Contents for this Newsletter|
About this Newsletter
Upcoming Meeting Schedule
April Chapter Elections
UW Platteville Symposium
Telecom Industry News
Broadband Networks Part 9
Amateur Radio News
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ABOUT THIS NEWSLETTER
The Chapter 24 Newsletter is published monthly by Chapter 24 of the Society of Broadcast Engineers; Madison, Wisconsin.
Original hard copy edited by Mike Norton on Pagemaker 5.0.
Submissions of interest to the broadcast technical community are welcome.
You can make your submissions by e-mail to: Mike_Norton@went.pbs.org
Information and/or articles are also accepted by US Mail. Please address them to:
SBE Chapter 24 Newsletter Editor
46 Trillium Court
Madison, WI 53719-2308
Please submit text file on DOS or Windows 3.5" floppy diskette if possible.
Leonard Charles is the editor for the Electronic Version of this Newsletter uploaded monthly onto SBE Chapter 24's web page.
Thanks to Chris Cain for his work on the Chapter 24 WWW page and electronic newsletter.
Contributors this month:
© 1997 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.
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Tuesday, March 18th, 1997
This month's program will be an in-depth look at Shockley Communications new uplink truck, and you'll hear about some of their recent experiences.
Dutch Treat Dinner and Business Meeting starts at 5:30pm at:
642 S. Whitney Way
Program begins at 7:00pm at:
5727 Tokay Boulevard
Visitors and guests are welcome at all of our SBE meetings!
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Tentative Program Subjects
Wed, Apr 16, 1997
Elections and NAB Review
Thu, May 22, 1997
Tue, Jun 17, 1997
Facility Tour - TBA
Sat, Jul 26, 1997
Annual Family Picnic
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MARCH BUSINESS MEETING MINUTES
Submitted by Submitted by Neal McLain, Secretary
Chapter 24 of the Society of Broadcast Engineers met on Tuesday, March 18, 1997, at J.T. Whitneys, in Madison. There were 18 persons in attendance,
including 17 members (14 certified) and one guest. The meeting was chaired by Chapter 24 Chairman Paul Stoffel.
Call to order: 7:00 pm. The minutes of the February meeting were approved, as published in the March Newsletter.
Treasurers Report (reported by Stan Scharch): the chapter balance is in the black.
Newsletter Editors Report (reported by Mike Norton): The deadline for the April Newsletter is midnight 4/4/97; the folding party is 5:30 pm 4/9/97 at
Membership Report (reported by Paul Stoffel): Chapter 24 now has 78 members, and mailed 127 newsletters last month.
Sustaining Membership Report (reported by Fred Sperry):Maney Logic has renewed its sustaining membership; the Chapter now has a total of 22 sustaining
Program Committee (reported by Denise Maney): The April meeting will be held April 16, 1997 at J. T. Whitneys. Annual elections will be held, and the
program will consist of reports by members who attended the NAB convention.
Certification and Education (reported by Jim Hermanson): (1) two new certification classifications have been created: Certified Engineer/Video (CEV) and
Certified Engineer/Audio (CEA). (2) The next local examinations will take place June 13-23; application deadline is April 25.
Elections Committee Report (reported by Jim Hermanson): Elections of chapter officers for 1997-98 will be held at the April meeting. Nomination deadline
is April 5. Nominations can be submitted to any member of the Elections Committee: Jim Hermanson (836-8340), Herb Jordan (271-4763) or Steve Paugh
Frequency Coordination Report (reported by Tom Smith): No activity.
National Liaison Report (reported by Leonard Charles): (1) Membership renewals are due April 1. (2) Nominations for Annual Awards are now open. (3)
SBE will host several events at the NAB Convention. (4) Registrations are now open for the Engineering Management Course. (5) Certification preparation
guides are now available. (6) The EAS Committee is preparing an FCC filing requesting two changes in the EAS rules.
Old business: none.
New business: none.
The business meeting was adjourned at 7:20 pm. The program featured a tour of Shockley Communications new satellite uplink truck.
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Welcome new member Richard Taugher from Madison, chief engineer at WHA-TV, Wisconsin Public Television.
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ITS ELECTION TIME!
By Jim Hermanson,
Chapter 24 Nominations Chair
Its April and time for our annual Chapter 24 elections. The newly elected officers will carry the torch in the year ahead and continue the fine leadership of
our award-winning chapter.
