SBE 24 September 1997 Newsletter


Contents for this Newsletter

About this Newsletter
Meeting Announcement
Upcoming Meeting Schedule
Upcoming Chapter 24 Events
SBE Files EAS Petition
National Elections Results
Certification and Education
Meeting Minutes
Membership Report
Local Legals
FCC Rulemakings
Amateur Radio News
Tech Tip
FCC to Consider Tower Pre-Emption
Peck to Relocate
Forfeitures are Back
Broadband Networks (Part 14)
SBE Short Circuits
Sustaining Members

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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:

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:
Leonard Charles
Neal McLain
Dan Maney
Tom Smith
Fred Sperry
Paul Stoffel
and Tom Weeden

© 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, September 23, 1997

Practical Choices for the DTV Transition / Guest Night
Rocky Rococo's
7952 Tree Lane
(Mineral Point Road at the Beltline)
Dinner at 5:30pm
Meeting and Program at 7:00pm

This month's program will feature a presentation on choices for the upcoming DTV transition. Jeff Conway from Tektronix will present information from an equipment vendor's perspective.

The Chapter is going to provide pizza and soda beginning at 5:30PM for guests that attend the meeting (Members will be asked to contribute $5.00 if partaking of the pizza and soda provided).

Visitors and guests are welcome at all of our SBE meetings!

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Tentative Program Subjects

Wednesday 10/22/97
Broadcast Clinic

Tuesday 11/18/97
Tour of Electronic Theater Controls

Wednesday 12/17/97
Lunch Meeting (Program TBA)

Thursday 1/22/98
Radio Station Automation

Tuesday 2/17/98
Test and Measurement Equipment

Wednesday 3/18/98
ATM Technology or Related Topic

Thursday 4/16/98
Elections and NAB Review

Tuesday 5/19/98
Telephone Company Tour

Wednesday 6/17/98
Sullivan NOAA Weather Office Tour

If you have any suggestions for program topics you'd like to see, please contact one of the Chapter 24 Program Committee Members.

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By Fred Sperry

There are a couple of upcoming Chapter 24 events I would like to bring to your attention.

As part of our September meeting on Tuesday the 23rd, the Chapter is sponsoring "guest night." This meeting is going to be held at Rocky Rococo's 7952 Tree Lane (Mineral Point at the Beltline). The Chapter is going to provide pizza and soda beginning at 5:30 PM for guests that attend the meeting (Members will be asked to contribute $5.00 if partaking of the pizza and soda provided). Please spread the word around your workplace and encourage those coworkers who may have an interest in the SBE to attend this event. Please contact me if you would like to have a flyer announcing this event to post at your workplace.

The Chapter's October meeting will take place on Wednesday October 22nd as part of the Broadcast Clinic being held this year at the Holiday Inn West. As has been the case the past several years, SBE Chapter 24 and the Midwest Region of the SBE are programming the Wednesday evening portion of the Clinic. We have lined up David Felland, Director of Engineering for Milwaukee Public Television and the ECB in Madison, to speak on the subject of planning for digital television (DTV) at WMVS/WMVT. Following David's presentation there will be a panel discussion that will address what stations are doing to plan for the transition to DTV. We are looking for participants to be on this panel. Please contact me at (608)264-9806 or via e-mail at if you or anyone you know is heavily involved in DTV planning and would be interested in being part of this panel. The success of this panel discussion depends upon finding participants for this portion of the program.

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By Leonard Charles, EAS Committee Chairman

The SBE EAS Committee has filed a formal Petition with the FCC for EAS Rules changes and additions. This filing follows an information gathering process from the SBE membership at large which began back in January of this year when the system officially went on line. The Committee used problem case scenarios submitted by Chapters and members across the country to write rules revision suggestions designed to make the EAS system work more reliably and consistently for all.

The submitted petition is published on the SBE Home Page at under the EAS Committee banner. The Committee asks members to review the suggested changes. Then, when the FCC releases the petition for comment, SBE members and Chapters are urged to file comments in support or in addition to those submitted by the Committee. The Committee feels that the greater the number of comments filed, the better the chance at improving system performance and use.

