Fixed multiple modulators lockup issue
This fixes issue #11. See issue for details. Now multiple modulators in the same baseband can run smoothly. However multiple modulators is different from multiple demodulators as for transmission mixing is required and adds complexity. Moreover the relative power of each modulator must be reduced as the number of modulators is increased. Having more than two of them is more or less a curiosity. An information message is displayed when more than one modulator is added to the baseband.
This fix however also improves performance of single modulator operation.