[mythtv-users] Tuning issues

[Tony Sauri]

On 16/12/13 11:01, Jean-Yves Avenard wrote:
> Hi there.
>
> something very weird here...
>
> I upgraded a mate's machine last thursday from ubuntu 10.04 (with myth
> 0.25) to 12.04 and 0.27.
>
> It was all working perfectly before that
> Since then all the recordings to one channels have failed (SBS).
>
> I made him do a full channel scan, and he can't receive that one
> channel anymore.
>
> The other weird thing I had personally never experienced is that when
> scanning for channels, it gives a message about finding conflicts
> (this is after deleting all channels and rescanning) and asking to
> enter channel numbers. That's for the now missing channel.
>
>
> Any ideas what would cause reception level to drop after only
> upgrading the OS? I don't believe there's been much change to the
> dvb-t card drivers (it's a DVICO Dual Digital 4 card)
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>
I am currently running up a test 027 mythtv system to replace
my ageing 024 system that still runs extremely well.

I am right now noticing something similar to what you report and have 
been documenting what I think may be sub-optimal processing by 
mythtv-setup during a channel scan and channel editing set-up.

In my case I get good signals from 2 sources:

A) The main regional transmitter with perfect line of sight and about 12 
km distant.

B) The back lobe of an infill transmitter ... again perfect line of 
sight but about 1.5 km distant.

It is further noted that the angular separation of these transmitters is 
less than 30 degrees.

The transmitters carry the same signals (3 multiplexes) on different 
frequencies:

Trans 1     Mux 1     Chan   32     Freq 562000000  Hz
Trans 2     Mux 1     Chan   33     Freq 570000000  Hz
Trans 1     Mux 2     Chan   34     Freq 578000000  Hz
Trans 2     Mux 2     Chan   35     Freq 586000000  Hz
Trans 1     Mux 3     Chan   36     Freq 594000000  Hz
Trans 2     Mux 3     Chan   37     Freq 602000000  Hz


So when I do a delete all capture card and re-add them and do a full 
scan I end up with twice as many potential channels as I need.

Now when I go through the channel editor I have no way of discriminating 
between the real or phantom channel records or to put it another way of 
associating a channel record with a particular mux frequency.

I have found that if you decide to just use the first channel record 
presented and add the xmltvid type stuff when you save it is rejected 
because of a duplicate channelids.

So then it becomes a dance to make sure both phantom and real channel 
record have different chanids before being able to save a channel record 
successfully.

The only way I have found to stay sane is to resort to a little sql. :-)

In your friends case I would suggest the transmission signals have 
changed meaning that he now has 2 SBS mux's  available.

In passing I will also note that all of the scan methods available

eg 	Full Scan
	Full Scan (Tuned)
	Import Existing Scan
	Scan of all existing Transports
	Scan of Single Existing Transports

have issues in my particular use-case.

I have partially documented these issues and  will submit them as bugs 
or post here for comment shortly but at the moment (This Time of Year) 
my wife seems to think I should spend my time in other ways.

Regards

Tony