Why is video inverted for transmission?

[Michael A. Terrell]

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.

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.

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[Michael A. Terrell]

NC meant "no connection" and one was advised not to use them because
voltage withstand was not assured. Pin 1 was listed NC on the glass
versions of the 6L6, but it was intentionally connected to the metal
shell (and usually grounded) in the metal version.

Jerry

Some of the tube design guides from the manufacturers warned you not
to use any N/C pins, because they may be used in the future.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[Michael A. Terrell]

Michael A. Terrell wrote:

(snip)

I used to have an oscilloscope built out of a WWII radar
receiver.

-- glen

My high school's Physic department had the entire RADAR system, with
manuals. It had been in storage since it was declassified, and they
finally decided to try to return it to the government. They were told
to destroy it, so it was sent to the electronics class to be parted
out. I managed to grab the receiver case, and the transmitter before it
was parted out. I had the 15E and 15R Eimac tubes that were designed
for that RADAR transmitter, but I don't know if I still have them.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[Michael A. Terrell]

My cable provider has claimed that the digital artifacts that I've
seen are due to squirrels chewing on cables and as soon as they get
around to replacing the lines, the artifacts should go away.

Squirrels do chew hardline, till they hit the 60 V squared wave 30 A
supply. That doesn't mean that they are full of crap. If you can find a
damaged spot they haven't repaired, report them to the FCC for radiation
problems. They will fix it, or be shut down.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[Michael A. Terrell]

He's probably complaining about how -- somewhat ironically -- as technology
advances and becomes easier to use, those using it tend to be less educated
and therefore more likely to get something wrong (such as colors)! Perhaps
the relevant example here was the "wall of CRTs" seen in big box stores before
LCDs/plasma displays took over -- inevitably they were all cranked up so
bright to "look good" that there was pretty bad geometric distortion,
blooming, and awful color rendition. But the average consumer cared about
little more than brightness, it would seem, and voted with their wallet
accordingly...

that's really strange, too. 30 years ago, when I worked in a TV shop
that sold TVs, people bought the one with the best picture. A lot of
them watched TV in a semi darkened room, and didn't want them to be
blindingly bright. Now, they want to watch them outdoors, in the noon
day sun.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[Michael A. Terrell]

Randy Yates wrote:
(snip)


How many vacuum tubes does it take to build a PLL?

More important: How many tons of air conditioning can you afford to
run 24/7?

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[ChairmanOfTheBored]

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

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.

 

[ChairmanOfTheBored]

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.

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.

 

[Jeff Liebermann]

I was given a two year old 32" Sony HDTV 'Capable' TV a few weeks
ago, and have no idea what I'm going to do with it. I have considered
converting it to a computer monitor.

You'll probably find that your Sony is limited to WXGA (1366x768).
Check the specs. WXGA is ok, but is nowhere near what can be done
with a "real" 32" LCD computah monitor. For example, an HP LP3065 30"
monitor will do WQXGA (2560x1600) or roughly twice the number of
pixels.

You can blame the cheap ass networks who switched to KU band digital
feeds with barely enough bandwidth to supply a fixed image without
problems. After they piggyback all the control and timing data, its no
wonder the system freezes.

DTV compression levels were established by cranking up the compression
until the complaints rolled in on the support phone numbers. I also
went through that exercise with CATV. Cramming extra channels into
the pipe is worth lots of money. What we have today is "adequate"
picture quality that paying customers can afford. There may be a
market for high quality broadcast video, but the GUM (great unwashed
masses) prefer cheap. So, we get maximally compressed video of
minimal quality. I don't like it, but my DirecTV subscription is
affordable, so I'll tolerate the loss in quality.

 

[Arny Krueger]

Randy Yates wrote:
(snip)


How many vacuum tubes does it take to build a PLL?

I think that a smple PLL might be done with 3 multi-section tubes. A
dual-diode for the phase detector, two tubes or a triode/pentode the VCO,
and a dual-triode for the op amp. Add more if you were trying to do
frequency division or multiplcation at the same time.

 

[Jerry Avins]

glen herrmannsfeldt wrote:

...

Lead gives a yellow tint. I have seen lead-glass bricks used for
radiation shielding that you can see through. They might be more
than 50% lead by weight and only a light yellow color.

