DVB-T2 reception problems

[tike64]

Hi,

I have two quad tuner cards, TBS6205 and Hauppauge WinTV Quad HD, and very hard time to get either of them receive DVB-T2 acceptably.

TBS have intermittent disturbances maybe one in every minute or a couple in every hour. I have no idea, what the frequency depends on. Of course I suspected antenna but installing amplifier made no difference. I have created an Ubuntu Jammy (22.04.5) qemu VM BE for this card so that I can build a custom kernel with TBS media tree for it. Kernel is 6.5.0-41-generic.

Hauppauge seems to work better but I installed it just a week ago (the card itself is 7 years old). The problem with it is that the tuners (or the driver) crash now and then. I suspected heat problems and installed a fan on the heat sink but I'm not sure if it made any difference. When a tuner crashes, the incident manifests itself with failed recordings. Then I have to reload cx23885 module. I have also seen a failed recording but tuner being still up (or again).

The BE using Hauppauge card is Ubuntu Noble (24.04.2) LXC VM running on Alpine Linux 3.20.0 with 6.6.31-0-lts kernel. Driver module is the one included in Linux itself. I have not tried to build Hauppauge media tree. Would it make a difference?

Machine is ASRock Rack EPYCD8 EPYC 7551P.

Any suggestions what I should try next? Is it possible that qemu causes disturbances? Should I put TBS into a dedicated physical machine? Is there any hope to stabilize Hauppauge? Are there any better options in the market? Are there any DVB-T2 success stories?

This is happening in Finland.

--

Timo

[white_haired_uncle]

If both cards have issues, I'd suspect the antenna (or something in the path) first. Keep in mind an amplifier only makes the signal "louder", which might help if your signal is too weak, or it might not do anything if your signal is "noisy" (it's going to amplify the noise too), or if your card has an internal amp like some devices with multiple tuners adding another amp can overload things. It's something to try, but the fact that it doesn't help doesn't rule out the "antenna". It also makes a difference where you put it.

Of course, if both cards use the same driver that could be a clue, but personally I'd still look at the input stream first.

There's a bunch of stuff to look at. Are you using the right type of antenna for the frequencies you're looking to record? Where is it (outside, attic, inside)? Is it connected with a high quality cable (with good connections, etc)? Pointed in the right direction? How long is the cable run? Do you have any splitters? Is the antenna grounded properly? Etc, etc.

Since you're using two cards and you said "antenna" (singular), I'm guessing you have at least one splitter. One of the very first things I'd do is to get rid of that and work with just one card at first. And then maybe hook a TV up instead of the card (using the exact same cable connection).

You might also look at TSreader Lite, free software for windows that works just fine with wine, if you want to eliminate mythtv while you troubleshoot. My gut says it'd be a waste of time since myth has nothing to do with your issues, but that's just my opinion.

[tike64]

Thanks for looking at this!

If both cards have issues, I'd suspect the antenna (or something in the path) first.

Yes both cards have issues but they are very different. I have seen no disturbances (yet) with Hauppauge but it occasionally crashes. It is most annoying to realize that my wife's recordings are failed for the last day.

Keep in mind an amplifier only makes the signal "louder", which might help if your signal is too weak, or it might not do anything if your signal is "noisy" (it's going to amplify the noise too), or if your card has an internal amp like some devices with multiple tuners adding another amp can overload things. It's something to try, but the fact that it doesn't help doesn't rule out the "antenna". It also makes a difference where you put it.

You're of course right but, if it really was antenna, I would have expected some difference. But as you say, it does prove nothing.

Of course, if both cards use the same driver that could be a clue, but personally I'd still look at the input stream first.

No, they are using even different kernel. TBS needs a custom kernel with vendor modified media tree. Thats why I have put the BE in that case into a qemu VM.

There's a bunch of stuff to look at. Are you using the right type of antenna for the frequencies you're looking to record? Where is it (outside, attic, inside)? Is it connected with a high quality cable (with good connections, etc)? Pointed in the right direction? How long is the cable run? Do you have any splitters? Is the antenna grounded properly? Etc, etc.

It is not long ago I constructed it. I bought a new antenna intended for the right band and not the cheapest one. It is outside at 5m height. There is less than 10m of cable and it is new. Antennawise Hauppauge seems to be good.

Since you're using two cards and you said "antenna" (singular), I'm guessing you have at least one splitter. One of the very first things I'd do is to get rid of that and work with just one card at first. And then maybe hook a TV up instead of the card (using the exact same cable connection).

The amplifier has two outputs. But when I didn't had it yet, I used only TBS and there was no splitters.

Actually, right now there is direct cable from amplifier to TBS. I didn't have a correct cable for Hauppauge and had to put extra dummy splitter into the path for adaptation. Still TBS have disturbances but Hauppauge don't (at least not yet seen).

You might also look at TSreader Lite, free software for windows that works just fine with wine, if you want to eliminate mythtv while you troubleshoot. My gut says it'd be a waste of time since myth has nothing to do with your issues, but that's just my opinion.

While I'm writing this in MythTV forum, I don't believe at all MythTV being at fault. I'm hoping someone to write how (s)he managed to get perfect DVB-T2 reception. If someone have succeeded with TBS then I'd really suspect my antenna or the qemu arrangement. Or if someone has stable Hauppauge card, I'd like to hear about driver version etc. Or are there better tuner cards people are using.

[kmdewaal]

My two cents is that running this on a VM is not a good idea. I would go with real hardware. Only networked tuners, i.e. the HDHomeRun boxes, do work well on a VM.

[dnalorernst]

For the TBS device:
There was a lengthy thread on the users mailing list named 'mythbackend in a KVM VM (thread started out as "in docker container")' in May 2024.
You may find the thread in the archives at https://lists.mythtv.org/pipermail/mythtv-users/
The outcome was, that PCI pass-through in a KVM causes glitches in the recorded file.
The recording device was an USB HD tuner, though.
Did you disable the IR remote control on that device? This is known to cause failures.

For the Hauppauge card, I would try to disable IR remote control as well.
On most cards, the IR sensor gets polled every 200 ms on the I2C Bus without any use.
Run 'modinfo' of the used driver which will tell you, if this is supported.
If you run "active EIT scanning" on that device which means that the device is always in use, you should try to reset it before starting a recording.

Roland

[tike64]

@dnalorernst, @kmdewaal thanks for the suggestions!

"mythbackend in a KVM VM" was good reading.

I made the TBS BE qemu instance into a slave backend and dedicated a CPU for it with taskset from the same node, where the TBS lives, and also steered the TBS interrupts into that CPU. In no time I saw a glitch again. Then I put up a physical machine for the TBS slave BE and have seen no glitches (yet). I'm more and more convinced that the virtualization causes some kind of overruns. Can I somehow debug and confirm it? How long interrupt latencies are too long? How big buffer there is in BE or FIFO in TBS HW?

Did you disable the IR remote control on that device? This is known to cause failures.

For the Hauppauge card, I would try to disable IR remote control as well.

For TBS modinfo didn't give any hints about how to disable IR. For hauppauge IR was disabled by default.

If you run "active EIT scanning" on that device which means that the device is always in use, you should try to reset it before starting a recording.

Do you mean the whole card (four tuners) or only for the tuners used for recording?

Running another server just for BE is a little bit sub-optimal. Maybe I should try to build a custom kernel with TBS drivers for the host system of my primary server so that I can use LXC for BE. I fear it is not too straightforward because the host is diskless Alpine Linux. If that doesn't work, maybe I go HDHomeRun path.

--

Timo