ghosts on digital OTA TV
Before the advent of mandatory digital over-the-air TV, it was said
that the picture would be near perfect, and that there woudl be no ghosts. Tonight I saw one, for a full half hour if the scene had the right kind of lines, including vertical lines. From the beginning I had doubts about the claim there would be no ghosts. I gleaned or understood that, aiui, if a ghost signal was less than, say, 50% as strong as the direct signal, and the direct signal were 0, the electronics would "round down" and output a zero. If the direct signal were 1 and the ghost was less than 0.5 and more than zero, or more than -0.5 and less than zero, the sum might be 1.5, but the electronics would interpret that as a 1. But that didn't account for every situation. What if the ghost signal was 0.6 the strength of the direct signal and the direct signal was a zero? Now, although I've never seen it discussed (and I do read a bit) I presume there are 3 signals making up the OTA video signal, and I'm ignoring that for now. Anyhow, for the first time in 9 months, with no changes to the tv wiring of my house, tonight I saw a ghost on an OTA tv show. On channel 7.3 in Wash. DC, and I live about 30 or 40 miles north of the transmitter. A black and white show, The Rifleman, with Chuck Connors, from the 60's I think, but maybe the 50's. I don't know from where the reflection could be coming. There is a 7 story building about 100 yards behind me and to the left (wrt channel 7) but that's not far enough away, is it, to account for 1/8" or 3/16" ghost displacement on a 19" tv? Woudln't any ghost from there be a small fraction of a millimeter from the main image? Could the ghost be in the coaxial connection between my TV tuner (a DVDR) and the tv. There is 15 feet of co=ax, an RF amp/splitter, 8 more feet of co-ax, a splitter, another RF amp, another splitter, 30 feet of co-ax, then another splitter, then 10 more feet of co-ax. If that were the source, it wouldn't be attributable to a digital signal, but I don't think those lengths are sufficient to account for a ghost 1/8" from the main image, are they? They also didnt' mention, said otherwise though I forget the words they used, that there would be checkerboard interference. I get that a lot on several stations, especially the ones that are 30 or 40 miles away. How much tv did these people watch before they made their false claims? Were they only a mile from the transmitter in rural Kansas? Does anyone know their names or email addresses so i could tell them how foolish they look? I get two new stations I like with digital, so I'm not angry. (I wouldn't be anyhow.) I just think they make themselves look stupid when they make false claims that they should have known better than to make, and to an extent, the impression this leaves spills over on to other "experts" and "scientists", in other fields. |
ghosts on digital OTA TV
mm wrote:
Before the advent of mandatory digital over-the-air TV, it was said that the picture would be near perfect, and that there woudl be no ghosts. Tonight I saw one, for a full half hour if the scene had the right kind of lines, including vertical lines. From the beginning I had doubts about the claim there would be no ghosts. I gleaned or understood that, aiui, if a ghost signal was less than, say, 50% as strong as the direct signal, and the direct signal were 0, the electronics would "round down" and output a zero. If the direct signal were 1 and the ghost was less than 0.5 and more than zero, or more than -0.5 and less than zero, the sum might be 1.5, but the electronics would interpret that as a 1. But that didn't account for every situation. What if the ghost signal was 0.6 the strength of the direct signal and the direct signal was a zero? Now, although I've never seen it discussed (and I do read a bit) I presume there are 3 signals making up the OTA video signal, and I'm ignoring that for now. It doesn't matter what the relationship is between the main signal and any reflected signals, they still won't cause ghosting in digital TV. They may mess the signal up to the point where the television doesn't produce a picture, but you won't get ghosting - digital TV simply doesn't work that way. Sylvia. |
ghosts on digital OTA TV
On Wed, 20 Jan 2010 18:25:14 +1100, Sylvia Else