Yellow: interesting. The best yellow glazes I've seen contain uranium.

...

Jerry

 

[Allen]

Randy Yates wrote:

"Richard Crowley" writes:
[...]
How easy it is for us to do arm-chair engineering here 50+
years after the original development *with the technology of
the day*! This entire "discussion" reeks of revisionism and
has turned just completely silly.
Richard, don't look now, but your old-fartness is showing.
Forgive me if I would rather take the word of the people
who actually did it over a bunch of prognostigations from
random Usenet users 50 years after the fact.
I don't recall challenging anything the original designers said or
developed, unless Michael Terrell is one such person.
What does "prognostigation" mean? I can't find it in my dictionary.
Try "PrognostiCation", or "PrognostiCate". Of course, if you looked up
the original spelling you would have seen this immediately the blank
space that you looked at, so you have probably identified yourself as
a troll.

Allen,

Is it that satisfying to you to sit behind your computer and write
nasty little messages like this to total strangers?

If you would read the adjacent post I made on this very subject
a few minutes ago, you would see my reasoning.

Or lack thereof.

Especially since his post was made later than mine.
Allen

 

[Jerry Avins]

He also apparently operated a _legal_ land based spark gap transmitter.
[I was once challenged on that statement - Checking with rep of Antique
Wireless Association of Holcomb NY showed claim was _feasible_.]

Absolutely... something a lot of people don't realize is that spark-gap
transmitters did have resonant circuits almost immediately after the first few
were built. Heck, strictly speaking I don't believe there's anything
inherently illegal about a spark-gap transmitter today -- it'd just that you'd
probably have to filter the daylights out of it to meet mordern emission
standards, so it wouldn't exactly be an "authentic" setup.

Spark-gap transmitters used tank circuits. Even Hertz's original
microwave transmitter used a resonant circuit, the tuned transmitting
antenna. Each spark excited the tank to ring for a few cycles, with
heavy damping. (What we now measure in time constants was called
"logarithmic decrement".) Most had no way to keep the phase of one burst
coherent with the preceding one, so splatter was heavy. (Various ways to
achieve coherence were truly ingenious.)

Spark-gap transmitters of any purity are illegal in US jurisdictions
because the FCC says so. Likewise illegal, no matter how stable it may
be, is an AM modulated oscillator.

Jerry

 

[Jerry Avins]

Randy Yates wrote:
(snip)


How many vacuum tubes does it take to build a PLL?

About as many as discrete transistors: too many. One synchronizes in
other ways. I remember when only very sophisticated scopes had triggered
sweeps. (Was Tektronix the first?)

Jerry

 

[Jerry Avins]

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.

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

 

[Jerry Avins]

Jerry Avins wrote:

(snip)

The TV of a century ago -- Nipkow, 1884 patent -- has absolutely no
influence on today's standard. There was one on-air broadcaster[1] and
one maker of bare chassis and kit receivers[2] (build your own
cabinet) in 1939.

Some years ago I had the book "Television To-day and To-morrow"
from the Caltech library. It was written in 1930. There were
descriptions of spinning disks and neon lamps. No CRTs.

It was called a "Nipkow disk", after the inventor. The spiral pattern of
holes was quite ingenious. It was a 2D version of what later became
facsimile technology.

It wasn't useful for questions about the color subcarrier,
the reason I went looking in the first place.

...

Jerry

 

[Ron Hunter]

glen herrmannsfeldt wrote:

...


Yellow: interesting. The best yellow glazes I've seen contain uranium.

...

Jerry

Grin.
Now there is a great idea, uranium glass for radiation shielding....
BTW, is there a warning on those lead glass bricks about not eating
them, or letting children play with them? More paranoia.

 

[Richard Crowley]

If you would read the adjacent post I made on this very subject

Especially since his post was made later than mine.

Remember that propogation of Usenet posts is "best-effort"
store-and-forward. There is no "handshaking" or feedback
mechanism to ensure transmission or reception. Remember
also that time/date stamps are not necessarily coordinated.
And finally, remember that every different Usenet NNTP server
may display messages in a different order than what you are seeing.

 

[Don Bowey]

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.

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

 

[Joerg]

Joerg wrote:
(snip)



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

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.

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.

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.