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Discussion Starter · #1 ·
I don't understand this QAM tuner thing as well as I thought and was hoping someone could explain to me how this works.


I have QAM tuners in a TV, a set-top-box (STB) and the Magnavox 515H recorder. The TV and the STB use aliases and the recorder uses RAW QAM numbers. My last batch of recordings got the wrong channels. After looking at the lineup, I found that CMT-Music, MTV2 and Disney were moved to new channel numbers and all the other channels slid up. For example FX-channel 64 was on 63.4 and now is on 63.3.


Given that information, I would have expected the TV, and the STB to not be able to find FX, but on either of these units, punching in 64 gets me FX even though the raw channel number has changed since I did the scan six weeks ago. Trying to tune in CMT, or MTV2 or Disney didn't work until I rescanned the channels.


Obviously this alias thing is more powerful that I realized. Does anyone know how QAM Aliases work.
 

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You mention a TV tuner, a STB and a recorder, how is everything wired?


The cable co will transmit the stations on a particular QAM carrier putting several stations on one carrier and most TV tuners will display them as such

64-1 64-2 64-3 etc.


The STB supplied by the cable-co will display them as the known channel number. (this is the aliasing function)

There are now some tuners available that (you can purchase) that do the same as the cable-co supplied boxes.
 

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Discussion Starter · #3 ·

Quote:
Originally Posted by RCbridge /forum/post/20795629


You mention a TV tuner, a STB and a recorder, how is everything wired?

Each of these digital tuners is connected to the wall. The STB is one that I purchased. I expect that the cable company tuners know what is where, but I was really really surprised that the STB and the TV could both find the channels that moved.

Quote:
The cable co will transmit the stations on a particular QAM carrier putting several stations on one carrier and most TV tuners will display them as such

64-1 64-2 64-3 etc.

Of all my digital equipment, the only one that displays the channels this way is the Magnavox. The others use 2, 3 and 12 for 64.1, 64.2 and 64.3




The STB supplied by the cable-co will display them as the known channel number. (this is the aliasing function)

There are now some tuners available that (you can purchase) that do the same as the cable-co supplied boxes.[/quote]
 

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Quote:
Originally Posted by vickyg2003 /forum/post/20795840


Each of these digital tuners is connected to the wall. The STB is one that I purchased. I expect that the cable company tuners know what is where, but I was really really surprised that the STB and the TV could both find the channels that moved.


Of all my digital equipment, the only one that displays the channels this way is the Magnavox. The others use 2, 3 and 12 for 64.1, 64.2 and 64.3
Maybe this Mag help file will help explain its "hybrid" tuner?


The Mag tuner maps channels to its own numbers but it can't "find" NEW locations for channels like your STB. YOU have to know there's been a change, then either rescan with Auto Channel Preset, or add/delete channels with Manual Channel Preset. All my cable channels have the same major numbers w/o a cable box, it's just the dash/dot subchannel numbers that are different.
 

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Discussion Starter · #5 ·

Quote:
Originally Posted by wajo /forum/post/20796060


The Mag tuner maps channels to its own numbers but it can't "find" NEW locations for channels like your STB. YOU have to know there's been a change, then either rescan with Auto Channel Preset, or add/delete channels with Manual Channel Preset. All my cable channels have the same major numbers w/o a cable box, it's just the dash/dot subchannel numbers that are different.


Yes, I think I understand the Magnavox. It goes to 60.1 no matter what is being sent on 60.1. The part I don't understand is the aliases. When I found that the magnavox recorded the wrong channel, I found that many of the channels had changed location. My cable company had moved a bunch of channels to a new major channel (81.1, 81.2, 81.3, 81.4, 81.5, 81.6). The major channels that originally had these channels, had all there sub channels moved up a notch.


None of the non-oem QAM tuners automatically found the channel 81 subchannels, they all needed to be rescanned. However the TV and the STB could find all the channels that had been slid to a new position since the last scan. This makes absolutely no sense to me, so I must not understand how this works.
 
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