The Nominations Committee has accepted nominations, contacted potential candidates, and prepared a ballot. This, however, is not to mean that
nominations are closed. If you wish to run for an office or nominate someone, please indicate so on the ballot in the appropriate space reserved for write-in
Voting will take place at the April 16th chapter meeting. If you are unable to attend the April meeting, you may vote with the absentee ballot that is enclosed
in this months newsletter. Absentee ballots must be received at the address indicated on the ballot by 5:00 p.m. Tuesday, April 22. Nominations and
elections will officially end when the absentee ballots are due.
Only current members of Chapter 24 in good standing are eligible to vote. Each eligible member may vote only once. SBE member numbers must be
included on all ballots, for membership verification only. Voters names will not be identified. We will use a numbers only list for verifications.
After the votes are counted, the nominations committee will communicate the results to the candidates and to the current officers. Results will also be
published in the May newsletter.
Thanks to Herb Jordan and Steve Paugh for serving on this years nominations committee! Dont forget to vote! Good luck to all candidates!
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Compiled by Tom Smith
WIBA-AM (1310 khz), WIBA-FM (101.5 mhz), WTSO-AM (1070 khz), WZEE-FM (104.1 mhz), All Madison, WI; WMLI-FM (96.3 mhz) Sauk City, WI; WMAD-FM (92.1 mhz) Sun Prairie, WI. - Point Acquisition Company, Inc., a division of Capstar Partners, Inc of Austin, Texas seeks FCC approval to purchase the group of 6 Madison area radio stations from Madison Radio group (a partnership of Point Communications [Richard Verne, Pres.] and Midcontinent Broadcasting). Capstar Partners, Inc. is a subsidiary of the investment firm of Hicks, Muse, Tate, and Furst, Inc. (Thomas Hicks, Chairman). Hicks, Muse, Tate, and Furst, Inc. also own GulfStar Communications and the newly Merged Chancellor/ Evergreen/ Viacom Group. When Hicks, Muse, Tate, and Furst, Inc. receive final FCC approval of their current radio station purchases, they will own 267 stations. There will be 127 stations in the Capstar group, 41 stations in the GulfStar group and 103 stations in the Chancellor/ Evergreen/ Viacom group. This will be the largest radio group in terms of number of stations and the second largest in revenue earned. The highest revenue earning group is Westinghouse-CBS/ Infinity.
WHIT-AM ( 1550 khz ), Madison, WI; WWQM-FM ( 106.3 mhz ), Middleton, WI - MidWest Family Broadcast Group, Oshkosh, WI (William R. Walker, Pres.) seeks FCC approval to purchase WHIT/WWQM from Enterprise Media Partners (Edward Rogoff, Pres.), Toledo, OH for $6.4 million. Enterprise paid $5.62 million in 1994 for the 2 stations. MidWest owns 37 stations in Wisconsin, Illinois, Michigan and Missouri. In Madison, MidWest owns WTDY-AM, WMGN-FM and WJJO-FM Watertown/Madison.
Mt. Horeb, WI - First Congregational Services proposes that the FCC allocate FM channel 294A (106.7 mhz) to Mt. Horeb. There is a site restriction for the transmitter location of 6 miles west of Mt. Horeb. Comments are due on this allocation on March 10th and replies due on March 25th. First Congregational Services is also proposing a new allocation for Two Rivers, WI. Released January 17, 1997.
Freeport, ILL - Highland Broadcasting Company proposes that the FCC allocate FM channel 295A ( 106.9 mhz ) to Freeport, ILL. There is a transmitter site restriction of 3.4 miles north of Freeport to avoid short spacing with WSJY-FM, Fort Atkinson and WSWT-FM, Peoria, ILL., both operate at 107.3 mhz. Comments are due April 7th and replies are due April 22nd. Released February 14, 1997.
