Freeview HD recordings failing

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loddonlily
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Freeview HD recordings failing

Post by loddonlily » Sun Mar 31, 2019 11:11 am

Hi all - first post with this account, but I've been using Myth for quite a long time now, and my current build has been pretty stable: 27.6+2016 fixes on Ubuntu 14.04. TBS dual HD tuner, configured with 10 encoders. UK Freeview recordings.

A few days ago, my recordings started to fail. If I initiate one manually from the Guide, the status says "Tuning" but gets no further. Experimenting suggests that I can record SD channels but not HD ones - obviously I normally record on HD because, well, SD looks so naff now! I have confirmed that I can actively record on both tuners (recording different multiplexes), so its not just that one tuner is bust.

As far as I can see, there haven't been any recent changes in the Freeview broadcast channels (and my TV hasn't demanded to be retuned).
There is plenty of unused recording space.
I've powered down and restarted the system a few times.
The Linux system is not configured to allow itself to update so nothing else *should* have changed.
The transmitter (Sutton Coldfield) is not reporting any issues.

Any suggestions? If my tuner card is broken then I guess I'll buy a new one, but they're not cheap and I'd rather not if its not necessary.

Is it conceivable that the broadcast stream has changed in some way?

Any thoughts gratefully received.

MikeB2013
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Re: Freeview HD recordings failing

Post by MikeB2013 » Sun Mar 31, 2019 1:01 pm

Is it all HD channels or only some?
According to https://ukfree.tv/transmitters/tv/Sutton_Coldfield
There are 3 HD (DVB-T2 DTG-6) Muxes PSB3 (C40+), COM7 (C55), COM8 (C56)
PSB3 carries the main HD Channels BBC One HD, ITV HD , BBC Two HD etc.
COM7 carries BBC NEWS HD etc.
COM8 carries BBC Four HD etc.

It would be helpful to know your kernel version (output of "uname -a") and details of your TBS tuner (output of "dmesg |grep frontend")

Mike

loddonlily
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Re: Freeview HD recordings failing

Post by loddonlily » Sun Mar 31, 2019 3:15 pm

Thanks for the response - very helpful, though I am now even more confused!

I find that all the channels that are failing to record are indeed on the same mux (Ch40), and I can record HD channels from other muxes. I've messed around with Live TV, forcing a Tuner change, and it seems to be consistent - I can record anything, on either tuner, unless its on the Ch40 mux.

So that broadcast channel must be down? Except it isn't - my TV is showing those channels fine, at full strength. And, yes, I did check that it has also selected the Ch40 option for those channels, same as my MythTV.

I'm probably missing something really obvious here but I can't see what it is...

loddonlily
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Re: Freeview HD recordings failing

Post by loddonlily » Sun Mar 31, 2019 3:19 pm

Sorry, should have answered your questions:

htpc@icarus:~$ uname -a
Linux icarus 3.13.0-43-generic #72-Ubuntu SMP Mon Dec 8 19:35:06 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux
htpc@icarus:~$ dmesg | grep frontend
[ 7.497243] DVB: registering adapter 0 frontend 0 (TurboSight TBS 62x0 DVBT/T2 frontend)...
[ 7.599237] DVB: registering adapter 1 frontend 0 (TurboSight TBS 62x0 DVBT/T2 frontend)...

MikeB2013
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Re: Freeview HD recordings failing

Post by MikeB2013 » Sun Mar 31, 2019 4:05 pm

The good news is that your TBS tuner seems ok, as you can get HD except on CH40+.

The only thing I can suggest is a rescan (mythtv-setup>Input Connections from memory - have not used mythtv 0.27 for a long time).
Try a scan of all existing transports first.
If that does not resolve your problem, try a Full scan.

Make sure mythbackend is not running before doing a channel scan.

Mike

loddonlily
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Re: Freeview HD recordings failing

Post by loddonlily » Sun Mar 31, 2019 4:11 pm

Thanks. I will probably do that - I can't think of anything else! But my experience of rescans is that they nearly always take a lot longer than I'd hope due to the manual tidying up I have to do afterwards and I have other chores to do today. It may be tomorrow before I get to that.

If anyone else reading this is thinking "ah, I know what that is..." then don't be shy, do please shout out!

wesnewell
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Re: Freeview HD recordings failing

Post by wesnewell » Sun Mar 31, 2019 6:22 pm

Assuming you receive these channels ota with an antenna, you may just be getting a weak signal at myth box, especially if you have spliters in the cabling. If you split the signal to more than a couple of receivers, you may need an amplifier and/or a better antenna. I have a very good antenna, but still needed a distribution amp to supply enough signal to the 9 tuners that I have. Here ota is VHF and UHF atsc (8-VSB) for now. Don't really know squat about what you use in the UK.
BE/FE-Asrock AB350 Pro AMD Ryzen 3 2200G, 6 atsc tuners. Frontends-GF8200's,,AMD Athlon II's. Mythtv user since 2005.

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Steve Goodey
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Re: Freeview HD recordings failing

Post by Steve Goodey » Sun Mar 31, 2019 7:06 pm

And on mine, also in the UK, an attenuator was needed to get HD DVB-T2.

loddonlily
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Re: Freeview HD recordings failing

Post by loddonlily » Mon Apr 01, 2019 10:08 am

Thanks for the additional comments. I do have a distribution amp: a coax cable goes into my TBS card and then out again to the adjacent TV, which is seeing a good strength signal. On Myth, signal strength seemed to be similar between the working and non-working channels. Investigations continue!

loddonlily
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Re: Freeview HD recordings failing

Post by loddonlily » Mon Apr 01, 2019 11:40 am

So the retuning made no difference at all. I am interested by Steve's comment about attenuation: I note that the HD channels that I can receive are transmitted at significantly lower power than the one I can't: and I have a big aerial and an amplifier. I did try inserting a splitter to feed the TV and Myth box, which should have given around 4dB of attenuation, but still no joy. Next stop will be to try some inline attenuation but there will be a bit of a delay while I wait for mail order to do its thing (where's a Maplins when you need one!!)

Not sure why this has suddenly changed after working (nearly all of the time) since I moved to this location three years ago - perhaps they turned up the wick on the transmitter? Can't see a note of that, though. Time will tell, hopefully.

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