Nyquist theorem proves that a signal of $B$ bandwidth, in order to be sampled correctly thus avoid aliasing, has to be sampled with a $f_c > = 2B$.
When it comes to calculating the capacity of a noiseless channel of bandwidth $B$, then this is calculated as:
$C=2B * \log_2 (M)$
where $C$ is channel capacity, and $M$ is the number of levels for the signal.
What I am not getting is the link between the two, cause for me one thing is to sample a signal of $B$ bandwidth and use so $2B$, while I do not succeed to digest the opposite, since a signal of $2B$ Bandwidth fits in a channel of $B$ Bandwidth only.
The multiplier 2 comes from the fact in time interval 1 sec, we have 2B samples. Therefore, given to modulation scheme, we have that formula.
in fact, since the channel does not have loss, the capacity is equal to bit rate of the source !
So, you have a channel with "whatever you want" Capacity !