Cuba City, WI - The FCC has returned the application of American Family Association for a non-commercial FM on 88.7 mhz. Released January 29, 1997
(Compiled from BROADCASTING & CABLE and the FEDERAL REGISTER)
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EMERGENCY ALERT SYSTEM FIRSTHAND
By Paul Stoffel
From Tom Weeden:
For you TFT owners (if any), there apparently is a lack of documentation on what auto-forward means if you happen to be a TV station which uses a
third-party software program to control your character generator. The third party, Broadcast Software Solutions (BSS) did not seem to mention that you
have to set the TFT to AUTO forward to the external computer, EVEN IF YOU WANT TO MANUALLY FORWARD EAS MESSAGES. The BSS
computer has a list of events that you can auto forward, manually forward, or wait-until-the-commercial-break-is-over-and-the-tally-contacts-open auto
forward. Everything on the BSS box is set to manual except the EAN/EAT.
After the February test didnt work right, I noticed that the RMT was set on the TFT to manually forward. That was then set to AUTO. I found that I also
have to program in all counties in our coverage area to auto-forward to the external computer, plus 055000 for all of Wisconsin and 999000 for the test
area just to be safe.
From Paul Stoffel:
Using Endec ROM, beta version 5.79, I experimented with HOLD and HOLD OVERNIGHT for the relaying of a Required Monthly Test. In the menu
item, Override Use, the operator can choose HOLD, where the message will hold, but go out as soon as a status has changed. This is also called the
commercial tally feature. Or the operator can choose HOLD OVERNIGHT, where the message is held, and goes out as soon as a status has changed ,
but after a fixed 15-minute countdown. The held message can be manually sent within that 15-minute window. This gives the day stations 15 minutes to
power up their transmitters.
If your Endec is in MODE = AUTO, you must have the INCOMING RMT filter set to have ACTION = TIME RELAY, instead of AUTOMATIC
RELAY. And, the INCOMING RMT filter set to HOLD TIME = 1, so that when an RMT is received during on-air hours, the RMT would go out after
one minute, or in other words, as close to automatic relay as possible. (Zero can not be entered as a HOLD TIME.)
If your Endec is MODE = TIMED RELAY or MANUAL, your INCOMING RMT filter is most likely already set to ACTION = TIME RELAY and
HOLD TIME = 15.
Anytime an incoming filter that has ACTION = AUTO, then HOLD or HOLD OVERNIGHT does not hold a message.
An incoming EAN will abort or cancel the held RMT. A new feature (MENU.ALERT.VIEW ALERT LOG) allows the logging of old alerts, with display,
print and send options. So, I could send the old RMT, but without the stored audio, since it was most likely was erased with the newer EAN audio. A
TORnado Warning with a priority of 61 will cancel a held RMT that has a priority of 60.
From Leonard Charles:
There are a couple of EAS update files on the EAS page of the SBE web site. One is a listing of suggestions received by the EAS Committee toward
changes in the system. The other is that latest in EAS and NOAA Weather Radio compatibility. Check it out at www.sbe.org(.)
TFT says they will release version .79(.) If TFT owners call their customer service department and give them your Serial Number and address, they will
send you the new eproms. Call 800-347-3383.
There are some new pages that have been put up on http://www.sbe.org that may be of interest to you:
Conferences and Conventions
Chapter Meeting Information
SBE Company Store
Special Items of Interest
The new 1997 FCC Self Inspection Checklist for AM/FM/TV is now available in browser printable text or WP 6 data format at: http://www.fcc.gov/cib(.)
Chapter 24 members and South Wisconsin Broadcasters are invited to share your EAS comments and experiences on the Chapter 24 listserver:
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Compiled by Tom Smith
EXTENSION OF COMMENT PERIOD
MM Docket Nos. 94-150, 92-51, 87-154, 91-221, 87-8, 96-222, and 96-197; DA-97-210
Broadcast Service; TV Ownership; Newspaper/Radio Cross Ownership
The FCC has extended the deadline for reply comments for the 4 inquiries concerning broadcast ownership rules from March 7, 1997 to March 21, 1997. This order was adopted and released on January 30, 1997 and published in the FEDERAL REGISTER on February 18, 1997 on pages 7203-7204.
MM Docket No. 96-90, FCC 97-17 Broadcast License Terms
The FCC has extended the license terms for all radio and TV stations and their auxiliary stations to 8 years. This action was required to make the rules for broadcast license terms conform to requirements enacted in the Telecommunications Act of 1996. These notice was adopted on January 23, 1997 and released on January 24, 1997. The rule became effective on March 5, 1997 and was published in the FEDERAL REGISTR on February 5, 1997 on pages 5339-5347.
