Return-Path: Received: by massis.lcs.mit.edu (8.7.4/NSCS-1.0S) id MAA18432; Sun, 30 Nov 1997 12:37:06 -0500 (EST) Date: Sun, 30 Nov 1997 12:37:06 -0500 (EST) From: editor@telecom-digest.org Message-Id: <199711301737.MAA18432@massis.lcs.mit.edu> To: ptownson Subject: TELECOM Digest V17 #335 TELECOM Digest Sun, 30 Nov 97 12:37:00 EST Volume 17 : Issue 335 Inside This Issue: Editor: Patrick A. Townson Re: Digital TV Towers (Greg Monti) Re: Digital TV Towers (Art Walker) Re: Digital TV Towers (Randy Hiser) Re: Digital TV Towers (James Bellaire) Re: Digital TV Towers (Chris Boone) Re: Digital TV Towers (Roy Smith) Re: Digital TV Towers (Ed Ellers) Re: Digital TV Towers (Neal McLain) Re: A Funny Thing Happened Calling 1-800-CALL-ATT (Steven R. Kleinedler) Re: A Funny Thing Happened Calling 1-800-CALL-ATT (Victor Aidis) TELECOM Digest is an electronic journal devoted mostly but not exclusively to telecommunications topics. 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Please make at least a single donation to cover the cost of processing your name to the mailing list. All opinions expressed herein are deemed to be those of the author. Any organizations listed are for identification purposes only and messages should not be considered any official expression by the organization. ---------------------------------------------------------------------- Date: Sun, 30 Nov 1997 00:07:47 GMT From: Greg Monti Subject: Re: Digital TV Towers On Mon, 24 Nov 1997 roy@mchip00.med.nyu.edu (Roy Smith) wrote: > The problem is that with the advent of digital TV, we are > going to see (if you can believe the aviation press) an explosion of > new TV transmission towers, and not only that, but taller ones. These > towers present a hazard to air safety, especially when built near > airports. All communications towers, whether for radio, TV, cellular, police, paging, or shortwave to Mars, and whether sending digital or analog transmissions must meet FAA filing regulations and restrictions for location, height, painting, lighting and other factors. As long as the FAA keeps the same rules for new towers as it has for existing ones, there will be no greater hazard to air navigation than there is now. All towers will appear on air navigation charts, which all pilots, of course, consult before determining their flight plans. However, an argument could be made that pilots "know" where all the local towers are because they've been at the same locations and heights for 40 or 50 years. Pilots have been lulled into believing that, if they follow their usual routes, everything will be safe. A new tower, especially a tall one of 1,000 or 2,000 feet, would break the lullaby of complacency. > What is do different about digital TV that requires the building of new > towers? I would think it would be fairly straight forward to just add > additional transmitter antennas to the same tower structures that exist > today for conventional TV transmission, with no net increase in the number > of towers ... Most broadcasters long ago discovered that towers are valuable not only for transmitting their own signal, but can be leased out as "vertical real estate" to transmit other people's signals, including those of competitors. Any broadcaster with a decent sized tower in a major or medium market already has it fully loaded with the number and weight of antennas it will support to maximize leasing revenue. It's not unusual for a TV station to have two or three additional TV stations, plus four or five FM stations, a microwave multipoint distribuition service (MMDS) "wireless cable" operator, a cellular or PCS carrier or two, plus the police and fire departments from two counties loaded onto his tower. The new digital TV standard will not be compatible with the existing analog NTSC standard we use today in the U.S. Therefore, there will need to be a long transition period to allow the analog TV sets of today to amortize. The date being talked about now is 2006, when the analog TV stations of today all go off the air and consumers are forced to buy the new digital sets in order to continue watching TV. By definition, this requires both the analog and digital versions of every TV station to be on the air simultaneously for up to eight years. Therefore additional towers are required -- if only to cover the eight-year transition period. Even if a TV station boots off all of the existing analog broadcasters that are leasing space on his tower (in order to make room for his own digital antenna), those analog broadcasters will *still* want to build their own new towers just to stay on the air. One thing's for sure: the number of broadcast towers won't be any fewer than it is today. I can't think of any reason why the new towers would be any taller (or any