 |
Search Sci.Electronics.Basics |
|
|
|
|
|
|
 |
|
|
Sci.Electronics.Basics -> What exactly is a four symbol pulse?
There are 3 messages in this thread.
You are currently looking at messages 1 to 3.
|
Author: MRWDate: 02:30 19-11-07
|
|
Hi! I'm reading this article:
http://www.broadcast.net/~sbe1/8vsb/8vsb.htm
I'm trying to get myself familiarized with Digital TV broadcasting. On
that page, there is this sentence:
"The ATSC segment sync is a four symbol pulse that is added to the
front of each data segment and replaces the missing first byte (packet
sync byte) of the original MPEG-II data packet."
I'm not quite sure what a four symbol pulse is. If a symbol is
represented by various voltage levels (+7, +5, +3, -3, etc.) and a
pulse can be looked at on paper as a square wave with a one max
amplitude, then how does this fit into a "four symbol pulse"
description? Maybe my assumption for symbols and pulse is wrong?
Thanks!
I'm trying my best to teach myself this stuff. I can ask my teachers
only so many questions before my time with them is up.
|
|
|
|
Author: Randy DayDate: 07:27 19-11-07
|
|
MRW wrote:
>
> Hi! I'm reading this article:
> http://www.broadcast.net/~sbe1/8vsb/8vsb.htm
>
> I'm trying to get myself familiarized with Digital TV broadcasting. On
> that page, there is this sentence:
>
> "The ATSC segment sync is a four symbol pulse that is added to the
> front of each data segment and replaces the missing first byte (packet
> sync byte) of the original MPEG-II data packet."
If it's a reference to Quadrature Amplitude Modulation,
QAM is a combination of signal amplitude and phase
representing a two-bit segment of the transmission.
If that's not what they're referring to, then I dunno...
HTH
|
|
|
|
|
|
On Nov 18, 11:30 pm, MRW <mr.whate...@gmail.com> wrote:
> Hi! I'm reading this article:http://www.broadcast.net/~sbe1/8vsb/
8vsb.htm
>
> I'm trying to get myself familiarized with Digital TV broadcasting.
On
> that page, there is this sentence:
>
> "The ATSC segment sync is a four symbol pulse that is added to the
> front of each data segment and replaces the missing first byte
(packet
> sync byte) of the original MPEG-II data packet."
>
> I'm not quite sure what a four symbol pulse is. If a symbol is
> represented by various voltage levels (+7, +5, +3, -3, etc.) and a
> pulse can be looked at on paper as a square wave with a one max
> amplitude, then how does this fit into a "four symbol pulse"
> description? Maybe my assumption for symbols and pulse is wrong?
>
> Thanks!
>
> I'm trying my best to teach myself this stuff. I can ask my
teachers
> only so many questions before my time with them is up.
The 4 symbol pulse is described as a 'sync' pulse 4 symbol times long
for the receiver to identify start of a data block . Not the same as
analog sync which indicates start of line or start of field. Look for
the paragraph "VSB modulator" near the end but I recommend reading all
of it.
http://www.hdtvprimer.com/ISSUES/what_is_ATSC.html
Keep in mind the data rate is 19.34 megabits/second but the
broadcaster can set the bit rate for the programming including sub-
channels. Therefore the 4 symbol sync has no reference to the video,
only the data blocks.
BTW the computer I'm writing this on is recording an HD ATSC stream
right now.
GG
|
|
|
|
1 |
|
|
|
|
Contact | Electronic Portal
|
|
|
