration of the concept. But we do use his name as the unit of frequency measurement. As for Marconi, he was a major contributor to the technology and is probably best known for putting the theory into practice. Marconi engineered the early radio equipment and demonstrated its capabilities. The real inventor of radio was Tesla, who did little to advance the science beyond a few clever demonstrations. Tesla was posthumously awarded the U.S. patent in 1943.
2. The Federal Communications Commission is the primary communications regulator.
The FCC implements the rules and regulations regarding most commercial and personal wireless products and applications. They manage the spectrum and define all kinds of guidelines like power, antennas, bandwidth, modulation, and interference. But they aren’t the only U.S. regulatory agency. The other agency that most of you have not encountered is the National Telecommunication and Information Administration (NTIA). The NTIA is the manager and regulator of all government and military wireless spectrum and equipment. It’s a division of the Department of Commerce. They work closely with the FCC to rule the airwaves.
3. Radio waves work like magnetic induction.
Not so. A radio wave is really a combination of an electric field at a right angle to a magnetic field. The two travel together in a direction perpendicular to both fields. As they propagate from the transmitting antenna to the receiving antenna, they stay together. Essentially the fields break away from the antenna, or radiate, and then actually support and rejuvenate one another along the way. The math describing that process was spelled out as far back as 1873 by James Clerk Maxwell. This signal that’s radiated is called the far field. It’s the real radio wave.
The field close to the antenna, typically within one wavelength, is called the near field. Transmission is more by magnetic field than by combined magnetic and electric fields. The near field signal is non-radiative. The near field is really inductive coupling that occurs between the primary and secondary windings of an air core transformer. The near field isn’t the real radio wave.
4. The propagation of a radio wave is basically the same for all wireless applications.
No way. Radio signals act differently depending on their frequency. Low-frequency signals in the 50- to 3000-kHz range travel by ground or surface wave. The vertically polarized signal hugs the ground and is mostly dissipated after a few hundred miles.
AM broadcast stations represent one example. Signals in the 3- to 30-MHz range travel by sky wave. The signals essentially are refracted by the ionosphere back to earth. Depending on the angle of radiation, time of day, and the specific ionosphere layer encountered, the signal could travel by skipping long distances nearly around the world. Frequencies over 30 MHz and up into the mmWave range travel by direct line of sight from antenna to antenna. These signals are usually reflected or absorbed, so range is generally limited.
5. We have totally run out of frequency spectrum.
Not completely, but we’re working toward that it seems. Most of the so-called “good” spectrum (~500 MHz to 6 GHz) is pretty much consumed, but plenty of spectrum exists at the higher frequencies beyond about 30 GHz.
Some say there’s a spectrum crisis as more wireless products and services are developed. One contributor to the shortage is the growing Internet of Things (IoT) movement. With billions of new devices coming on line, spectrum usage is something to worry about. But it’s the cellular industry that lusts after spectrum the most. The FCC hosts auctions to sell off available chunks of spectrum when they become available. Billions of dollars are collected.
6. Radio broadcasting is dead.
You may have gotten the impression that AM, FM, and TV broadcasting were on their way out thanks to all the internet streaming of music and video. But it’s not. While the number of AM stations has declined a bit, FM is growing. Satellite radio is also healthy. Furthermore, almost 20% of the U.S. population gets its TV by over-the-air (OTA) broadcasts. This includes satellite TV broadcasting. On top of that, short wave broadcasting is still around; not so much in the U.S., but it’s still big in Europe, the Middle East, Africa, and other more remote parts of the world.
7. The most widely used wireless standard is Wi-Fi.
Wi-Fi is certainly a heavily used wireless standard. But in terms of sheer volume of radios in use, Bluetooth is probably the more widespread. It’s in all cell phones, most cars and trucks, headphones, speakers, retail beacons, and a mixed bag of other applications. It takes two chips to implement any Bluetooth applications. That’s why billions of Bluetooth radio chips are sold annually.
8. Cell phones give you a brain tumor.
That myth has been around ever since the first cell phones emerged in the late 1980s. It’s been studied multiple times, and the outcome is that cell phones don’t cause brain tumors. Perhaps if you held the phone to your head eight or so hours a day, you may get brain damage. But today, instead the process of holding the phone to your ear and head for a voice call has been replaced by holding the phone in your hands in front of you while you text, read email, or watch a YouTube video. No cancer.
9. Wireless data transfer is always faster than wired data transfer.
Not true. Wired data communications say by Ethernet or fiber optics, is very solid and usually faster than wireless. Ethernet can do 100 Gb/s and optical is now doing up to 400 Gb/s using PAM4. With a solid link, data can be faster because it doesn’t have to deal with all of the free space link and path problems of wireless.
Wireless free space path loss is very high; there’s always noise and interference that limits the data rate. But wireless has come a long way over the years with error correction, multichannel modulation like OFDM, MIMO, and phased arrays. As a result, wireless begins to approach wired speeds. Under ideal conditions, wireless data can hit levels of 10 to 100 Gb/s.
10. Rain and snow make satellite TV, phones, and data services unreliable.
You have probably heard of this one but it not true. Actually, at some frequencies in older systems, rain does attenuate the signal. But today, most components, equipment, and systems compensate for it with good link margins. We would not be using so many satellites if the coverage were iffy. What would we do without things like GPS, worldwide sat phones, space telescopes, and military surveillance?
11. Millimeter waves will never be practical.
Maybe that was true in the past, but today mmWaves are widely used thanks to the availability of semiconductor devices to generate and process these signals. Millimeter waves cover the 30- to 300-GHz range. All sorts of systems use them, especially radar and satellite. The 802.11ad WiGig WLAN products at 60 GHz are now available. Automotive radars use 77 GHz. And many of the forthcoming 5G cellular and fixed wireless access systems use mmWaves. Researchers are working on terahertz wave technology now.
There should be a wireless appreciation day to celebrate its existence. How about every day?
>> Website Resources
.. >> Library: TechXchange
.. .. >> TechXchange: Radio Design 101
