Opened 6 years ago

Closed 19 months ago

#12657 closed Bug Report - General (Fixed)

Missing HD channel multiplex

Reported by: Nick Whitehead <nick@…> Owned by: Klaas de Waal
Priority: minor Milestone: 32.0
Component: MythTV - Channel Scanner Version: 0.27.6
Severity: medium Keywords: DVB, frequencies
Cc: Ticket locked: no


Using 0.27.6 and HDHomeRun Connect dual tuner (UK). Freeview aerial pointed at Sandy Heath transmitter.

All channels one multiplex are missing.

Frequency table is set to 'try-all' (with 'europe-west' get no HD channels at all). Region is set to United-Kingdom.

Scanning (TV+radio) results in 131 channels. None of the BBC HD channels are found. On looking carefully nothing on multiplex PSB 3 is found. In backend 'edit transports' 8 frequencies are listed, and Sandy Heath does use 8, but not the same 8 - 474MHz is missing, and PSB 3 uses 474MHz.

If a new one is added (ATSC, 474000000, QAM-256), and channels rescanned, 141 are found and PSB 3 is found, and all expected HD channels are there.

Therefore, wondering if some embedded frequency table in the backend setup has an out of date list?

Change History (5)

comment:1 Changed 6 years ago by stuartm

MythTV doesn't use an hard-coded frequency table, instead it scans a particular range of frequencies until it finds the first multiplex. With DVB each multiplex (frequency) broadcasts a list of all the other multiplex frequencies in use and this is what MythTV is using.

There are a couple of possibilities - either that list from the broadcaster is wrong which is less likely or you are able to pick up a weak signal from another transmitter and it's using the wrong multiplex list.

comment:2 Changed 6 years ago by Karl Egly

There is a known issue when services / transports get shuffled around. #11864

There is also a known issue when you receive transports with the same original_network_id and transport_id (hopefully with identical content) on multiple frequencies. #12107

What could be happening is that a good local frequency is overwritten with a correct but distant frequency of the same transport, or a similar case, leading to missing a good transport.

comment:3 Changed 6 years ago by J.Pilk@…

I have a saved scan of Sandy Heath from 20151206. It shows qam256 muxes at 474166700 and 522000000 Hz, agreeing with the data from I saw only 6 muxes in total, but the signal strength wasn't good. For retuning I would delete all unwanted transports and rescan all known transports, with links enabled.

comment:4 Changed 23 months ago by Klaas de Waal

Milestone: unknown32.0
Owner: set to Klaas de Waal
Status: newassigned

It is a good idea to check the frequency ranges used in the "Full Scan" for the various countries as the high end of the UHF spectrum is now reallocated to be used for mobile applications.

comment:5 Changed 19 months ago by Klaas de Waal

Resolution: Fixed
Status: assignedclosed

The scanning problems reported in this ticket have all been fixed in v31 and v32. The scan frequency range for the UK channels is not yet reduced to 700MHz as the reallocation is not completed there yet. However, limiting the scan frequency range will reduce the time for a "Full Scan" but it is not related to the scanning of channels in the range.

Therefore this ticket is now closed.

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