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CHAPTER 24 SEPTEMBER 1996 NEWSLETTER
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Newsletter edited on Pagemaker 5.0 by: Mike Norton Chapter 24 World Wide Web Site http://www.broadcast.net/~sbe24 © 1996 by SBE Chapter 24. Views expressed herein do not necessarily reflect the official positions of the Society, its officers, or its members. SBE Chapter 24 regrets, but is not liable for, any omissions or errors. The Chapter 24 Newsletter is published twelve times per year. Other SBE Chapters are permitted to use excerpts if attributed to the original author, sources, and SBE Chapter 24.
Jim Hermanson Fred Sperry Tom Smith Tom Weeden Neal McLain Kevin Ruppert Paul Stoffel Contents for this Newsletter
NEWSLETTER EDITOR'S STATS
Information and/or articles are also accepted by US Mail. Please address them to: SBE Chapter 24 Newsletter Editor Please submit text file on DOS or Windows 3.5" floppy diskette if possible. MEETING ANNOUNCEMENT
LOCAL EAS UPDATE AND DIGITAL TV HIGHLIGHTS Dutch Treat Dinner at Nitty Gritty, 223 N. Frances St.
Then, David Felland, ECB Director of Engineering, recently spoke about Digital TV. His presentation was recorded on tape and excerpts from that presentation
will be shown (in NTSC). UPCOMING MEETINGS
Wed, Oct 30, 1996 Wed, Nov 20, 1996 Tue, Dec 17, 1996 Wed, Jan 22, 1997 Thu, Feb 20, 1997 Tue, Mar 18, 1997 Wed, Apr 16, 1997 Thu, May 22, 1997 Tue, Jun 17, 1997 Sat, Jul 26, 1997 AUGUST BUSINESS MEETING MINUTES
Chapter 24 of the Society of Broadcast Engineers met on Thursday, August 22, 1996, at Grassland Media, in Madison. There were 18 persons in attendance, 14 of whom were certified. The meeting was chaired by Chapter 24 Chairman Paul Stoffel. Call to order: 7:05 pm. The minutes of the July meeting were approved as published in the August Newsletter. Treasurer's Report (reported by Stan Scharch, Treasurer): the chapter balance is in the black. Newsletter Editor's Report (reported by Mike Norton): The deadline for the September Newsletter is midnight 9/6/96; the folding party is 5:30 pm 9/11/96 at WKOW-TV. Sustaining Membership Report (reported by Fred Sperry): Four renewals have been received: Sony, Video Images, Skyline Communications, and Fuji. Two former sustaining members declined to renew. The Chapter now has 23 sustaining members. Frequency Coordination Report (reported by Tom Smith): "Nothing major". All stations are requested to submit coordination requests related to the upcoming football season as soon as possible. Special Events: no report. Certification and Education (reported by Paul Stoffel in Jim Hermanson's absence): the next opportunity to sit for an examination will be at World Media Expo in Los Angeles; application deadline is August 26. National Liaison Report (reported by Leonard Charles and Paul Stoffel): Old business: none. New business: none. Professional Announcements: Tom Smith reported on recent FCC actions relating to: Submitted by Neal McLain, Secretary CHAPTER 24 OFFERS BROADCAST CLINIC SCHOLARSHIPChapter 24 is offering a scholarship consisting of any two days of the three day Broadcast Clinic taking place October 29, 30 and 31, 1996 in Madison. The scholarship will be awarded on the basis of the following criteria and maximum number of points accumulated: • Must be a current member of Chapter 24 Points will be assigned as follows: • 5 points for each month applicant has at least one article published in the Chapter 24 newsletter spanning the 12 issues prior to the October 4th application
deadline In the case of a tie, final selection will be by the elected officers of Chapter 24 or by a committee appointed by those officers, excluding any who may have applied. If there is more than one applicant, an alternate will also be selected based on the second highest number of points. The scholarship winner will be required to write a summary article to be published in the chapter newsletter. Applications should be in the form of a letter which is signed, dated and received no later than October 4, 1996. Please send the application to Fred Sperry at the following address: Educational Communications Board CHAPTER 24 BAKE OFF!!By Kevin Ruppert In conjunction with this year's Broadcaster's Clinic, Chapter 24 is having a Bake Off!! Put down that soldering iron, or that mouse! This is your chance to "really cook!" All chapter members are encouraged to participate. All you have to do is make a dozen homemade cookies. (Think of it as an edible "batch file.") All of the cookies from all of the members will be displayed (and eaten) in the chapter's booth at the Broadcaster's Clinic. A ballot box will provide Clinic goers a