[question] problem with real OFDM spectrum

Hi all,

I have trouble with spectrum visualization of OFDM signal.

I implemented OFDM system on Stratix II ES180 board and convert the
Q-signal to analog via on-board DAC 14bit. I got the result like the
figure I attached.
I wonder why the firs edge and end edge of spectrum is far away to each
other? the different is large: around 20dB (in the matlab simulation, I
got the same level of them)

the second is, there is a mini circuit (transformer) before the DMA
output, so, the DC component should be eliminated form signal, why I
still get the DC component on the spectrum analyzer (see the figure I

Thanks very much,