[mythtv-users] HDHomeRun issues following OS upgrade to Ubuntu 18.04 from 16.04

[Jan Ceuleers]

On 29/08/2020 11:47, Klaas de Waal wrote:
> 
>     I however confirm that my channel changing script (which is plugged into
>     MythTV as an event handler since HDHR tuners don't support a channel
>     changing script directly) is indeed necessary. I'm not sure why as I
>     don't know what commands MythTV issues to the HDHR. Perhaps the commands
>     MythTV sends cause the HDHR to rely on defaults for some unspecified
>     parameters which work in many places around the world but not with my
>     particular cable provider (which is Telenet in Belgium).
> 
> 
> Older MythTV versions give an "auto:frequency" command and then the
> HDHomeRun tries all modulation schemes configured in parameter
> /sys/dvbc_modulation. If you modulation scheme is not in this list then
> tuning will fail. Setting /sys/dvbc_modulation to what your provider
> uses (256qam and 6875 ksym/sec if the Internet is right) with the
> hdhomerun_config utility should fix it.
> This is solved in MythTV version 31. For the HDHomeRun DVB-C there is
> now a more explicit tuning command given that includes the symbol rate
> so it should now always work.
> For the full details see
> tickets https://code.mythtv.org/trac/ticket/12792 
> and https://code.mythtv.org/trac/ticket/13371#ticket.

Revisiting this old-ish topic.

Some months after I pressed MythTV 31 into service on my Ubuntu 18.04
backend I was finally sufficiently motivated to try and resolve an issue
whereby tuning one specific channel would always fail on the HDHR. Since
I also have that channel available from another video source I had just
disabled the HDHR version of the channel and left it at that.

My investigation revealed that this was the only channel (that I'm
recording from) that is transmitted on the 290MHz multiplex; all other
channels (the ones that consistently tune OK) are on the 298MHz multiplex.

So I looked in the database for differences between how these
multiplexes are configured, and what I found is the following:

- Field dtv_multiplex.frequency contained 290 for the failing multiplex,
and 298000000 for the working-one. So I also added six zeroes.

- Fields dtv_multiplex.symbolrate, modulation, and constellation
contained auto, so I set them to the same values as for the working
multiplex (which is 6875000, qam_256 and qam_256, respectively)

- Field dtv_multiplex mod_sys contained something other than DVB-C/A
which is what that field contains for the working transport, so I
changed it to that value. Sorry, I don't remember what value it had
before I changed it.

I don't know which of the above changes made it work, but it does now work.

I hope that this helps someone.

Cheers, Jan