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The results of the SBE National Elections were tabulated Thursday, August 28, by volunteers from Chapter 25 in Indianapolis. Our thanks to Chapter Chairman, Stephen Lampen and the eight other members who provided this service.


Elected to Serve One One-Year Term:

President - Ed Miller, CPBE Cleveland, OH

Vice President - Troy Pennington, CSRE Birmingham, AL

Secretary - Thomas Weber, CPBE Indianapolis, IN

Treasurer - James "Andy" Butler, CPBE Alexandria, VA

Elected to the Board of Directors (top six vote-getters)
Elected to Serve One Two-Year Term

Richard Edwards, CPBE* Fort Lauderdale, FL

Dane Ericksen, PE, CSRTE San Francisco, CA

Ralph Hogan, CPBE Boise, ID

Keith Kintner, CSTE Los Angeles, CA

Chriss Scherer, CBRE Overland Park, KS

Larry Wilkins, CPBE* Montgomery, AL

*denotes incumbent

Congratulation to these members and our thanks go to them, and all those who ran for elected office. Also, to the 1,000 members who participated in this years' election. The new Officers and Board will be installed at the SBE Annual Meeting, Friday, September 26 in Syracuse at the SBE National Meeting.

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By Jim Hermanson

The remaining 1997 certification exam date is November 14 - 24.

Local chapters application deadline is September 26th. Operator exams may be given at other times by coordinating through the local chapter certification chair and national SBE office.

Recertification forms are available from the SBE national office. The chapter certification/ education chair also has a few.

Thanks to Tim Trendt at UW-Platteville for assisting with Chapter 24 certification administration. Contact Jim Hermanson for further information.

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Submitted by Neal McLain, Secretary

Chapter 24 of the Society of Broadcast Engineers met on Wednesday, August 27, 1997, at T. J. Whitney's, in Madison, Wisconsin. There were 17 persons in attendance, including 14 members (13 certified), one certified non-member, and two guests. The meeting was chaired by Chapter 24 Chairman Fred Sperry and called to order at 7:02 pm.

The minutes of the July meeting were approved, as published in the June Newsletter.

Treasurer's Report (reported by Stan Scharch): the chapter balance is in the black.

Newsletter Editor's Report (reported Newsletter Editor Mike Norton): The deadline for the September Newsletter is midnight 9/5/97; the folding party is 5:30 pm, 9/10/97 at WKOW-TV.

Sustaining Membership Report (reported by Sperry): Recent renewals include BCS Wireless (formerly Broadcast Communications Services) and Skyline Communications. The Chapter now has 24 sustaining members.

Program Committee (reported by Steve Zimmerman): Plans for the September program were announced.

Certification and Education (reported by Sperry in Jim Hermanson's absence):

Frequency Coordination Report (reported by Tom Smith): "Getting organized for the football season." Tom also reported on several pending FCC issues which will affect the future availability of broadcast auxiliary frequencies.

National News (reported by Sperry): The chapter, and its members, have received four awards. They will be presented at an SBE Regional Conference in Syracuse, New York on September 26, 1997.

National Liaison Report (reported by Leonard Charles).

Old Business: none.

New Business: Tom Smith reported on: (1) recent FCC actions concerning tower siting; (2) pending changes to the Frequency Coordination database.

Announcements (reported by Sperry in Jim Hermanson's absence): The annual Broadcasters Clinic is scheduled for October 21-23, 1997. Copies of the agenda were distributed.

The business meeting was adjourned at 7:25 pm. The program featured a presentation about Video Servers and Automation Technology presented by David Scally of Odetics Broadcast and Jon Gedymin of Hewlett-Packard.

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By Paul Stoffel

The National SBE's membership information for Chapter 24 states: 68 members, 39 certified. Becoming a member of the Society of Broadcast Engineers is easy: either connect to <> or telephone Paul Stoffel, 263-2175, Chapter 24 membership Chair.

The National's webpage is full of information about the Society and how you can join. If you prefer, Paul has printed material on SBE Membership and Program of Certification. Currently, Chapter 24 mails monthly 135 newsletter to its members, sustaining members, and station managers.