shorter) than they are today. Greg Monti Jersey City, New Jersey, USA gmonti@mindspring.com http://www.mindspring.com/~gmonti [TELECOM Digest Editor's Note: I have noticed that when any one of the stations sharing tower space needs to do repairs to the antenna that everyone on the tower has to go off the air. There is a large cluster of antennas on the roof of Sears Tower in Chicago; the other night at about midnight several (radio and television) stations all signed off the air saying repairs and adjustments would be done for a couple hours. I guess if the others stayed on the air there would be a hazard to the people on the tower doing repairs to the one station which needed it. PAT] ------------------------------ From: walker@cx60550-a.omhaw1.ne.home.com (Art Walker) Subject: Re: Digital TV Towers Date: 28 Nov 1997 06:27:37 GMT Organization: OneSource Technologies - Omaha, NE Reply-To: walker@phantom.onesourcetech.com On Tue, 25 Nov 1997 16:23:42 GMT, Henry Baker wrote: > One problem with 'digital' TV has nothing to do with 'digital': the > digital broadcasts are going out over UHF rather than VHF frequencies. > UHF doesn't have as good propagation characteristics as VHF, and hence > requires more towers and more power. Also, the licenses for the new > frequencies do not cover the same geographical territory as the old > frequencies, although the FCC has gone to some effort to try to make > sure that the number of viewers is approximately the same. Wouldn't it make a lot more sense to just require all television programming to go direct to cable or direct-broadcast satellite? Then we could free up a big chunk of spectrum for far more constructive purposes. Art Walker | Internet: Art.Walker@onesourcetech.com Network Analyst | Snail Mail: 5020 Leavenworth St. OneSource Technologies | Omaha, NE 68106 (402) 575-3400 F:(402) 575-2011 | [TELECOM Digest Editor's Note: Of course if most television programming was sent to a bit bucket somewhere, then we could free up a big chunk of the cable, to say nothing of freeing up our minds for more construc- tive purposes. :) PAT] ------------------------------ From: Randy Hiser Subject: Re: Digital TV Towers Date: Fri, 28 Nov 1997 23:06:42 +0300 Organization: Netcom Roy, I would have to agree with you. The premise here for higher and more dispersed towers across a set region is amiss. I currently manage an MMDS wireless system that covers a radius of 25 miles. Our trans- mission tower is well below 150ft. One reason, however, for increased tower height would be to overcome natural and man-made obstructions (buildings,etc.) specific to that region. Otherwise, the channel separation between those used within Digital TV and those for aviation is typically adequate to prohibit any interference from occuring. ------------------------------ Date: Fri, 28 Nov 1997 08:51:34 -0500 From: James Bellaire Subject: Re: Digital TV Towers In article , roy@mchip00.med.nyu. edu (Roy Smith) wrote: > There has been a lot of talk in the aviation mass media about > digital TV towers. The problem is that with the advent of digital TV, > we are going to see (if you can believe the aviation press) an > explosion of new TV transmission towers, and not only that, but taller > ones. > My question is why? What is do different about digital TV that > requires the building of new towers? I would think it would be fairly > straight forward to just add additional transmitter antennas to the > same tower structures that exist today for conventional TV transmiss- > ion, with no net increase in the number of towers (and thus, no net > increase in the air navigation hazard). Why would this not be the > case? One factor that has been mentioned in radio and TV trade papers is the size of the new antennas. There will also be a transition period where the station will broadcast in both forms and need two antennas. Towers can only hold so much weight. The addition of an extra antenna to an existing tower may not be possible, hence the new towers. Some stations will be able to support both a digital and an analog antenna on the same mast, but only if they get rid of a few of their rental customers. For that reason new towers will be needed for some of the FM radio and low power television who rent space from television tower owners. Tall FM towers will be yet another addition to the antenna farms. The shift to digital TV will affect more than just the broadcast industry, wireless providers also rent space from TV stations. Cellular (at least in this area) have been adding towers and lowering their antennas on existing towers. They should not be too affected by being kicked off of a TV tower. Paging companies will probably need to find another tower, either an existing FM tower, a new FM / digital TV tower, or their