October 21, 2016

WiFi Radios and Modulation Techniques (Part 3 of 5)

As mentioned in our History of Wireless Technology post, getting data sent over the air without wires isn't as easy as it is when you have a wired, or cabled, connection system. 

Think about a standard two-way radio. The correct name for this kind of radio is a "transceiver". It both transmits and receives, therefore it's called a "transceiver". 

It's probably safe to say that most people know at least something about how a radio like this works. If you've ever watched a television show that feature police, fire, or other people that use two-way radios, like airline pilots, you've seen these radios in use. When you want to talk, you pick up the microphone and push the button on the microphone. When you're done talking, you let up on the button. The person you're talking to will then reply to you and you can hear them.

Unfortunately, for data communications, trying to use radios in this manner won't work. This doesn't begin to allow data to be sent and received with the speed, accuracy and reliability that is needed.


Radios used for data have to be fast, with lots of bandwidth, and be reasonably immune to natural and man-made noise and interference. They also have to be able to accept data streams in various protocols and translate the digital data (the ones and zeros, if you will) into something that can be impressed upon a radio signal. Following that, the signal has to be of a high enough quality that it can be received and turned back into the original data (again, the ones and zeros).

The proper word for putting any information onto a radio wave is called "modulation". We don't have time here to delve deeply into all the math and theory involved to explain the way digital data is modulated into a radio wave. However, we will look at the main method used for LANs, WANs, mobile cellular phones and data communication in general.

The modulation technique that's almost always used is a method called "spread spectrum". It's got an interesting history. Spread spectrum was developed for use in military communications. The idea was to keep the enemy from being able to intercept and decode secret communications, yet also make it hard for the enemy to jam radio signals. 

The original spreading technique was called "frequency hopper", or it's more modern term, Frequency Hopping Spread Spectrum (FHSS). It worked by actually changing the frequencies as it was transmitting the signals. Every few milliseconds, the transmitter would hop to a new frequency. So, even if you could tune into one of the frequencies in use, it wasn't long before it was gone. Then, on the other end, the receiver had to be able to follow the transmitter when it changed. This took a lot of careful timing and delicate control, but it did work. It kept the enemy from being able to intercept the communications.

Frequency Hopping Spread Spectrum (FHSS)

The first patent for this type of modulation was issued in 1942 to music composer George Antheil and Hollywood actress Hedy Lamarr. The two were introduced at a party where they originally bonded over the women's magazine articles Antheil wrote about endocrinology and ways to increase Lamarr's bust size to make her more attractive in Hollywood. But it was during these scientific discussions that they turned their conversations over to the war and how the Germans were struggling with their torpedoes missing their targets. This is rather a fascinating story as told in a previous blog post, Beauty, Brains and Secret Communication, or if you're a podcast listener, check out the You Must Remember This episode featuring Hedy Lamarr.

For many years, the frequency hopping communication system was classified as "SECRET" by the United States government. The Army Signal Corps was the only organization that used it or knew all of the details on how it worked. As time passed, however, researchers in the private sector began discovering how spread spectrum functioned. When the scientists and engineers outside of the military figured out the secret, it wasn't really a secret anymore. Finally, after the patent expired in 1962, it was declassified and available for use by the civilian sector.


In addition to the original Frequency Hopping Spread Spectrum (FHSS), the other spread spectrum system is the Direct Sequence Spread Spectrum, or DSSS for short. This works differently, as it doesn't "hop". DSSS takes the digital signal and combines it with the radio signal in such a way that the signal is spread out over a large number of adjacent frequencies, at the same time.
Direct Sequence Spread Spectrum (DSSS)

There are several ways to do this, but one of the more common spreading methods is called Code Division Multiple Access, or CDMA. Almost all mobile phones used in the United States operate using this method. Among its many advantages, it allows a high level of security for phone calls to help eliminate eavesdropping on phone conversations. It also allows several mobile cell phone calls to exist in the same general frequency band at the same time. By allowing that, more mobiles can be used by more people without the problem of running out of available channels, which was a common issue in the early days of mobile cell phones.

