The Model 415E SWR Meter is a high-gain amplifier, tuned to an audio frequency, with a square-law calibrated meter readout. The Model 415E is designed for use with square-law detectors in the measurement of SWR and attenuation. In addition, because of the high-sensitivity and tuned amplifier, it can be used as a null detector for audio frequency bridges. The Model 415E is a tuned audio amplifier designed to operate at a mean center frequency of 1000 cps (Hz), adjustable 7% with a variable bandwidth of from 15 to 130 cps (Hz). Operating center frequency and bandwidth are both variable at instrument front panel. Tuned amplifier gain is only slightly changed due to any change in bandwidth and is typically less than 0.5 db. In addition to the front panel meter readout provided by the SWR Meter, two rear panel outputs are also available: An AC amplifier output is provided to allow using the 415E as a high-gain (126 db) tuned amplifier; a DC recorder output providing a convenient means of obtaining a permanent record of measurement data. Either or both of these rear panel outputs can be used without affecting instrument meter operation provided power line ground is not connected to the instrument through either rear panel connector.