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

I know all the differences between analog and digital tuning in general, just not what happens when one enters 1 3, for example, on the remote.
What is the difference between scanning for channels and going directly to one?
I thought that letting a VCR or DVD recorder or TV scan for channels was only to compile a list in advance of stations a device could receive, by checking out every channel and noting which had signals.
And that pushing 1 3 on the remote would go to channel 13 whether one had scanned for channels 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? But because the signal is bad.
Or are digital tuners different from analog, in that scanning first and whenever the channel frequency changes is essential?
Thanks.
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Right, that is usually a one time deal and then the TV has a memory of those channels. You can usually edit the channel listing also. By eliminating the ones you never watch, the TV will skip over them when you hit the UP or DOWN buttons.

Yes
As effectively as

Yes
Don't think so. It will go to 13 but it won't scan looking for it AFAIK
And

I don't have OTA so I'm not going to comment

Why would the frequency change?
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I think it may vary depending on the particular tuner implementation. Some might not accept a direct channel entry from the remote without that channel having been recognized previously during a scan. Others might accept any channel entry, even one that you don't have and attemp to tune to that channel.
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On Sat, 12 Mar 2011 07:49:09 -0500, "Ed Pawlowski"

The tv station can change the frequence it uses. They do this on rare occassions I think.
Or, maybe a power failure at my house could cause it to forget things. IIRC, unplugging an analog tv long enough would cause it to forget *which* stations are preset, but of course it would have no trouble going to one directly.
What happened is that one of 3 network statiosn whose transmitting antennas are less than 10 miles away stopped coming in. After about 3 days, I emailed them and they wrote back a short nice letter saying with some tvs I need to rescan and would I try that please. (In other words, his transmitter is working as normal, he thinks)
After I wrote them, I noticed that another of the 3 network stations wasn't working and the third sometimes didn't, EVEN though the independent stations in DC, 45 miles away were working.
Now I'm wondering if my antenna amp is malfunctioning and putting out too strong a signal for the strong stations. Hmm, there is a way to test that without going into the attic.
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Why would they do that? Sure it happens, perhaps once, in a station's life but it takes permission (or direction) from Washington to do it.

Generally they default to all enabled. You then program in the channels to be skipped.

If it's a strong station try a wire stuck in the back of the set.
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On Sat, 12 Mar 2011 13:13:52 -0600, " snipped-for-privacy@att.bizzzzzzzzzzzz"

Yes, to cooperate with other stations when the FCC says to.

If it really forgets "everything" it has to scan before it knows the statiosn. Of course brand new digital devices insist on scanning, come to think of it, I think, (and some analog ones did too, but only like they insisted on your putting in the correct time. It wasnt' necesary to make the tv work.)

Exactly. I should have thought of that. I'm getting slow-witted with age or distraction.
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Sounds like you have a bad antenna amp or failing signal splitter...
~~ Evan
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On Sun, 13 Mar 2011 04:30:24 -0700 (PDT), Evan

There's a little more to the story, that the question didn't concern itself with.
I got local stationjs pretty good, put in an attic antenna and it improved some, put in an antenna amp and the locals stopped having outages for a secodn or two, and I got a lot of stations from DC.
Then in January, all the stations from DC disappeared, I kept checkking for weeks, and I thought something went wrong with the amp or maybe the connection in the attic. (I was going to buy an amp from solidstate.com, but came across one at Radio Shack, 55 dollars marked down to 8. So I figure they know it's going to fail soon.)
Then the local network stations disappeared almost entirely while the local non-network inc. fox were good. Later the DC stations were back, I noticed.
Maybe the amp was over-amping, but I didnt' think to check until someone here suggested it and then I didn't have time because last night, after I started the thread, all the stations came back.
If this happens again, I'll be more prepared.
Thanks, and thanks everyone for all the help

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For some tuners if channel 13 was not put into memory during scan, and if channel 13 does not give an adequate signal during direct entry the channel will take.
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On Sat, 12 Mar 2011 09:44:14 -0500, snipped-for-privacy@mucks.net wrote:

Correction: should not take.
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mm wrote:

Hi, Scanning is like a roll call triggering channel register counter. Direct entry of ch. # is like calling one address of the register. In analog circuit it is a mess, lot of discrete circuitry. In digital it is PLL based and ASICs take care of it with more precision and stability.
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wrote:

So is that a yes or a no?

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On 03/12/2011 02:47 AM, mm wrote:

Well, if you input channel 13 and there is a "Channel 13" in memory, it will go to that channel. If there's not, it will go to true RF channel 13 generally.
http://en.wikipedia.org/wiki/North_American_broadcast_television_frequencies http://en.wikipedia.org/wiki/Virtual_channel
when we did the DTV transmission, the channel as it appears on your display no longer necessarily - and usually doesn't - conform to the actual RF channel on which the signal is being broadcast.
for instance, this is the results of a search from antennaweb.org
DTV    Antenna Type    Call Sign    Channel    Network    City, State    Live Date    Compass Heading    Miles From    RF Channel *    yellow uhf    WNVC-DT    30.1    IND    FAIRFAX, VA        261    2.3    24 *    green vhf    WUSA-DT    9.1    CBS    WASHINGTON, DC        62    7.1    9 *    green vhf    WJLA-DT    7.1    ABC    WASHINGTON, DC        62    7.1    7 *    red uhf    WHUT-DT    32.1    PBS    WASHINGTON, DC        62    7.1    33 *    red uhf    WFDC-DT    14.1    UNI    ARLINGTON, VA        66    6.6    15 *    red uhf    WDCA-DT    20.1    MNT    WASHINGTON, DC        58    7.3    35 *    red uhf    WTTG-DT    5.1    FOX    WASHINGTON, DC        58    7.3    36 *    red uhf    WPXW-DT    66.1    ION    MANASSAS, VA        62    7.1    34 *    red uhf    WRC-DT    4.1    NBC    WASHINGTON, DC        66    6.6    48 *    blue uhf    WETA-DT    26.1    PBS    WASHINGTON, DC        62    7.1    27 *    blue uhf    WDCW-DT    50.1    CW    WASHINGTON, DC        68    9.9    50     blue uhf    WMDO-CA    30    TFA    WASHINGTON, DC        65    6.0    30 *    blue vhf    WMDO-LD    47.1    TFA    WASHINGTON, DC        66    6.6    8 *    violet uhf    WNVT-DT    30.6    IND    GOLDVEIN, VA        229    22.5    30
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