[mythtv-users] MythTV and TV

R. G. Newbury newbury at mandamus.org
Mon Jan 30 15:45:17 UTC 2006

Yan Seiner wrote:
> Chad wrote:
>>> Q:  Where do I put in the correct freq table for US
>> When you run mythtv-setup on the backend, under the General option,
>> you come upon a screen that says:
>> Global Backend Setup
>> In that screen there lies that option.
> Right, I put in US broadcast but it doesn't seem to be the correct one..
> ISTR US cable uses the same freqs for channels 2-13, and if I put in 
> US-Cable I can in fact receive channel 9 OK. If I put in US-Broadcast I 
> get green screen on channel 9....  I am hooked up to an off-air antenna, 
> no cable.
> So whatever programs the freqs for the bttv card isn't doing it 
> right...  Or something.
You cannot just change the Input Connection if the Source is a different 
The order in which things are done in mythtv-setup is slightly 
misleading in that a user can infer that the *card* is the most 
important part of the process. Actually the *lineup* is the most important.
The channel lineup, at least for North American users, will 
differentiate among cable, cable digital and broadcast.  Labs.zap2it.com 
will allow you ONE lineup of each of those types. Each of those has 
different connotations:  'cable' runs from 2 to 71 or so, 
'cable-digital' has "channel numbers" which run up to 999 I guess, but 
the frequencies involved are all actually the same range as 'cable' but 
with subchannels. Broadcast can be analog or digital. Broadcast digital 
is handled in a similar manner to cable-digital, but the numbering 
scheme is different.

Cards handle either analog or digital streams (NTSC or ATSC),  BUT NOT 

That differentiation also determines what tuning information ( a 'tuning 
set') that mythtv sends to the card. Changing the information in mythtv, 
without any change to the lineup can produce a useless tuning set. I 
don't know what your card is, but if you are using an HD level (ATSC) 
card for OTA, then no wonder it will not work properly if you tell the 
card (through myth) that it should tune as if the input were a cable 
channel. Although transmission frequencies are the same for analog 
broadcast and analog cable channels and the underlying frequency may be 
the same for an HD digital broadcast, the manner in which the card 
abstracts the digital stream is quite different for a digital broadcast. 
To get an analog stream (channel 9 not channel 9_1) needs an analog 
module setup. ( For the pcHD3000, you use cx88_dvb for ATSC, and cx8800 
for NTSC).

Digital broadcast is not the same thing as Analog broadcast and requires 
not only a different kernel module for the card but also a different 
setup in myth even if the lineup is still the same.

Note also, that if the lineup type remains the same, you will run into 
problems if that lineup includes both analog and digital channels, since 
myth does not actually know that a card cannot do both. You must set up 
lineup <-> card pairings where that card can actually tune all of the 
channels in that lineup. So a PVR500 should never be paired against a 
cable-digital lineup or a broadcast lineup which includes digital 
channels: it cannot tune those channels. Similarly, a pcHD3000 should 
not be paired with a lineup which includes analog channels unless the 
card is set up to use an analog tuning module...

And as far as I can tell, you cannot switch modules, 'on-the-fly' while 
myth is running, since myth checks each input card on startup, and would 
fail when it did not find the 'other' type of input.


       R. Geoffrey Newbury			
     Barrister and Solicitor
 Suite 106, 150 Lakeshore Road West
    Mississauga, Ontario, L5H 3R2

  905-271-9600  Fax 905-271-1638
       newbury at mandamus.org

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