[mythtv-users] Signal strength, Freeview uk.

[Daniel Kristjansson]

On Fri, 2007-06-29 at 12:00 +0100, Matthew McClement wrote:
> Neil Milne wrote:
> > Also, I think the kernel drivers don't always report the correct
> > strength - mine have always shown between 18-22 strength, but I have a
> > standalone freeview box which reports a much higher signal strength so
> > I think the numbers coming from the driver are wrong.
> 
> Yes, the figures reported by the drivers can be all over the place for 
> different tuners. For a while my KWorld 100s reported a 7% signal 
> strength even although recording wise they're the most reliable 
> tuners(compared to the Compro's and dibcom based USB tuners I have).
> 
> I believe the MythTV wiki covers this, but when it comes to signal 
> quality having a tune lock with steady snr and ber values is what you're 
> really looking for. The signal strength at best tells you that the tuner 
> is getting something vaguely signal-like from your aerial.

The Signal Strength & S/N are not normalized across drivers.
While theoretically S/N should be unit-less, most DVB drivers
are reversed engineered, and the DVB API does not define how
this value should be reported anyway. The signal strength is
similar, the API does not define any units. Even if it did
only a few of the driver writers would have the information
to present this data accurately.

These values are still useful to aim your aerial, but you can
not compare the values you get from two different cards. The
BER & UB data can be compared across cards, but these should
always be zero when you have a halfway decent signal so they
aren't all that useful for comparing cards.

-- Daniel