wrote: mm wrote: Before the advent of mandatory digital over-the-air TV, it was said that the picture would be near perfect, and that there woudl be no ghosts. Tonight I saw one, for a full half hour if the scene had the right kind of lines, including vertical lines. From the beginning I had doubts about the claim there would be no ghosts. I gleaned or understood that, aiui, if a ghost signal was less than, say, 50% as strong as the direct signal, and the direct signal were 0, the electronics would "round down" and output a zero. If the direct signal were 1 and the ghost was less than 0.5 and more than zero, or more than -0.5 and less than zero, the sum might be 1.5, but the electronics would interpret that as a 1. But that didn't account for every situation. What if the ghost signal was 0.6 the strength of the direct signal and the direct signal was a zero? Now, although I've never seen it discussed (and I do read a bit) I presume there are 3 signals making up the OTA video signal, and I'm ignoring that for now. It doesn't matter what the relationship is between the main signal and any reflected signals, they still won't cause ghosting in digital TV. They may mess the signal up to the point where the television doesn't produce a picture, but you won't get ghosting But I did get ghosting. - digital TV simply doesn't work that way. Who am I going to believe, your theory-based answer, or my own eyes? Do you watch OTA tv these days? Maybe it matters that the station is 30 or 40 miles away. Do you watch stations like that? Sylvia. I also saw what was probably ghosting during a commercial right after that show. The commercial had big thick red letters against a white background, and the red continued about an eighth or three sixteenths of an inch to the right, lighter than the main red image. |
ghosts on digital OTA TV
mm wrote:
On Wed, 20 Jan 2010 18:25:14 +1100, Sylvia Else wrote: mm wrote: Before the advent of mandatory digital over-the-air TV, it was said that the picture would be near perfect, and that there woudl be no ghosts. Tonight I saw one, for a full half hour if the scene had the right kind of lines, including vertical lines. From the beginning I had doubts about the claim there would be no ghosts. I gleaned or understood that, aiui, if a ghost signal was less than, say, 50% as strong as the direct signal, and the direct signal were 0, the electronics would "round down" and output a zero. If the direct signal were 1 and the ghost was less than 0.5 and more than zero, or more than -0.5 and less than zero, the sum might be 1.5, but the electronics would interpret that as a 1. But that didn't account for every situation. What if the ghost signal was 0.6 the strength of the direct signal and the direct signal was a zero? Now, although I've never seen it discussed (and I do read a bit) I presume there are 3 signals making up the OTA video signal, and I'm ignoring that for now. It doesn't matter what the relationship is between the main signal and any reflected signals, they still won't cause ghosting in digital TV. They may mess the signal up to the point where the television doesn't produce a picture, but you won't get ghosting But I did get ghosting. - digital TV simply doesn't work that way. Who am I going to believe, your theory-based answer, or my own eyes? They are not necessarily inconsistent. You may have seen something, but it wasn't ghosting, in the sense that it wasn't caused by your antenna receiving a main signal and some delayed reflections. Do you watch OTA tv these days? Maybe it matters that the station is 30 or 40 miles away. Do you watch stations like that? Sylvia. I also saw what was probably ghosting during a commercial right after that show. The commercial had big thick red letters against a white background, and the red continued about an eighth or three sixteenths of an inch to the right, lighter than the main red image. If you're using a set-top-box and feeding a composite video signal into a conventional TV, you may just be seeing an effect where abrupt changes in luminance feed into the colour signal. Sylvia. |
ghosts on digital OTA TV
On Wed, 20 Jan 2010 19:53:33 +1100, Sylvia Else
wrote: mm wrote: On Wed, 20 Jan 2010 18:25:14 +1100, Sylvia Else wrote: mm wrote: Before the advent of mandatory digital over-the-air TV, it was said that the picture would be near perfect, and that there woudl be no ghosts. Tonight I saw one, for a full half hour if the scene had the right kind of lines, including vertical lines. From the beginning I had doubts about the claim there would be no ghosts. I gleaned or understood that, aiui, if a ghost signal was less than, say, 50% as strong as the direct signal, and the direct signal were 0, the electronics would "round down" and output a zero. If the direct signal were 1 and the ghost was less than 0.5 and more than zero, or more than -0.5 and less than zero, the sum might be 1.5, but the electronics would interpret that as a 1. But that didn't account for every situation. What if the ghost signal was 0.6 the strength of the direct signal and the direct signal was a zero? Now, although I've never seen it discussed (and I do read a bit) I presume there are 3 signals making up the OTA video signal, and I'm ignoring that for now. It doesn't matter what the relationship is between the main signal and any reflected signals, they still won't cause ghosting in digital TV. They may mess the signal up to the point where the television doesn't produce a picture, but you won't get ghosting But I did get ghosting. - digital TV simply doesn't work that way. Who am I going to believe, your theory-based answer, or my own eyes? They are not necessarily inconsistent. You may have seen something, but