[Discuss-gnuradio] Re: Questions on usrp_tv_rcv.py

[Anastasopoulos Achilleas]

I guess I am attempting an answer to myself here:

the slow horizontal sliding reveals a
missalignment on the order of
200 samples/sec.
(I measured that by seeing how much the black strip moves
to the right within the 1 sec of video stream).

For a sampling rate of 8Msps this is can be explained by a
drift/jitter of the ADC on the order of 25ppm

Is this within the drift/jitter specs of the ADC?

Thanks
Achilleas


On Tue, 23 Jan 2007, Anastasopoulos Achilleas wrote:

> Thanks for pointing out all theses raw files
> for testing the usrp_tv_rcv.py application.
> I tried a couple of them and they work fine.
>
> Now I have the following question:
>
> Why is it that the video shown on sdl moving
> slowly to the right?
>
> The fact that there is no vertical or horizontal
> synchronization should NOT explain this:
>
> I use a decimation of 8 thus the video rate is 8M.
> With 625 lines per frame and 25 frames per second, this results in
> 512 samples per line (exactly), ie, 8,000,000/25/625=512.
>
> So one would have expected to see the corresponding picture
> not aligned in the vertical/horizontal dimension,
> BUT AT LEAST the misallignment should have been CONSTANT over time.
> This is clear in the vertical dimension (no up/down sliding)
> but not in the horizontal...
>
> What is the explanation of this?
>
>
> Thanks
> Achilleas
>
> PS: one explanation I can think of is the
> instability of the 64M ADC...