Michael A. Terrell wrote:> Martin Heffels wrote: >> On Tue, 04 Sep 2007 12:23:52 -0400, "Michael A. Terrell" >> <mike.terrell@earthlink.net> wrote: >> >>> Never worked at a TV transmitter site, have you? If they are >>> operating under the specified power, they are in violation of their >>> license, and no one is stupid enough to overbuy on the transmitter >>> requirements. >> Help me here..... Since when would this be a violation? A >> transmitter-license usually states the _maximum_ amount of power, so what >> is different here? Stories are plenty of radio and television-stations >> cutting down their power for power-saving reasons (money, money, money). > > > In the US a station has to notify the FCC if they are not operating > at the power they are licensed for. It has to be logged on a set > schedule and kept in the station's permanent files for the FCC field > inspectors. If a station is operating below the level they are licensed > for, they are not serving the area they agreed to provide service to. > VERY few stations were ever allowed to differ from their rated power. > The only two I ever saw were on military bases where the transmitter > power was listed, with "Or as deemed necessary". These were in remote > locations and major repairs were consider as 'Depot Level' repairs. > Reduced or increased power was allowed, to stay on the air, but none of > these were high power stations. The license was deemed a 'Courtesy > License' by the FCC, which meant that they had little authority over a > military transmitter, but the 'Courtesy License' was granted to make > sure the frequency coordinators didn't assign a civilian station an > allocation that would interfere. > > > If your power level is too high, you can cause problems for other > stations, and if it's too low, your advertisers will demand refunds. > > I was a broadcast engineer at one military and two civilian TV > stations over a 17 year period. I lost count of the AM radio stations I > did work for, or located parts and equipment to keep on the air.At least at one time, a station's backup transmitter could have lower power than it's main, and anything went if it was the only way to put a station on the air at all. Nobody liked it, but it was considered better than dead air. Jerry -- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Visual "clipping"?
Started by ●September 4, 2007
Reply by ●September 4, 20072007-09-04
Reply by ●September 4, 20072007-09-04
Richard Owlett wrote:> > Michael A. Terrell wrote: > >[snip] > > > > Never worked at a TV transmitter site, have you? If they are > > operating under the specified power, they are in violation of their > > license, ... > > *WHAT?* > Please quote a specific regulation that _prohibits_ operating at *LESS* > than authorized power. My commercial license (2nd class phone) may have > expired 40 years ago, but I never heard of such. We even had a backup > 1Kw transmitter for when our 50Kw transmitter went down. There were > occasions (ice storms) when we switched to backup BEFORE primary went > down as it was more tolerant of bad SWR. [now this was an FM rather than > TV but don not see difference for this case]That is an emergency situation, not normal operation. If any single emergency lasted more than three days, the FCC required notification. If a station is 'dark' more than a set number of days because of equipment failure, they can lose their operating license, and have to fight anyone else who wants that frequency allocation when they reapply for a operating license. They may also be required to repalce any oldder, adn all defective equipment that was grandfathered under the old operating license. All the FCC requlations are part of Title 47 CFR, so help yourself at the link below. There are months of reading involvled to wade through all of it. http://www.gpoaccess.gov/cfr/index.html -- Service to my country? Been there, Done that, and I've got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida
Reply by ●September 4, 20072007-09-04
Richard Crowley wrote:> "Gene E. Bloch" wrote ... >> However, the original remark was not about the *licensed* power, it was >> about the *rated* power. I.e., the electrical or electronic limits, not >> the legal limits. > > But as Mr. Terrell also observed, profit-making businesses don't > commonly waste money buying an over-powered transmitter. > They are frightfully expensive in any case.No engineer would design a 500 KW transmitter that would burn out 502. Can you imagine a bus coming to a bridge so tightly rated that the driver calls for three passengers to walk across after the bus makes the far side in order not to overload the bridge? If you wanted to design a bridge that would safely carry the unloaded bus but fail with the extra three passengers on board, could you? TV transmitters have substantial built-in safety factor. Jerry -- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Reply by ●September 4, 20072007-09-04