it wasn't ghosting, in the sense that it wasn't caused by your antenna receiving a main signal and some delayed reflections. Do you watch OTA tv these days? Maybe it matters that the station is 30 or 40 miles away. Do you watch stations like that? Sylvia. I also saw what was probably ghosting during a commercial right after that show. The commercial had big thick red letters against a white background, and the red continued about an eighth or three sixteenths of an inch to the right, lighter than the main red image. If you're using a set-top-box and feeding a composite video signal into a conventional TV, you may just be seeing an effect where abrupt changes in luminance feed into the colour signal. No. I'm using a DVDR with a hard drive and a digital tuner and sending an RF signal on channel 3 to an analog tv. Isn't that what people with digital cable and satellite do if they don't have composite or component inputs on their tvs? Assuming for the sake of this paragraph that this makes a difference, those many people who promoted the high quality of digital tv never said anthing about this making a difference. Sylvia. |
ghosts on digital OTA TV
mm wrote in message
... On Wed, 20 Jan 2010 19:53:33 +1100, Sylvia Else wrote: mm wrote: On Wed, 20 Jan 2010 18:25:14 +1100, Sylvia Else wrote: mm wrote: Before the advent of mandatory digital over-the-air TV, it was said that the picture would be near perfect, and that there woudl be no ghosts. Tonight I saw one, for a full half hour if the scene had the right kind of lines, including vertical lines. From the beginning I had doubts about the claim there would be no ghosts. I gleaned or understood that, aiui, if a ghost signal was less than, say, 50% as strong as the direct signal, and the direct signal were 0, the electronics would "round down" and output a zero. If the direct signal were 1 and the ghost was less than 0.5 and more than zero, or more than -0.5 and less than zero, the sum might be 1.5, but the electronics would interpret that as a 1. But that didn't account for every situation. What if the ghost signal was 0.6 the strength of the direct signal and the direct signal was a zero? Now, although I've never seen it discussed (and I do read a bit) I presume there are 3 signals making up the OTA video signal, and I'm ignoring that for now. It doesn't matter what the relationship is between the main signal and any reflected signals, they still won't cause ghosting in digital TV. They may mess the signal up to the point where the television doesn't produce a picture, but you won't get ghosting But I did get ghosting. - digital TV simply doesn't work that way. Who am I going to believe, your theory-based answer, or my own eyes? They are not necessarily inconsistent. You may have seen something, but it wasn't ghosting, in the sense that it wasn't caused by your antenna receiving a main signal and some delayed reflections. Do you watch OTA tv these days? Maybe it matters that the station is 30 or 40 miles away. Do you watch stations like that? Sylvia. I also saw what was probably ghosting during a commercial right after that show. The commercial had big thick red letters against a white background, and the red continued about an eighth or three sixteenths of an inch to the right, lighter than the main red image. If you're using a set-top-box and feeding a composite video signal into a conventional TV, you may just be seeing an effect where abrupt changes in luminance feed into the colour signal. No. I'm using a DVDR with a hard drive and a digital tuner and sending an RF signal on channel 3 to an analog tv. Isn't that what people with digital cable and satellite do if they don't have composite or component inputs on their tvs? Assuming for the sake of this paragraph that this makes a difference, those many people who promoted the high quality of digital tv never said anthing about this making a difference. Sylvia. So what you were seeing were fringes introduced in overdriven RF stages or harmonics/sub-harmonics/beats within the IFs or combinations between I would rather have ghosts instead of "no signal" blank screen and sound in bad reception environment but unfortunately not an option these days |
ghosts on digital OTA TV
On Wed, 20 Jan 2010 10:31:09 -0000, "N_Cook"
