Re: [Discuss-gnuradio] Status of BTTV/CX88 capture

[Martin Dvh]

Hi Hew How Chee,

Hew How Chee wrote:
> Hi Martin,
>
> Pretty good hacking you have done there. Maybe I'll
> try it one day, after the warranty expires :)  
>
> > I think I am going to look for a nice cx2388x
> > capture card.
> > What card are you using ?
> > What tuner is on it? (Is it easy to hack?) 
>
> I am using Pixelview PlayTV Pro Ultra card. It has a
> cx23881 chipset on it. It has also a different tuner
> from my bt878 tv card (which is similiar to the
> Philips FI1216 tuner module). Never try hacking it
> since the main concern is to get continuous adc data.
> Pinout is different also, 
>
> I have uploaded the source code  and a few more
> capture.
Thanks,
Did you copy the risc code from another driver or did you specially make it for 
this driver?
I have been strugling with the risc code in the bt878 driver to get all samples.
(It drops samples which it thinks are illegal because they are marked as sync)

Or did you copy a driver and just add the RAW bit to the configuration?

> You might want to look at the noise I talk
> about. The noise might be cause by the PCI burst
> during DMA. I have never tried capture more than 32
> Mbyte of data (due to my PC setup), perhaps others 
> can try out the code first before you invest in a
> card. Even so, you might want to look at other cards
> since I feel that the ADC power section of my card is
> not clean and cause all this noise.
My bt878 also has some noise and signals which shouldn't be there.
Your signal actually looks cleaner then mine.
Some of the noise is just short sparks.
They go away when you use a (lowpass) fir filter to reduce the bandwidth.
(Even if you just reduce the bandwidth from 14 Mhz to 8 Mhz you get rid of a 
lot of noise)

My experience is that a lot of pci-cards are not well designed for analog 
signal quality.
(TV-capture cards, audio cards, graphic cards)

Sometimes you can increase the signal quality by placing good capacitors at the 
Vcc right next to the (ADC/DAC) chips.

Greetings,
Martin