[mythtv-users] HD3000 and High-Def

Cory Papenfuss papenfuss at juneau.me.vt.edu
Thu Sep 1 17:36:57 UTC 2005

> Not only that, but it appears that different types of signals can be
> handled by the same physical input port. The card has only one coax
> port, but if it can handle both digital and analog cable, it follows
> that it magically detects which signal is on the coax port and does the
> right thing with it? Or is this determined by which driver is loaded?
 	Coax is an ambiguous word, although it generally refers to 
RF-modulated signal on a F-type connector.  Basically, the same way 
multiple channels come in over one antenna, these channels can also have 
different type of modulation techniques.

> I'm now hazarding a guess; unless I'm still confused, if one uses the
> V4L drivers with this card, that works if you have an analog SD signal
> (I know this works because I have done it), and the DVB drivers would be
> required if you have a digital signal, but it's the same physical coax
> port in either case. Am I getting closer now? This probably also
> explains why I have never been able to get the DVB drivers to work: I
> don't have a digital signal. All this time I thought QAM was analog
> cable which is why I am so terribly confused about all of this.
 	Yes, that would lead to terrible confusion.  Analog cable is just 
that... analog, regular RF-modulated TV signals.  The reason there's such 
a big deal about HD3000 supporting QAM is that if the cable company 
doesn't encrypt their digital channels, you can then use the HD3000 to 
receive those... SD or HD.

> It does matter though, because I have this card still in my system even
> though it is not currently being used. The PVR-150 in the same system is
> doing the work now. But I'd like to use both cards if I can. I could
> either hook up an antenna to the HD3000 and use it for capturing HD OTA
> signals (maybe later as I don't have an HD-capable TV yet), or just hook
> it to the same analog cable signal as the PVR-150 is using, and use it
> as a second tuner for PIP or for watching one program while recording
> another (all the usual reasons why one might want multiple tuners). But,
> if my confusion is less than it was before, it looks like those two uses
> of the card would require different drivers. Is that correct?
> Thank you for helping me become less confused, or at least confused on a
> higher plane :-)
 	I don't actually have any HD tuner card, but my understanding is 
that there are two drivers for the pchdtv cards... the original V4L one 
hacked up by the company that mades them.  The DVB version is a fairly new 
addition, but it's the one that supports QAM demodulation.

 	I haven't followed the drivers enough to keep track of which 
drivers support both "sides" of the card.  At the risk of providing 
further confusion, let me restate the "3 in 1" explanation of the card. 
Both of the "digital" modes of the card operating (QAM and 8VSB) use the 
CX88 chip as "glue logic" for the demodulation chip to talk to the PCI 
bus.  In the *analog* mode (VSB), the CX88 chip is doing the analog 
sampling and decoding directly.

 	With that in mind, there are probably limitations on how much of 
the card can be used at once.  In other words, it's probably not possible 
to simultaneously record an OTA HDTV signal while capturing SDTV via the 
svideo input... the CX88 chip would have to do two things at once, which 
it probably cannot do.  I also suspect that periodically, driver changes 
to fix the HDTV mode of the card break the SDTV mode... since the SDTV 
isn't any differe/better than a $20 cheapo framegrabber.



* Cory Papenfuss                                                        *
* Electrical Engineering candidate Ph.D. graduate student               *
* Virginia Polytechnic Institute and State University                   *

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