[mythtv-users] Forcing QAM256 for digital tuners

R. G. Newbury newbury at mandamus.org
Thu Oct 9 02:54:39 UTC 2008

Larry T wrote:
> How do I force QAM256 for tuning?
> After fighting with the cable and digital tuners (present in both a HDHR and
> pcHDTV-5500) for a while, I have found that it appears that when I tune a
> channel it is automatically determining the frequency.
> When issuing the following commands
> hdhomerun_config FFFFFFFF set /tuner0/channel 105
> hdhomerun_config FFFFFFFF set /tuner0/channel qam256:105
> the results differ drastically. If I do not specify the modulation as in the
> first example, the process of auto-identifying can take anywhere from a
> couple seconds to minutes. If I specify the modulation, it locks on within a
> couple seconds. By comparing the observed behavior, it appears that tuning
> from MythTV is setting it in the auto mode. Looking in mythtv-setup, I could
> not find an option to force the modulation. Is this a supported
> configuration value somehow?
> My other channels seem to lock on to QAM256 right away but only channel 105
> gives me trouble very frequently. My signals are acceptable and once locked
> it plays a strong stream. Am I misdiagnosing the problem and I should be

Have you set the channel mapping on the hdhomerun?

As in
hdhomerun_config 12345678 set /tuner0/channelmap us-bcast
hdhomerun_config 12345678 set /tuner0/channel 8vsb:105
hdhomerun_config 12345678 set /tuner0/program 4

The foregoing would tune to channel 105 and PID 4 (105.4 in 
'channelspeak), ready for watching with vlc


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