You speak of the limits of echo tolerance in receivers. Can anyone explain what the physics or economic limitations are that makes this such a problem? Is there a simple reason why we can't make cheap receivers with huge echo tolerance?
- Tom Manfredi, Albert E wrote:
Receivers do not lock into any one transmitter and ignore the rest. Not unless "the rest" are so much lower in strength that they are totally overpowered by the one. The problem is always in areas of equal or near equal power density, from two or more towers. Unless, of course, there's some obstacle, at and near the contour lines, that makes reception unimportant.More completely, I should have said that I was speaking mostly of SFNs with towers far apart, which is what a lot of people think about when they mention "SFN" and "increased area of coverage" in the same sentence. Even if you synchronize the towers, to try to keep the symbols lined up in time in the contour lines, with more than two towers you will at best be able to adjust the location of the difficult reception areas. Not eliminate them. Directional receive antennas help, at least in devices that can actually use them. And when far-apart towers are involved, you can't forget how weather conditions can change the relative power density of different towers at different locations. On the other hand, if you cluster a few SFN towers close together enough so as not to exceed the echo tolerance of receivers, then you will ease reception near that cluster, but you will not gain anything compared with a single big stick in terms of coverage area. At least, not with ATSC, or the original DVB-T at reasonably spectrum-efficient settings of GI. 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.
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