chance to vote for their favorite cookies! Here are the simple rules. Any Chapter 24 member is eligible. The cookies must be made from scratch. No mixes! The Chapter member must be the one who actually bakes the cookies. No spouses! (You can get minimal assistance from your spouse, such as having him/her show you where the kitchen is, or looking for the secret multigenerational family recipe, but nothing more!) A special prize will be given to the person with the most votes. Even if you don't bake a batch, come to the booth, chat for a while, and have some homemade cookies. And don't forget to vote! CERTIFICATION NEWSby Jim Hermanson The next local certification exam session is November 8-18. The cutoff date to submit applications to the National SBE Office is September 26. From the National Office...Jim Wulliman, the "father" of certification officially retired as of June 30, 1996. Terry Baun, SBE National President, appointed David Carr as Chairman of the National Certification Committee. Mr. Carr resides in Houston, TX and is Director of Engineering at KHOU-TV. He has served on the SBE Board of Directors and the SBE Engineering Conference Committee as well as being a member of the National Certification Committee. Other appointments to the National Certification Committee include Richard Ryan from Roscor, Milwaukee, WI and Ralph Hogan, Boise State University, Boise, ID. This brings the National Certification Committee to 16. LOCAL LEGALSCompiled by Tom Smith PROPOSEDWKOW-TV Channel 27, Madison, WI. Shockley Communications Corp. seeks permission to operate at 5,000 kw visual at 455 meters, overall height of tower at 434 meters. Transmitter to be located at 6963 Mineral Point Road. Announced June 7, 1996 New FM, Madison, WI. The Educational Communications Board seeks to construct a FM translator in Madison to rebroadcast WHHI-FM in Highland. The proposed translator would operate on 90.9 mhz from the Madison Community tower with a power of 10 watts. Filed on August 6, 1996 (Compiled from Broadcasting and Cable and The Wisconsin State Journal) AMATUER RADIO NEWSby Tom Weeden • As Hurricane Fran approached the East Coast, the FCC issued a voluntary communications emergency declaration for amateurs. The declaration requested hams to relinquish use of 10 kHz windows around 3923 kHz in North Carolina and 3993 kHz in South Carolina. The frequencies were reserved for stations handling emergency traffic resulting from the hurricane. The communications emergency was declared on September 5th and lifted on the 6th. • The space shuttle Atlantis was returned to the launch pad, in the wake of the threat of Hurricane Fran to central Florida. Atlantis was moved off the pad and into the nearby vehicle assembly building as a precaution, due to the approach of the storm. NASA managers have set a new launch date of September 16 for mission STS-79, which will carry the Shuttle Amateur Radio EXperiment, or SAREX. Prearranged ham radio contacts are scheduled with schools in Kansas, Ohio, and England, and with family and friends of the crew. The astronauts will also make random contacts with the amateur community as their schedules permit. Three hams will be aboard Atlantis for STS-79: Jay Apt, N5QWL, Carl Walz, KC5TIE, and John Blaha, KC5TZQ. • New FCC RF safety standards effective January 1, 1997, could affect the way some hams operate, perhaps especially those using vehicle-mounted antennas. As a result of a Report and Order adopted by the FCC on August 1, Part 97 will require hams running more than 50 watts peak envelope power (PEP) to conduct routine RF radiation evaluations to determine if RF fields are sufficient to cause human exposure to RF radiation levels in excess of those specified. In comments filed earlier with the FCC, the American Radio Relay League (ARRL) strongly opposed adoption of the new requirements. The ARRL said most Amateur Radio users do not possess the requisite equipment, technical skills, and/or financial resources to conduct an environmental analysis. The ARRL also argued that amateur stations, because of their intermittent operation, low duty cycles, and relatively low power levels, rarely exceed the 1992 ANSI/IEEE standard. But the FCC expressed concern that Amateur Radio operations "are likely to be located in residential neighborhoods and may expose persons to RF fields in excess of the MPE guidelines." • The FCC has announced that vanity call sign filing Gate 2 will open September 23. Under Gate 2, Amateur Extra class licensees may request a vanity call sign on or after that date. (Excerpted from W1AW/ARRL bulletins) FCC RULEMAKINGSBy Tom Smith Final RulesGen. Docket 86-285, FCC 96-332 Schedule of Application