When the change from low def to high def was done it also changed the picture signal from AM to FM and became pretty much line of sight?

Is that correct...my memory is a bit fuzzy, to say the least.

 

But they did sell adapters that could convert the HD digital signal to standard NTSC analog.

True, but at least the one we tried was less than satisfactory.

 

So when the CRT TV would Start to Draw would it Start at the Top Left of the Screen or the Top Center of the Screen?

 

NTSC 525/60 system is lower-field (or even-field) dominant. The first field starts at the top left.

 

So when the CRT TV would Start to Draw would it Start at the Top Left of the Screen or the Top Center of the Screen?

Top left to bottom right..

 

The rather disturbing thing is that the newer sets do not seem to be any more reliable than the old tube-type TV sets, despite no longer having those high power deflection circuits.

Your experience must be quite different than mine. I have not had an HD TV fail on me. This includes two plasma models and 3 LCD models acquired for two houses over the last 15 years or so.

Bob

 

Hello,

You might also want to have a look at this page:
http://www.danalee.ca/ttt/analog_video.htm

Bertus

 

So with CRT TVs we Say they work 525 Lines at 60 Hz.

And this Says it would Draw 525 Lines in 1. Second.
And 525 Lines would make up 1. Image Right?

 

So with CRT TVs we Say they work 525 Lines at 60 Hz

No. It draws 1/2 of 525 in 1/60 of a second. It draws all of the image 30 time a second.
Vertically the beam is moving 60hz but drawing half of the picture at a time.
60-Interlaced,
Your eye would be very unhappy if the picture flashed at 30hz but it is ok at 60hz. The center of your vision is slower than the edge of your vision. You look at TV using the center of vision.

 

When the change from low def to high def was done it also changed the picture signal from AM to FM and became pretty much line of sight?

The US HD signal is not FM, it's 8VSB.
(8VSB is 8-level vestigial sideband modulation. In essence, it converts a binary stream into an octal representation by amplitude-shift keying a sinusoidal carrier to one of eight levels).

The line-of-sight reception results from many HD channels going to UHF frequencies, which are more line-of-sight than the lower frequency VHF channels.

 

Thanks for that crutschow.

 

Ok so let me See if I have this Right?

One Frame is made of 525 Lines.
The Odd Lines are Drown First witch are 262 Lines.
Then Even Lines are Drawn Second witch are 262 Lines.

And the Odd Lines and Even Lines are Interlaced to make One Frame.
Now I have to Ask this about the Lines?

If the Odd Lines Start at the Top Left does the Even Lines Start at the Top Center?

I thought I Read that the CRT TV Started one of the Lines at the Top Center.

 

525 lines in full, but only 241.5 lines per interlace, meaning 483 lines visible, the other lines are for frame blanking and synchronization pulses.

 

Sorry about that.

If Even Lines Start at Top Left then do the Odd Lines Start at Top Center?

 

Yes, the reason they had a lot of lines for blanking was because of the time taken for the frame timebase to get from bottom to top, as they used valves which were slow, modern TV's using semiconductor's are a lot faster , so the beam is at the top ready waiting for the next frame scan , so in the 21 lines of blanking they used to transmit Teletext info .

Then there were two types of crt, Delta gun and PIL,. Every TV engineer hated the Delta gun convergence settings.. including me!.

You can tell which type of crt you have by looking closely at the screen, ( easily magnified by droplets of water on the screen) if the dots are in a triangle shape it's a Delta,if they are in line it's a PIL.

 

If Even Lines Start at Top Left then do the Odd Lines Start at Top Center?

The picture line do start in the corner or center every other time. The hardware does not know what. The hardware starts every line at the left because it can't do other wise. The line that starts at the center, really started in the corner and it is black or blancked until it reaches the center of the picture.

 

The Lines are Drawn like a "Z" like this.

The Beam would Start Even Lines at Top Far Left and Zig Zag down and End Bottom Far Right.

The Beam then would Start Odd Lines Top Center and Zig Zag down and End Bottom Center.

Is this Right?

If not I am Looking on Google for the Scan Lines image but they are hard to See.

 

Think of it this way.

For 525/60 system, all 525 lines start from the left side of the screen at the Horizontal Scan frequency.
The Vertical Scan is synchronized to the Horizontal Scan.

The 262nd line starts at the bottom left of the screen.
Halfway through line 262 the Vertical Scan signal resets to the start of its 60Hz cycle.
Thus, by the second half of line 262 the electron beam is back to the top of the screen. The Horizontal Scan signal has not changed. It is still scanning line 262.

 

somehow there is an interlace circuit so that the lines do not over lap. Otherwise it would not make sense to interlace.

 

somehow there is an interlace circuit so that the lines do not over lap. Otherwise it would not make sense to interlace.

That is why there is a 1/2 line delay to getting started for the second field. Where we say the top line (on the second field) starts in the center, that 1/2 line delay moves the beam down a little. (1/525 of a picture)