own new tower. BTW: One of my favorite towers is owned by WMRI Radio and is located just north of Marion, Indiana. It holds an 8-bay FM (50kw ERP) antenna plus two low power TV antennas, plus a cellular array and microwave links, plus several paging, ham radio, and civil defense antennas, as well as an FM translator antenna set. Not bad for a city of 20,000. James E. Bellaire (JEB6) bellaire@tk.com Telecom Indiana Webpage http://members.iquest.net/~bellaire/telecom/ * Note new server - old URL should still work * ------------------------------ From: Christopher W. Boone Subject: Re: Digital TV Towers Date: Sat, 29 Nov 1997 16:08:34 -0600 Organization: The Walt Disney Company / ABC Radio Networks Engineering, Dallas Reply-To: cboone@earthlink.net Tony Pelliccio wrote: >> My question is why? What is do different about digital TV that >> requires the building of new towers? I would think it would be fairly >> straight forward to just add additional transmitter antennas to the >> same tower structures that exist today for conventional TV transmiss- >> ion, with no net increase in the number of towers (and thus, no net >> increase in the air navigation hazard). Why would this not be the >> case? Old towers were NOT built for the added windload that DTV will require while TRYING to install a second or more antennas to the current tower. > Higher frequencies. They'll be line of sight, and in line of sight the > higher you go, the more folks receive your signal. But some conventional > TV towers are already in the 1000 and 2000 foot range. I doubt they'll > see anything higher than that. Nope ... that's not the case ... a lot of DTV stations will go to UHF but a lot are staying VHF as well (channels 7-13 will stay active). Those on VHF who go UHF will have power changes to compensate for LOS (Line of Sight at VHF is same as UHF; only the LOSS of the signal strength increases at higher freqs.) Henry Baker wrote: > One problem with 'digital' TV has nothing to do with 'digital': the > digital broadcasts are going out over UHF rather than VHF frequencies. > UHF doesn't have as good propagation characteristics as VHF, and hence > requires more towers and more power. Also, the licenses for the new > frequencies do not cover the same geographical territory as the old > frequencies, although the FCC has gone to some effort to try to make > sure that the number of viewers is approximately the same. Line of Sight VHF to UHF is no different; the RF horizon remains the same; only ERP (Effective Radiated Power) needs to be increased to compensate for LOSS of signal over the same path. HEIGHT has NOTHING to do with the HIGHER freqs (and SOME DTV stations will stay VHF!) Besides, lack of tower space for the added antenna weight (a TV TX antenna weighs as much as 5 TONS!) is the main reason for new towers. The stations must simulcast during the transition and a new tower for the DTV station is required unless their current tower can stand the added load (and most cannot; a lot of current towers are over 20 years old and NOT built for the additional weight.) Chris ------------------------------ Date: Sat, 29 Nov 1997 18:46:43 -0500 From: roy@mchip00.med.nyu.edu (Roy Smith) Subject: Re: Digital TV Towers Organization: New York University School of Medicine tonypo@ultranet.com (Tony Pelliccio) wrote: > some conventional TV towers are already in the 1000 and 2000 foot range. > I doubt they'll see anything higher than that. The reason the aviation people are up in arms is that 1000-2000 foot tall towers are plenty of hazard. Without going into the gory details, some types of approaches require a clear area with a 40:1 slope from the runway, i.e. a 2000 foot tall tower needs to be 40*2000 = 80,000 feet from the runway to allow instrument approaches to that runway. That means a 2000 foot tower could (with the right combination of other factors) shut down an airport as far as 15 miles away. ------------------------------ From: Ed Ellers Subject: Re: Digital TV Towers Date: Sat, 29 Nov 1997 19:22:28 -0500 Organization: EarthLink Network, Inc. Michael D. Sullivan (mds@access.digex.net) wrote: > The stations got new channels for their digital signals, mostly in > the UHF band. The move to higher frequencies and the use of digital > transmission both cut back on coverage; to keep coverage about the > same, stations must use higher power and/or higher antenna towers." Actually the 8-VSB transmission system needs *less* power at a given frequency than analog NTSC AM transmission. The only reason you'd need more power is if your transitional digital channel is much higher than your existing channel. I say "transitional" because, if and when NTSC telecasting ends in the 21st century, it's likely that many stations will be able to move their