Retuning problem

For discussion of topics specific to MythTV on linux
Post Reply
pinnerite
Senior
Posts: 108
Joined: Mon Apr 07, 2014 2:34 pm
Great Britain

Retuning problem

Post by pinnerite » Fri Apr 13, 2018 9:30 pm

Recently the frequencies at which various TV stations were operating in the UK were changed.
My local transmitter is Crystal Palace in London.

I had to install a new wide-band aerial to be able to receive the newly sited group of stations.
After retuning my Panasonic TV access was resumed.

BUT my dedicated Home Theatre computer running Mageia 5 and MythTV 0.27, even when retuned still has no access to the shifted group of stations.
Before anyone rushes to tell me the version of MythTV that I am using is hundreds of years out of date, I will only be able to update once I have access to all the systems using the Mageia 5 backend.

So the purpose of this long-winded explanation is to ask for any advice?

User avatar
Steve Goodey
Moderator
Posts: 85
Joined: Fri Feb 07, 2014 6:30 pm
Location: Colchester, England
Great Britain

Re: Retuning problem

Post by Steve Goodey » Sat Apr 14, 2018 10:05 am

Have you tried extending the signal and tuning timeouts? Might help.
mythtv-setup, setup capture cards.
https://www.mythtv.org/wiki/Setup_Capture_Cards

MikeB2013
Senior
Posts: 427
Joined: Mon Jul 25, 2016 4:16 pm
Great Britain

Re: Retuning problem

Post by MikeB2013 » Sat Apr 14, 2018 1:43 pm

There is a recent trac ticket against mythtv 29 concerning autodetection of Freeview multiplexes, particularly in relation to the recent Crystal Palace change see https://code.mythtv.org/trac/ticket/13257

I know the channel scanner has changed since mythtv 0.27, but adding the multiplexes manually as in the trac ticket may help.

Mike

pinnerite
Senior
Posts: 108
Joined: Mon Apr 07, 2014 2:34 pm
Great Britain

Re: Retuning problem

Post by pinnerite » Sat Apr 14, 2018 6:45 pm

I would like to follow the suggestions what technical information does one need to hand?

I tried asking this on https://code.mythtv.org/trac/ticket/13257 but my entry was rejected as likely spam!

MikeB2013
Senior
Posts: 427
Joined: Mon Jul 25, 2016 4:16 pm
Great Britain

Re: Retuning problem

Post by MikeB2013 » Sun Apr 15, 2018 11:33 am

This is the place to ask questions (not on a trac ticket)

Assuming you are on the main Chrystal Palace transmitter.
You need the information from https://ukfree.tv/transmitters/tv/Crystal_Palace.
This lists each of the multiplexes, in your case 9 (including the local multiplex)


Examples for transport editor, within mythtv-setup Channel Editor or Channel Scan Tuned in mythtv-setup Input Connections

Mux PSB1 has frequency C23 (490.0MHz) you need the 490 and add 000000 (6 zeros) so you input 490000000 for Frequency Hz
Mode DTG-3 64QAM 8K 2/3 24.1Mb/s DVB-T MPEG2 you need Modulation = 64QAM , Modulation System = DVB-T

Mux com8 has frequency C35 (586.0MHz) you need 586 and add 000000 (6 zeros) so you input 586000000 for Frequency Hz
Mode DTG-6 256QAM 32KE 2/3 40.2Mb/s DVB-T2 MPEG4 you need Modulation = 256QAM, Modulation System = DVB-T2

Bandwidth in all cases should be set to 8 MHz
The other parameters should be at default (Inversion, LP Code Rate, HP Code Rate, Trans.Mode etc)

pinnerite
Senior
Posts: 108
Joined: Mon Apr 07, 2014 2:34 pm
Great Britain

[SOLVED[ Re: Retuning problem

Post by pinnerite » Mon Apr 16, 2018 12:53 pm

Thank you. It all went very smoothly.

PhilB
Senior
Posts: 224
Joined: Sun May 11, 2014 6:23 pm
Great Britain

Re: Retuning problem

Post by PhilB » Fri Jun 15, 2018 8:01 pm

Assuming you are on the main Chrystal Palace transmitter.
You need the information from https://ukfree.tv/transmitters/tv/Crystal_Palace.
This lists each of the multiplexes, in your case 9 (including the local multiplex)
Two comments:
I just do not trust that site.
a) All the frequencies mentioned on that site are receivable with a group A aerial. The HD channels have been moved up into the 50s and the site is wrong.
b) As an example, my Mythtv setup which has DVB-t but not DVB-T2 tuners shows that 586MHz carries channels like London Live which I am able to receive. That frequency is not an HD multiplex.

This is more reliable, but rather cryptic!
http://www.digitaluk.co.uk/coveragechec ... +1DX/300/0

As for the tuning problem, I have come to the conclusion over the years that during a channel scan, if Mythtv finds a fresh frequency which is not in the database, then it will populate the database with the information it finds (QAM etc.) and the frequency is usable.
If the frequency is already in the database then it assumes that the database does not need changing. Hence, if the transmitting authorities change things (eg changing QAM) then the change is not noted and the multiplex fails.

See:
https://www.mythtv.org/wiki/DVB-T_Recep ... _multiplex

Regards
Phil

Post Reply