The 624XA Communications Counters Series consists of four counters designed to provide frequency measurements from 20 Hz to 4.5 GHz. The four counters differ primarily in frequency range. All models offer excellent sensitivity, overload protection, and accuracy. In addition, each counter can be equipped with a variety of options to satisfy the needs of individual users. Available options include low frequency tone measurements, built-in battery operation, and digital outputs. The instruments are lightweight, easy to carry and easy to use. In addition to communications requirements, any of these compact counters can be used wherever high sensitivity, wide range frequency measurements are required.