[mythtv-users] Signal strength now reporting 50% instead of 100%

Stephen Worthington stephen_agent at jsw.gen.nz
Sat May 7 03:57:12 UTC 2022


On Fri, 6 May 2022 22:05:30 -0400, you wrote:

>1. I'm using the standard Kubuntu 22.04 kernel 5.15.0-27-generic. So I'm
>not using the special Hauppauge kernel.  I've been doing this for several
>years.  I don't think there is anything in the Hauppauge kernel that is not
>in the main kernel.
>2. I'm not sure how I would test the on-board amplifier. At this point I'd
>lean toward it being a display software issue because in the past if the
>signal on Live TV showed 50% or less I could not lock the signal enough to
>view it.  At this point I get no errors on any channel and the signals are
>mostly in the 50s.  My PBS station 40 miles away is usually around 50 now
>reads 25 and it's coming in clear.
>
>Jim A

MythTV just reports the signal strength values it receives from the
tuner.  It does no calculations.  It is not possible to compare the
signal strength reports between different types of tuners (even from
the same manufacturer) as they are not calibrated, so you do not know
what the numbers actually mean.  There has always been significant
difference between various tuners as to what they report from the same
aerial connection.  Your getting 90-100% from the HDHRs and only
40-50% from the WinTV Quads is quite normal.  The only thing that the
signal level reports can be used for is to compare with previous
reports from the exact same tuner.  If the WinTV Quad tuners are now
reporting a different signal strength when the HDHRs are not, either
there has been a change in your aerial system (maybe you have a
splitter that is going bad), or the WinTV drivers have been updated to
cause the change.  If you are actually getting a lower signal on the
WinTV Quad tuners, but are still getting good recordings, that is
possible as TV tuners have a very wide range of signal levels that
they operate over, and the modern tuners typically have an even wider
range than older ones.

Tuners can also report signal to noise ratios and bit error rates. The
bit error rates (if reported), are the most important - if there are
any errors, you have a problem that needs fixing as your signal is bad
enough that the digital side of the receiver is seeing errors. The
signal to noise ratio values are also calculated by the tuner and are
uncalibrated, but they are usually a better indicator of reality as
they are a ratio which is therefore less affected by the lack of
calibration.  But in order to interpret them, you have to know the
characteristics of the specific tuner (what s/n ratio it needs to
perform properly), and that data is almost never provided by the
manufacturer.

In the case of the modern multi-tuner devices like the WinTV Quad, the
aerial input goes through an onboard low noise amplifier (LNA), and
then into a splitter that sends the signal to the individual tuners.
Normally, for a 4 tuner device, the LNA will amplify the incoming
signals to 4 times the level plus a little, so that when it is split 4
ways to the individual tuners, each tuner will receive the same level
that is seen at the aerial input before the LNA.  But it is also
possible to design the individual tuners to have a different
sensitivity so that they expect a larger or smaller level in their
individual inputs compared to the aerial input, and then adjust the
amplification in the LNA to match that sensitivity.


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