What is the difference between scanning for chhannles and going
directly to one?

I thought that letting a VCR or DVD recorder or TV scan for channels/
stations was only to compile a list in advance of channels a device
could receive, by checking out every station and noting which had
signals.

And that pushing 1 3 on the remote would go to channel 13 whether one
had scanned for stations or not, whether digital station frequencies
had changed since the last time one scanned or not. As effectively as
if one scanned the whole spectrum, and then channeled up or down to
get to 13.

Am I right about the paragraph just above?


And that for timed recording, when the dvd recorder goes to channel 13
directly, it looks for it if necessary, just like scanning does. And
if it gives some reception, though bad reception, even though the
transmitter is only 10 miles away, it's not because it's off
frequency?

Or are digital tuners different from analog, in that scanning first is
essential?

Thanks.

"mm" wrote in message
...
What is the difference between scanning for chhannles and going
directly to one?

I thought that letting a VCR or DVD recorder or TV scan for channels/
stations was only to compile a list in advance of channels a device
could receive, by checking out every station and noting which had
signals.

And that pushing 1 3 on the remote would go to channel 13 whether one
had scanned for stations or not, whether digital station frequencies
had changed since the last time one scanned or not. As effectively as
if one scanned the whole spectrum, and then channeled up or down to
get to 13.

Am I right about the paragraph just above?

Well, I don't know about over there in the U.S. but here in the UK, if you
pressed "1" and "3" on the remote control, it would just cause the TV / DVDR
/ PVR to go to the thirteenth channel storage position, in which could be
stored the frequency information for any channel, anywhere in the band. So,
that could be any valid channel that you had chosen to store in that
location, or just as easily, some arbitrary channel frequency that you can't
receive at your location. Scanning for channels causes the tuner to move up
from the bottom of the band to the top, stopping each time that it finds a
channel that it can receive, and then storing the frequency information for
that channel in the next available 'slot'.



And that for timed recording, when the dvd recorder goes to channel 13
directly, it looks for it if necessary, just like scanning does. And
if it gives some reception, though bad reception, even though the
transmitter is only 10 miles away, it's not because it's off
frequency?


I think that you are perhaps getting confused between a channel's name, and
the actual physical channel that it's broadcast on ? Even over there, I
think that VHF has long gone, hasn't it ? We have channels here called
"Channel Four" and "Channel Five", but they have never been broadcast on VHF
channels 4 and 5. They have always been up in the UHF band on various
physical channel numbers between 21 and 68, in different parts of the
country.



Or are digital tuners different from analog, in that scanning first is
essential?

Thanks.

Digital is way way different from analogue. Take everything that you ever
knew about how analogue TV was transmitted, and just forget it. Digital
transmissions are 'lumped together' into blocks of frequencies called
multiplexes. Within a single multiplex, there may be many channels, and no
single one is independently identifiable, because various techniques are
used to 'mix' the data from individual stations to produce a form of spread
spectrum transmission containing encoded interleaved data. In order to
resolve this into individual stations, a channel scan has to take place
initially, and as each multiplex is found, the information about what is in
that multiplex, and how to get it out, has to be decoded and stored and used
to build the EPG that is a fundamental part of digital TV

Arfa

I thought that letting a VCR or DVD recorder or TV scan for channels/
stations was only to compile a list in advance of channels a device
could receive, by checking out every station and noting which had
signals.

It is.

And that pushing 1 3 on the remote would go to channel 13 whether one
had scanned for stations or not, whether digital station frequencies
had changed since the last time one scanned or not. As effectively as
if one scanned the whole spectrum, and then channeled up or down to
get to 13.

Correct. If you select a channel that hasn't been stored in the set's
scanning memory, you'll get that channel, whether or not a signal is
present.

The "go to" is instantaneous. The set does not scan from 2 through 12 before
hitting 13. The basic principle (I assume) is the same as for any digitally
tuned receiver -- the LO is directly set to the frequency needed to receive
channel 13.

In article ,
mm wrote:
What is the difference between scanning for chhannles and going
directly to one?

Or are digital tuners different from analog, in that scanning first is
essential?

On analog tuners, the frequency is a direct function of the channel
number as seen by the user.

On ATSC digital, that is no longer true. The "channel number" seen by
the user is no longer a 1:1 function of the transmission frequency.

There are actually two channel numbers involved... the transmission-
frequency channel number (which corresponds to the old NTSC analog
channel number) and the station-identification channel number. They
may very well be different.

This architecture was put in place so that stations which were
previously down in the VHF range, could move their transmitters up to
UHF, without losing their commercially-valuable "channel number"
identity.

So, when you tell a digital TV or DVR or set-top box to do a "channel
scan", it's doing several things:

- It scans the frequencies, looking for NTSC and ATSC signals, and
"remembering" which channels are in use.

- When it sees an ATSC digital signal, it pauses briefly, decodes and
parses the signal, and "remembers" which "channel numbers" and
sub-channels are being multiplexed/transmitted on that frequency.

Subsequently, when you tell it to "tune to channel 13", it will look
ints memory. If it previously saw that "channel 13" was NTSC, it just
tunes to the traditional Channel 13 frequency slot. If, however, it
detected a "Channel 13" ID in an ATSC digital stream on *any*
frequency (even if not the traditional "channel 13" frequency) it will
tune to that frequency, start decoding, and begin extracting that
program.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

On Fri, 11 Mar 2011 10:03:30 -0800, "William Sommerwerck"
wrote:

I thought that letting a VCR or DVD recorder or TV scan for channels/
stations was only to compile a list in advance of channels a device
could receive, by checking out every station and noting which had
signals.

It is.

And that pushing 1 3 on the remote would go to channel 13 whether one
had scanned for stations or not, whether digital station frequencies
had changed since the last time one scanned or not. As effectively as
if one scanned the whole spectrum, and then channeled up or down to
get to 13.

Correct. If you select a channel that hasn't been stored in the set's
scanning memory, you'll get that channel, whether or not a signal is
present.

The "go to" is instantaneous. The set does not scan from 2 through 12 before
hitting 13. The basic principle (I assume) is the same as for any digitally
tuned receiver -- the LO is directly set to the frequency needed to receive
channel 13.


Aren't you and Arfa disagreeing? Is it different from the UK to the
US?