wrote: mm wrote in message .. . On Wed, 20 Jan 2010 19:53:33 +1100, Sylvia Else wrote: mm wrote: On Wed, 20 Jan 2010 18:25:14 +1100, Sylvia Else wrote: mm wrote: Before the advent of mandatory digital over-the-air TV, it was said that the picture would be near perfect, and that there woudl be no ghosts. Tonight I saw one, for a full half hour if the scene had the right kind of lines, including vertical lines. From the beginning I had doubts about the claim there would be no ghosts. I gleaned or understood that, aiui, if a ghost signal was less than, say, 50% as strong as the direct signal, and the direct signal were 0, the electronics would "round down" and output a zero. If the direct signal were 1 and the ghost was less than 0.5 and more than zero, or more than -0.5 and less than zero, the sum might be 1.5, but the electronics would interpret that as a 1. But that didn't account for every situation. What if the ghost signal was 0.6 the strength of the direct signal and the direct signal was a zero? Now, although I've never seen it discussed (and I do read a bit) I presume there are 3 signals making up the OTA video signal, and I'm ignoring that for now. It doesn't matter what the relationship is between the main signal and any reflected signals, they still won't cause ghosting in digital TV. They may mess the signal up to the point where the television doesn't produce a picture, but you won't get ghosting But I did get ghosting. - digital TV simply doesn't work that way. Who am I going to believe, your theory-based answer, or my own eyes? They are not necessarily inconsistent. You may have seen something, but it wasn't ghosting, in the sense that it wasn't caused by your antenna receiving a main signal and some delayed reflections. Do you watch OTA tv these days? Maybe it matters that the station is 30 or 40 miles away. Do you watch stations like that? Sylvia. I also saw what was probably ghosting during a commercial right after that show. The commercial had big thick red letters against a white background, and the red continued about an eighth or three sixteenths of an inch to the right, lighter than the main red image. If you're using a set-top-box and feeding a composite video signal into a conventional TV, you may just be seeing an effect where abrupt changes in luminance feed into the colour signal. No. I'm using a DVDR with a hard drive and a digital tuner and sending an RF signal on channel 3 to an analog tv. Isn't that what people with digital cable and satellite do if they don't have composite or component inputs on their tvs? Assuming for the sake of this paragraph that this makes a difference, those many people who promoted the high quality of digital tv never said anthing about this making a difference. Sylvia. So what you were seeing were fringes introduced in overdriven RF stages or harmonics/sub-harmonics/beats within the IFs or combinations between Okay. But then I used the same system with analog tv transmission. For 23 years I used a VCR and later for a year I used the DVDR using its analog tuner, in both cases with RF output to this tv and other tvs, all set on channel 3. Maybe the ghosts I saw then were also fringes introduced in overdriven RF stages as you describe. ?? I would rather have ghosts instead of "no signal" blank screen and sound in bad reception environment but unfortunately not an option these days Me too. In fact picture quality has never mattered to me much (despite this thread of mine about ghosts.) Much of the time I'm reading the newspaper, cooking, or looking at the computer screen, and even when I'm looking at the tv I don't care much. But even analog tvs in the last several years have blanked out the screen and the sound if the signal wasn't strong enough. It should have been an option. It should still be an option. |
ghosts on digital OTA TV
On Wed, 20 Jan 2010 01:35:45 -0500, mm
wrote: Before the advent of mandatory digital over-the-air TV, it was said that the picture would be near perfect, and that there woudl be no ghosts. Tonight I saw one, for a full half hour if the scene had the right kind of lines, including vertical lines. ... Please confirm that you do not drive a motor vehicle... If in fact you do drive, please indicate what areas we should be on the watchout for you. |
ghosts on digital OTA TV
PeterD wrote:
On Wed, 20 Jan 2010 01:35:45 -0500, mm wrote: Before the advent of mandatory digital over-the-air TV, it was said that the picture would be near perfect, and that there woudl be no ghosts. Tonight I saw one, for a full half hour if the scene had the right kind of lines, including vertical lines. ... Please confirm that you do not drive a motor vehicle... If in fact you do drive, please indicate what areas we should be on the watchout for you. I missed the original post, but the appearance of ghosts can be caused by a limited bandwidth of the video circuit. Ghosts can also be caused by improper termination of the feed line from the antenna to the TV. |
ghosts on digital OTA TV
root wrote:
Ghosts can also be caused by improper termination of the feed line from the antenna to the TV. On second thought, the digital processing should eliminate any such effects on the RF side. |
ghosts on digital OTA TV
On second thought, the digital processing should
eliminate any such effects on the RF side. I, too, am confused. A sufficiently strong ghost should garble the data to the point where the image is corrupted -- not duplicated. My guess is that the "ghosting" has some other source. It might even be in the signal itself. If the low-pass video filter is not properly phase-equalized, there can be severe ringing on the trailing edge of objects, which would appear as "ghosts" of vertical lines. |
ghosts on digital OTA TV
Hi!
