[mythtv-users] Poor recording of races only

[Stephen Worthington]

On Tue, 14 Oct 2014 03:35:49 +0000 (UTC), you wrote:

>I get that.  What I'm not sure about is what kind of signal strength I'm looking for.  Do I want a higher signal strength, or do I want it as close to 1 or 0 as possible?  What about signal to noise ratio?  I read somewhere that around 35 dB is optimal.  That seems a bit arbitrary.
>Also, looking at the numbers for my channels, I don't see anything that stands out that would make one channel worse than another.  The signal strengths and S/N ratios are all very close.  Could there be another cause?
>Mike 

The signal strength and signal to noise ratio numbers from tuners are
generally somewhat arbitrary.  They can normally only be compared
between identical cards.  Higher signal strength is good, within
limits, as there is an upper limit to what a card will handle.  I
could not find any real specifications for your card (their "Tech
specs" page is sadly lacking), so I have no idea what the limit will
be.  There is probably a specification somewhere for cable networks
that should give some idea as to the acceptable range of signal levels
for that sort of cable.

Higher signal to noise ratio is always good (more signal and less
noise).  With S/N ratios, the dB scale is logarithmic, so numbers that
appear quite close can be different enough for the card to work with
one and not the other.  It is also possible that the four tuners on
your card are not all equal.  It would be interesting to see the
numbers given for each tuner when tuned to the same good channel, and
when tuned to the same bad channel.  And also if having all four
tuners active at the same time gives different numbers from having
only one active.

Again, there is probably some cable network specification that gives
acceptable S/N ratios.  But the numbers from your card may not be real
- cards often do not give the same numbers as a proper signal meter.

The problem may simply be that the tuners work better at some middle
frequency and fall off in performance on either side of that
frequency.  So a level and S/N that are fine on a mid frequency
channel are not with a channel that is further out.  Tuners often work
like that.