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

James Abernathy jfabernathy at gmail.com
Sat May 7 10:49:27 UTC 2022


On Fri, May 6, 2022 at 11:57 PM Stephen Worthington <
stephen_agent at jsw.gen.nz> wrote:

> 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.
>

In the past both the HDHR Quatro and WinTV Quad all had about the same
signal strength reported between 90 and 100%. Except for the PBS station 40
miles away which was 50-60 depending on weather and which tuner.

To debug this, I guess for starters I could take the splitter out of the
loop and cable the antenna to the WinTV Quad directly and then to the HDHR
Quatro and see if things change.

My location is unique in the sense that I can literally see the flashing
aircraft warning lights on the TV towers about 10 miles away.  The issue
has always been to turn the antenna 25 to 40 degrees away from the straight
line of sight from those towers so I could get a signal from the PBS
station at all. If I point the antenna directly at the TV tower farm I get
100 percent on all signal, quality, and symbol quality on all channels but
can't get PBS.

Not sure when this all changes, but this is the first time I've noticed the
reduction of WinTV Quad signal. The only change is I've upgraded my v32
Kubuntu 21.10 to Kubuntu 22.04.

Since I'm getting no errors in recording, no listing of programs in the
library that have the text in Yellow indicating excessive errors, I'm going
to assume I have no problem at all, but I'll investigate. I could always
install Kubuntu 21.10 and MythTV v32 on a USB3 SSD and boot that to test if
it's a software thing.

Jim A
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