digital service to their older, lower channel. The FCC hasn't decided whether TV will remain on channels 2 through 46 or 7 through 51, but in either case many stations' original channels will be in this "core spectrum," and in many cases stations within that spectrum were deliberately given transitional channels outside it while others now outside that range have been given channels within it. Because of this some stations plan to operate only a medium-power digital transmitter during the transition period, just large enough to cover their community of license as required by the FCC, and then unload or scrap it when they move back to their old channel. There are some cases where this principle has been superseded to give a station a digital channel adjacent to their existing one; for example WBBM-TV, on channel 2 in Chicago, will have its digital service on channel 3 and may be able to use its existing antenna for the new service, but may be forced to move if the FCC decides to drop channels 2 through 6. (I'm betting that they won't -- the political stink would be fierce, not only from the major station groups but also some smaller-market stations that won't be able to match their present low-band coverage on UHF. Take a look at http://www.kyes.com for an example of the latter.) ------------------------------ Date: Sat, 29 Nov 1997 18:06:52 -0500 From: Neal McLain Subject: Re: Digital TV Towers In Volume 17 Issue 330, Roy Smith wrote: > There has been a lot of talk in the aviation mass media about > digital TV towers. The problem is that with the advent of > digital TV, we are going to see (if you can believe the > aviation press) an explosion of new TV transmission towers, > and not only that, but taller ones. These towers present a > hazard to air safety, especially when built near airports. > My question is why? What is do different about digital TV that > requires the building of new towers? I would think it would be > fairly straight forward to just add additional transmitter > antennas to the same tower structures that exist today for > conventional TV transmission, with no net increase in the > number of towers (and thus, no net increase in the air > navigation hazard). Why would this not be the case? Two reasons: REASON #1: Mechanical loading on the tower. During the so-called "transition" period, each broadcast station has the right to use two channels, one for its new DTV service and one for its current analog service. In most cases, that means it needs two antennas, one for each channel. A typical VHF broadcast antenna is maybe 100 feet long, two or three feet in diameter, and weighs several tons. UHF antennas are smaller (the higher the frequency, the shorter the wavelength; consequently, the shorter the antenna requirement). But even a UHF antenna adds a big load to a tower. The real problem is dynamic (wind) loading. Tower design codes require that the entire tower structure, including all antennas, withstand various combinations of ice and wind; in northern states, a typical requirement is three inches of radial ice on all surfaces with a 100-mph wind. Most existing towers were originally designed to support one antenna, and cannot safely support the additional load of a second antenna. REASON #2: Pattern distortion. The "pattern" of an antenna is a graph of its signal strength plotted against distance from the antenna. The ideal pattern for an omnidirectional antenna is a circle with the antenna at the center. With careful design, it's possible to intentionally alter the pattern to direct the signal in specific directions; for example, antennas in Chicago are designed with a kidney-shaped pattern to force the signal north, south, and west, but not east (there aren't many viewers out in Lake Michigan). If a broadcast antenna is installed on the side of a tower, the tower itself distorts the pattern. If two or more antennas are installed side-by-side, each antenna distorts the pattern of the others. These types of pattern distortions aren't intentional: they can cause all sorts of undesired anomalies such as ghosts and no-signal gaps. Consequently, every broadcaster wants to have his antenna placed on the top of the tower, with no other antennas anywhere around. The usual result is that each station has its own tower. In many cities, the towers are grouped in the same general geographic area ("antenna farm"), but the individual towers are still several hundred feet apart to minimize pattern distortion. With the advent of DTV, the broadcaster faces a question: where does he put the new DTV antenna? Even if the existing tower can support the mechanical load of a second antenna, it's usually not possible to place it so that the two antennas don't distort each other's patterns. The obvious