FeesThe FCC has issued a new fee schedule for the processing of applications and other filings. The fees are adjusted every two years and reflect the change in the consumer price index. The new fees will become effective on September 12, 1996 unless there are changes from Congress. Anyone filing an application should check on these fee changes before sending their application into the Commission. The fees are listed in the FEDERAL REGISTER in the August 12, 1996 issue on pages 41967 through 41984. The broadcast fees are listed on pages 41975 through 41978. The FCC adopted and released this action on August 7, 1996. ET Docket No. 93-62, FCC 96-326 Guidelines for Evaluating the Environmental Effects of Radiofrequency Radiation.The FCC has issued new rules and guidelines concerning exposure to RF radiation. These rules cover Personal Communications Service, unlicensed Personal Communication Service devices, unlicensed RF devices (part 15), Cellular Telephone services, Specialized Mobile Radio, Land Mobile services, Multipoint Distribution Services, Satellite Communication Services (low orbit, satellite phone), Maritime Services, Experimental Radio Services, Broadcast Services and Auxiliaries, and Amateur Radio. Much of this report and order for the rulemaking covered the effect of these rules on small business. There were a number of paragraphs on what describes a small business and how many small businesses would be affected under these rules. The rules call for a rewrite of OST Bulletin No. 65 so that it will be easier for small business to understand and assess their compliance with the rules. The commission created exclusions that will require transmitters that have the greatest potential for causing RF exposure to be evaluated. The rules will require evaluation when antennas are under a minimum height or power is above a maximum level that will create exposure problems. A number of testing methods will be allowed so that a small business can perform tests in the least burdensome way. Exposure limits have been updated to comply with the results of new research. A note to ham operators, you will have to comply with RF exposure rules when operating with more than 50 watts PEP. These rules where published in the FEDERAL REGISTER on August 7,1996, on pages 41006 through 41019. They were adopted and released on August 1, 1996 and became effective on August 6, 1996. ET Docket No. 95-144, FCC 96-219 UHF Noise Figure Performance MeasurementsThe FCC has eliminated its requirement that TV manufacturers file reports concerning the UHF noise figure performance of their TV's. The FCC found the manufacturers were in compliance with the rules concerning UHF TV tuner performance and there was no longer a need for the data to be filed with the FCC to insure compliance. These rules were created originally to help UHF stations to compete with VHF stations by improving UHF reception. The FCC adopted this notice on May 14, 1996 and released it on June 3, 1996. It became effective on August 16, 1996 and was published in the FEDERAL REGISTER on June 17, 1996 on page 30532. WT Docket No. 95-47, FCC 96-224 Permitting Mobile Operation in the Interactive Video and Data Service (IVDS)The FCC has amended its rules to allow for mobile operation for IVDS licenses. These mobile units will be limited to 100 milliwatts, and are used for subscriber return transmissions. The FCC also removed the requirement for auto power control on subscriber transmitters 100 milliwatts or under. In another action in this rulemaking the FCC removed the transmit time limitation on subscriber response transmitters located outside any TV channel 13 grade B contour. It should be noted that IVDS operates just above channel 13. These rules were adopted on May 16, 1996 and became effective on July 25, 1996. The FCC released them on May 30, 1996 and they were published in the FEDERAL REGISTER on June 25, 1996 on pages 32710 and 32711. MM Docket No. 87-286, FCC 96-317 Advanced Television Systems and Their Impact on Existing Television ServiceThe FCC has released another request for comments concerning digital television. In this notice of proposed rulemaking, the FCC released a proposed table of assignments for the new digital television service and the method it used to create the table. The FCC is also seeking comments on the effect of the proposed rules on low-power stations and translators. The FCC is proposing to condense the TV spectrum to fit from channel 7 through channel 51 at the end of the transition to DTV, with early recovery of some of the spectrum on channels 60 through 69. As part of this notice the FCC deleted all unused and unapplied for allocations for use by