From The Secret Lives of INTs…Bringing the INT into the 21st Century to Solve AC Interference Issues Affecting IPTV Services, by Russ Gundrum, published by OSP Magazine
in March 2011.
“AT&T’s new advertising message, “Rethink Possible”, is very appropriate for what is being discussed here, because most people would consider the INT an old technology. However, the information provided in this article could result in an eventual commercially available product by rethinking what could be possible here! For instance, how many of you readers even know about the INT, ever used one, or had to pick one up? For those of you who have, you know you can’t just hold it in the palm of your hand like an IC chip or solid-state piece of equipment, although it IS a very solid piece of telecom gear! That said, it should be considered a critical piece of equipment to using the telco’s embedded copper infrastructure for the successful operation of IPTV services.”
”What can be done about all of this induction? Even though this problem has been known about since the open-wire days of telephony, until the invention of the INT there had yet to be a perfect solution. What’s more: All the bonding and grounding you can do out there with that little aluminum sheath will NOT solve this problem! That’s the job of the INT. This is a multi-pair device, which is important to understand when you start weighing the economics of the technology. It substantially reduces both the induced voltage AND current, which is unique with surge protection devices. Later in the article I will show how a 98% reduction was achieved with my prototype unit. So, there is hope yet.”
“On October 13, 2010, I gave a 1-hour presentation on “AT&T’s Patented DSL INT for IPTV Applications” at OSP EXPO in San Antonio, Texas. Three years earlier I had given a full-day seminar at OSP EXPO in San Jose, California, on “The Lost Art (and Science!) of AC Interference Mitigation: Solve Induction Problems Affecting your FTTN/IPTV Services, While Extending Your Reach”. While I discussed the use of the Induction Neutralizing Transformer (INT) as a practical and cost-effective mitigation technique, unfortunately I couldn’t discuss an idea I had given the company in January 2002 for a specially designed Digital Subscriber Loop (DSL) INT, since a patent was pending. However, one week after I returned home, AT&T received the first patent (7,266,154) and 2 years later a second patent (7,433,412) on my network design improvement idea.”
“Since the idea had not captured much interest, I decided to make a prototype unit in December 2009 for testing on a U-verse circuit at the University of Houston. This article presents the latest results that I’ve been able to achieve, and discusses potential field applications of the device.”
“AT&T’s new advertising message, “Rethink Possible”, is very appropriate for what is being discussed here, because most people would consider the INT an old technology. However, the information provided in this article could result in an eventual commercially available product by rethinking what could be possible here!”
“It’s also important to have some background on this powerful INT. To do that, we must go back to spring of 2002 when the patent application was being prepared. At that time, SBC (as the company was then called) was starting to push fiber closer to the customer to deliver higher speed Internet services. Fiber was being extended from the central office to the remote terminals (RTs) in what was called ‘Project Pronto’. These RTs were small shelters that housed the Digital Subscriber Loop Access Multiplexer (DSLAM) and were designed to work on copper loops less than 12,000’ in length.”
“The patent design showed placing the DSL INT at this point in the circuit. However, it also showed placing a unit at the Serving Area Interface (SAI). When AT&T continued to push fiber closer to the customer in its ‘Project Lightspeed’ deployment some 5 years ago, this is where the DSLAM was placed. It’s now commonly referred to as the Video Ready Access Device (VRAD) and is part of a Fiber-to-the-Node (FTTN) topology that is the primary way the U-verse service is delivered.”
“So, when fiber cable was placed between the CO to an RT out at the 18 Kf point, and it shortened the copper loop to 12 Kf in length, a lot of folks were surprised to learn that there were still induction problems. Interestingly, beyond the RT the induction can build up exponentially -- as shown in the above illustration. This is due to a more suburban and rural environment. With it being less developed, the power system loads are more unbalanced, which contributes to induction problems.”
”What can be done about all of this induction? Even though this problem has been known about since the open-wire days of telephony, until the invention of the INT there had yet to be a perfect solution. What’s more: All the bonding and grounding you can do out there with that little aluminum sheath will NOT solve this problem!”
“That’s the job of the INT. This is a multi-pair device, which is important to understand when you start weighing the economics of the technology. It substantially reduces both the induced voltage AND current, which is unique with surge protection devices. Later in the article I will show how a 98% reduction was achieved with my prototype unit. So, there is hope yet.”
“A few of you may recall those large, heavy oil-filled High Voltage NT’s that were used on wireline facilities entering power plants and substations. This is the most expensive kind of NT at a couple hundred dollars a pair, which really isn’t too bad when you realize it will neutralize several thousand volts.”
“This kind of NT is what led to the development of the much smaller, lighter weight, and much less expensive Induction or Low Voltage NT’s (according to the Bell System Practice [873-505-107] I wrote way back in 1974).”
“However, the key to understanding how the device works is the large iron core surrounding the coil. Consider the 1934 Edison Electric Report on low frequency shielding. It basically said that you either distribute a large inductance as in steel armor plating along the cable in the form of the sheath, or you “lump” it in the form of a neutralizing transformer. Of course this lumped inductance is what makes the INT so big and heavy!”
“That design criteria the inventor of the INT had more than 40 years ago was intended to neutralize more than 300 Vg, because that’s when the primary station protector would begin to operate. In fact, some of the commercially available INTs such as the 50 pair unit can even handle up to 600 Vg.”
“Part of my patented idea was to have a much lower rated unit that could handle only 50 to 100 Vg. This new design criterion should create a smaller, less heavy and less expensive unit. The other key design element is using Cat 5 or higher cable for the DSL application. This tighter twist eliminates any possible crosstalk issues.”
“The patent for the new device shows the overall network design aspects regarding the recommended placement of the INT, and how it can receive the necessary current for proper operation. But it also has one more important design criteria: It calls for the transformer core to be of a higher longitudinal inductance value like a choke, so it is more effective in suppressing the higher frequency impulse noise type of problems that are so prevalent these days.”
“This fact is underscored in the book abc of the Telephone that I wrote in 1981 on Power Line Interference Problems and Solutions. Though it is no longer published, it is available on Google Books. On page 16, I wrote: ‘Today's growing demand for more sophisticated circuits that have to transmit data with extremely high reliability, impulse noise becomes an area of concern. If the frequency of the noise begins to approximate the frequency of the signal, threshold levels in a digital data bit stream can be exceeded, resulting in errors and re-transmissions. Although sources of impulse noise are hard to locate and eliminate, their effects can be suppressed if the impulse energy is overriding on excessive levels of 50/60 Hz induction and its voice frequency harmonic components. By reducing the level of induction, impulse noise levels can also be substantially reduced.’”