Anritsu   The ML422B is a Selective Level Meter which is designed for use with Bell System FDM hierarchy. The ML422B covers the wide frequency range of 50Hz to 30MHz. This remarkable instrument offers highly accurate measurements of signal levels, and it has the frequency accuracy and stability needed to manufacture and maintain FDM systems, from voice frequencies up to 3600 channels. The ML422B can also function as a wideband level meter, psophometer, or voice band analyzer.Options:11 = ICC-2 Transformer Connector (GPIB to IEC-IB) 21 = Modifies the 124 and 135 ohm balanced input frequency ranges 31 = Modification of selective bandwidth 43 = Modification of FDM channel plan