# Signal spectrum when carrier width changes

If I have spectrum $X_k$ of the signal evaluated at frequencies $k \delta f$ and I want to know what is the value of that same signal at some other frequencies , i.e., $k' \delta f'$.I know that $\delta f$ and $\delta f'$ are somehow reelated (e.g. $\delta f = 12 \delta f'$) how can I express spectrum of the signal with this new carrier spacing ($k' \delta f'$) having only info about $X_k$ or in other words what is the coefficient, $X_k' = coefficient \cdot X_k$. Thanks in advance for any help.

• Thx for the answer. But what I would simply like to know (from mathematical point of view) is if I have info about $X_k$ how can I obtain info about $X_k'$. I sould obviously multpily $X_k$ with some complex exponential but what is the exact value? – user7879 Feb 12 '14 at 16:14
• Ok, but the question is how to compute that coefficient vector? how it relates to $\delta f'$ and $\delta f$? – user7879 Feb 12 '14 at 16:37