ET Docket No. 96-35; FCC 97-1 Flexible Standards for Directional Microwave Antennas
This action amends the Rules on performance standards for directional microwave antennas. The FCC amended the rules to allow for the development of new antenna technology. These rules allow for licenses to show compliance with antenna standards using either minimum gain or maximum radiation beamwidth measurements. This will allow for narrow beamwidth, low gain antennas. These rules include broadcast auxiliary antennas used for microwave transmissions above 1,990 mhz. This rule became effective on March 5, 1997 and was adopted on January 2, 1997. The action was released on January 17, 1997 and published in the FEDERAL REGISTER on February 3, 1997 on pages 4920-4925.
(Compiled from the FEDERAL REGISTER)
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UW-PLATTEVILLE SYMPOSIUM PLANNED
The fifth annual UW-Platteville Symposium, titled "Convergence, Collision, or Chaos" will be held Wednesday, April 23 on the UW-Platteville campus. The luncheon keynote speaker will be Peter Dare from Sony. Look for a registration brochure in mid-March or call (608)342-1627 to be added to the mailing list.
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TERRESTRIAL DIGITAL TELEVISION
By Kevin Ruppert
Recently, I had the opportunity to attend some of the meetings of the Model HDTV Station Project Technical Committee, also known as Terrestrial Digital Television.
Many of the leaders of the industry, TV stations, networks and electronics manufacturers, gathered at The Shrine - the David Sarnoff Research Center. As you come into the visitors entrance of the Sarnoff Center in Princeton, N.J., you will see a portrait of the General David Sarnoff himself. This is the place from which many of the developments in consumer electronics have come from. It has a 1950's college campus atmosphere to it. The dedicated researchers here have been working with various manufacturers to solve many of the problems of broadcasting DTV.
There were many topics of discussion for the various working groups, such as possible scenarios for the start up of a digital television station. Just a few short weeks prior, the engineers and planners that are part of the committee were discussing the concept of pass through for the early DTV stations. This scenario consists of basically passing through the compressed digital bitstream from a network or other program provider without being able to do anything else with it.
At the meeting in early February, the hottest topic was a demonstration of switching of the compressed bitstream. Until now, there was no way to cleanly switch the compressed video bitstream. Interrupting the flow of the stream at a random point would create a huge disruption of the bitstream, causing the video at the receiver to break up for several seconds while the system relocked.
The people at Sarnoff introduced us to the concept of splicing the compressed bitstream. Splicing is switching from one source to another so that the output stream appears to have a scene cut. Right now with NTSC, we do this in the vertical interval. That way, a frame of video is not interrupted right in the middle.
Because of the predictive coding, uneven timing of frames, and the buffer overflow and underflow of MPEG streams, the task of splicing video becomes much more difficult than before. A lot of things have to be looked at for the gear to decide where to put that splice.
In conjunction with the people at Sarnoff, Phillips has created a Play to Air switcher that is capable of creating the clean splicing of the compressed bitstream that TV stations will need in order to insert commercials and ID's into the network digital video bitstream. Because of the need to look ahead and decide where the splice can go, the switcher has an inherent delay, similar to the pre-roll that broadcasters have become used to.
At this point, the system is limited to cuts only. Effects as simple as dissolves are not yet possible. Supers or split screens of any type are also not possible. The Committee realized right away that this is a limitation that will not set well with our station managers or promo directors! (Think about it, NO BUG! Right now it's back to the CAD board!)
Another unexpected challenge for the Sarnoff people was simply uplinking the DTV signal. In order to demonstrate carriage of the signal over a satellite link, the researchers at Sarnoff used a conventional uplink/downlink path that had been on the grounds for several years. Because it fits in a regular 6 MHz channel, this should be possible in theory. The researchers, however, found unexpected transmission problems that created occasional crashes of the system. Researchers believe that small glitches in the uplink,that are basically imperceptible with NTSC, cause bursts of errors that severely challenge the DTV correction systems.
Our next visit took us to the headquarters of the Zenith Electronics Corporation in Glenview, Ill. Gary Sgrignoli has been involved with the Model HDTV Station Project for some time now, having also been involved with the field tests performed in Charlotte, N.C.
After a brief tutorial on the 8VSB system, Gary gave a demo of Zenith's Adaptive Equalizer, which should improve the performance of DTV in high multipath environments (including indoor reception via rabbit ears!).
