Bert wrote: >As Doug says, such low power repeaters can also be used >with 8-VSB, as shown in Ottawa, but you need decent >receivers which accept pre-echo. They exist. Just not on >store shelves. Why not on store shelves? The ATSC A/111 standard and the companion A/110A Recommended Practice, address the uses of 8VSB SFNs and Repeaters. One major station group is currently testing this concept in a relatively large market but findings are yet to be published. As you say, this requires 5th Gen type receiver hardware to be successful, which seemingly can only be obtained thru the purchase of a new DTV set. -----Original Message----- From: opendtv-bounce@xxxxxxxxxxxxx [mailto:opendtv-bounce@xxxxxxxxxxxxx]On Behalf Of Manfredi, Albert E Sent: Monday, February 13, 2006 2:24 PM To: opendtv@xxxxxxxxxxxxx Subject: [opendtv] Re: Doug is Missing the Point Stephen Long wrote: > With COFDM you can implement Single Frequency Networks, > using much lower power transmitters in locations much > closer to the actual consumers/viewers. True, but there are practical limits, such as cost, that result in very few actual towers being installed. The most I've seen is in the Paris SFN: the Eiffel tower and three smaller, low power sticks. Coverage still often requires outdoor antennas, due to the low power of the sticks. (And in practice, only Channel 35 is operated as a single SFN. For the other 4 multiplexes, the Eiffel Tower uses differemnt freqs from the small sticks.) As Doug says, such low power repeaters can also be used with 8-VSB, as shown in Ottawa, but you need decent receivers which accept pre-echo. They exist. Just not on store shelves. Why not on store shelves? Who knows. Maybe it's the same people that kept COFDM away in 2001? > 8VSB requires big stick mentality, Not necessarily. But even Paris and Berlin, with their SFNs, adopt what the French TNT calls "umbrella" configuration. One big stick, assisted by smaller sticks. This sort of arrangement could be used with 8-VSB as well. http://www.csa.fr/pdf/Rapport-GT2-Aspects_Radiofrequence_de_la_TNT.pdf Page 19. > Also, I have yet to hear any meaningful conversation > about the wasted bandwidth (wasted channels) required > by 8VSB to support translators in remote areas > (following the current analog model of a big stick with > remote translators on separate frequencies). With COFDM, > a television station could transmit using their big > stick and then have their repeaters (not translators now) > use the same frequency. Not quite. They are limited by the guard interval. In practice, COFDM uses translators too, if they need coverage outside the tight constraints of the guard interval (which are typically 7 or 14 miles max distance between towers, respectively for 1/16 and 1/8 GI). That's why, for example, the Paris channels are on different frequencies from the Mantes channels, where Mantes is the next town, 29 miles west of the Eiffel Tower. http://www.csa.fr/pdf/Frequences_TNT_phases_1_2.pdf They *could* synchronize their towers, of course. It's something no one seems to want to do. 8-VSB can also synchronize towers. Synchronization is used to guarantee that the signal level of one tower in the SFN becomes very weak by the time it exceeds the GI with the next tower. And that when both signals are strong, they are assured to be within the GI. The same would happen if we wanted to link upo the PBS stations in the DC area. Aside from the fact that they have different schedules, they are too far apart. To tie themin an SFN requires synchronization. I don't think there are major differences here. Bert ---------------------------------------------------------------------- You can UNSUBSCRIBE from the OpenDTV list in two ways: - Using the UNSUBSCRIBE command in your user configuration settings at FreeLists.org - By sending a message to: opendtv-request@xxxxxxxxxxxxx with the word unsubscribe in the subject line. ---------------------------------------------------------------------- You can UNSUBSCRIBE from the OpenDTV list in two ways: - Using the UNSUBSCRIBE command in your user configuration settings at FreeLists.org - By sending a message to: opendtv-request@xxxxxxxxxxxxx with the word unsubscribe in the subject line.