Re: does this look like I'm clipping?

On Apr 29, 2:33 am, dbd <d...@xxxxxxxx> wrote:
On Apr 28, 8:21 pm, Jerry Avins <j...@xxxxxxxx> wrote:



George Nychis wrote:
Hi all,

I am trying to tune a board to receive a sine wave. When I use the
standard code to tune it, I get the following I/Q plot:
http://cyprus.cmcl.cs.cmu.edu/tmp/flex_graphs/sine_regular_rvi.jpg

What is the board like? What is standard code?

Whenever I try to tune it myself, I get the following:
http://cyprus.cmcl.cs.cmu.edu/tmp/flex_graphs/is_this_clipping.jpg

What do the axes of these fraphs represent?

It seems like the circle is pushed inwards on the four corners of the
resulting graph. Is this a result of clipping?

It doesn't look like clipping or even wraparound to me. Not knowing what
I'm looking at makes that a wild guess.

Jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

The first plot resembles what Matlab gives for:

x = exp(-i*2*pi*linspace(0,2,30));
plot(x)

The second could then be wrap around on an overdriven signed 15 bit
representation. There are also a scattering of other points on the
graph.

Dale B. Dalrymplehttp://dbdimages.com

Dale,
Try
plot(real(x)); figure; plot(imag(x))
To look at the time series. Clipping will be easier to see in that
domain.

Cheers,
David
.