modulation with a fixed reference

例句：

1. 1. The radio's frequency was setto 98.5 MHzfor optimal modulation.
   收音机的频率被设置为98.5兆赫，以获得最佳的调制效果。
2. 2. The engineer used atuning fork to tune the instrumentto the desired frequency.
   工程师使用一把调音叉将乐器调到所需的频率。
3. 3. Thescientist conducted experiments to study the effects ofdifferent modulation techniques on the system's performance.
   科学家进行了实验，研究不同的调制技术对系统性能的影响。