NTSC stations. They also will not accept any petitions for new allocations as of the date this notice was adopted. The FCC will accept applications for new stations for 30 days from the date this notice was published in the FEDERAL REGISTER which was August 21, 1996. This notice was adopted on July 25, 1996 and released on August 14, 1996. It was published in the FEDERAL REGISTER on August 21, 1996 on pages 43209 through 43214. The full text of this notice of rulemaking is on the FCC web site (www.fcc.gov) and includes the proposed table of allocations. The full text runs about 175 pages. Comments are due on November 22, 1996 and replies on December 23,1996. IB Docket No. 95-59 Preemption of Local Zoning Regulation of Satellite Earth Stations CS Docket No. 96-83 Implementation of Section 207 of the Telecommunications Act of 1996, Restrictions on Over-the-air Reception Devices: Television Broadcast Services and Multipoint Distribution ServiceThe FCC has issued a Report and Order, a Memorandum and Order and a further Notice of Rulemaking concerning the local regulation of outdoor antennas used for the reception of broadcast TV, direct broadcast satellite and MMDS (wireless cable). In this action the FCC adopted rules concerning the preemption of rules prohibiting the use of outside reception devices by local zoning land use or building regulations by local governments and by private covendents including those by deed restrictions and homeowner associations. Communitities could still regulate in historic districts and for some safety reasons (power line and roadway fall clearance areas). The FCC and Congress claim the right to preempt local regulations due to the fact that they interfere with interstate commerce. This is because radio services are considered interstate commerce because the signals cross state lines. Besides the FCC adopting these rules, they are also seeking comment concerning extending further rules pertaining to commonly owned and rental property such as condos and apartments. This notice was adopted on August 5, 1996 and released on August 6, 1996. Comments on the further notice of rulemaking are due September 27, 1996 and replies are due on October 28, 1996. The full Text of this notice is avaible on the FCC's wed site (www.fcc.gov) Compiled from the Federal Register and the FCC WEB Page) TELECOM INDUSTRY NEWSBy Neal McLain PSC SEEKS COMMENTS ON AREA CODE 414 RELIEF PLANAs previously reported in these pages, Wisconsin's Area Code 414 is expected to need relief in 1997. Planning for the relief code is now under way. Earlier this year, representatives from a group of telecommunications companies, known as the 414 Telecommunications Industry Team, held a series of meetings to examine the alternatives and suggest a relief plan. As usual, split-vs.-overlay was a big issue. That's no surprise, but some of the arguments put forth by some of the players were unexpected: • Ameritech, clearly the major incumbent local telephone company within 414, argued in favor of a split on the grounds that it would be least disruptive to their customers. This position is diametrically opposed to the position Bell Atlantic has taken in its territory: in the Maryland and Pennsylvania cases, BA asserted that an overlay would be least disruptive. • BellSouth Cellular (the Cellular One franchisee) argued in favor of an overlay so that their users wouldn't have to reprogram their phones. This is a departure from the position taken by other cellular companies (notably Southwestern Bell): that overlays aren't "fair" because cellular customers usually end up with numbers in the new code. But many of the arguments were familiar. GTE favored an overlay so its customers (most of whom are well outside the Milwaukee metro area) wouldn't have to change their telephone numbers. MCI favored a split so its new local telephone service wouldn't have odd-looking phone numbers. In the end, the Industry Team wasn't able to resolve the issue, so it's now up to the Public Service Commission. The Commission has issued a NOTICE OF INVESTIGATION, TECHNICAL CONFERENCE, PUBLIC HEARINGS, AND REQUEST FOR COMMENTS seeking public comment. Four public hearings are scheduled later this month, in Green Bay, Oshkosh, Waukesha, and Watertown. The Commission originally hoped to resolve the issue by the end of September, but it now looks like they won't reach a decision until the end of October. A special thanks to Albert F. Schams, a Communications Analyst with the PSC, for information used in this article. CENTRAL OFFICE CODE UPDATEIn last month's article, I missed several recent central office code assignments. Thanks to Chapter 24 member Stan Scharch for the