I Uwe,
thanks a lot for your reply ..

My code is based on the spectrogram example.. and about axis i don't find important differences...
I haven't any problem with axis and plot on screen, but only to print...

I tried whit a simple:
QwtPlotRenderer renderer;
renderer.renderDocument(this,"F:/pippo.pdf","pdf",QSizeF(300,250));
with default setting.. but the result is the same.

If you have some idea, please suggest me..
I hope to find the way to render my plot with axis as soon as, and I 'll write here the solution..

thanks
Claudia

I used QwtPlotRenderer::FrameWithScales only to try something because I don't understand ...