Remember that DTV will use many of the taboo channels, including the adjacent channels. Every piece of real estate will probably be full, at least during the DTV/NTSC simulcast period. An RF mask has been created for DTV transmissions to minimize DTV to NTSC interference for adjacent channels.
Despite having done a lot of field testing over the last couple of years in Charlotte, there are still many unanswered questions right now. For instance, we know very little about how well DTV will actually perform in an urban environment. The test bed for Charlotte was a large truck. The only standard DTV receivers that presently exist are contained in a couple of large equipment racks and need to be driven around in a truck. They cannot easily be brought up to the upper floors of an apartment building in Manhattan.
The Transmission Committee is trying to decide how future field tests should be performed. Can urban settings be successfully used for the tests? How much testing of indoor antennas is needed? What is the effect of aluminum siding on the DTV signal?
There are still many questions to be answered. How much time can be spent answering these questions is another important matter. With Dish TV, DVD and other media entering the consumer's home, will consumers forget about terrestrial TV all together? Stay tuned!
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TELECOM INDUSTRY NEWS
By Neal McLain,
COMPUSERVE INTRODUCES ALPHANUMERIC SCREENNAMES
As the above byline attests, CompuServe has finally introduced alphanumeric screennames and e-mail addresses. All current CompuServe subscribers have been invited to register for new screennames of their choice, on a first-come-first-served basis.
Screennames and e-mail addresses in the old all-numeric format (like firstname.lastname@example.org) will remain valid.
TDS TO ACQUIRE WISCONSIN CELLULAR ONE PROPERTIES
TDS Telecom, through its subsidiary United States Cellular Corporation (USCC), has agreed to acquire several Wisconsin cellular properties presently owned by BellSouth Corporation. In exchange, BellSouth will acquire several USCC properties. Both companies will end up with properties closer to home: TDS (based in Chicago) will take over properties in Illinois and Wisconsin, while BellSouth (Atlanta) will acquire properties in Alabama, Louisiana, Mississippi, and Tennessee.
Under the terms of the agreement, USCC will acquire the Cellular One franchises in Appleton, Green Bay, Janesville, Kenosha, Madison, Milwaukee, Racine, and Sheboygan. Also included are three "rural service areas" in Wisconsin, and the Rockford, Illinois market. These markets represent a total population (or "pops," as potential customers are known in the cellular business) of over 4 million.
BellSouth operates these properties under the brand name Cellular One. TDS hasn't announced whether it will retain the Cellular One name, or operate them under the USCC brand name.
TDS Telecom's engineering office is located here in Madison. TDS owns several landline telephone companies in Wisconsin, including Mount Vernon Telephone (serving Mount Vernon and Verona) and Waunakee Telephone.
AREA CODES, CONTINUED
The area-code saga continues ...
In the Houston area, the split-vs.-overlay battle dragged so long that the original area code (713) simply ran out of central office codes. So Southwestern Bell had no choice: it started blindly assigning new numbers in area code 281, hoping that an overlay would be approved eventually. It wasn't. Perverse result: some customers with 281 numbers are now being forced to switch to 713. And some of them are even being forced to change numbers, in cases where central office codes were duplicated in both area codes,
Two overlay area codes go into effect in Maryland on May 1. After that date, the state will have four area codes in two geographic areas, and ten-digit dialing will be mandatory for all local calls. Bell Atlantic is now in the midst of a massive consumer-education program to introduce what they call a "Ten-Number-Numbersm." And, yes, they really are claiming that the phrase "ten-number-number" is a registered service mark.
In California, 213 is about to split again, creating one of North America's smallest area codes: a 3-mile diameter spot in downtown Los Angeles. Since it was introduced in 1953, 213 has already been split nine times (spawning 310, 562, 619, 626, 714, 760, 818, 909, and 949); the latest split creates yet another area code (323), shaped like a doughnut surrounding 213.
A deeply-divided Public Utilities Commission approved the split (as opposed to an overlay) on a 3-2 vote; as one observer noted, the PUC is "split over splits."
California isn't the champion splitter, however: in the Caribbean, United States Virgin Islands will get its own area code (340) effective June 1, 1997. This marks this last phase of a 19-way split: by the time the dust settles, every one of the 19 geopoliticial entities (U.S. territories, British colonies, and sovereign nations) which formerly shared 809 will have its own area code. The Dominican Republic will retain 809.