following update: • There are now at least 38 N1X/N0X codes in 414 — far more than the three reported last month. • There are now five NN0 codes in 608: in addition to the four reported last month, 850 has been assigned to TDS Telecom for landline service in Waunakee. • There is already one N1X code in 608: 513, assigned to Cellular One in Madison. The original supply of 608-NNX codes still has plenty of unused capacity. Several recent assignments have been drawn from this pool: 236 and 287 in Madison (Ameritech); 745 in Portage (GTE); 827 in Middleton (Mid-Plains); and 848 in Verona (TDS Telecom). INVENTION & TECHNOLOGY: "THE BIRTH OF CABLE TV"The Fall, 1996 issue of American Heritage of Invention & Technology contains an excellent article titled "The Birth of Cable TV," authored by George Mannes, a reporter for the New York Daily News. The article relates the history of the world's first commercial cable television system, located in Astoria, Oregon. My wife and I visited Astoria several years ago. We made the obligatory trip up Coxcombe Hill looking for the site of the original headend. The headend is long gone, but a bronze plaque commemorates the day in 1948 when the system first operated, carrying one channel: KING-TV, Channel 5, from Seattle. For those not familiar with Invention & Technology, it's a fascinating magazine. Published by Forbes, it is sponsored by a single advertiser, General Motors. The title says it all: it covers the history of invention and technology in the United States. The editors at Forbes are solely responsible for editorial content: articles about General Motors get equal billing with articles about its competitors. The Madison Public Library includes Invention & Technology in its periodical collection. BROADBAND NETWORKS PART 6 - FEEDER DESIGNBy Neal McLain This is the sixth in a series of articles about coaxial broadband networks. In this article, we'll discuss the design of feeder lines. EDITORS NOTE: There are many references to figures and diagrams. These figures and diagrams were not graphically reproduced for this electonic version of the newsletter. The complete hard copy with figures and diagrams can be obtained by contacting the editor. DESIGN TAP LEVELIn last month's article, we described premises wiring. We noted that the Design Tap Level (DTL) is the starting point for the design of premises wiring: the designer starts with the DTL and works downstream, toward the terminal devices. We also assumed a value for DTL: +18 dBmV at 500 MHz (which is approximately the visual carrier for cable channel 70). Design Tap Level is also the starting point for the design of feeder lines, except that we work backwards: the designer starts with the DTL and works upstream, back toward the headend. The best way to describe the design process is by using an example. In the following example we will assume that: •The feeder line is constructed entirely of 0.500" hard cable having a maximum loss of 1.82 dB per 100 feet (or 0.0182 dB per foot) at 500 MHz (1). •Taps losses are as specified in Figure 1 (2). • DTL = +18 dBmV at 500 MHz. A TYPICAL DESIGNWe'll start with a typical residential neighborhood of single-family homes: • Figure 2(a) shows the feeder line as we described it in last month's article. • Figure 2(b) shows this same feeder line redrawn as it would be shown on a typical field map. Note that individual drops are no longer shown; instead, a single figure ("drop count") indicates the total number of drops which must be accommodated by each tap. Note further the "tap number." In this simplified map, I've numbered them P1 through P6, although in an actual broadband system, the tap numbering scheme would reference some physical location system such as street address or pole number. • Figure 2(c) shows the same feeder once again, this time with the taps replaced by standard tap symbols. A 2-way tap is a circle; a 4-way tap is a square, and an 8-way tap is a hexagon. We start at the end (tap P6) and work backwards (Figure 3). Selecting tap P6 is straightforward: we know it's a terminating tap with four drops. Only one tap meets these criteria: 7T-4. The "T" tells us that it's a terminating tap, and the "4" tells us that it can feed 4 drops. The "7" tells us the nominal tap loss is 7 dB, although Figure 1 tells us that it's actually 7.5 dB. We begin by calculating the signal level at the tap input. We take the DTL and add the tap loss (remember, we're working backwards, so we add losses): INPUT = DTL + tap loss = +18 + 7.5 = +25.5 dbmV. Working upstream, we next calculate the signal level at the output of tap P5 by adding the loss in the intervening cable: +25.5 + (0.0182)(110) = +27.5 dBmV. Thus, the