Before the advent of mandatory digital over-the-air TV, it was said that the picture would be near perfect, and that there would be no ghosts. Ghosts in a digital over the air TV signal won't be caused for the same reasons that analog over the air TV signals had them. What's going out over the air in a digital TV transmission is a data stream, complete with some degree of error correction. Any such "ghosting" would show up in the signal as a duplicated datastream, which is probably ignored or considered errant by the video decompressor in the unit. If you were to get enough of these, you might notice some glitching ("checkerboard pattern") in the video. When you receive digital TV broadcasts, they will be an all or nothing affair. Either you are receiving enough of the datastream to receive a picture and sound, or you are not. Tonight I saw one, for a full half hour if the scene had the right kind of lines, including vertical lines. The flaw could have been in the material being broadcast. No broadcasting method can make up for flaws in the original material. Older material is more likely to suffer from problems. It sounds like you have a significant length of cable between your converter box and TV set, going to a significant number of places and through some amplifiers. If you are looking for interference, you are looking there. But I don't think you'll find any--or at least not much. In other words, this isn't the ideal situation, but I doubt it is the problem. Everything after the converter box's RF output is an analog TV signal and therefore subject to the same things that can interfere with a much more powerful analog TV broadcast signal. The only major thing I don't like about digital TV is the unwatchability of weak signals. Watching weak analog TV signals was never much fun, but at least it was doable if you had to. William |
ghosts on digital OTA TV
On Wed, 20 Jan 2010 06:21:44 -0800, "William Sommerwerck"
wrote: On second thought, the digital processing should eliminate any such effects on the RF side. I, too, am confused. A sufficiently strong ghost should garble the data to the point where the image is corrupted -- not duplicated. My guess is that the "ghosting" has some other source. It might even be in the signal itself. If the low-pass video filter is not properly phase-equalized, there can be severe ringing on the trailing edge of objects, which would appear as "ghosts" of vertical lines. Is the trailing edge on the left side or the right side? |
ghosts on digital OTA TV
In article , mm wrote:
On Wed, 20 Jan 2010 18:25:14 +1100, Sylvia Else wrote: mm wrote: Before the advent of mandatory digital over-the-air TV, it was said that the picture would be near perfect, and that there woudl be no ghosts. Tonight I saw one, for a full half hour if the scene had the right kind of lines, including vertical lines. From the beginning I had doubts about the claim there would be no ghosts. I gleaned or understood that, aiui, if a ghost signal was less than, say, 50% as strong as the direct signal, and the direct signal were 0, the electronics would "round down" and output a zero. If the direct signal were 1 and the ghost was less than 0.5 and more than zero, or more than -0.5 and less than zero, the sum might be 1.5, but the electronics would interpret that as a 1. But that didn't account for every situation. What if the ghost signal was 0.6 the strength of the direct signal and the direct signal was a zero? Now, although I've never seen it discussed (and I do read a bit) I presume there are 3 signals making up the OTA video signal, and I'm ignoring that for now. It doesn't matter what the relationship is between the main signal and any reflected signals, they still won't cause ghosting in digital TV. They may mess the signal up to the point where the television doesn't produce a picture, but you won't get ghosting But I did get ghosting. You may be seeing spikes before and after due to filtering. It might be more or only noticable viewing on an analog TV. I was seeing filtering and emphasis effects on my 36 in CRT Toshiba on analog signals which i assumed to be due to digital processing. greg - digital TV simply doesn't work that way. Who am I going to believe, your theory-based answer, or my own eyes? Do you watch OTA tv these days? Maybe it matters that the station is 30 or 40 miles away. Do you watch stations like that? Sylvia. I also saw what was probably ghosting during a commercial right after that show. The commercial had big thick red letters against a white background, and the red continued about an eighth or three sixteenths of an inch to the right, lighter than the main red image. |