Michael A. Terrell wrote: ...> Its obvious that you've never built a TV station from the ground up. > Even a spare 10% transmitter power capacity could cost a couple hundred > thousand dollars in capital assets. and its unlikely the governing > agency will allow you to use equipment capable of excess power, any more > than you can build whatever tower height you want. It costs millions of > dollars to build a full power commercial TV station.You need to distinguish between rated capacity and transient overload capacity. My sewage plant is rated 20 million gallons a day. During periods of heavy rain (and therefore groundwater infiltration) it regularly processes 26 MGD without violating any discharge limits. After a few days, however, effluent quality suffers. Certain floors are required by code to carry 300 lb./sq.ft. If such a floor fails catastrophically at 350 lb./sq.ft., the designer could well lose his license. Jerry -- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Reply by ●September 4, 20072007-09-04
Tim Wescott wrote:> Gene E. Bloch wrote: >> On 9/04/2007, Michael A. Terrell posted this: >>> "Gene E. Bloch" wrote: >>>> >>>> On 9/04/2007, Michael A. Terrell posted this: >>>>> Martin Heffels wrote: >>>>>> >>>>>> On Tue, 04 Sep 2007 12:23:52 -0400, "Michael A. Terrell" >>>>>> <mike.terrell@earthlink.net> wrote: >>>>>> >>>>>>> Never worked at a TV transmitter site, have you? If they are >>>>>>> operating under the specified power, they are in violation of their >>>>>>> license, and no one is stupid enough to overbuy on the transmitter >>>>>>> requirements. >>>>>> >>>>>> Help me here..... Since when would this be a violation? A >>>>>> transmitter-license usually states the _maximum_ amount of power, >>>>>> so what >>>>>> is different here? Stories are plenty of radio and >>>>>> television-stations >>>>>> cutting down their power for power-saving reasons (money, money, >>>>>> money). >>>>> >>>>> >>>>> In the US a station has to notify the FCC if they are not operating >>>>> at the power they are licensed for. It has to be logged on a set >>>>> schedule and kept in the station's permanent files for the FCC field >>>>> inspectors. If a station is operating below the level they are >>>>> licensed >>>>> for, they are not serving the area they agreed to provide service to. >>>>> VERY few stations were ever allowed to differ from their rated power. >>>>> The only two I ever saw were on military bases where the transmitter >>>>> power was listed, with "Or as deemed necessary". These were in remote >>>>> locations and major repairs were consider as 'Depot Level' repairs. >>>>> Reduced or increased power was allowed, to stay on the air, but >>>>> none of >>>>> these were high power stations. The license was deemed a 'Courtesy >>>>> License' by the FCC, which meant that they had little authority over a >>>>> military transmitter, but the 'Courtesy License' was granted to make >>>>> sure the frequency coordinators didn't assign a civilian station an >>>>> allocation that would interfere. >>>>> >>>>> >>>>> If your power level is too high, you can cause problems for other >>>>> stations, and if it's too low, your advertisers will demand refunds. >>>>> >>>>> I was a broadcast engineer at one military and two civilian TV >>>>> stations over a 17 year period. I lost count of the AM radio >>>>> stations I >>>>> did work for, or located parts and equipment to keep on the air. >>>> >>>> However, the original remark was not about the *licensed* power, it was >>>> about the *rated* power. I.e., the electrical or electronic limits, not >>>> the legal limits. >>> >>> >>> Its obvious that you've never built a TV station from the ground >>> up. Even a spare 10% transmitter power capacity could cost a couple >>> hundred >>> thousand dollars in capital assets. and its unlikely the governing >>> agency will allow you to use equipment capable of excess power, any more >>> than you can build whatever tower height you want. It costs millions of >>> dollars to build a full power commercial TV station. >> >> Do you *really* think I've never built a TV station form the ground up? >> >> Really? >> >> Well, you're correct. It doesn't keep from speculating, however. >> >> For example, it *might* be true that it's a good idea to spend extra >> money to put in safety factors (although, to be fair, I *do* run my >> 100W lightbulbs at 100W). It could be cheaper in the long run than >> fixing the reasult of not doing so. >> >> The above has certinaly been true in civil construction for millennia. >> > Oh. So that's why small rural bridges never have weight limits posted > on them? > > Not. > > Any system has to be designed with some sort of limits in mind. If the > broadcasters want to make decisions about how much of a screen can be > black and for how long, it's their decision to make.Do we know that the final of a TV transmitter has the most dissipation when it's outputting the most power? IIRC -- it was 1957 when I last had to know -- those finals operate class B linear. Such amplifiers experience maximum dissipation at well below full output. J -- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Reply by ●September 4, 20072007-09-04
