[mythtv-users] Do HD channels fallback to SD on tuning problems ? [was: multiple transmitters - same channel]

Mark Perkins perkins1724 at hotmail.com
Mon Mar 24 05:53:21 UTC 2014

> I get SBS 1 at about 75% to 76% according to the signal monitor that
> briefly flashes up when I change channels from a different multiplex.

I'm not sure the absolute value means a lot, for a while I had channels reporting 25% strength with flawless reception. So 75% seems excellent to me! I think different tuners will give wildly divergent numbers.

> Unfortunately, when I select SBS HD it does that weird thing and tunes to
> SBS 1 instead so I can't tell you what mythtv signal level SBS HD is
> getting for the moment.

Just to be clear - this is new behavior? Your original message (IIRC) only talked about the channel appearing and disappearing, not cross tuning to a different channel. I've not heard of this sort of behavior before (although others may have).

> Newcastle appears to be a far more powerful transmitter than Bouddi or
> Gosford. Newcastle is 250kW as opposed to Bouddi 650W-1.25kW and Gosford's puny
> 330W.

Good point, I never thought to check relative transmitter power. My 'feel' is that these little transmitters are just black hole patches so if 'in-the-main' the Newcastle reception works for you then I suspect it will be the right one to aim for.

> If I do try to dvbscan using any of:
> /usr/share/dvb/dvb-t/au-Sydney_North_Shore
> /usr/share/dvb/dvb-t/au-Sydney_Kings_Cross
> No channels are found due to the hill methinks.

Check that the frequencies specified in these files are correct, I don't know how they get updated but my Adelaide one was out of date on a couple of channels. I just tweaked my local copy to fix.

> I tried to make up my own au-bouddi and au-gosford dvbscan files but only
> got successful tuning to the ABC channels which share frequencies with the
> Newcastle transmitter. In fact, the Bouddi and Gosford transmitters have
> completely identical frequencies according to http://ozdigitaltv.com:
Yep, definitely target Newcastle.

> I am not really as concerned about which transmitter has the strongest
> signal (and my guess is that it¹s Newcastle) but more about why my mythtv
> SBS HD channel seems to switch to SBS 1
> I¹d still be surprised if mythtv was substituting SBS 1 for SBS HD based
> on a poor signal. I'd have thought that it would simply look up the
> channel frequency for SBS HD, try to tune to it and fail rather than
> somehow know it could tune to SBS 1 for the same content but at Standard
> Definition. Maybe there's some new smart HD to SD fallback, who knows ?
This definitely seems odd? Did I see you mention somewhere that it will tune to SBS HD sometimes, other times it is SBS 1? How do you tell? (OSD? Currently showing program? Is your EPG source accurate now that you know you are on Newcastle channels?). Do you still get nothing at times?
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