Re: Why is video inverted for transmission?

That is not what the masses need. The masses on living room couches need something that turns their old analog TV into a digital TV. Walmart used to have a converter for around $250, about the same amount our whole TV had cost (!). Maybe they still do. What I wanted is to test the Walmart guys. If a technology is supposed to be widespread I would at least expect the manager to know. He didn't.

Give him... mmm... about a year and a bit: By Christmas session next year, I'm willing to bet there's going to be a large pile of ATSC->NTSC converters sitting in a noticeable pile, with price tags $99 or below.

And then the moment of truth cometh. I am a bit concerned that the chosen system could waffle under really strong multipath conditions like where we live. Right now we don't know because none of the neighbors has digital OTA reception. If it doesn't work and people find themselves cut off from watching the news the situation at the phone desk of the local politicians may become ugly.

Digital transmission do NOT suffer, in ANY WAY, SHAPE, OR FORM, from multipath distortions!

Move out to the signal fringe and check again. You missed something.

(snip)

I believe DVD recorders with ATSC tuners are now available for around $200 or less. They at least have composite video output, probably RF out, too.

Otherwise the government is supposed to subsidize the converters.

-- glen

There is a difference between bit error rate and multipath distortion. Big difference.

With digital, and of course, the FEC that gets included, it is either ALL there or not displayable. There is NO distortion ever.

^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Now you've got it. I was not talking about distortion. In heavy multipath your analog picture might look yucky (out here it does) but it's there. You can still watch the news. When the digital gets hit with too much multipath the picture ain't there at all. Huge difference. Grandma Miller and uncle Leroy won't have any tolerance for that. They'll fly off the handle.

And what, among other things, do you think causes it to be *not there*? Magic?

Yes, I believe Costco has one right now. Probably only online though.

It's a bit late in the game now. If serious issues for example with multipath are discovered that won't leave much time to deal with that. Since the standard is cast in concrete the only option would be repeaters. The permit procedure alone would eat up much of the remaining time.

Get on board. You're locked into distortion of the signal delivered *by* the receiver, while the chaps who know the real world are discussing distortion of the signal delivered *to* the receiver. If you took the time to bone up on how things are done, you might not be bored any more.

Jerry

Joerg wrote: (snip)

Isn't multipath usually in big cities, where you probably have good access to cable?

In far fringe areas where the signal might be low, and where cable isn't easily available it could be harder. With a big antenna and a good amplifier it might still work.

-- glen

Do you live in an area with no large steel buildings, towers for power lines, or any other RF reflective structures for miles? I have had to aim antennas at large steel buildings to use a clean reflection, rather than the main signal, with multiple reflections causing ghosting. With analog, its just irritating, but the right spacing on a digital TV signal can cause the two out of phase signals to cancel, or attenuate enough to cause a dropout.

I spent the last four years of my working life working on dual diversity telemetry receivers. Even signals from space cane have propagation and path problems that can only be corrected by having multiple 100' sat antennas, as far apart as possible. We built both analog,, and DSP based equipment. The analog could decode weaker and noisier signals than the DSP based.

When the bit error rate exceeds the capacity of the FEC to correct the missing data. D'oh! Multipath is NOT missing data in most cases, save the most extreme.

I'm not bored, dumbfuck. I am the chairman of those that are.

The acronym for today is:

FEC

When you get some time, perhaps you can seek and even get a clue.

I live about half way between New York and Philadelphia and receive pretty good signals from each. (Antenna has a rotator.) Multipath was a problem that showed up as ghosting until a nearby water tower was taken down. The Verrazano-Narrows Bridge across the Hudson caused weaker multipath on New York stations while the antennas were on the World Trade Center. Multipath can happen anywhere.

Jerry

That's obviously the best you can do, so why not just wuit?

No idea, I don't like to live in big cities. But cable has one downside: $$$. Out here it starts at around $30-40. OTA is $0. Why pay that money when all you want to see is the evening news? Ok, we'd have that money but there are people who don't and they might become rather miffed in early 2009.

It's extreme here in the foothills. You can sometimes see echoes several (!) lines down. On some channels the ghosts are actually before the signal because the TV syncs on an echo that happens to be much stronger than the direct path. And yes, we've got a big antenna and I spent half a day finding the best compromise. Even a rotator won't help. All but one station (Spanish language) will have strong multipath wherever you point the antenna.

Oh, and then there are the freighters lumbering in from the East. Since most stations are in the same direction as their approach path you'd see the picture wobble and twist for up to five minutes. But you can still see it. I have a hunch that digital will scoot over to an error message, no audio, no video, or just gradually freeze up into those "walking square blocks" and that'll have people fuming.

Multipath is extreme here. I don't know yet but I have heard that DTV quickly falls apart under those conditions. When you watch "All in the Family" out here you sometimes have 3-4 Archie Bunkers in there. When a Fedex Cargo jet lumbers in that increases to almost 10 of them. And we have a rather large Yagi antenna on a mast, low noise preamp, head distribition amplifier and all that. The distribution has been carefully designed, calculated and built by yours truly and causes no reflections. Yet there is only one channel (Ch19) with no ghosting at all. It's Spanish only ...

The Seattle area is much easier. My first employer's HQ is there, in Bothell. AFAIR the RF situation doesn't become nearly as tricky until you get to somewhere significantly east of Issaquah.