[mythtv-users] channel scan missing channels

Steven Adeff adeffs.mythtv at gmail.com
Wed Dec 15 16:33:10 UTC 2010

On Tue, Dec 14, 2010 at 7:56 PM, Michael T. Dean
<mtdean at thirdcontact.com> wrote:
>  On 12/14/2010 06:06 PM, Steven Adeff wrote:
>> On Tue, Dec 14, 2010 at 3:06 PM, Michael T. Dean wrote:
>>>  On 12/14/2010 01:50 PM, Steven Adeff wrote:
>>>>>>  On 12/13/2010 04:54 PM, Steven Adeff wrote:
>>>>>>> In doing a channel scan on my parents new mythbackend we've noticed
>>>>>>> that Myth isn't finding all the channels that we find using the
>>>>>>> digital tuner in their HDTV. I've done full scans of "Cable", "Cable
>>>>>>> IRC" and "Cable HRC" at QAM-64, 128 and 256. I just can't seem to get
>>>>>>> Myth to see the channels. I need to try to create the channel by hand
>>>>>>> to see if Myth can tune them, but I'm wondering if anyone else has
>>>>>>> run
>>>>>>> into this before?
>>>> anyone have any ideas? there's a few channel's Myth just won't find
>>>> that the digital tuners they have *do* find, and they are HD channels
>>>> so it would be nice if I could get Myth to tune them.
>>> Have you tried to see if any other application using the exact same
>>> hardware
>>> (the PC and the PC tuners) can find them?  Something like dvbscan?
>>>  http://www.mythtv.org/wiki/Dvbscan
>>> Could well be tuner sensitivity/interference, etc., so we need to prove
>>> that
>>> it's actually the software--meaning we need to see some other software
>>> that
>>> uses the same hardware find those channels.
>> I have tried other channel scanners, the problem is, none of them give
>> me a usable output since they just show frequencies and sub channels,
>> but not the "virtual" channel shown by Myth or the TV's digital tuner.
>> On top of that, the mplexid value, which is basically the "channel" to
>> the service value's sub channel is not the number shown as the channel
>> on the digital tuner. So it makes it basically impossible to figure
>> out how to use something like dvbscan/scan to manipulate Myth's
>> channel database.
>> here's the output from scan,
>> http://www.mythtv.org/wiki/Westchester,_CA
>> I created the link so as I figure out what channels are what I can put
>> them there and hopefully help any others in that area.
>> I've tried scanning multiple times, but there are just certain channel
>> frequencies that Myth doesn't find/add.
>> The cable line has plenty of signal strength and a strong S/N ratio.
>> One of the digital tuners doing the scanning uses an output from the
>> same splitter that goes to Myth (for the time being as we set Myth up)
>> and has no trouble finding these channels.
>> And Robert, yes, thank you for your channel scanner work, along with
>> whomever helped. I remember trying to add QAM channels to Myth
>> compared to doing things the old manual way 4 or 5 years ago, and it
>> was not fun. I recently had to rescan my channels due to Comcast
>> moving things around and I was up and running almost immediately with
>> a proper channel mapping. I just wish Time Warner where my parents
>> are, and whom this is for, was as easy...
> So what specifically is missing from MythTV?
> Mike

Myth found about 80% of the channels that two digital tuners in the
house found on a scan. There are two types of missing (sub)channels,
1) some sub channels are missing while others were found, all on the
main channel. For instance, one channel/frequency has 8 sub channels
(standard definition but digital), the TV's found all 8, Myth only
found 5.
2) Some channels/frequencies only have one or two sub channels, the tv
digital tuners found them, and Myth found none of them.

for the first case I created my own channels by copying other channel
entries on the main channel and just changing the sub channel. I don't
know if this will work.

Also, since the channel database mplexid entry (for the main
channel/frequency) does not correspond with the main channel number
used by the digital tuners and by Myth when it does find them, it
makes things difficult/confusing. Since I don't know where the
database holds the relation between the mplexid value, the channel
number, and the channel frequency I can't easily "create" my own
channels to see if they work. If the mplexid value matched the main
channel number it would be great, ie. for channel 77-5, mplexid does
not equal 77, but serviceid always equals 5, or 68-398, mplexid!=68,

My dad was able to get the VCTID from the cable box, so I'm running a
new scan with scte65scan to see if it can find any channel info,
perhaps even find the "missing" channels.

I hope this explains a little better what's going on here.

Thanks for the help all! I keep telling my parents Myth runs great in
my house, they'll never believe me till I get theirs running as

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