[mythtv-users] fine tuning on Plextor ConvertX

Dale E. Martin dale at the-martins.org
Fri Feb 17 04:14:40 UTC 2006

> I'll bet you're on a cable system, and your operator is not using  
> "standard broadcast" channel frequencies.

Yes, I'm on SELCO cable.  (http://www.shrewsbury-ma.gov/cable/)

> The cable industry has a couple of frequency allocation schemes that  
> are different from broadcast standard - IRC and HRC (Incrementally  
> Related Carriers and Harmonically Related Carriers, in case you're  
> interested).

I'm actually casually familiar with the difference between these standards,
but don't have any way of proving or disproving that I'm on IRC or HRC.
You theory sounds reasonable.

> The most obvious difference to normal folks is that channels 5 and 6  
> operate on slightly different frequencies from their over-the-air  
> equivalents. Other channels on HRC systems are "off" as well, but not  
> as far as 5 and 6.

I see.

[snip more interesting info] 

> Other than channel tables for dvb cards, I've never seen any  
> provision for STD, IRC or HRC in MythTV, I think it is left to the  
> controlling card drivers to handle it.

As I mentioned, the fine-tuning in the channel editor got me close enough
with the bttv cards that it was useable.  (Without the fine tuning it was
not, just like with the Plextor channels 5 and 6 are unusable right now.)

> I don't know if the Plextor has provision to change the tuning table to
> accomodate non-broadcast channel frequencies, I know some devices just
> relay on very wide AFC windows to deal with it.

The driver looked to me like it takes tuning requests in terms of frequency
specified as an integer in kilohertz.  (This was a quick perusal several
days ago, so I might have the details wrong.)  Of course, I don't know if
the hardware downstream of the ioctl is doing something 'clever' with the
request either - the driver loads a binary blob into the hardware.  (And
it's not like I have schematics or data sheets anyways ;-))

> If you can find any reference to changing your drivers for IRC or  
> HRC, and can implement one or the other of them, I'll bet that clears  
> up your problem.


> Maybe this will get you pointed in the right direction ???

It's definitely an interesting thought - I'll have to google a bit and see
if anything comes up.  Thanks for the idea!

Take care,
Dale E. Martin - dale at the-martins.org

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