Opened 3 years ago

Last modified 3 years ago

#12657 new Bug Report - General

Missing HD channel multiplex

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

Description

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Therefore, wondering if some embedded frequency table in the backend setup has an out of date list?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 (3)

comment:1 Changed 3 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 3 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 3 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 ukfree.tv. 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.

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