solution to both of these problems is to build a second tower, as many broadcasters are now attempting to do. But this leads to further problems: - FAA Approval. As Smith noted in his original posting, towers present a hazard to air safety, especially when built near airports. The FAA has an elaborate notification and approval procedure; in theory, if the FAA approves a new tower, it meets all FAA safety requirements and does not pose a hazard to aviation. But getting FAA approval for a new tower near a major city is difficult, and it's becoming more so as air traffic congestion increases. - Local Zoning Approval. Local zoning authorities typically oppose new towers on a variety of grounds including aesthetics, environmental concerns, and RF radiation hazard. - Land Acquisition. When the original analog-TV towers were built 30 or 40 years ago, they were usually placed in rural areas. By now, many of these towers are surrounded by urban sprawl, and land prices have soared. So new antenna farms must be found, often many miles from the original ones. This, of course, exacerbates the FAA and zoning approval problems. One way to alleviate these problems is to construct "community towers". A community tower is single large tower designed from the outset to support multiple antennas. Even broadcasters who compete ferociously for viewers sometimes jointly own community towers. Non-broadcast entities, such as paging, cellular, and PCS companies, also can participate. There are compelling reasons for this: a community tower for all antennas requires less land than multiple towers. The FAA generally encourages community towers as an alternative to multiple single-use towers, especially if it means getting rid of some existing towers. Even local zoning authorities can accept a new community tower on the promise that existing towers will be removed. So how do you put several television broadcast antennas on one tower if everybody wants to be on the top of the tower? One way is vertical stacking: placing one antenna on top of another in a sort of totem pole. Another way is to place the antennas side-by-side, but spaced far enough apart that pattern distortion is negligible. A horizontal spacing of 100 feet is generally accepted as sufficient. By combining these two approaches, it's possible to put a dozen or so antennas on one tower. The end result looks something like this: | | | | | | | | | | | | | | | | If there are only two antenna stacks, a horizontal support, perhaps 100 to 150 feet long, supports the stacks (for obvious reasons, this is called a "T-top" design). If more antennas are required, a triangular platform can be used ("candelabra" design). Of course, community towers aren't new: residents of San Francisco will recognize this design: | | | | | | | | \ / \ / / \ / \ But the advent of DTV has made this whole issue far more complicated because every television broadcast station is now going to have to find a place for a second antenna. In view of all the problems associated with constructing a second tower for each broadcaster, we're likely to see more community towers in the future. Neal McLain nmclain@compuserve.com ------------------------------ From: srkleine@midway.uchicago.edu (steven r kleinedler) Subject: Re: A Funny Thing Happened Calling 1-800-CALL-ATT Organization: The University of Chicago Date: Sat, 29 Nov 1997 19:39:50 GMT In article , Robb Topolski wrote: > Calling from the local baby-bell (GTE) owned coin phone in Hillsboro, > OR, I was answering a page when I realized I didn't have any coinage > to feed it. So I dial 1-800-CALL-ATT except it didn't "feel right." > Suspecting that I probably misdialed, I waited to hear what would come > up on the line. A close-but-no-cigar female recording came on the > line asking for my destination phone number. I hung up. I had > apparently dialed 1-800-228-8288 (1-800-CATT-ATT) instead of > 1-800-225-5288 (1-800-CALL-ATT). It's an easy misdial. Beware. Apparently whoever owned 1-800-OPERATOR stopped using it because so many people can't spell and a competitor snagged 1-800-OPERATER. If this is an urban legend, please forgive me. Actually, now that I think about it, I probably first heard it here several months ago. Steve Kleinedler ------------------------------ From: Victor Aidis Subject: Re: A Funny Thing Happened Calling 1-800-CALL-ATT Date: Fri, 28 Nov 1997 08:30:07 -0500 Organization: Erol's Internet Services An easier mistake to make is to dial 1-800-ATT-CALL, which used to connect you to MCI (1-800-COLLECT). I tried it this morning and it now connects you with LDDS/Worldcom, with automated prompts for credit card, calling card, and operator-assisted calls. ------------------------------ End of TELECOM Digest V17 #335 ******************************