[mythtv-users] Tuning problems

Damian myth at surr.co.uk
Tue Jan 1 19:53:11 UTC 2019

On 29/12/2018 06:44, Stephen Worthington wrote:
> On Fri, 28 Dec 2018 16:11:59 +0000, you wrote:
>> Hi all,
>> I've had tuning issues for months now, but we mainly watch downloaded
>> content, so I've not worried too much about it.
>> However, there's not much point using MythTv without the TV bit! :-) And
>> I know how great it can be when it's working, so I'd like to sort this
>> out if I can.
>> Here's the issue ...
>> To keep things simple, I've got 2 SD tuner sticks installed at the
>> moment. I've got a HD one waiting to be used too, but I'm not too
>> worried about HD TV. I'd rather just get the 2 SD sticks working again.
>> I'm in the UK and should be (at least we used to be!) in the Mendip area.
>> Here are the details hoe how Mendip 'should' tune ...
>> https://ukfree.tv/transmitters/tv/Mendip
>> The settings are different to what they were a few years ago, but to me
>> it looks like I the main channels are at 562000000Hz, 578000000Hz.
>> When I do a full scan, with MythTV, it gives me transports like ...
>> 698000000 Hz,
>> 738000000 Hz
>> 690000000 Hz
>> 721833330 Hz
>> Auto turn always results in finding channels, but they are temperamental
>> and unreliable.
>> This wouldn't be a problem as MythTV always seemed to tune to the wrong
>> transports. The problem is that if I edit the transports, like I have in
>> the past, to mathc up frequencies, then the system fins nothing!
>> Back when things used to work, manually editing the transports would
>> solve everything and I'd have rock solid tuning. however, that's not
>> been the case for along time now.
>> Any ideas how to get to the bottom of this?
>> I should mention that if I need to go to the command line, my level is
>> 'ls' and 'top'! :-) I can follow instructions, but have no idea what I'm
>> doing in there.
>> One final thing to mention is a new error message that I'm noticing when
>> I go into the Multiplex editor. It's stated saying:
>> "Sorry, the Transport Editor can only be used to edit transports which
>> are connected to a card input."
>> However, it then seems to work fine.
>> Hope some of you geniuses can help! :-)
>> Cheers,
>> Damian
> First, you have a slight misconception as to SD and HD tuners. There
> is no such thing. I am guessing that you mean DVB-T when you say SD
> and DVB-T2 when you say HD, but that is not correct. To broadcast an
> HD channel requires more bandwidth than an SD channel, but it is
> entirely possible to do it on a DVB-T transmitter - you just wind up
> being able to broadcast usually only one HD channel on the frequency,
> with only one or two more SD channels. That is what is done here in
> New Zealand. The DVB-T2 standard allows higher bandwidth transmission
> using the same amount of radio spectrum as a DVB-T transmitter,
> allowing multiple HD channels on the same transmitter. In the UK, I
> believe that when the HD channels were added, they were all put on new
> DVB-T2 transmitters, and they were done as duplicates of the same SD
> channels on the old DVB-T transmitters. It was done that way so that
> people who had DVB-T only receivers (older TVs and set top boxes)
> would still be able to receive the SD channel. In New Zealand, we do
> not have as many channels so we just kept using DVB-T and added two
> more frequencies and moved some SD channels on to them to allow HD to
> be broadcast on the original DVB-T frequencies. So we do not have
> duplicate SD and HD versions of the HD channels, just the HD versions,
> but all the older receivers can receive the HD channels as they are
> broadcast using DVB-T.

Thanks Stephen,

That all makes sense.