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Compiled by Tom Smith


New FM Station, Cuba City, WI. 89.7 mhz

Positive Programming Foundation of Dallas, Texas (R. Barton Irby, President) has applied to construct a new non-commercial FM on 89.7. The proposed station would operate with 9.9 kw with an antenna at 122 meters. The transmitter is to be located 5.4 mi east of Cuba City at intersection with Oak Road on Hwy O. Announced August 14.


New FM Station, Mount Horeb, WI. 106.7 mhz

The FCC has allocated FM channel 294A (106.7 mhz) to Mount Horeb in response to a petition from First Congregational Services. There is a site restriction of 6 miles west of Mount Horeb which is at the coordinates of 42-59-22 and 89-51-12.

Shopper Stopper Ltd. has filed a counter proposal to substitute channel 294A for channel 257A at Dodgeville, WI. and allocate channel 257A (99.3 mhz) at Mazomanie. The FCC denied this proposal.

This allocation becomes effective on September 29, 1997. The filing window will open on September 29, 1997 and ends on October 30, 1997. This notice was adopted on August 6, 1997 and released on August 15, 1997. Published in the FEDERAL REGISTER on August 21, 1997 on page 44,416


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Compiled by Tom Smith


FCC 97-218 Forfeiture Proceedings

The FCC has Amended the rules concerning forfeitures for violations of FCC rules. The FCC made many of the fine amounts equal for violations that are similar between services such as tower lights. The maximum fine levels were also increased by 10%. The FCC will still adjust fine levels from the base rates according to the ability to pay and circumstances of the violation. Some of the base fines are listed in the notice.

These rules become effective on October 15, 1997. These rules were adopted on June 19, 1997 and released on July 28, 1997. The notice was published in the FEDERAL REGISTER on August 14, 1997 on pages 43,474-43,477.


MM Docket No. 97-187 Preemption of State and Local Zoning and Land Use Restrictions on the Siting, Placement and Construction of Broadcast Station Transmission Facilities.

The FCC has issued a notice of proposed rulemaking to consider if and when it should preempt local and state zoning and land use ordinances. This notice was prompted by the FCC's desire for rapid implementation of DTV service. Because zoning and land use reviews can last for several months and appeals can go on for years, the FCC has received petitions from various broadcast associations for relief.

They have proposed that the FCC set time limits in which local zoning boards must act, restrict local laws concerning environmental and health effects and radio interference due to RF emissions to Federal standards.

Comments are due October 30, 1997 and replies are due on December 1, 1997. This notice was adopted on August 18, 1997. This notice is available on the FCC web site as FCC97296 in both text and Adobe formats.

Wireless Docket No. 97-192, ET Docket No. 93-63, Cellular Telecommunications Industry Association Petition for Rulemaking RM-8577

Procedures for the Reviewing Requests for Relief from State and Local Regulation, Pursuant to Section 332(c)(7)(B)(v) of the Communications Act of 1934.

Guide Line for Evaluating Environmental Effects of Radio Frequency Radiation.

Petition for Rulemaking of the Cellular Telecommunications Industry Association Concerning the Amendment of the Commission Rules to Preempt State and Local Regulation of Commercial Mobile Radio Service Transmitting Facilities

The FCC is seeking comment on its rules concerning RF exposure limits and preemption of local regulation. This is a large notice and covers many issues concerning RF exposure.

A few of the proposals include extending the deadline for the compliance of the existing guidelines to September 1, 2000 and increase of thresholds of responsibility of licenses from multiple transmitter sites from one to five percent. Another proposal would allow ham operators to increase blanket power limits from 50 to 500 watts on the 160, 80 and 40 meter bands. limits on the VHF bands remains at 50 watts.

Comments are due on October 9, 1997 and replies are due on October 24, 1997. Full text is available on the FCC web site as FCC 97303.

Compiled from the FEDERAL REGISTER (, the FCC web site ( and Doug Lung's RF CURRENT (

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By Tom Weeden, WJ9H

Scanner enthusiasts and receiver equipment manufacturers are concerned about a bill introduced in Congress, the Wireless Privacy Enhancement Act of 1997. HR 2369, if passed, would amend the Communications Act of 1934 to ban the sale of scanning receivers capable of receiving transmissions on frequencies allocated to the Commercial Mobile Radio Service (CMRS). CMRS is an umbrella designation of subscriber-based radio services that act like telephone services. The bill appears to also affect amateur radio transceivers that can receive signals outside of the ham bands. An incident in which House Speaker Newt Gingrich's cellular telephone conversation was illegally intercepted, taped and published prompted calls in Congress for stronger anti-eavesdropping legislation.

