[mythtv-users] All my unencrypted HD channels are in the 700s. Can Myth tune that high?

R. G. Newbury newbury at mandamus.org
Mon Sep 17 16:51:14 UTC 2007

Eric Robinson wrote:
>> I have Charter cable tv. I just picked up a QAM capable TV, but it
>> doesn't tune past channel 114.5. All my HD channels like ESPNHD,
>> ABCHD, etc, are up around channel 700. I am assuming that these are
>> unencrypted since they are non premium channels - Please correct me if
>> I'm wrong.
>> Anyways, since my TV doesn't tune that high, I was wondering if I
>> could get to these channels via Myth and an HD card, like the pcHDTV
>> HD-5500. My tv has a VGA input so I was thinking (hoping) that the
>> signal from HD to MythTV to TV would be high quality enough. Is there
>> a limit to how high Myth will tune an HD card, or is it a limit of the
>> card? Is anybody using Unencrypted HD on Charter? I'm in Massachusetts
>> and my TV is a Vivitek 46D1. Thanks.
> The person I'm building a MythTV network for, my father, lives in
> southern New Hampshire and also has Charter Cable.  I did a little
> research and found that you will likely need to upgrade your
> rented-from-Charter set-top-box to something that uses Firewire (at
> least that's my understanding of the matter).  The following web page
> shows connections to the DCT6200, a Firewir-capable set-top-box that you
> can rent from Charter:
> http://www.charter.com/Visitors/Support.aspx?SupportArticleID=1156
> A quick search of the MythTV wiki shows that people have been connecting
> that set-top-box to MythTV networks for over a year now.
> My father is currently renting the Scientific Atlanta Explorer 3000,
> which is Firewire-less.  We're going to be requesting a switch to the
> DCT6200 once the backends get built.
> *SPECULATION - or, Educated Guessing*
> That being said, maybe I'm missing something.  Take a look at this:
> http://www.silicondust.com/wiki/hdhomerun/channels
> When I add our zip code I get a big table.  The second table shows
> Digital Cable QAM-256 channel information.  I have to admit that I don't
> quite understand the columns.  The channels have two columns to define
> one of them: Channel and Program.  That makes me wonder if there isn't a
> lot of stuff happening behind the scenes where, say, "Cartoon Network"
> is actually a "program" within a wider "channel" (such that each channel
> has multiple programs that set-top-boxes and TVs map to
> human-understandable Channels).  I'm making a guess here, but that
> appears to be the case.
> That being said, what QAM does your television support?  Is it QAM-256?
>  The higher that number (I believe the max is 256 at this point), the
> more data can be physically pushed through a cable.  Perhaps your TV
> can't read that high?
> *END SPECULATION - okay, no more guessing*

You are labouring under some misapprehensions here. This might help.

TV can be delivered by analog or digital transmission.
(This is 'how'). Of course you need the proper type of tuner.
TV can be Standard Definition or High Definition.
(This is 'what')
The categories set out above are MUTUALLY EXCLUSIVE and not all 
combinations are possible.

	Analog	Digital

SD	Yes	Yes

Digital !== HD.

Lots of digital transmissions are in fact Standard Definition.

Cable companies can encrypt Standard Definition or High Definition 
content as they like, but nowadays, that will only be on digital feeds. 
(Differentiation of analog cable supply is usually done by a frequency 
bandpass filter, not encryption).

Broadcast (OTA) television uses certain channel frequencies, defined by 
a number. Broadcast stops at about 65 (offhand. I'm not sure of that number)
Cable television uses a different set off analog frequencies, also 
defined by number. The usual channel numbering scheme stops at channel 135.

Digital transmissions are also transmitted on the same frequencies, but 
are defined by the channel number and a stream number, eg. 29.1. That 
combination is either broadcast channel 29, stream 1 or cable channel 
29, stream 1. Which frequency that represents depends upon whether it is 
a broadcast or cable transmission.

Cable companies often have more than 135 streams to deliver. They 
*arbitrarily* number a 'channel plus stream' combination as a "channel". 
So frequency 29, stream 1 becomes "channel" 702. *Absolutely arbitrary*

The FCC requires that cable co's must carry local broadcast channels. 
These will often be re-mapped to different numbers from the broadcast 
number. And if the station is simulcasting in analog and digital, there 
may be 2 feeds on the cable..28 and 142 for example.

"Free" digital channels are usually QAM256 encoded on cable. Encrypted 
digital channels (premium content) require a set top box. The FCC 
mandates that firewire output be enabled on set top bozes. Ths rules 
seems to be avoided by many cablecos. The CRTC does not know what a set 
top box is, apparently.

Cablecos must transmit identifying information in the digital stream for 
all 'must carry' channels, by FCC mandate. They need not do so for any 
other channesls. The cableco communicates with the set top box by an 
otherwise unused stream, so the box is aware of channel lineup changes.

Determining the *actual* stream from the information provided by an ATSC 
tuner is difficult. The known information is only the frequency channel 
and the stream. These two data points match with NOTHING that we 
otherwise know! Matching with a cableco 'channel' requires watching the 
channel and cross checking with an external tv guide such as 
tvlistings.zap2it.com until you are sure of what you are seeing. Local 
newscast programs are often good differentiators. Then you use the 
channel editor to enter the callsign or xmltvid into the mythconverg 
database. Duplicate network affiliate stations are especially 
annoying...Trying to do this while a Presidential address has preempted 
every channel is a complete waste of time!

Re: "When I add our zip code I get a big table.  The second table shows
Digital Cable QAM-256 channel information.  I have to admit that I don't
quite understand the columns.  The channels have two columns to define
one of them: Channel and Program."

Part of the work has been done by someone else. it is telling you that 
what you find as 80.2 for example has been determined to be WHOMDT2. 
Then you only need look at your cableco's info to check which "channel" 
number that is, in your area (may differ by area/city etc.).

And finally, to feed the trolls, this is not legal advice, because 
giving advice about anything remotely legal is supposedly a felony if 
you are not a lawyer whereever the advice is delivered, so this must be 
illegal advice given by a lawyer... NOT! or NOT NOT! depending....


              R. Geoffrey Newbury			
            Barrister and Solicitor
       Suite 106, 150 Lakeshore Road West
          Mississauga, Ontario, L5H 3R2

         o905-271-9600 f905-271-1638
           newbury at mandamus.org

        Helping with the HTTP issue
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