And finally, Nevada'a only area code (702) is about to split. Gambling interests in the Las Vegas area have requested assignment of 777, as in "LUCKY 7-7-7." As it happens, this combination has been reserved for some unspecified future service; however, the Nevada Public Service Commission, supported by one of Nevada's U.S. Senators, has requested a waiver. If the waiver is granted, 777 presumably will be assigned to Clark County and neighboring counties in southern Nevada.
Some contributors to TELECOM DIGEST have suggested that Las Vegas' new area code should be 666.
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Part 10 - Broadband Fiber Links
By Neal McLain
Editor's Note: The diagrams referred to in this article have not been reproduced for the electronic version. A complete hard copy of the article can be aquired by contacting the Chapter 24 hardcopy newsletter editor; Mike Norton.
This is the tenth in a series of articles about coaxial broadband networks. In this article, well discuss the use of fiber optics to get around the noise and distortion constraints of trunk cascades.
In previous articles, we have noted:
Trunk is optimized to carry signals over long distances, so its carefully designed to minimize both noise and distortion. In order to maintain a balance
between noise and distortion, trunk amplifiers operate at relatively low signal levels.
Feeder amplifiers (bridgers and line extenders) must operate at relatively high signal levels in order to provide the necessary tap level to drive the drops
feeding customer premises. Thus, their noise contributions are negligible, but their distortion contributions are significant. In the example we cited last month,
the distortion contribution of just one bridger amplifier equals the distortion contribution of an entire 32-amplifier trunk cascade.
If the distribution network is relatively small, and carries a limited number of signals, its possible to balance the noise contribution of the trunk against the
distortion contribution of the feeder to achieve an acceptable design.
However, as weve noted before, other factors also enter into the design: trunk cascade depth (number of cascaded amplifiers), channel loading (number of
carriers carried on the network), and amplifier characteristics (the inherent noise and distortion ratings of the individual amplifiers). Even using the best
amplifiers available today, the design weve discussed so far simply cannot be extended indefinitely to distribute a large number of signals over long cascades
without unacceptable noise and/or distortion performance.
If the project calls for distribution of a large number of signals over a large land area, it is therefore necessary to significantly lower the noise and distortion
contributions of the amplifiers in the distribution network. So the big question is: how do we do this?
BREAKING UP THE CASCADES
We do it by breaking the cascades into shorter pieces:
We shorten each feeder line to, at most, just one line extender. Many designers like to eliminate line extenders altogether, so that each feeder line contains
just one high-level amplifier: the bridger.
We shorten trunk cascades by breaking them up into shorter pieces. Figure 1 illustrates this concept in a simple case where the 32-amplifier cascade is
broken into three shorter cascades. Two of these cascades are fed from a single run of optical fiber originating at the headend. This idea can, of course, be
extrapolated: many designs limit trunk cascades to only two or three trunk amplifiers; in the extreme case, some designs reduce each cascade to just one
Of course, in an actual distribution network, things are more complicated than Figure 1. A trunk cascade covering an urbanized area would be split many
times to create a two-dimensional network (or even a three-dimensional network, if high-rise buildings are involved). In this case, the network is broken up
into dozens of small areas, each fed by a single optical fiber (Figure 2).
The resulting network is called a hybrid fiber-coaxial (HFC) distribution network. The topology is a combination of star and tree (or, as
Scientific-Atlantas Bob Luff calls it, star and bush).
FIBER TRANSMISSION SYSTEMS
Fiber transmission systems used in HFC networks are similar to other fiber systems in that similar components are utilized: an infrared light source, an optical
transmission medium, and an infrared light receptor. However, there are many crucial differences, discussed in the following sections.
The typical light source is a semiconductor laser packaged with circuitry to modulate the light output. The modulating signal is the entire RF broadband signal
received from the headend. This signal is amplitude modulated onto the laser to produced a monochromatic output light beam of varying intensity. The
linearity of the laser and the modulating circuitry is an important specification; nonlinearity in the laser introduces the same kinds of distortion which amplifiers
introduce: second order and third order. Obviously, if distortion levels are excessive, they negate the whole purpose of using a fiber link in the first place.