Milwaukee hams may be affected by a new tower ordinance which puts strict requirements on new towers in the city. The law, apparently inspired by the proliferation of cellular and PCS towers, is uniform and makes no exceptions for hobby or public service towers. To erect a tower over 40 feet in height, an applicant would have to pay a $300 fee and submit to a public hearing. Milwaukee hams may challenge the ordinance in Federal Court, as the law apparently fails to meet the requirements of "PRB-1," the FCC's "Federal Doctrine of Pre-Emption" over local control of amateur radio towers.

The wide-area 146.88 MHz Baraboo WI repeater that went off the air in the WOLX tower collapse of December 31st is now back on the air in its permanent location. After WOLX's new tower was completed, the Central Wisconsin Repeater Association was allowed to install a new antenna and 7/8" feedline. As of August 21st the repeater was up and running at the 500 foot level, along with remote receive sites linked in from Madison's east side and on Vilas Hall on the UW campus.

(Excerpts from September 1997 "Badger State Smoke Signals" and "The ARRL Letter")

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By Dan Maney

The following problem with differential outputs (such as RS-422) has repeated itself, so I thought I would share the experience with other techs.

In the first case, an open connection on one of two comlpimentary outputs of a differential line driver worked fine into PVW series Betacam VTR's but never controlled the BVW series. In the second case, an A-42 still store's computer board worked fine in a known good system, but never worked in the perfectly good system it came from. Again it was a half dead (half alive?) differential line driver chip. Here's what's happening. The RECEIVERS simply compare both complimentary levels and report which is more positive. Receivers like at least 200mv differential voltage in order to report the signal reliably.

If the dead half rests at nearly the same voltage as the plus or minus excursion of the good half, it just might work perfectly. Another perfectly good receiver might never work with this bad output. To complicate troubleshooting, the termination resistor across the receiver inputs causes the good signal to appear back at the dead output. If you aren't watching polarity (dual trace scope?) this can trick you (me).

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Excerpted September from SBE Chapter 28 "Broadcast Newsletter"

The FCC has invited comments on whether and under what circumstances it should pre-empt state and local ordinances that might slow station efforts to erect new transmitting antennas.

Many broadcasters have reported they will have a hard time meeting the DTV timetables if they become involved in local hearing on zoning clearances for new tower facilities. The Commission invited comments on a proposal by NAB and the Association for Maximum Service Television (MSTV) to cap the amount of time local authorities have to act on requests to

modify or move transmission facilities; it would require state and local regulators to act within 21 days on such broadcaster requests. The SBE has generally supported such a proposal in order to facilitate DTV implementation.

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By John L. Poray, Executive Director

Steve Peck, with Philips BTS, has relocated to Denver, Colorado. Steve was offered the chance to be District Manager for Philips, a sales position covering the mountain states of Colorado, Utah, Arizona and New Mexico. Steve's wife, Sue, and daughter, Jamie, are with him in Colorado. His oldest son Brian is a Junior at UW Madison and other son Rob a Freshman at Concordia University in Milwaukee.

Steve moved to Madison in 1979 and worked as an engineer at WHA-TV until 1986. He worked for two different dealers until joining Philips five years ago. During the last year, Steve was in a camera marketing position, which required extensive travel including two trips to Brazil last year.

Steve was a Chapter 24 member and a sustaining member. He will surely be missed. You can reach him via E-mail at: or by phone, 303-471-2155.

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From Wireless Spectrum Resources, Inc. Info Update, 8/97 and SBE Chapter 28 Sebtember "Broadcast Newsletter"

After years of issuing fines on a case-by-case basis, the FCC in 1991 adopted a forfeiture policy to be used as a basis for determining fines. But in 1994 the US Appeals Court vacated that policy, and the Commission returned to the case-by-case basis.

In 1995 the Commission issued a Notice of Proposed Rulemaking seeking to reinstate the former policy. As a result of the comments and reply

comments generated by that NPRM, the FCC adopted its new forfeiture policy as of June 19, 1997.