output of tap P5 must be at least +27.5 dBmV. We now come to tap P5 (Figure 4). We must select a specific 4-way tap, and calculate its input level. The tap we select must meet three criteria: • The tap level must be at least equal to the required DTL, +18 dBmV. • The output level must be at least equal to +27.5 dBmV. • The input level must be as low as possible so that we don't waste any signal unnecessarily. By inspection, we can see that the input level must be something around +30 in order to provide the required +27.5 output level. A quick mental calculation (+30-18) tells us that the tap loss has to be around 12 dB. Referring to Figure 1, we see two possibilities: 10-4 (tap loss = 10.5) or 14-4 (tap loss = 14.0). We now make four test calculations: • Assume a 10-4, and determine the required input to satisfy the tap level requirement: +18 + 10.5 = +28.5 dBmV. • Assume a 10-4, and determine the required input to satisfy the output level requirement: +27.5 + 4.3 = +31.8 dBmV. • Assume a 14-4, and determine the required input to satisfy the tap level requirement: +18 + 14.0 = +32.0 dBmV. • Assume a 14-4, and determine the required input to satisfy the output level requirement: +27.5 + 1.8 = +29.3 dBmV. This process yields two pairs of possible input levels: 10-4 +28.5 and +31.8 dBmV 14-4 +32.0 and +29.3 dBmV We now have the information we need to select the tap: • For each individual tap, we have to select the higher of the two possible input levels in order to ensure sufficient level at both of its outputs. This step reduces the number of possible choices to two: +31.8 for the 10-4 or +32.0 for the 14-4. • In order to conserve signal, we select the tap which allows the lowest possible input level. Comparing +31.8 and +32.0, the obvious answer is +31.8. We select the 10-4 tap. Continuing upstream, we next calculate the signal level at the output of tap P4 by adding the loss in the intervening cable: +31.8 + (0.0182)(160) = +34.7 dBmV. Thus, the output of tap P4 must be at least +34.7 dBmV. We now come to tap P4 (Figure 5). We repeat the process: by inspection, we can see that the input level must be something around +36 in order to provide the required +34.7 output level. A mental calculation (+36-18) tells us that the tap loss has to be around 18 dB. Referring again to Figure 1, we see three possibilities: 14-4 (tap loss = 14.0) 17-4 (tap loss = 17.0) 20-4 (tap loss = 20.0) Again, we make test calculations for each tap and select the lowest of the highs. The 17-4 wins. And so it goes. Repeating this process three more times (Figures 6, 7, and 8) completes the design. This process can, of course, be computerized; several software packages are available. With a good design package, the designer simply enters the drop count and cable footage; the software the makes the test calculations, selects the tap, and places the appropriate graphic symbol on the map. TILTAs we noted in Part 3 in this series, cable loss varies as a function of frequency. The above calculations were based on the cable loss at 500 MHz. The loss at 50 MHz (Channel 2) is much lower. This differential loss causes a phenomenon called "tilt": at the end of a feeder line, higher frequencies are attenuated more than lower frequencies. Consider the feeder line we discussed previously: this line was assumed to be constructed entirely of 0.500" hard cable. The total length of the cable is 731 feet. Resulting cable losses are: At 500 MHz: (0.0182)(731) = 13.3 dB At 50 MHz: (0.0052)(731) = 3.8 dB Thus, the expected output levels at the tap P6 would be: At 500 MHz: +18.0 dBmv At 50 MHz: +27.5 dBmV For most terminal devices, including recent-vintage television receivers, this amount of tilt would not cause a problem. But tuners in older television sets frequently have poor selectivity, and may not be able to reject out-of-band signals. The resulting distortion can vary anywhere from multiple herringbones in the picture to the total loss of a viewable image. To compensate for tilt, feeder lines are usually "pre-equalized": the signal feeding the feeder line is filtered to force a tilt opposite to the tilt introduced by the cable. In the example above, if we pre-equalize the signal such that the signal level at Channel 70 exceeds the level of Channel 2 by about 5 dB, the maximum tilt at the end of the line would also be about 5 dB. At the midpoint, the signal is flat across the band. In extreme cases, "block equalizers" can be inserted into the line to provide additional tilt compensation. HOT TAPS AND HOUSE AMPSNow we come to the question: what do we do if we need more level than the specified DTL? As an example, let's take another look at the six-TV home