[mythtv-users] pcHDTV signal strength issue

John Patrick Poet john at BlueSkyTours.com
Wed Jun 30 13:01:56 EDT 2004

On Wed, 30 Jun 2004, David George wrote:

> On Wed, 30 Jun 2004, Doug Larrick wrote:
> > David George wrote:
> >
> > > I also went into the channel editor and changed the freqid as per messages
> > > I found in the pcHDTV forum and in the Myth mailing list.  I got kinda
> > > conflicting info on what to use for the freqid.  For example in
> > > Charleston, CBS broadcasts NTSC on channel 5 and ATSC on channel 47.  I
> > > tried putting 47 in the freqid, but then found other messages that seemed
> > > to imply that the freqid field should be 5-1.  I have tried both and get
> > > the same 13% signal strength.  This is on a channel that dtvsignal says is
> > > about 85%.
> >
> > Freqid should be 47-1 for that channel (though the '-1' is not important
> > unless the channel has subchannels).
> Yep, tried 47-1 also.  The two highest strength stations here have
> subchannels.  The rest of the local stations aren't quite up to power yet
> and have a low signal strength even with dtvsignal.
> > > I am running FC2 with kernel.org 2.6.7 with kraxel v4l2 and pcHDTV
> > > patches.  I am running MythTV CVS as of maybe 2 days ago.
> >
> > Does dtvsignal take a while to stabilize for you?  You might try
> > increasing the amount of time Myth samples the signal strength (one of
> > the settings in Mythfrontend).
> Nope, dtvsignal takes about two seconds to get to its max reading.  I see
> 24%, then 66%, then 88%, then it stabilizes.  From the backend log it
> looks like it is waiting 5500ms for the signal strength.
> >
> > On my system, I have to use one of the utilities that sets the channel
> > (dtvsignal, etc.) once before running Myth for the first time after a
> > reboot.  Haven't had time to look into it.
> Tried that also.
> > Signal strength can vary from hour to hour and day to day.  Make sure to
> > do your debugging in the same session as you're seeing failures.
> Yep, made sure of that.  I did the dtvsignal and then went into myth and
> scheduled a one-time record of something on an HD channel that was
> currently playing.
> > You might also disable the signal strenth check in Myth (requires
> > rebuilding) to see if it's giving bad results -- though it uses the same
> > code as dtvsignal so I'm not sure why it should.
> I will try that.  I am a coder so I will dig into this further.  After
> spending an evening on it, I figured I would post a message and see if I
> was missing something.  Hopefully tonight I will be able to spend some
> time changing the sample time and removing the signal strength check if
> necessary.

I have been using Myth with the HD-2000 card for 6 months.  As soon as
pcHDTV came out with "official" 2.6.x drivers, I switched to Fedora Core 2,
and had NO problems.

Last week, I decided I wanted to install everything from scratch.  I even
nuked my mythconverg database.  After getting everything setup, I could no
longer tune any channels in Myth.  I was having the exact same symptoms you
are seeing.  I tried re-installing my backup of the mythbackend code -- did
not help.  Tried a few various other things -- nothing worked.  Finally, I
tried restoring a backup of my mythconverg database -- problem solved.

So, it appears as if current versions of myth don't get the mythconverg
database initialized correctly for the HD-2000 card.  I have not had the
time to figure out what is different between a virgin mythconverg DB and the
one I have been using for months.  Maybe I will have time to investigate on

> Also, I did fix the VIDIOC_S_STD problem.  The latest (2.6.7-1) kraxel
> patches changed the V4L2_STD_ATSC_* values.  So I changed
> libs/libmythtv/videodev2_myth.h from:
> #define V4L2_STD_ATSC_8_VSB     ((v4l2_std_id)0x01000000)
> #define V4L2_STD_ATSC_16_VSB    ((v4l2_std_id)0x02000000)
> to:
> #define V4L2_STD_ATSC_2_VSB     ((v4l2_std_id)0x02000000)
> #define V4L2_STD_ATSC_4_VSB     ((v4l2_std_id)0x04000000)
> #define V4L2_STD_ATSC_8_VSB     ((v4l2_std_id)0x08000000)
> #define V4L2_STD_ATSC_16_VSB    ((v4l2_std_id)0x10000000)
> These values were found in
> linux-2.6.7-v4l2-pcHDTV/include/linux/videodev2.h

Cool.  Did you send this to support at pchdtv.com or jack.kelliher at pcHDTV.com ?

> Thanks,
> David

Glad to have you in the club.


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