Here are some of the amounts applicable to broadcast operators:

• Construction/Operation without authorization: $10,000;

• Tower Marking (Painting, Lighting) Violations: $10,000;

• Public File Violations: $10,000;

• EAS Equipment not installed or operational: $8,000;

• Failure to permit inspection: $7,000;

• Exceeding power limits: $4,000;

• Using unauthorized frequency: $4,000;

• Transmitter control/metering violations $3,000;

• Failure to make required measurements/conduct required monitoring $2,000;

• Failure to file required forms $3,000;

• Failure to provide station ID $1,000;

• Failure to maintain required records $1,000;

• Failure to maintain directional pattern within parameters $7,000;

• AM tower fencing violations $7,000.

In addition to the prescribed fines, they can be adjusted upward or downward depending upon other criteria, such as intentional violation, substantial harm, good faith or voluntary disclosure, or inability to pay.

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PART 14 - Bandwidth Allocation

By Neal McLain,

This is Part 14 in a series of articles about coaxial broadband networks. In this article, we begin a discussion of the bandwidth allocation scheme used in broadband networks.


The original broadband networks were cable television systems designed to carry NTSC television signals in 6-MHz channels; thus, the 6-MHz channel became the basic unit for dividing up the bandwidth of a broadband network. This unit is still in use today, even for non-video signals.

The standard channel-numbering plan in use in the United States today is listed in Figure 1. Note that, in most cases, the bandwidth is 6 MHz.

Figure 1. United States Cable Television Channel Numbering Plan.
54-602 55.25255.25
60-663 61.25361.25
66-724 67.25467.25

This chart specifies the cable television channel-numbering scheme currently used in the United States. Column headings are:

• BAND - The band of frequencies, in MHz.

• CABLE CHANNEL - The channel number assigned by the FCC.

• LETTER DESIG - The channel designation commonly used in the 60's and 70's.

• CABLE CARRIER FREQUENCY - The nominal frequency, in MHz, of the visual carrier of an NTSC television signal operating in this cable channel.

• AIR CHANNEL - The broadcast television channel, or other service using this band for over-the-air transmissions.

• BROADCAST CARRIER FREQUENCY - The nominal frequency, in MHz, of the visual carrier of a television broadcast transmitter operating in this air channel.

Codes used in the AIR CHANNEL column are:

• 2, 3, 4, ... - Broadcast television channel number assigned by the FCC.

• FM BAND - FM radio broadcast band, 88-108 MHz.

• FAA - Non-broadcast spectrum assigned to the Federal Aviation Administration.

• NON-BCAST - Non-broadcast spectrum assigned to any service other than the FAA.

Source: EIA Interim Standard IS-132: Cable Television Channel Identification Plan. Electronic Industries Association, Washington, DC, 1994. This standard is incorporated by reference into the FCC Rules at 47 CFR 76.605(a)(2).


Note that the broadcast spectrum is divided into three bands. These bands are spaced so that the second harmonic of any visual carrier never falls in any other channel, thus assuring that no television transmitter can interfere with another television signal.

Cable television systems carrying only 12 channels (2-13) utilize the same frequency assignments as the broadcast spectrum. This band-spacing scheme assures that second-order distortion products generated by the trunk amplifiers fall outside the bands of interest.

In short, the same band-spacing technique that the FCC devised to protect television stations from mutual interference also protects cable signals from second-order distortion products.


Figure 1 specifies two channel-numbering systems:

• CABLE CHANNEL - The number assigned to this channel by the FCC. These assignments are specified in EIA Interim Standard IS-132, and are incorporated by reference in the FCC's cable television rules.

• LETTER DESIGNATION - The channel designation commonly used in the 60s and 70s. These designations had evolved over the years in a rather haphazard fashion, with no official FCC sanction. In the late 70s, when converter manufacturers began making converters with digital channel-number displays, letter designations were replaced with numeric designations beginning with 14.

The carrier frequencies specified in these figures are nominal, and do not account for FCC-mandated offsets. We will cover offsets in a future article.


So why are cable channel and band designations so mixed up? Why aren't they assigned sequentially?

The short answer to this question is historical: the order in which channel numbers were assigned approximately corresponds to the chronological order in which they were first used by the cable television industry.