Jerry Avins wrote:> > Michael A. Terrell wrote: > > Martin Heffels wrote: > >> On Tue, 04 Sep 2007 12:23:52 -0400, "Michael A. Terrell" > >> <mike.terrell@earthlink.net> wrote: > >> > >>> Never worked at a TV transmitter site, have you? If they are > >>> operating under the specified power, they are in violation of their > >>> license, and no one is stupid enough to overbuy on the transmitter > >>> requirements. > >> Help me here..... Since when would this be a violation? A > >> transmitter-license usually states the _maximum_ amount of power, so what > >> is different here? Stories are plenty of radio and television-stations > >> cutting down their power for power-saving reasons (money, money, money). > > > > > > In the US a station has to notify the FCC if they are not operating > > at the power they are licensed for. It has to be logged on a set > > schedule and kept in the station's permanent files for the FCC field > > inspectors. If a station is operating below the level they are licensed > > for, they are not serving the area they agreed to provide service to. > > VERY few stations were ever allowed to differ from their rated power. > > The only two I ever saw were on military bases where the transmitter > > power was listed, with "Or as deemed necessary". These were in remote > > locations and major repairs were consider as 'Depot Level' repairs. > > Reduced or increased power was allowed, to stay on the air, but none of > > these were high power stations. The license was deemed a 'Courtesy > > License' by the FCC, which meant that they had little authority over a > > military transmitter, but the 'Courtesy License' was granted to make > > sure the frequency coordinators didn't assign a civilian station an > > allocation that would interfere. > > > > > > If your power level is too high, you can cause problems for other > > stations, and if it's too low, your advertisers will demand refunds. > > > > I was a broadcast engineer at one military and two civilian TV > > stations over a 17 year period. I lost count of the AM radio stations I > > did work for, or located parts and equipment to keep on the air. > > At least at one time, a station's backup transmitter could have lower > power than it's main, and anything went if it was the only way to put a > station on the air at all. Nobody liked it, but it was considered better > than dead air.Sure, but the backup was only intended for emergency operations. Some AM stations operated at reduced power at night, so the secondary transmitter shared both functions. BTW, have you ever seen the pictures of the WLW 500 KW 700 KHz transmitter in Cincinnati, Ohio? It also has one of the few remaining Blaw Knox diamond towers. http://hawkins.pair.com/wlw.shtml I saw that transmitter around 1970, along with the bethany Ohio Voice of America radio facility that was just down the road. The VOA station is gone, torn down and turned into yet another golf course. :( It had the original WWII Crosley transmitters when i toured it. The were being replaced by custom designed transmitters built by National. They would operate from the AM broadcast band, to 30 MHz, at any frequency in that range. All of the transmitters were 50 KW, and could be run singly, in pairs or whatever configuration they wanted. There was a huge, high gain curtain antenna strung between three towers that fired East-West to transmit to people behind the iron curtain. It would handle up to 500 kW from the ten transmitters one anything from one to ten frequencies at once. I wasn't allowed to take any pictures, because it was a US Government facility, and the military guards searched us for cameras before we were allowed through the gates. -- Service to my country? Been there, Done that, and I've got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida
Reply by ●September 4, 20072007-09-04
Reply by ●September 4, 20072007-09-04
On Tue, 04 Sep 2007 15:16:32 -0400, "Michael A. Terrell" <mike.terrell@earthlink.net> wrote:>"Gene E. Bloch" wrote: >> >> > On 9/04/2007, Michael A. Terrell posted this: >> > >> > Its obvious that you've never built a TV station from the ground up. >> > Even a spare 10% transmitter power capacity could cost a couple hundred >> > thousand dollars in capital assets. and its unlikely the governing >> > agency will allow you to use equipment capable of excess power, any more >> > than you can build whatever tower height you want. It costs millions of >> > dollars to build a full power commercial TV station. >> >> Do you *really* think I've never built a TV station from the ground up? >> >> Really? >> >> Well, you're correct. > > > I HAVE built a complete TV station, starting with an empty building >and no tower. > > >> It doesn't keep from speculating, however. > > > Speculate all you want, and let everyone see that you have absolutely >no grasp of the subject. > > >> For example, it *might* be true that it's a good idea to spend extra >> money to put in safety factors (although, to be fair, I *do* run my >> 100W lightbulbs at 100W). It could be cheaper in the long run than >> fixing the reasult of not doing so. > > > Do you know that a TV station's EIRP is transmitter power output, >multiplied by antenna gain?...less cable losses and backoff. Cable loss is pretty substantial in most broadcast applications. Nevertheless, transmitter headroom on broadcast amplifiers is pretty expensive, as has been mentioned. So even getting a dB or two of headroom can be not only a big NRE cost, but cost a lot of power consumption during operation. The "black picture" thing is a real concern in most NTSC transmitters, but it's pretty much just a typical engineering concern of limiting the amount of black-picture time to keep the thing from overheating or exceeding whatever spec is limited by that particular design. And I've never run across an NTSC transmitter, even a reasonably cheap one, that didn't have automatic protection circuits that would keep the PA safe even if conditions went wonky. i.e., it's tough to really damage one of those dude. Not to say that I haven't done it. ;) A low-power NTSC transmitter for which I used to be responsible went through a long string of PA tubes, all covered by the manufacturer, before we figured out what was wrong with it. Eric Jacobsen Minister of Algorithms Abineau Communications http://www.ericjacobsen.org