It also helps in allowing what is called "duplex" communications. This means that you don't have to push a button to talk, like you do with the two-way radios as described in those previously mentioned tv shows about police and firemen. This makes a mobile cell phone call sound and function almost the same as a regular landline telephone call.


With the development of the capabilities described above, mobile phones and data communications entered a new era. Now, there are ways to create radio-based systems that emulate a cabled system. The age of the wireless router came about as a result of these advancements in radio-frequency systems. However, despite all of the wonderful capabilities we now have, there are still some pitfalls, land mines and other difficulties that a radio/wireless data communication system is subject to. In our next installment, we'll explore some of the what-not-to-do's.

If you'd like to read more on all of this, plus more that we didn't cover here, I recommend reading "Wireless Communications and Networks", by Dr. William Stallings. It's very easy to read and makes all of the theories very understandable.

Paul Black is a freelance writer and broadcast engineer in Northern California. He holds a Certified Professional Broadcast Engineer certification from the Society of Broadcast Engineers and an FCC Lifetime General Class Operator License. He is a licensed amateur radio operator (call sign N6BBZ) and has worked for several broadcast companies, including Bonneville Broadcasting, RKO General Broadcasting, and CBS Television. Visit his website at www.paulblackcopy.com

September 20, 2016

The History of Wireless Technology: Wireless or Radio? (Part 2 of 5)

Back in the latter half of the nineteenth century, uses for electricity were just being discovered. By 1880, Thomas Edison had improved his original light bulb to the point that it was a viable product, and early wiring of cities for power had begun. But scientists were discovering that there was a lot more to this new source of energy than first appeared.

In 1888, at the University of Karlsruhe in Germany, a young professor named Heinrich Hertz, proved what other scientists had only suspected; you could send electric "waves" through the air.

However, there hadn't been much work on the practical use of these waves at that point. So, the scientific and technical community just called them "Hertzian waves", since Hertz was the first to prove their existence. But it wasn't long before experimenters were looking at ways of using these new "waves" to do some useful work.

The wired telegraph had been around for a long time. In the United States, Samuel Morse created the first useful wired telegraph as early as 1844. Of course, to make it work, you had to string wires. That was time-consuming and expensive.

Some of the early pioneers of electrical science got the idea that maybe they could get rid of the wires by using these "waves" Hertz had already proven existed to send telegraph code instead. The scientific term that describes the sending of the waves is "radiation". You are "radiating" electricity when you create and send the waves. Once you do that, you have to have a way to "hear" them. The human ear can't hear these waves, so it was necessary to build something to do this. 

In 1890, Edouard Branly, a French physicist, developed a device that would do just that. He called it a "radio-conductuer", since it could receive waves that were being "radiated". However, not everyone used "radiation" or "radio" when discussing this new form of communication.

Gugelielmo Marconi, working in England between 1896 and 1898, showed that you could send signals through the air at considerable distances, and you could send Morse code on these signals.

Marconi called the company that he founded "The Wireless Telegraph and Signal Company" to make sure everyone knew that you didn't need any wires to send Morse code by this method. So, "wireless" became a common term for this new form of communication in England.

However, some technical people began to gravitate more towards using the term "radio" in place of the term "wireless". In the January 21, 1898 issue of The Electrician (London), a letter from a reader suggested that the term "radio-telegraphy" might be preferable to "wireless-telegraphy". 

In 1904, the British Post Office, which was the branch of the government that sent telegrams, specified that any telegram sent by an over-the-air method had to insure that "...the word "Radio"... is send in the Service Instructions". 

Meanwhile, in 1906, in Berlin, Germany, the Berlin Radiotelegraph Convention included a Service Regulation specifying that "Radiotelegrams shall show in the preamble that the service is 'Radio'", again to distinguish it from the use of wired telegraphs.

There were some holdouts on this, however. Electrical engineer William Maver, Jr., who, in the preface to his 1910 book "Wireless Telegraphy and Telephony", said that he intended to stay with the older term "wireless". Apparently, he was a traditionalist.

Between 1907 and 1920, "radio" and "wireless" were used to describe the new communication method interchangeably. In the United States, Lee de Forest, an early researcher who is credited with developing some of the first tubes used in receivers, called it "radio". This led to a general migration to the term "radio" in the United States. However, in England and Europe, "wireless" was still widely used.

It wasn't until the early years of broadcasting, around 1920, that the term "radio" began to become the more common term used everywhere. In 1923, the British Broadcasting Company (BBC) launched it's magazine devoted to broadcasting, called "Radio Times" (still in publication today). The BBC's decision to use "radio" pretty much put "wireless" aside. In most places around the world, "radios" became an understood term for over-the-air broadcasting and communications.

That is, until the rise of computer networks in the latter half of the 20th century.

Just like the early telegraph signals that were sent in the nineteenth century, early computer networking was done using wires, or, more properly, cables. Many times, the choice of cabling was either a coaxial cable or a twisted-pair cable. (Today, the bulk of the wired networking is done with twisted-pair cables.)

As computer networking evolved, it was easy to see that the need for over-the-air, un-cabled networks would provide a lot of convenience and solve a lot of problems. Just like what happened in the early 1900's with Morse code communications, scientists and technologists knew that, somehow, a way would be found to get rid of the cables.

Some early over-the-air computer communications with microwave systems was successful, due to the wide-band capability of these systems. Because of the bandwidth available at the higher microwave frequencies, these systems could transmit a large amount of data at a fast rate. Satellites, too, had this advantage due to the frequencies at which they operate. Uplinks and downlinks could replace terrestrial cable systems, including those that ran under oceans.

Finally, regulatory agencies created radio bands which were originally intended for use in "Industrial, Scientific and Medical" research, appropriately called ISM bands. Hardware designed to operate in these bands did not require users to obtain licenses. This opened the door to allow unwired computer networking systems to be implanted without users having to comply with complex regulatory filings.

And so, as these systems became more common, the term "wireless" arose again, due mainly to the fact that the use of these bands allowed elimination of the wires (or again, more properly, cables) needed to tie computer systems together.

So, now we're back to defining these systems as "wireless", just like in the early part of the last century. To quote baseball's Yogi Berra, "It's déjà vu, all over again".

Interestingly enough, today one major technical group defines wireless networking as: "Using radio, microwaves, etc. as opposed to cables to transmit computer networking signals". 

"Wireless" or "radio", the term used is less important than the ability to perform the work needed to get data across given distances. Call it what you will, it has revolutionized our ability to connect computers into a network and contributed greatly to the rise of the world-wide web.

Timeline: Radio vs Wireless

In part 3 of our series, we'll look at some of the requirements necessary to make radio/wireless systems capable of sending and receiving data without interfering with each other, as well as touch on the software systems that create these results.

Paul Black is a freelance writer and broadcast engineer in Northern California. He holds a Certified Professional Broadcast Engineer certification from the Society of Broadcast Engineers and an FCC Lifetime General Class Operator License. He is a licensed amateur radio operator (call sign N6BBZ) and has worked for several broadcast companies, including Bonneville Broadcasting, RKO General Broadcasting, and CBS Television. Visit his website at www.paulblackcopy.com

September 16, 2016

ROAD REPORT: Space...the Wireless Frontier

Ok...time to get out your Star Trek communicator pin, your Mr. Spock ears and Klingon mask and sash. Clear-Com brings us to the edge of space exploration - or at least to the training centers.

We start with a 6 million gallon pool that's bigger than a football field. A major space agency uses this pool to train astronauts from around the world, simulating the weightless conditions of working in low earth orbit.

The astronaut trainees put on their space suits and, through an umbilical of tubes and cables to the poolside tender positions, get their air, medical telemetry and communication needs. They all connect via standard 4-wire connections (line-level inputs and outputs to a matrix port in the main control server room). There are controllers at poolside and controllers simulating Mission Control Center-like consoles that guide the trainees and the scuba diver assistants through the paces of their exercises. A beautiful techno-ballet in the slow motion world of the underwater, weightlessness of simulation training.

Why Do Astronauts Use Training Pools?

Imagine you are all suited up in your cool, high-tech space suit. HAL900 has opened the Pod Bay door. You stand on the step, taking in the unbelievable view and....you step off into the abyss to do your spacewalk in order to fix an antenna on the other side of the Space Station. In the weightlessness of space, you turn your wrench to tighten the bolt on the antenna. But, if you haven't practiced your task while weightless, just as you move your body to turn the bolt....it's quite possible you might also turn the whole Space Station! Didn't know your own strength, did you?

Well, this training is why the astronauts do simulation training at the pool. Using Clear-Com's FreeSpeak II wireless and Eclipse HX digital matrix systems, the team is able to coordinate communications between the Control Room simulations, the Dive Boss' station, the medical team (who constantly monitor the astronauts' and assistant divers' vitals), and the technical coordinators, while maintaining clear and open lines of communications. This way, the task of learning how to work in weightless conditions can be run in a smooth, efficient and safe manner. 

Wireless Work Flow

Wireless communication can be very persnickety, as we all know. In this decade, we are seeing the loss of wide swaths of the narrow UHF spectrum. As these bands are sold off to the highest bidder, we are all left looking for new places to use our small signals for mics, comms and IFB (interruptible fold back for talent and in-ear monitors). 

Clear-Com's FreeSpeak II plays a big part in the workflow here. First off, the 1.9 GHz model keeps the comms well out of the way of other frequency traffic, both in the remaining UHF and the now very crowded 2.4 GHz spectrum. With that said, with the deployment of Frequency Hopping Spread Spectrum (FHSS) technology and recent Clear-Com innovations, the use of 2.4 GHz wireless systems are becoming more attractive. The FreeSpeak II 2.4 GHz has been chosen for some of these training facilities because of the redundancy transmission of the FHSS scheme, which helps with the immensity of the room and reflective nature of the architecture and the huge water surface reflectiveness. 

The FreeSpeak II solution uses a deployment of an array of Transceiver Antennas that can service up to 5 beltpacks per transceiver. These are then spread out around the needed coverage area and the beltpacks hand-off from one antenna to another as the users move about the covered areas. Their seamless hand-off is clean and has a killer clear sound. The high quality spectrum of audio makes the FreeSpeak the best sounding multi-channel communication system around. And when using the matrix integration card option, as the large training pool area has, it makes it possible for any intercom panel in the facility to directly talk with any and every beltpack user, and vice versa. When programming the FreeSpeak II through the Eclipse HX's EHX software, it's just a simple drag and drop function. BINGO...you're all set to get to work. When using this integrated method, the beltpacks can do just about anything that the wired matrix user panels can do. If there's a telephone interface in the matrix, the FreeSpeak II beltpacks can be programmed to make a telephone call (including speed dial to the actual destination phone number) or trigger relays or GPI's with the touch of a button.

The award-winning audio clarity of the FreeSpeak II wireless system makes for crisp and clear communications, in an environment where it's most vital, like simulated training courses for astronauts going into space. These expert technicians need a system that can adapt to their unique workflow and one that they can trust will work in any environment. Perhaps, one day......even in space. 

Rom Rosenblum has always been a capable, yet rebellious audio-guy. Originally in the music recording business as an engineer, with a long Emmy Award winning career in live TV broadcasting, Rom worships at the altar of All Things Audio. As one of the Applications Engineers at Clear-Com, he works as a catch-all fixer for folks who need tech support, commissioning, systems design, product development, and sales support.