A more detailed answer follows.


The earliest cable television systems were constructed in the 50s. They were capable of carrying just one or two channels in the VHF low band.

In those days, even using the low band presented a major challenge because of the high signal attenuation of the available coaxial cables. Modern low-loss cables didn't exist, so amplifiers were required every few hundred feet. The amplifiers themselves (typically single-ended vacuum-tube devices) exhibited high cross-modulation distortion levels, severely limiting channel capacity.

Further complicating the situation was the poor selectivity of the television sets of the day, making the use of adjacent channels impossible. Even the most advanced systems could carry only three channels: 2, 4, and either 5 or 6.

In one respect, however, this limited channel capacity was a blessing: all second-order (and most third-order) distortion products fell outside the band of interest. Thus, cross-modulation was the limiting form of distortion.

Carrying Channels 7-13 was out of the question because of the substantially higher cable loss at the VHF high band.


Making the jump to the VHF high band was an even bigger challenge: the visual carrier frequency at Channel 7 (175.25 MHz) is over twice the frequency of the Channel 6 carrier (83.25 MHz). Hence, cable loss was higher, so more amplifiers were required; this led to higher distortion levels. And, of course, the increased channel loading itself also led to higher distortion levels.

The first attempts to carry the high band incorporated an ingenious trick for getting around these problems: Channels 7-13 were carried in the so-called "subband" below Channel 2 (Figure 3). Channels in this band were designated T7 through T13. "Upconverters" installed at various points in the distribution network converted the T-channels back to their proper positions. In some systems, upconverters were installed outdoors, each serving a relatively small area, such as a city block. In other systems, an upconverter was installed at each subscriber's home.

Figure 3. Subband Channel Assignments.
T75.75 - 11.757.00
T811.75 - 17.7513.00
T917.75 - 23.7519.00
T1023.75 - 29.7525.00
T1129.75 -35.7531.00
T1235.75 -41.7537.00
T1341.75 -47.7543.00

These channels were originally used to carry Channels 7-13 in the unused bandwidth below Channel 2. Although they are no longer used for this purpose today, these original channel assignments are still in use.


This system allowed cable operators to carry as many as seven channels: 2, 4, 5 (or 6), 7, 9, 11, and 13. But they still couldn't carry adjacent channels because of the poor selectivity of the subscribers' receivers.

But even this restriction had its bright side: second-order distortion products never fell in occupied channels. The four new visual carriers (at 7, 19, 31, and 43 MHz) produce five second-order products at 26, 38, 50, 62, and 74 MHz. These products all fall in unused channels (T10, T12, 3) or unused guard bands.

Ingenious though it was, this system didn't work very well. The old vacuum-tube upconverters weren't stable, and they must have been very expensive to operate.

The T-channel distribution scheme didn't last long. But its legacy lives on to this day: the T-channel numbering scheme is still used to identify channels in the subband. Although these channels are no longer used for subscriber distribution, they are frequently used for closed-circuit applications such as distribution of instructional programming to schools or to carry locally-originated signals back to the headend.


By the mid-60s, distribution equipment was improving dramatically. Cable manufacturers had introduced low-loss cables with solid aluminum sheaths — the same types of cable still in use today. Amplifier manufacturers had designed new products utilizing transistors in push-pull circuits, greatly improving distortion performance. These improvements made it possible for cable operators to carry Channels 7-13 at their proper frequencies.

TV receiver manufacturers were improving their products as well. The introduction of varactor tuners and solid-state IF strips made it possible to utilize adjacent channels. By the late 60s, virtually all new cable television systems were capable of carrying all 12 VHF channels.

A typical amplifier of the day was Jerrold's "Starline" series. This product utilized a strand-mounted housing with plug-in solid-state modules. Besides greatly-improved performance, this arrangement simplified field maintenance: a defective module could be replaced quickly. The original cable systems constructed in Madison (Complete Channel TV) and Fitchburg (Fitchburg Cable Communications) utilized Starline equipment.

As always, distortion control remained a significant design constraint. Fortunately, even on a fully-loaded 12-channel cable system, all second-order distortion products fall outside the bands of interest: either below Channel 2, above Channel 13, or in the unused space between Channels 6 and 7. This fortunate situation is, of course, a direct result of the FCC's original channel allocation plan for VHF broadcasting.


