The 353A is used with an oscillator and a voltmeter. This combination of instruments is used for measuring transmission and system characteristics such as attenuation, frequency response, and gain.
Input:
Frequency Range: 50 Hz to 560 kHz.
Impedance: 135, 600, and 900 Ohms and Bridging (10 K) Center tapped.
Maximum Level: +22 dBm (10 Vrms at 600 Ohms).
Output:
Frequency Range: 50 Hz to 560 kHz.
Impedance: 135, 600, and 900 Ohms and Bridging (10 K) Center tapped.
Maximum Level: +22 dBm (10 Vrms at 600 Ohms).
Distortion <1%.
Attenuation: 110 dB by 1 dB steps.

6 with No Options
2 with Option H03 = Has jacks for Western Electric 241, 309, 310, and 347 plugs