[mythtv-users] Different mux frequencies for 2 DVB-T cards possible? (due to buggy hardware/firmware/driver)

Kevin Page mythtv-users-list at krp.org.uk
Wed Sep 26 11:21:18 UTC 2007


My local transmitter uses offsets from the main channel frequencies for
its DVB-T muxes - i.e. the transmitted mux frequencies that the hardware
must tune to are offset from the normal "centre" frequencies.

I have a Nova-T PCI that _must_ be given the broadcast frequencies
including offset to tune; this works fine in MythTV and the
dtv_multiplex table shows the frequencies stored for each mux are those
including the offset.

I also have a Freecom USB stick (WT-220U / ZL353 based) which
unfortunately behaves incorrectly - to tune it needs to be given the
centre frequency _without_ the offset. To make things worse, once tuned
to a mux it seems to report back (I know not how or why) the "correct"
frequency _including_ the offset (i.e. the one that won't work if you
tell the tuner to use it!).

In MythTV, the Freecom stick won't work by default - the full automatic
channel scan doesn't find anything. If fed a fudged channels.conf with
the frequencies it needs to hear, Myth will find all the muxes/channels
BUT the frequencies stored in dtv_multiplex are those including the
offset (presumably because this is what the Freecom reports back). So to
get it to work in Myth you then need to manually subtract the offsets
from the appropriate entries in dtv_multiplex.

The problem is: I'd like to use both the Nova-T and the Freecom on the
same mythbackend.

If I change the dtv_multiplex frequencies to work for one, they won't
work for the other.


1) From what I can see the mux frequency is referenced from channel, and
therefore from videosource - there's not a direct association with
cardinput/capturecard? It doesn't make sense to e.g. have double the
entries in dtv_multiplex (with working frequencies for both cards)
because each channel entry will only use one mplexid?

2) So to use both cards I need to have two videosource, either xmltv or
EIT - but identical in all but name - and tie one to each one to a card,
then fudge the frequencies for the mplexid used by the Freecom? Myth
will then fix channel equivalence higher up the stack using channel
number/callsign matching?

3) Apart from fetching xmltv twice, are there any other problems or
downsides I'm likely to experience?

I'm not sure whether the freecom misbehaviour is down to broken
hardware, firmware, or software - but it's been reported on linux-dvb
several times over a couple of years and no fixes seem to be



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