ghosts on digital OTA TV
On 20/01/2010 06:35, mm wrote:
Before the advent of mandatory digital over-the-air TV, it was said that the picture would be near perfect, and that there woudl be no ghosts. Tonight I saw one, for a full half hour if the scene had the right kind of lines, including vertical lines. From the beginning I had doubts about the claim there would be no ghosts. Cabling signal crosstalk between multiple tuners at the baseband. -- Adrian C |
ghosts on digital OTA TV
"William Sommerwerck" wrote in
: On second thought, the digital processing should eliminate any such effects on the RF side. I, too, am confused. A sufficiently strong ghost should garble the data to the point where the image is corrupted -- not duplicated. My guess is that the "ghosting" has some other source. It might even be in the signal itself. If the low-pass video filter is not properly phase-equalized, there can be severe ringing on the trailing edge of objects, which would appear as "ghosts" of vertical lines. it could even be a coax cabling problem;some mismatch or cable defect,or too long a cable from settop to TV. OR the TV itself.... -- Jim Yanik jyanik at localnet dot com |
ghosts on digital OTA TV
mm wrote in message ... Before the advent of mandatory digital over-the-air TV, it was said that the picture would be near perfect, and that there woudl be no ghosts. Tonight I saw one, for a full half hour if the scene had the right kind of lines, including vertical lines. From the beginning I had doubts about the claim there would be no ghosts. I gleaned or understood that, aiui, if a ghost signal was less than, say, 50% as strong as the direct signal, and the direct signal were 0, the electronics would "round down" and output a zero. If the direct signal were 1 and the ghost was less than 0.5 and more than zero, or more than -0.5 and less than zero, the sum might be 1.5, but the electronics would interpret that as a 1. But that didn't account for every situation. What if the ghost signal was 0.6 the strength of the direct signal and the direct signal was a zero? Now, although I've never seen it discussed (and I do read a bit) I presume there are 3 signals making up the OTA video signal, and I'm ignoring that for now. Anyhow, for the first time in 9 months, with no changes to the tv wiring of my house, tonight I saw a ghost on an OTA tv show. On channel 7.3 in Wash. DC, and I live about 30 or 40 miles north of the transmitter. A black and white show, The Rifleman, with Chuck Connors, from the 60's I think, but maybe the 50's. I don't know from where the reflection could be coming. There is a 7 story building about 100 yards behind me and to the left (wrt channel 7) but that's not far enough away, is it, to account for 1/8" or 3/16" ghost displacement on a 19" tv? Woudln't any ghost from there be a small fraction of a millimeter from the main image? Could the ghost be in the coaxial connection between my TV tuner (a DVDR) and the tv. There is 15 feet of co=ax, an RF amp/splitter, 8 more feet of co-ax, a splitter, another RF amp, another splitter, 30 feet of co-ax, then another splitter, then 10 more feet of co-ax. If that were the source, it wouldn't be attributable to a digital signal, but I don't think those lengths are sufficient to account for a ghost 1/8" from the main image, are they? They also didnt' mention, said otherwise though I forget the words they used, that there would be checkerboard interference. I get that a lot on several stations, especially the ones that are 30 or 40 miles away. How much tv did these people watch before they made their false claims? Were they only a mile from the transmitter in rural Kansas? Does anyone know their names or email addresses so i could tell them how foolish they look? I get two new stations I like with digital, so I'm not angry. (I wouldn't be anyhow.) I just think they make themselves look stupid when they make false claims that they should have known better than to make, and to an extent, the impression this leaves spills over on to other "experts" and "scientists", in other fields. I've not had ghosting, but in the beginning of the transition, I used to get something that looked like the reds were shifted, like bad convergence. The shift changed, so that the red picture would sort of float around it's target. It might have been a combination of the broadcasters working out the bugs, and me working out the antenna, because my picture has been flawless for about 6 months. I did cut way back on my signal level by removing a distribution amp and padding the antenna output. |
ghosts on digital OTA TV
On Jan 20, 12:28*pm, "bg" wrote:
mm wrote in message ... Before the advent of mandatory digital over-the-air TV, it was said that the picture would be near perfect, and that there woudl be no ghosts. * Tonight I saw one, for a full half hour if the scene had the right kind of lines, including vertical lines. From the beginning I had doubts about the claim there would be no ghosts. *I gleaned or understood that, aiui, if a ghost signal was less than, say, 50% as strong as the direct signal, and the direct signal were 0, the electronics would "round down" and output a zero. If the direct signal were 1 and the ghost was less than 0.5 and more than zero, or more than -0.5 and less than zero, the sum might be 1.5, but the electronics would interpret that as a 1. But that didn't account for every situation. *What if the ghost signal was 0.6 the strength of the direct signal and the direct signal was a zero? *Now, although I've never seen it discussed (and I do read a bit) I presume there are 3 signals making up the OTA video signal, and I'm ignoring that for now. Anyhow, for the first time in 9 months, with no changes to the tv wiring of my house, tonight I saw a ghost on an OTA tv show. * On channel 7.3 in Wash. DC, and I live about 30 or 40 miles north of the transmitter. *A black and white show, The Rifleman, with Chuck Connors, from the 60's I think, but maybe the 50's. I don't know from where the reflection could be coming. *There is a 7 story building about 100 yards behind me and to the left (wrt channel 7) but that's not far enough away, is it, to account for 1/8" or 3/16" ghost displacement on a 19" tv? * *Woudln't any ghost from there be a small fraction of a millimeter from the main image? Could the ghost be in the coaxial connection between my TV tuner (a DVDR) and the tv. *There is 15 feet of co=ax, an RF amp/splitter, 8 more feet of co-ax, a splitter, another RF amp, another splitter, 30 feet of co-ax, then another splitter, then 10 more feet of co-ax. * If that were the source, it wouldn't be attributable to a digital signal, but I don't think those lengths are sufficient to account for a ghost 1/8" from the main image, are they? They also didnt' mention, said otherwise though I forget the words they used, that there would be checkerboard interference. *I get that a lot on several stations, especially the ones that are 30 or 40 miles away. How much tv did these people watch before they made their false claims? * Were they only a mile from the transmitter in rural Kansas? Does anyone know their names or email addresses so i could tell them how foolish they look? I get two new stations I like with digital, so I'm not angry. (I wouldn't be anyhow.) I just think they make themselves look stupid when they make false claims that they should have known better than to make, and to an extent, the impression this leaves spills over on to other "experts" and "scientists", in other fields. I've not had ghosting, but in the beginning of the transition, I used to get something that looked like the reds were shifted, like bad convergence. The shift changed, so that the red picture would sort of float around it's target. It might have been a combination of the broadcasters working out the bugs, and me working out the antenna, because my picture has been flawless for about 6 months. I did cut way back on my signal level by removing a distribution amp and padding the antenna output.- Hide quoted text - - Show quoted text - If it was a black and white picture, it could be there were some artifacts caused by the film to video conversion. Did you check any other sets or neighbors' tvs to see if they saw the same thing. |
ghosts on digital OTA TV
If it was a black and white picture, it could be there were some artifacts caused by the film to video conversion. Did you check any other sets or neighbors' tvs to see if they saw the same thing. I had the same effect with two different brands of convertor boxes and on different TV's. My antenna was common to both. I don't know if too much signal could have caused it, or if it was broadcast with a problem. Most of the local broadcasters did seem to need a month or two to get things right, such as the sync between the video and audio, going off air etc ... and I was tweaking the antenna quite often too, wondering if it was me or them. |
ghosts on digital OTA TV
On Thu, 21 Jan 2010 00:21:06 -0700, "bg" wrote:
If it was a black and white picture, it could be there were some artifacts caused by the film to video conversion. Did you check any other sets or neighbors' tvs to see if they saw the same thing. No. I figure I'll have a chance to do this later. To check this tv on a different episode (Heck, I watched the show last night but forgot to look.) I had the same effect with two different brands of convertor boxes and on different TV's. My antenna was common to both. I don't know if too much signal could have caused it, or if it was broadcast with a problem. Most of the local broadcasters did seem to need a month or two to get things right, such as the sync between the video and audio, going off air etc ... I've seen lack of sync but only once, I think, and not at the start. and I was tweaking the antenna quite often too, wondering if it was me or them. I just got an antenna, but have to crawl into the attic to set it up. |
ghosts on digital OTA TV
On Jan 20, 2:31*am, "N_Cook" wrote:
So what you were seeing were fringes introduced in overdriven RF stages or harmonics/sub-harmonics/beats within the IFs or combinations between I would rather have ghosts instead of *"no signal" blank screen and sound in bad reception environment but unfortunately not an option these days Not how it works at all Nigel. Anything you're describing would prevent proper demodulation of the data. With enough errors it would fall off the 'cliff' and give no useful data. I don't doubt he saw 'ghosts' but they weren't RF multipath problems. I've been seeing a bit more 'enhancement' artefacts on some HD signals which makes me a little sad to see a good system get mis-used. OR, it may have been SD material again 'enhanced' to cause the cartoon-like outlines. I have seen some commercials that clearly (well, to me) came from a composite source (likely a D2 machine) with decoding artefacts. Fortunately THAT variety is fading away. G² |
ghosts on digital OTA TV
On Jan 19, 10:35*pm, mm wrote:
Before the advent of mandatory digital over-the-air TV, it was said that the picture would be near perfect, and that there woudl be no ghosts. * Tonight I saw one, for a full half hour if the scene had the right kind of lines, including vertical lines. Digital broadcast TV doesn't support ghosts from transmission artifacts. The link from DTV adapter to analog TV, or the video amplifiers inside a vacuum-tube CRT television, can support some kinds of ghost/ringing that might be perceptible. Could the ghost be in the coaxial connection between my TV tuner (a DVDR) and the tv. *There is 15 feet of co=ax, an RF amp/splitter, 8 more feet of co-ax, a splitter, another RF amp, another splitter, 30 feet of co-ax, then another splitter, then 10 more feet of co-ax. But the important question is, is this connection from tuner an analog NTSC (USA old TV standard) connection, or a digital ATSC connection? Does your TV get this signal over channel 3, or is it a digital channel, like 7.3, that it tunes? I presume it's analog (i.e. your DVDR is converting ATSC input to NTSC output). If it's really a poorly-terminated bunch of coaxial wiring, or even a loose connection somewhere in the coaxial knotwork, your sixty-feet of wire can cause a resonance with circa 120 ns of delay (that's a signal reflection doing the sixty feet of travel in round-trip style). Full screen-width, NTSC, is about 55 uS, so 120 ns is a couple of percent of the screen size. Whether that's consistent with '1/8 inch', I can't say. Reflections in wiring are caused by (1) stub transmission lines - like splitters with long cables connected that DO NOT have a receiver attached. You can fix that by disconnecting long cables, or by putting a 75 ohm terminator on the unused end. This applies to cables that are NOT part of the connection to your target television, as well as to the connecting channel; the echo from the cable can be related to wiring to the spare bedroom. It all connects. (2) loose connections. While watching the signal, adjust/loosen/ tighten any and all connectors in the coaxial maze. (3) faulty or overdriven amplifiers- For most use, a simple splitter is better than an amplifier; the signal/noise is not improved by amplification on the OUTPUT of a tuner, you don't NEED any amplifier to drive a bit of cable from that output. If the amplifier(s) cause signal overload, or support oscillation, they're a problem rather than a solution. None of these reflection issues is related to the digital transmission. It is also possible that the TV has a weak video amplifier that has started to create dark shadows behind bright vertical lines because of aging of the video amplifier's filter capacitors. Plug a video game into the TV and see if it has the same artifacts (if it does, it's TV repair time). |
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