[mythtv-users] pcHDTV signal strength issue
david at thegeorges.us
Wed Jun 30 10:02:21 EDT 2004
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
> 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
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
#define V4L2_STD_ATSC_8_VSB ((v4l2_std_id)0x01000000)
#define V4L2_STD_ATSC_16_VSB ((v4l2_std_id)0x02000000)
#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
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