The TR 503 may be used to measure the frequency response of a device or component over a 100 kHz to 1.8 GHz range. It is used in conjunction with a TM 500 mainframe and a 492 Spectrum Analyzer. The tracking generator/spectrum analyzer method of response measurement has intrinsically greater rejection of device or environmental noise than the alternate swept sine-wave method. The greater noise rejection is gained by having the 492 Spectrum Analyzer track the TR 503 output. Noise rejection is improved as the Resolution Bandwidth of the 492 is decreased; this is due to the 492 being immune to noise outside of the VR (Variable Resolution IF) bandwidth. The TR 503 uses the 1st and 2nd LO (local oscillator) outputs of the 492 to generate a frequency that tracks the input of the 492. The TRACKING ADJUST control of the TR 503 allows fine adjustment of this frequency. Points on the 492 display may have their frequencies measured by adding a frequency counter, such as the DC 508, to the TR 503/492 system. Measurements may be made directly from an external rf spectrum or obtained from the response curve of a device under test.