[mythtv] Problems with Hauppauge Nova TD Dual Tuner USB Stick and Mythtv, no problems in Windows!

Stephen Worthington stephen_agent at jsw.gen.nz
Sat Apr 13 02:11:28 UTC 2013


On Fri, 12 Apr 2013 16:46:29 +0000, you wrote:

>On Fri, Apr 12, 2013 at 1:39 PM, Stephen Worthington
><stephen_agent at jsw.gen.nz> wrote:
>...
>> As it is a dual tuner, it will need to split the aerial signal to feed
>> it to both tuners.  A splitter typically causes around 6 dB of signal
>> loss.
>
>As I recall, that would have been more like ~3.5dB (about half
>power (which would be 3.0dB), but there are insertion losses too).
>One would have to be purchasing very cheap splitters to see a
>6dB loss.
>
>> So that means that any dual tuner will be that much less
>> sensitive than a single tuner.
>
>With the presumption that the tuner uses only a splitter.
>While most low cost devices do (and Hauppauge is a low
>cost device), there are alternatives (including using an
>internal amp) which can mitigate such issues.

True, but I have yet to meet a dual tuner that had an internal amp.

>I will point out that whether the splitter is internal or
>external, the losses are (approximately) equivalent.
>So dual vs. single is not the issue (two singles with
>your splitter is no different than a dual with an internal
>splitter).  Adequate power level to the tuner is.

My point was that you can not avoid the splitter inside a dual tuner -
its losses will add to the losses of your external splitter, and will
always add up to much more loss than if you only have one splitter. So
if your signal levels are marginal and you need more than two tuners,
dual tuners will always give a worse result than single tuners.  Lots
of people have discovered that single tuners of the same type as are
used in a manufacturers dual tuner work better and have blamed the
tuner, when the problem is actually the two levels of splitter.

If you have say 5 tuners (which seems to be what you need in the UK
now), and you have a 4-way splitter feeding three single tuners and
one dual tuner, then the signal to each of the tuners in the dual
tuner will be way lower than that to the single tuners, because of the
extra splitter.  Each feed from the 4-way splitter will get a bit less
than 1/4 of the signal, and then that 1/4 signal to the dual tuners is
split in half again, giving only 1/8 signal to the each of the dual
tuners.  So the tuners in the dual tuner may be exactly the same model
as in the single tuners, but will perform much worse.  If you use 5
single tuners with a 5-way splitter, each would get a bit less than
1/5 of the signal.

So, no it does not matter whether a splitter is internal or external,
but it really, really matters that you have two splitters, one feeding
the other.

>Note too that the design of the tuner (whether in a tuner
>card/dongle, or a TV) can impact the signal sensitivity.  It
>is common in "fringe" areas for one TV to get a subset of
>channels that another TV receives fine.  Tuner cards are
>no different (which is why the "it works with my TV, why
>does my tuner card not see channel X" simply suggests
>that the signal may be marginal to begin with).

Yes, my different tuners all have different sensitivity.  It was
noticeable as problem until I fitted my amplifier/splitter and fixed
things for good.

>Unfortunately, to validate the real signal power and quality
>requires equipment that few individuals will have access
>to.  So most are left to try this, try that, and try the other
>thing.
>
>I do agree with Stephens conclusion though, adequate
>signal level (with low noise) is the key.
>
>Gary

If you are looking for a single USB tuner with good sensitivity, I
have found my two Pinnacle PCTV nano sticks to be the most sensitive
tuners I own.  Unfortunately, here in New Zealand, they are one of the
most expensive single USB DVB-T tuners available.


More information about the mythtv-dev mailing list