MODULATION FREQUENCY-TUNE NETWORK FOR CW HIGH FIELD SPECTROSCOPY

这个子项目是许多研究子项目中的一个 由NIH/NCRR资助的中心赠款提供的资源。子项目和 研究者（PI）可能从另一个NIH来源获得了主要资金， 因此可以在其他CRISP条目中表示。所列机构为 研究中心，而研究中心不一定是研究者所在的机构。 目前在ACERT c.w.中采用的场调制系统。高频光谱仪由一个适当修改的音频功率放大器驱动场产生线圈。因为线圈代表高电抗性负载，所以场调制网络在串联调谐到谐振时最有效地并且以最高峰值场值操作。历史上，场调制系统的调谐需要插入中间网络，用于将阶跃值系列电容器中的一个切换到调制电路中，同时用示波器观察所得线圈电压幅度。这种调整的目的是在选定的激励频率下，使给定的恒定放大器输出信号的线圈电压最大化。然而，由于所需的大电容范围和有限数量的开关位置，通过开关设置的变化在现有网络中可用的电容器值仅粗略相关。因此，导致最大幅度的所选电容器值实际上可能与获得真实谐振峰值所需的值有相当大的位移。 通过设计和构建我们指定为（高场）调制微调网络（HF-MFTN）的替换调谐单元，我们解决了场调制调谐分辨率不足的历史问题，同时为可选的外部仪器（例如，示波器、频率计数器）。我们最近建造了3台HF-MFTN装置。经过调试、测试和校准后，其中两台设备将在ACERT使用，其余设备将交付给SUNY奥尔巴尼。在ACERT单元中，一个网络将安装在我们的170/240 GHz频谱仪中，另一个将安装在我们的95 GHz c.w./脉冲分光计

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Field modulation systems currently employed in the ACERT c.w. HF spectrometers consist of an suitably-modified audio power amplifier driving a field-generating coil. Because the coil represents a highly reactive load, the field modulation network operates most efficiently and at highest peak field value when series-tuned to resonance. Historically, tuning of the field modulation systems has entailed the insertion an intermediary network for switching one of a stepped-value series of capacitors into the modulation circuit while observing with an oscilloscope the resulting coil voltage amplitude. This adjustment is made with the goal of maximizing the coil voltage for a given constant amplifier output signal at the chosen excitation frequency. However, the capacitor values available in the existing networks through variation of the switch setting are only coarsely related due to the large capacitance range required and finite number of switch positions. Therefore, a selected capacitor value that results in maximum amplitude may, in actuality, be considerably displaced from the value required for attaining the true resonance peak. With design and construction of a replacement tuning unit which we have designated the (high-field) Modulation Fine-Tuning Network (HF-MFTN), we have addressed the historical problem of inadequate field-modulation tuning resolution and at the same time added both built-in monitoring capability and galvanically-isolated outputs for optional external instrumentation (e.g., oscilloscope, frequency counter). We have recently constructed 3 HF-MFTN units. After debug, test and calibration, two of these devices will be used at ACERT and the remaining device will be delivered to SUNY Albany. Of the ACERT units, one network is to be installed in our 170/240 GHz spectrometer and the other in our 95 GHz c.w./pulse spectrometer.