By the mid-70s, the cable television industry was growing rapidly. Program suppliers, eager to cash in on this new market, began creating programming services for distribution via satellite. HBO was the first to make the leap to satellite; two others quickly followed: Ted Turner's Atlanta TV station WTCG (now WTBS), and Pat Robertson's Christian Broadcasting Network (now The Family Channel). By the end of the 70s, dozens of programming services were available by satellite.

With all these new services available, it wasn't long before cable systems were filled to capacity and needed more channels. The obvious place to find space for new channels was in the unused "midband" between the FM Band and Channel 7.

Theoretically, there's enough space in this band for eleven 6-MHz television channels:

(174-108)/6 = 11

However, only nine channels were assigned; the two channels in the 108-120 MHz band were skipped. The reason: as you will note in Figure 1, this band is assigned to the FAA for a service called VHF Omnidirectional Range, or VOR. VOR transmitters serve as location beacons, enabling aircraft pilots to navigate from one VOR station to the next by following VOR "radials." It doesn't take much imagination to dream up all sorts of nightmare scenarios which might result if leakage from a cable system caused interference to a VOR transmitter.

The nine remaining midband channels (120-174 MHz) were adopted as cable television channels, raising the total channel capacity to 21. These channels were originally designated A through I; however, with the advent of settop converters and cable-ready TV sets equipped with digital channel-number displays, they were redesignated 14 through 22.

Using the midband imposed a whole new set of constraints on amplifier design. As always, adding more carriers resulted in higher distortion levels. But an even greater problem was second-order distortion: designers could no longer ignore it on the assumption that it would fall outside the bands of interest. Indeed, in a fully-loaded 21-channel cable system, hundreds of second-order distortion products are generated, and many of them fall in active channels. In short, second-order distortion replaced cross-modulation as the dominant form of distortion.

Amplifier manufacturers adopted many techniques to control second-order distortion:

• Pair-matching: hand-selected matched pairs of transistors operating in push-pull circuits.

• Power doubling: four matched transistors in a push-pull parallel configuration.

• Feedforward: a circuit in which a separate transistor circuit is used to amplify the distortion. This distortion signal is then inverted and used to cancel the distortion added by the main amplifier.

And, as we've noted in previous articles, second-order distortion forced a reduction in the number of amplifiers which could be connected in cascade. A maximum of 20 amplifiers came to be accepted as the limit.


The insatiable demand for more channel capacity continued unabated, and 21-channel cable systems soon became obsolete. By the late 70s, the 216-300 MHz band was being used. This band contains 84 MHz, enough space for 14 channels.

These channels were originally designated J through W, and were later redesignated 23 through 36.

Of course, adding yet another 14 channels made distortion control even more difficult. As we noted in a previous article (November 1996) third-order distortion becomes significant as channel loading increases, and becomes dominant when the number of carriers exceeds 30 or so.

Some manufacturers tried to get around the distortion problem by using various frequency-control and frequency-offset techniques. We'll discuss these techniques in a future article.


Another 18 channels, in the 300-402 MHz band. These channels were originally designated AA through RR, and were later redesignated 37 through 54. Note that X, Y, and Z were never used.

At this point, the boundaries of the various "bands" became somewhat indefinite. Many authors identify this group of channels as part of the superband.

Some authors also include channels above 54 in this band, although there is no consensus on how far it extends. The EIA standard defines channel numbers all the way up to Channel 158, topping out at 1002 MHz, but makes no attempt to break the spectrum into bands.

A memory device for those who still like to use letter designations: Channel SS = Channel 55.


Remember those two channels in the 108-120 MHz band that were skipped when the midband was first used?

In the years since, the cable industry has been able to recover the use of these channels. Two developments made this possible:

• Improved technology allowed equipment manufacturers to build headend modulators capable of very precise frequency control, typically on the order of ±1 Khz.

• The FCC, working in cooperation with the FAA, established frequency-assignment rules for the cable industry. These rules specify cable frequency offsets so that the cable frequencies don't conflict with VOR frequencies. For example, a visual carrier nominally assigned to 109.25 MHz is actually offset +0.025 MHz, to 109.275 MHz, where it falls halfway between VOR frequencies at 109.25 and 109.30 MHz.