we discussed last month (Figure 10) If we start with DTL = +18 dBmV, the level arriving at TV3 is: +18.0 (DTL) - 7.0 (drop loss) -10.5 (splitter loss) - 6.8 (inside wire loss) or -6.3 dBmV, well below the minimum 0 dBmV required at each terminal device. How can we pick up an extra 7 dB? The easiest solution would be the "house amplifier" shown in Figure 10. Typical house amps are available in 10-, 20-, and 30-dB versions; in this case, a 10-dB amplifier would fit nicely. The disadvantage to this solution is reliability: every active device is a potential outage. House amps are especially prone to failure because homeowners have a tendency to unplug them. A more difficult, but more reliable, solution is a "hot tap" — a special tap inserted into the feeder line in place of (or in addition to) the original design. Sometimes this works and sometimes it doesn't: it depends on where the problem falls within the feeder line. Consider two cases: • Suppose the problem falls at tap P1 (Figure 8). Referring to Figure 1, we note that a 17-dB tap would provide 9 dB of additional tap level — enough to solve our problem with an extra 2 dB to spare. There are two ways to accomplish this: replace the 26-8 with a 17-8, or cut in a 17-2 next to the 26-8. Referring again to Figure 1, we note how these choices affect insertion loss: replacing the tap would increase insertion loss by 1.1 dB, while cutting in a 17-2 would increase insertion loss by 0.7 dB. Since we want to minimize insertion loss, we would select the latter choice (Figure 9). We realize, of course, that this reduces the DTL at all downstream taps by 0.7 dB; however, it's a reasonably safe gamble that this won't be a problem. • Now suppose the problem falls at tap P5 (Figure 4). We can't replace the tap with a lower value: the only possibility would be a 7T-4, and that would terminate the feeder line right there. We can't cut in a two-port tap either; a 4T-2 would terminate the line, and a 7-2 wouldn't provide sufficient additional tap level. There are only two possible solutions: use a house amp or redesign (and rebuild) the entire feeder line. MULTI-DWELLING UNITSThe term multi-dwelling unit (MDU) includes duplexes, apartment and condominium buildings, motels, hospitals, and similar structures. This term is frequently applied to commercial buildings as well, even though they are obviously not "dwellings." If an MDU exists when the distribution system is designed, a special tap can be incorporated into the design. While each network owner has its own policy regarding MDUs, a common policy specifies the following: • For duplex or triplex buildings: a separate tap port, at standard DTL, for each dwelling unit. • For larger apartment and condominium buildings: a single tap port for each building, at a level sufficient to provide standard (or perhaps somewhat lower) DTL to each dwelling unit after splitting in a common junction box located at the building. Commercial buildings, including hotels, motels, and hospitals, usually require special designs, and are frequently fed with dedicated feeder lines. If an MDU building is constructed after the distribution system is constructed, it's sometimes possible to cut in a dedicated hot tap. But in many cases, the designer must re-design the feeder line to accommodate the additional load. IN-LINE AMPLIFICATIONIn the above example, we worked our way upstream to tap P1, where we discovered that the required signal is +46.4 dBmv — almost 0.5 volt. What happens if we want to continue upstream? We can't continue this same feeder-design process indefinitely. If we tried that, we'd quickly find ourselves dealing in signal levels measured in volts if not kilovolts. In an actual broadband network, we insert amplifiers into the line periodically to amplify the signal. Next month, we'll tackle amplifiers. —————— (1) "Broadband Networks" Part 3. SBE Chapter 24 Newsletter, June, 1996, p. 5. SBE SHORT CIRCUITSBy John L. Poray, CAE, SBE Executive Director SBE NAMES FELLOW, ANNOUNCES ANNUAL AWARD WINNERSThe Society of Broadcast Engineers (SBE) has announced winners of its annual awards program, and has named one member a Fellow of the Society. The Board of Directors elected Martin "Sandy" Sandberg, CPBE a Fellow of the Society. To be elected a Fellow, an individual must have rendered conspicuous service to SBE or have made valuable contributions to the advancement of broadcast engineering. Sandberg becomes only the 48th recipient of the Fellowship honor in the 33 year history of SBE. Leonard J. Charles, CSTE, has been named Broadcast Engineer of the Year by the Society. Charles is a Television Engineer at WISC-TV in Madison, Wisconsin. SBE recognizes one