Theres a common misconception about amplitude-modulated fiber links: the assumption that the modulation circuitry generates optical sidebands, similar
to the modulation sidebands produced by an amplitude-modulated RF modulator. In fact, the incoming RF signal is carried solely by the varying intensity of
the amplitude-modulated infrared light; the wavelength (and hence, the frequency) of the light remains constant: a single monochromatic spectrum line.
This concept may be easier to understand by recalling that the modulating signal, even though it may consist of hundreds of individually-modulated RF
carriers, is still one electrical signal. This single electrical signal modulates the amplitude of the laser.
The wavelength of the laser output is a function of the internal design of the laser, and is determined at the time of manufacture.
The light source, including the modulating circuitry and all supporting circuitry, is typically packaged in a rack-mount cabinet.
OPTICAL TRANSMISSION MEDIUM
The optical transmission medium is, of course, the glass fiber.
Glass used in the manufacture of optical fiber has two minimum-attenuation points, at 1310 and 1550 nm (Figure 3). Between these two wavelengths,
attenuation rises slightly due to the presence of an impurity: the hydroxyl radical OH-. (1)
Most HFC fiber transmission systems operate at one of these two frequencies; consequently, lasers and light receptors are optimized to operate at these
frequencies. However, two or more wavelengths can be operated over the same fiber (a process known as wave division multiplexing, or WDM).
Dual-wavelength systems, operating at both 1310 and 1550 nm, have been in use for several years. In recent years, systems have been designed which
utilize three or more wavelengths. For example, Philips Broadband recently introduced a system operating on three wavelengths, 1310, 1552, and 1557 nm.
The fiber is typically packaged in a much larger cable to provide mechanical and weather protection.
The typical light receptor is a photodetector diode packaged with circuitry to demodulate the received light beam. A single integrated circuit receives the light
beam from the fiber, demodulates it, amplifies it, and outputs the broadband RF signal at 75 ohms characteristic impedance. After a stage or two of further
amplification, the signal is inserted into the coaxial portion of the network.
Again, the linearity of the photodetector and demodulation circuitry is crucial for proper operation.
The optical wavelength of the photodetector input is a function of the internal design; again, its determined at the time of manufacture.
The light receptor, along with the demodulating circuitry and all supporting circuitry, is typically packaged in a strand-mounted weatherproof housing, suitable
for outdoor installation on a utility pole or in a pedestal. Rack-mounted configurations also are available.
Even the best-designed optical fiber link produces some noise and distortion of its own. Actual specifications vary from manufacturer to manufacturer; on
average, however, the noise and distortion contributed by one fiber link approximately equals the noise and distortion contributed by three trunk amplifiers.
At this juncture, we should note that noise and distortion arent the only reasons for breaking up trunk cascades. Other reasons include reliability, hum
modulation, and frequency distortion. Well discuss these in a future article.
Next month, well discuss another method for breaking up long trunk cascades: AML microwave.
(1) Apparently, for all the R&D money that manufacturers have spent developing optical glass, they still cant keep water out of the manufacturing process.
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AMATEUR RADIO NEWS
By Tom Weeden, WJ9H
• In mid-January, ham-astronaut Jerry Linenger, KC5HBR, became the fourth American to occupy a position on the Russian space station Mir. On January 14, Linenger officially traded places with fellow ham-astronaut John Blaha, KC5TZQ, who had completed 118 days as a Mir crew member. Earth-bound hams can attempt contacts with the Mir crew on both FM voice and packet on the uplink frequency of 145.200 MHz and downlink of 145.800 MHz.
• Another space shuttle mission will also involve amateur radio. STS-83, scheduled to launch April 3, will carry three hams. Eighteen schools, including institutions in the People's Republic of China and on Okinawa, have been scheduled for radio contacts during the mission.
•The FCC has proposed revising its Part 5 Experimental Rules to permit longer license terms and to permit the use of the 2402-2450 MHz and 10.0-10.5 GHz bands for experimental services. These two bands would be shared with the amateur service. The experimental license is for students experimenting with radio technologies in colleges, universities, and elsewhere.
• The Solar Cycle 23 Project, carried out by the NOAA Space Environment Center with the support of the NASA Office of Space Science, predicts big things for the upcoming solar cycle. The panel predicts a solar cycle comparable to the last two 11-year cycles, but not as big as Cycle 19, which it called "the largest cycle on record" (peaking around 1959). Other predictions: Cycle 23 should peak in early 2000, annual average geomagnetic levels will be among the highest in the 128-year record, and the probability of severe geomagnetic storms "will be the greatest during an extended period lasting from 1999 through 2005." The failure of Telstar 401, thought to be due to solar activity, occurred near the solar cycle minimum.