These two channels have had several designations. At the outset, they were called A-1 ("A minus one") and A-2 ("A minus two") because they fall just below Channel A.

For obvious reasons, converter and TV-set manufacturers didn't want to use such klunky channel numbers. But there was no accepted numeric identification plan at the time, so manufacturers pretty much did what they pleased:

• Some manufacturers called these channels 0 and 1 (or 00 and 01).

• Some manufacturers used the next two available numbers at the top of the band; however, what was considered the "top" of the band varied from manufacturer to manufacturer. This led to such designations as 54/55, 57/58, 60/61, and probably others.

When the EIA standard was drafted, these channels were officially designated 98 and 99.


Many cable systems use the FM band for FM audio services. TCI, for example, carries all Madison-area FM broadcast stations, plus WXJ-87 and stereo simulcasts of several video channels.

But some cable systems use the FM band for video services. There's enough space for three television channels, extending from 90 to 108 MHz.

These channels were originally called (in order of increasing frequency) A-5, A-4, and A-3. The EIA Standard identifies them as 95, 96, and 97.


In a standard NTSC television channel, the nominal frequency of the visual carrier is 1.25 MHz above the lower edge of the channel. However, many cable television channels are operated at frequencies slightly offset from nominal. There are two reasons for this:

One reason is aviation safety. As Figures 1 and 2 make clear, many conflicts exist between the cable television frequency spectrum and the frequency allocations used in the open airspace. Conflicts with FAA frequencies are particularly significant due to the FAA's role in aviation safety. In an effort to mitigate these conflicts, the FCC has imposed a number of frequency-offset requirements on the cable television industry.

A second reason is distortion control. As we noted earlier, some equipment manufacturers have tried to get around distortion problems by using various frequency-control and frequency-offset techniques.

Next month, we'll discuss offsets in detail.

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By John L. Poray, Executive Director


"At the Forefront of Technology" will be the theme at the Kentuckiana SBE Regional Convention in Louisville, Saturday, October 18. The Convention will feature three 90 minute Ennes Workshops.

The Kentuckiana SBE Regional Convention will be at the Holiday Inn-Hurstbourne. Cost of the Workshops is $29 for members of SBE, SMPTE and the Broadcast Section of IEEE. and $39 for others.


If you are planning to attend the Central New York SBE Regional Convention and SBE National Meeting September 26, you'll want to take in the SBE National Awards Dinner that night. Tickets are just $10, with the remaining cost picked up by our sponsor, Leitch, Inc. The program will include a presentation by our keynote speaker, Bernard Wise, President of Energy-Onix, comments from new SBE National President, Ed Miller, and the presentation of the SBE National Awards and Fellowship honor. You can order your ticket(s) with your Mastercard, Visa or American Express by calling or faxing the SBE National Office at (317)253-1640 (voice) or (317)253-0418 (fax). Tickets are limited and are available on a first come, first served basis.


The SBE National BBS ended service this past July, after the computer which houses the system went down. Because the BBS has received little use in the last year, it was determined that replacing the computer in order to continue BBS service would not be cost-effective. The SBE Web Site,, contains a wealth of information about SBE, including the full SBE Job Line text. Members are encouraged to use the Web Page as their 24 hour-a-day source for information about the Society.


The deadline for the November Certification Exam period in local chapters is September 26. Why not plan now to become SBE Certified and receive the recognition you have earned in your profession. Register today to take a SBE Certification Exam.

Exam dates for 1998 have been released. See the SBE website and determine when you would like to take an exam.

For more information about SBE Certification, see your Chapter Certification Chairman or contact Linda Godby-Emerick, Certification Director at the SBE National Office at (317) 253-1640.

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Welcome to our new sustaining member:


Thanks to all our Sustaining Members: Alpha Video
BCS Wireless
Clark Wire and Cable
Comark Communications
Fuji Film
Harris Corporation
Louth Automation
Niall Enterprises
Norlight Telecommunications
Panasonic Broadcast
Richardson Electronics
Roscor Wisconsin
Scharch Electronics
Skyline Communications
Sony Broadcast
Teleport Minnesota
Video Images

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