broadcast engineer each year for outstanding contributions to the industry and the Society. Michael P. Scott, CPBE, has been named Educator of the Year by SBE. Scott is the Lead Instructor at the Communications Technologies Department of Bates Technical College (BTC) in Tacoma, Washington. Winners of the following awards were also announced: • Best Regional Convention or Conference, 18th Annual Electronic Media Expo '95 and Conference, Seattle, Washington, Chapter 16 • Best SBE Chapter Newsletter, Chapter 24, Madison, Wisconsin; Editor: Mark Croom. • Best SBE Chapter Frequency Coordination Effort, Chapter 26, Chicago, Illinois; Frequency Coordinator: Ken Steininger. • Best Article, Paper or Program by a Student Member, "The Magic of March" by James Stellpflug and Vicki Way of Madison, Wisconsin . • Best Technical Article or Program, "Geostationary Orbits" by Neal McLain of Madison, Wisconsin. • Most Certified SBE Chapter, recognizing the chapter with the greatest percentage of members holding SBE Certification, Chapter 56, Tulsa, Oklahoma; Chapter Chairman: Troy Cook. • Highest Member Attendance at SBE Chapter Meetings, recognizing the chapter with the highest average percentage of members in attendance at chapter meetings, Chapter 29, Corpus Christi, Texas; Chapter Chairman: Anita Easter. • SBE Chapter with the Greatest Growth in New Members, Chapter 87, Holdrege, Nebraska; Chapter Chairman: Verne Killion. Awards will be presented during the SBE Engineering Conference and World Media Expo in Los Angeles, October 12. 40+ SPEAKERS, 300 EXHIBITORS FEATURED AT SBE ENGINEERING CONFERENCE & WORLD MEDIA EXPOThe Society of Broadcast Engineers will present its annual national SBE Engineering Conference & World Media Expo, October 9-12, 1996 at the Los Angeles Convention Center. More than 40 technical papers and workshops will be presented during the SBE Conference and over 300 exhibitors will display their products in two exhibit halls. If you still need to register, you can get everything you need from the SBE National Office by calling (317) 253-1640, or by downloading the forms from the SBE Home Page - http://www.sbe.org, or by calling the SBE Fax-On-Demand Line at (301) 216-1853. Discount registration rates are available through October 4. Housing reservations can be made through Rogal America by calling (800) 722-0508, or by completing the housing form and faxing or mailing it to Rogal. SBE's headquarter hotel is the Universal City Hilton & Towers, in Universal City. Many other hotels are also available in various price ranges. Convention shuttle busses connect the hotels with the Convention Center. Updated detailed program information is also available on the SBE Home Page. SBE Full Conference attendees will receive passes to one session of each of the other conferences that run concurrently with the SBE Conference. They include the NAB Radio Show, RTNDA International Conference and the SMPTE Conference. MEMBERSHIP DIRECTORY MAILED IN OCTOBERSBE's annual Membership Directory and Buyer's Guide will be mailed to all members in late October. The Directory will include an alphabetical listing of all members, as well as a listing of members by state and chapter. Sustaining members will also be listed in a handy "yellow pages" style classified section. You'll also find information about SBE services and how to use them. Your copy is free with your membership. Extra copies are available to members only, at $35 each. SIGHT & SOUND EXPO SEPTEMBER 12-13SBE will participate in the second Sight & Sound Expo, to be held in Columbus, Ohio, September 12-13, at the Greater Columbus Convention Center. Sight & Sound Expo is a regional event, attracting broadcast engineers as well as people working in various production fields, from the Great Lakes States area. SBE is presenting six seminars during the Expo, including sessions on Digital Audio for Video, Television Facilities Design and Digital Interconnectivity. To register for the Expo, call Sight & Sound Expo at (614) 895-1355 for a registration form. SBE members receive a discount on registration. TOWER SURVEY BEING CONDUCTEDThe American Society of Civil Engineers is conducting a survey regarding performance of freestanding and guyed telecommunications towers and monopoles. The survey will be used as part of a study to further the safety and functionality of towers world wide. SBE members are encouraged to participate in the survey. To participate in the survey, contact James S. Cohen, P.E., at (609) 730-0510. CHAPTER 24 SUSTAINING MEMBERS
Recent Renewals:Broadcast Communications Thanks to all our Sustaining Members:CCA Electronics |
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