(Excerpts from March 1997 "QST" Magazine)
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MARCH SBE SHORT CIRCUITS
By John L. Poray, CAE
GO GET A MEMBER DURING THE 1997 SBE MEMBERSHIP DRIVE!
SBE Membership Committee Chairman Robert Hess, CPBE has announced plans for the 1997 Annual Membership Drive. Like last year, anyone who recruits a member during the campaign will receive a $5 discount on his 1998 membership dues, up to $25.
And, for each new member recruited, you will earn an entry into a drawing to win this year's grand prize: a trip to the 25th Annual Central New York SBE Regional Convention and SBE National Meeting, September 26, 1997.
Other prizes will also be given away during the membership drive, such as broadcast engineering-related books from the SBE Bookstore and SBE signature items from the SBE Store.
Both portions of the membership drive begin March 1 and continue through May 31, 1997. To qualify for the drawing, new members must be Regular, Associate or Sustaining Member candidates. New Student memberships do not qualify for the drawing.
The new member must complete the membership application and return it with the proper dues payment to the SBE National Office, along with the SBE "One New Member" entry slip, indicating the sponsor. All entry slips and applications must be received at the National Office by May 31, 1997. Prize winners will be drawn on June 21, 1997. The Grand Prize winner will have the option of choosing a $500 cash prize instead of the trip.
SBE Meetings Set for NAB'97
Most of the locations have been confirmed for the SBE meetings that will be held during NAB'97. The spring meeting of the Board of Directors, open to all members, will be Sunday, April 6 from 8:00am to 12:00 noon. A Membership Meeting will be held on Tuesday, April 8, after sessions conclude at 5:15pm, in Rooms N111/N112 of the Las Vegas Convention Center.
Conference registration is not required to attend the Board Meeting, Membership Meeting or to take an exam. However, only Full Conference Registrants will have access to educational sessions and workshops.
TIME TO RENEW MEMBERSHIP
SBE Membership renewals have been mailed to all Regular, Associate and Student members. Be sure to return your renewal form with your payment by April 1. Regular and Associate dues remain at $55 for the sixth year while Student Dues are $15.
REGISTER NOW FOR ENGINEERING MANAGEMENT COURSE
Registration is now open for the Leader Skills Course for Broadcast Engineers, presented by SBE. The course will be conducted in Indianapolis, Indiana, June 9-13, 1997. Course instructor will be Richard D. Cupka, well-known management trainer who, for 28 years, had conducted similar courses for broadcast engineers in conjunction with NAB.
Designed to take technically adept people and instill in them sound supervisory and management skills, the Leader-Skills Seminar can also be viewed as a tremendous tool for personal growth and development, even for those without management or supervisory responsibility.
The course fee of $650 includes five days of instruction, materials, classroom refreshments and a certificate of completion. Transportation to and from the seminar site, housing accommodations and meals are additional. To have a registration form faxed or mailed to you, call the SBE National Office at(317) 253-1640.
STUDY GUIDES DISCONTINUED - PREPARATION GUIDES AVAILABLE LATE FEBRUARY
SBE has discontinued sales of the SBE Certification Study Guides. The software version of the "Study Guide" was last updated in 1993. Understanding that most people want a tool to help prepare them for the exam, the National Certification Committee is preparing a "paper" version "Preparation Guide" that will be used for the immediate future.
The guide will have 50 updated sample questions and include an answer key. It will allow you to get a feel for the flavor of a certification exam. The Preparation Guide will list reference books that may help you in preparing for the exams. The new guide will be convenient to use as a study tool in groups, such as your chapter. The cost of the Preparation Guide is $19 and can be ordered through the SBE National Office at (317) 253-1640.
Your National Certification Committee is working on a new software version of the Preparation Guide. We will keep you informed as to when it's available. Any questions can be directed to: David Carr, CPBE, Certification Chairman at(713)284-8741 or Linda Godby, Certification Director at (317)253-1640.
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CHAPTER 24 SUSTAINING MEMBERS
Thanks to all our Sustaining Members:
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