[mythtv-users] Poor recording of races only

[Yippee Three-eight]

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 

     On Monday, October 13, 2014 9:28 PM, Stephen Worthington <stephen_agent at jsw.gen.nz> wrote:
   

 On Tue, 14 Oct 2014 15:00:50 +1300, you wrote:

>On Tue, 14 Oct 2014 00:49:23 +0000 (UTC), you wrote:
>
>>I've finally gotten my Ceton InfiniTV 4 PCie working on Mythbuntu.  <YAY!>  Anyway, I've set up a bunch of shows to record, all of them HD.  Many of those shows record just fine.  However, I'm a racing fan, and every race I've recorded so far has been of really poor quality except one.
>>
>>All of those recordings show up with a yellow border.  I think that means the recording is damaged from what I've read.  When I watch the recording, every time a scene changes, the screen gets very blocky (macroblocking?) and the audio cuts out, then it will return to a beautiful recording for a moment until the camera changes, then it repeats.  It gets worse and worse as the show goes.  I haven't let it run, but I have noticed that the file size is very small.  For example, a normal TV show recorded for 1 hour at 5.xx Gb.  A formula 1 race (3 hours) recorded at 0.5 Gb.
>>I've also had some problems with BBC America.  Some recordings are great.  Some show up as yellow like the races.  Of those, some just hang the frontend.  Others come back with a message saying the file is missing.
>>
>>The one race recording I recorded without problem was a NASCAR race that was not scheduled to record, but I turned it on in Live TV.  It looked great, so I went back to the program guide and tried recording it.  It recorded fine.  As I said, these shows are all HD.
>> Initially, I was unable to record anything when I set up the box.  I was getting buffer errors.  I found that my network was running at 10Mb/s.  I fixed that so it's running at 1000MB/s, but I still have some Cat5 (not 5e) cable in the walls.
>>I looked at the channels that I've recorded on and here's what I got for signal strength and S/N ratio:TNTHD - always good:  Signal Strength - 3.8 dBmV, Signal to Noise Ratio - 32.6 dBWMAQHD - always good:  Signal Strength - 4.1 dBmV, Signal to Noise Ratio - 33.4 dBWBBMHD - always good:  Signal Strength - 5.9 dBmV, Signal to Noise Ratio - 34.6 dB
>>BBCAHD - sometimes good recordings, other times not:  Signal Strength:  2.3 dBmV, Signal to Noise Ratio:  34.1 dBNBCS1HD - always bad:  Signal Strength - 3.9 dBmV, Signal to Noise Ratio - 34.8 dBFS1HD - always bad:  Signal Strength - 3.5 dBmV, Signal to Noise Ratio - 32.1 dB
>>Since it seems like a channel thing (higher channels have problems, lower channels don't), I figured I'd look at improving my signal strength.  I've had a Motorola 1-2 amplified splitter (http://www.amazon.com/Motorola-Signal-Booster-BDA-S2-Amplifier/dp/B0017I1PVC/ref=pd_sim_e_5?ie=UTF8&refRID=0REJCWJTGHQ0WF945342) on the line coming into my house for a while now.  It helped a lot as before I couldn't tune.  I've got one of those lines going to my old STB, and the other going to a 1-2 splitter.  From the splitter, one line goes to the cable modem, and the other line goes to my backend's cable tuner card.  I've always read that splitters degrade signal, so I tried disconnecting the STB and connecting one long line directly from the Motorola amplifier to my cable card.  On all channels, SS goes up by 2 - 3 and S/N goes up a bit too.  I've read that a perfect signal strength would be 0 dBmV, but I'm wondering if that's wrong.
>>Can anybody offer any suggestions on what I should look at to be able to record these shows?
>>Mike
>
>Basic physics applies to splitters, as in all things.  If you split a
>signal into two, then each split signal will be less than half the
>signal strength of the incoming signal.  The "less than" bit is due to
>whatever losses occur in your splitter - some are much more lossy than
>others.  The only reason that splitters work in aerial systems is that
>tuners usually have a very wide range of signal strength that they can
>work with, so halving the strength in a two-way splitter still leaves
>a signal that is easily enough for a tuner to work with.
>
>When your signal strength as received at the aerial is too low but of
>OK quality, or you are reducing the strength by using splitters,
>amplifying it helps reception.  But if the signal strength at the
>aerial is so low that the quality of the received signal is not good
>enough for the tuners to use, amplifying it does not help, and in fact
>degrades the signal quality further as amplifiers are not perfect.
>
>Aerials are a compromise - they normally have one frequency they work
>best at and their performance drops off the further away from that
>frequency a channel is being transmitted on.  So higher and higher
>frequency channels (in your case) will likely be getting lower and
>lower quality as received by the aerial, even if they are all
>transmitted with the same strength and quality.  Which they are not -
>transmitters vary in quality and transmission power, even when all
>your channels are transmitted from the same site.  Aerials are also
>more or less directional - if your channels are transmitted from
>different sites, your aerial will likely be pointed in a compromise
>direction somewhere between the transmitters.
>
>So, as you can see, aerial systems can become very complicated.  I
>would suggest that the first thing to find out is if the quality of
>your signal for the bad channels is good enough to work with at all.
>That means plugging your aerial signal as directly as possible onto
>one tuner without any splitters (or amplifiers initially).  Can you
>record from it then?  You may need to try adding amplification, but no
>splitting.  If that works, then you can probably organise amplifiers
>and splitters that will work.  But if it does not work, then the
>problem is the aerial itself.  You may need a different aerial to pull
>in the problem channels, for example, one aerial pointed in the
>direction of each transmitter site and selected for the frequencies
>involved.
>
>If the quality is OK with just one tuner on the aerial, then you may
>need to get a better signal path from the aerial to your tuners.  The
>ideal setup with amplifiers is to have one amplifier/splitter at the
>aerial or as close to it as possible (eg where the aerial cable enters
>the house).  That amplifier/splitter would have individual aerial
>cables going from it to every tuner (including your TVs).  Also,
>amplifiers and splitters come in widely varying quality - choosing
>good ones is important when dealing with lower quality signals.  It
>really helps to have a professional quality signal meter when setting
>up aerial systems like that, and some experience with aerials - so if
>you have a good aerial company you can hire to do the job, that may be
>the best option.  There seem to be plenty of bad aerial companies
>around though.

Oops, I did not read your email thoroughly enough - you are on cable,
not an aerial.  The same rules apply though - the signal at the end of
the cable has to be good enough quality for an amplifier to work, so
try a direct path with no splitting to one tuner.  If that does not
work, then you will likely need to get your cable company to fix the
signal.  However, on looking at the infiniTV 4 PCIe card on the Ceton
web site, it looks like it only has one cable input.  Since it clearly
has four tuners, it must contain a four way splitter.  Possibly it may
also have an amplifier to make up for the splitter, but even if it
does, the signal quality at each of the four tuners will be less than
it is on entry to the card.  So you may find that a single tuner cable
card can pull in your bad channels, where a four tuner one can not.
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