Reply by ●September 4, 20072007-09-04
On Tue, 04 Sep 2007 12:56:25 -0400, "Michael A. Terrell" <mike.terrell@earthlink.net> wrote:> In the US a station has to notify the FCC if they are not operating >at the power they are licensed for.True, but �73.1560 of the FCC regulations says: <quote> (c) TV stations. (1) Except as provided in paragraph (d) of this section, the visual output power of a TV or Class A TV transmitter, as determined by the procedures specified in Sec. 73.664, must be maintained as near as is practicable to the authorized transmitter output power and may not be less than 80% nor more than 110% of the authorized power. </quote> So they could run at 80% theroretically, with the excuse that receivers have improved, and people who live in the grade-B zones (or grade-Z ;-) ), will probably have satellite-receivers by now anyway. Saving them a lot of meny, and not actually violating the FCC-regulations. cheers -martin- -- Official website "Jonah's Quid" http://www.jonahsquids.co.uk
Reply by ●September 4, 20072007-09-04
Eric Jacobsen wrote:> > On Tue, 04 Sep 2007 15:16:32 -0400, "Michael A. Terrell" > <mike.terrell@earthlink.net> wrote: > > >"Gene E. Bloch" wrote: > >> > >> > On 9/04/2007, Michael A. Terrell posted this: > >> > > >> > Its obvious that you've never built a TV station from the ground up. > >> > Even a spare 10% transmitter power capacity could cost a couple hundred > >> > thousand dollars in capital assets. and its unlikely the governing > >> > agency will allow you to use equipment capable of excess power, any more > >> > than you can build whatever tower height you want. It costs millions of > >> > dollars to build a full power commercial TV station. > >> > >> Do you *really* think I've never built a TV station from the ground up? > >> > >> Really? > >> > >> Well, you're correct. > > > > > > I HAVE built a complete TV station, starting with an empty building > >and no tower. > > > > > >> It doesn't keep from speculating, however. > > > > > > Speculate all you want, and let everyone see that you have absolutely > >no grasp of the subject. > > > > > >> For example, it *might* be true that it's a good idea to spend extra > >> money to put in safety factors (although, to be fair, I *do* run my > >> 100W lightbulbs at 100W). It could be cheaper in the long run than > >> fixing the reasult of not doing so. > > > > > > Do you know that a TV station's EIRP is transmitter power output, > >multiplied by antenna gain? > > ...less cable losses and backoff. > > Cable loss is pretty substantial in most broadcast applications. > > Nevertheless, transmitter headroom on broadcast amplifiers is pretty > expensive, as has been mentioned. So even getting a dB or two of > headroom can be not only a big NRE cost, but cost a lot of power > consumption during operation. The "black picture" thing is a real > concern in most NTSC transmitters, but it's pretty much just a typical > engineering concern of limiting the amount of black-picture time to > keep the thing from overheating or exceeding whatever spec is limited > by that particular design. And I've never run across an NTSC > transmitter, even a reasonably cheap one, that didn't have automatic > protection circuits that would keep the PA safe even if conditions > went wonky. i.e., it's tough to really damage one of those dude. > > Not to say that I haven't done it. ;) A low-power NTSC transmitter > for which I used to be responsible went through a long string of PA > tubes, all covered by the manufacturer, before we figured out what was > wrong with it. > > Eric Jacobsen > Minister of Algorithms > Abineau Communications > http://www.ericjacobsen.orgThe lowest power NTSC transmitter I ever used was a 90 Watt gates on Ch 8 at an AFRTS TV station. It was a standby transmitter, but every panel in it fit the exciter cabinet of the matching Gates main transmitter. This was late '60s design, and I was using it in '73 & '74. That station was intended to only cover the base. Some idiot ham radio operator had the transmitter so screwed up, it wouldn't operate. He was trying to tune it, like he did his beat up old Swan SSB mobile. Both transmitters were damaged when i arrived. It took the better part of a week to find the problems, only to discover that replacements for the damaged parts had been ordered 18 months earlier and were still on backorder. So they had 90 watts of Visual power, from the standby transmitter and over 250 Watts of Aural power from the main transmitter. I did some scrounging and found the needed parts and repaired both transmitters. After a full alignment of the 500 W transmitter, the output was 756 watts. I backed it down to an even 600 and ran it that way for the year I was in charge. The biggest transmitter I maintained was a 130 KW Comark (Thales) on Ch 55, with a 5 MW EIRP and a 1749 foot tower. -- Service to my country? Been there, Done that, and I've got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida
