My experiences with ATSC HDTV

[wa2ise]

Originally Posted by peverett

I have seen the same issue in high winds. However, I am not sure the power increase will fix this. What is happening is that the digital locking circuit(probably some sort of PLL) is losing lock temporarily(and dropping data) due to the incoming wave varying. The variance is due to the distance from the transmitter to the receiver changing as the transmission tower moves in the wind. This is a basic problem with all broadcast digital transmissions.

A very directional antenna aimed at the transmitter tower solves this. The directivity allows your receiver to ignore the ghosts, as the antenna doesn't let those ghosts get into the receiver. The ghosts that add and subtract signal strength and varyingly messing up the digital symbol "eye pattern". An "eye pattern" is a diagram (or scope trace) that shows the ability for a receiver to tell 1's from 0's in the received signal. Ghosts also cause earlier bits to mess up the bits now being received from the direct signal from the trannsmission tower. As the ghost signal path is longer, and the speed of light is not infinite, but is about a foot per nanosecond.

If there are no ghosts, the transmitter tower moving back and forth in the wind won't hurt reception. It doesn't impose enough doppler shift to be anything close to become a problem for the receiver.

[Jeffhs]

ATSC television still has problems occasionally, even on cable systems. Time Warner Cable, the cable operator in my area, is supposedly completely digital now, but some of its channels act up from time to time. Case in point: I was watching a program on our area's ION-TV affiliate the other day, but couldn't follow the show worth a plugged nickel because the picture kept dropping out (leaving a blue screen), freezing and pixelating. (I have a recent-vintage 19" analog CRT TV with a digital cable set-top box ahead of it.) I think this may have been due to technical problems at the cable headend, the TV station itself, or even weather conditions at the time (I think it was raining or snowing when this showed up); difficult to tell now. I had a similar problem not long after Time Warner converted its systems (including the one serving my area) to digital; I was watching NBC Nightly News one evening and noticed the picture was freezing and pixelating like mad. I can only hope that once digital TV has completely taken over from analog, next year, that these problems don't happen more than once in a great, great while; it's no fun having your favorite show interrupted by aberrations such as pixelization or freezing in place for minutes at a time, not to mention dropping out entirely. Did analog TV ever have problems similar to this in the late 1940s-1950s, when the idea of transmitting pictures over the air was new?

[peverett]

As I have worked on integrated circuits used in digital telecommunications, I am very aware of what an eye pattern is. However, I am not yet convinced that ghosts (multipath signals) are the only issue.

It is probable that a directional antenna would help this. However, since I do not need a directional antenna for decent analog reception-I contend that this is one area where digital is not as good as analog. As I am only 30 miles from the transmitter in an area that is not terribly windy, and still have some trouble on windy days, I suspect people far away from the transmtter in windy areas(west Texas/Oklahoma for example) could have real trouble if they are depending on broadcast TV in 2009.

[OvenMaster]

I picked up a Magnavox TB100MW9 at Wal-Mart last night for $50. I've got a small RatShack TV-FM combo up on a 25 foot mast, with a rotator and inline amplifier. I connected the converter with RCA patchcords to my Sanyo VCR, using the VCR as an RF modulator. This will enable me to videotape DTV programming.

For NTSC programming, I was able to pick up a maximum of 13 channels, with only six or seven of them able to be classed as "average" or better. Most of the others were always ghosting, or snowy to some degree. Some were downright awful.

With the converter, I can pick up 16 DTV channels (including subchannels) with no effort at all, and all look great. I don't even have to spin the antenna around to get the local channels! There was one CW channel I really wanted to get that's about 40 miles away because of religious programs on Sunday, but their DTV channel is a no-show. Their analog signal was rarely better than in the past, and I'm positive it's because of signal loss due to the hilly terrain between the transmitter and my antenna.

So overall, I'm content. Not thrilled, but content.

Tom

[MRX37]

Just finished watching a two hour long documentary on PBS about the steaming pile of failure known as the Iraq war. The video didn't drop out once.

My homemade antenna is VERY directional. In fact one of my issues is that the wind will rotate it a bit, and the signal strength will drop by 40%. However, when it's aimed right, reception is beautiful.

As for the problems on cable systems. That's happened with analog as well in the past. I remember as a kid having some cable channels that were either fuzzy, had ghosting, or interference, or spots on the screen, etc. Even had channels just drop to static. I expect there to be bugs in the digital system as well.

[peverett]

As far as drop outs, I only see these when it is fairly windy. Otherwise reception of DTV around here is fine. (The sets that I have been viewing DTV on are all 20+years old, so I cannot call it HDTV).

I do like the fact that there is no snow on DTV but hate it when drop outs occur. Unlike analog, even the sound can stop and the program you were watching cannot be followed again until the dropout is over.

[ChrisW6ATV]

Originally Posted by Jeffhs

the picture kept dropping out (leaving a blue screen), freezing and pixelating. (I have a recent-vintage 19" analog CRT TV with a digital cable set-top box ahead of it.) I think this may have been due to technical problems at the cable headend, the TV station itself, or even weather conditions at the time (I think it was raining or snowing when this showed up); difficult to tell now.

Check to be sure all the cable connections and splitters or any other devices you have within your home are tight and in good condition. If they are, call the cable company and tell them to fix their lousy system! You are paying them for a constant, high-quality signal under all conditions; weather is no excuse at all for signals carried over wires, any more than it would be for your wired telephone. (Digital cable is actually not ATSC in almost every case, but rather "QAM".)

73

[andy]

Originally Posted by ChrisW6ATV

Check to be sure all the cable connections and splitters or any other devices you have within your home are tight and in good condition. If they are, call the cable company and tell them to fix their lousy system! You are paying them for a constant, high-quality signal under all conditions; weather is no excuse at all for signals carried over wires, any more than it would be for your wired telephone. (Digital cable is actually not ATSC in almost every case, but rather "QAM".)

73

That's good advice. Every new place I've lived had serious cable signal quality problems. The Time Warner man spent over 4 hours here a few days ago replacing just about everything between the house and the pole until the internet, and digital cable worked properly. Don't let them blame your house wiring, or equipment. They always try to do that so they don't have to repair their own system. If you have to, tell him to run a new (temporary) wire between your cable box (or modem) and the main splitter.

[wa2ise]

Originally Posted by peverett

As I have worked on integrated circuits used in digital telecommunications, I am very aware of what an eye pattern is. However, I am not yet convinced that ghosts (multipath signals) are the only issue.

Turns out the ATSC transmission standard uses an 8 level eye pattern


More info at:
http://www.broadcast.net/~sbe1/8vsb/8vsb.htm

[NowhereMan 1966]

Originally Posted by MRX37

I just confirmed that today...

Yes, I finally found something that affects the digital signal: Winds of 25MPH or more...

I had to point my antenna directly at the transmitter of the channel I was watching to eliminate the dropping out.

I hope this problem is solved when the stations go all digiotal and hopefully increase their output power...

I noticed that too, we had winds over 25 MPH yesterday here in Pittsburgh. I'm watching the WVU game on my 1964 Sony B&W portable using a Zenith DTV box. Excellent picture.

[OvenMaster]

Something else I've been noticing the past week or so.

As time goes by, I've been seeing more tiling and random colored blocks on signals from stations about 25-30 miles away. I've also noticed that it seems to be getting worse by the day...

...in lock step with the leaves budding on all the trees.

You used to be able to see other neighborhood houses through the branches. Now that the leaves are all coming in, you can't see them. The more the leaves grow in, the weaker the DTV signals are getting. Some days I'm lucky to get a 10 on a 0-to-100 scale on the weaker channels... if I don't get a black screen and a "No Signal" message. This is all with an amplified TV/FM antenna with a rotator and inline amplifier, no less.

Swell. That means no digital CBS until late autumn. I think there's going to be a local digital translator next year, however. I hope.

Tom

[NowhereMan 1966]

Originally Posted by OvenMaster

Something else I've been noticing the past week or so.

As time goes by, I've been seeing more tiling and random colored blocks on signals from stations about 25-30 miles away. I've also noticed that it seems to be getting worse by the day...

...in lock step with the leaves budding on all the trees.

You used to be able to see other neighborhood houses through the branches. Now that the leaves are all coming in, you can't see them. The more the leaves grow in, the weaker the DTV signals are getting. Some days I'm lucky to get a 10 on a 0-to-100 scale on the weaker channels... if I don't get a black screen and a "No Signal" message. This is all with an amplified TV/FM antenna with a rotator and inline amplifier, no less.

Swell. That means no digital CBS until late autumn. I think there's going to be a local digital translator next year, however. I hope.

Tom

True. I once read a story about a UHF station in West Virginia back in 1952, one guy got a perfect signal from them in the winter but when the leaves came out, they blocked the signal and he lost all signal. The UHF station only put out in 12000 watts so as UHF goes, it was pretty weak. So far, here in Pittsburgh, I haven't noticed too much but I'll keep my eye on it. I know I live in the flight path and it seems the planes are taking off my house more than usual. I saw a 767 so low, I thought he was going to take out my maple trees. However, I notice some pixelation when planes fly over but it is tolerable.

I know after the 2009 sign off of NTSC, most stations will return to their normal frequencies, KDKA-TV's digital signal is on UHF channel 25 but will be back on VHF channel 2 and so on. The only exception is our Channel 11, it will stay on channel 48 and CW will take the channel 11 slot from where they are at on 19.

[MRX37]

Ok, another update:

Don't rely on OTA HDTV if you want to get a perfect recording...

Recorded a PBS documentary on the Samurai sword. Even though I had a signal strength of 100%, there were still two occasions where half second drop outs caused blockiness.

The video is by all means watchable, but those two errors keep it from being perfect.

[OvenMaster]

I tape stuff daily for other family members from the local NBC and ABC outlets' DTV signals. I'd say that at least once every week or so, either one of them is off the air for extended periods. The analog signals keep going, though.

The local cable company AFAIK still picks up and redistributes the off-the-air analog signals, so subscribers don't see any DTV OTA dropouts. Won't cable subscribers be in for a surprise when analog broadcasts are done and the cable company delivers OTA feeds of DTV signals that crap out every now and again!

Was early analog broadcasting this unreliable (if anyone remembers)?

[Jonathan]

I'd like to comment on this even though the thread is old. Last year I went on the FCCs web site to check the licenses of my local stations. In the Scranton-Wilkes Barre area in Pennsylvania, there is ABC, CBS, NBC, PBS, FOX, and Ion affiliates. Right now, they all digitally transmit at 10 to 30 percent of their analog counterparts. All of them. As an example, my local ABC affiliate transmits at 1150 kW ERP in analog. Their temporary (starter license when they first started transmitting ATSC) digital license has them broadcasting at 68kW ERP. Their permanent "pre-transition" license has them broadcasting at 100kW ERP. At 100kW ERP, I have occasional reception issues when using a vintage dual dipole with parasitic array, mainly because it has to be pointed in the right direction. Bad weather makes it worse but I have not really tested it because I have no interest in the programming on broadcast TV.

Their "post-transition" license is for broadcasting at 180k ERP (Wow). I'm guessing antenna location and transmit power is what it is for reasons such as the terrain, etc, but it just seems low. A rooftop antenna is required, at least in my area, for trouble free reception even in crappy weather. In my area you see rooftop antennas on many houses. Almost all of them are not used anymore, but the small indoor antennas just never cut it for this area. You can use them, and get acceptable quality, but rooftop antennas provided a stable picture.

Jonathan