I was using SD and HD as a shortcut for the two types of tuners that I 
have, but I understand that it's not an accurate way to describe them.
> Next, exactly what are you using for your DVB-T tuners? There are
> plenty of DVB tuners that work with Linux, and many that do not work
> at all, but there are also quite a few that sort-of work with Linux
> but cause problems. If you have one of the problematic tuners, then
> you may need a fixed driver, but if that is not available, then you
> would be better off getting a tuner that is in the category of "just
> works" with Linux. Your new DVB-T2 tuner might be one of them, so if
> you are having problems with your DVB-T tuners, using the new DVB-T2
> one might be the solution. All DVB-T2 tuners are in fact DVB-T/T2
> tuners - they will receive DVB-T or DVB-T2 signals. The driver
> normally has to control the selection between DVB-T and DVB-T2, except
> for some of the very first DVB-T2 tuners where the firmware inside the
> tuner automatically tried both standards. The automatic switching was
> actually a violation of how the Linux drivers were supposed to work,
> but it made the early DVB-T2 tuners work with DVB-T only drivers.

I've got 2x Hauppage Nova Win TV sticks (the one's that I've been 
calling SD).
And one pctv 292e stick (the one's that I've been calling HD).

I assume that the drivers are OK, as I've had everything working fine 
with them in the past.

> According to the web page you cited, these are the frequencies you
> should be receiving, sorted in frequency order:
> 562000000 DVB-T
> 570000000 DVB-T
> 578000000 DVB-T
> 586000000 DVB-T2
> 594000000 DVB-T
> 690000000 DVB-T
> 714000000 DVB-T
> 746000000 DVB-T
> 754000000 DVB-T
> The frequencies above are in Hz, as should be stored in your
> mythconverg database's dtv_multiplex table. When you do a scan, the
> scan should pause on each of those frequencies (except possibly the
> DVB-T2 one) while it locks on and reads the data to tell it what
> channels are present. It may also pause on other frequencies if there
> are other transmitter sites it can receive.

Yes, that's what should be found, but it just isn't!

It just goes passed the correct ones and sometimes finds wrong ones. I 
can't explain why.

The only correct one that it seems to find is 690000000 DVB-T
> If the scan is not seeing those frequencies, there are some settings
> to check. In mythtv-setup, go to Capture Cards and then for each of
> your tuners check that Signal Timeout is set to 1000 ms (or more). If
> I remember correctly, that is the default value, but check anyway.
> Then check the Tuning Timeout. That will likely be set too low for
> the way things work now. Around the world, there seem to be some
> channels that now need a rather longer timeout. Here in New Zealand,
> we need over 7 seconds for one of our channels ("Three"). I have mine
> set to 10000 ms (10 seconds). Until a couple of versions of MythTV
> ago, having this setting too low did not matter too much, as when
> mythbackend was tuning a channel, if it timed out there were several
> retries and it usually tuned on one of the retries. Now, if it times
> out on this timer, there are no retries and tuning fails. I am not
> sure if this timer affects scanning, but it is best to have it set
> properly.

I've made those changes and re-scanned.
Got the same results.

> The other thing to check is the frequency table being used for the
> scan. This is able to be set globally and also for each video source,
> and is a list of all the frequencies used in a country or region. It
> also sets the bandwidth used for each frequency. The standard
> bandwidth for DVB-T and DVB-T2 in most countries is 8 MHz, but some
> countries (Australia for example) use 7 MHz and fit fewer channels on
> each frequency, but have more frequencies available. The bandwidth is
> a critical setting for tuning as if it is set wrongly, the tuner will
> not tune at all even if the frequency it is tuning to is correct.
I've got it set to europe-west. That used to work fine.
> The global setting for the frequency table is found in General >
> Locale Settings > Channel frequency table. For the UK, I think it
> needs to be set to "europe-west", but I am not sure. I hope some UK
> user on this list can confirm that. The per video source setting is
> found in Video Sources > (your source) > Channel frequency table. It
> is normally set to "default", in which case the global setting gets
> used, but you can override the global setting by changing it to
> something else. In New Zealand, the values in the frequency table
> have had to be updated a couple of times as new frequencies have
> started to be used. If your channel table is not up to date, then it
> is possible the scan my miss some (or all) frequencies. If you think
> that is happening, you can try changing the "Channel frequency table"
> settings to "try-all". That is supposed to check all the DVB-T/T2
> frequencies used world wide, so it makes a scan take much longer. I
> am not sure if it checks with both 8 MHz and 7 MHz bandwidth settings
> (making it take twice as long), but I would hope that is the case.
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