7265 frequency response sensitivity problem

From: james wallace
email: jamesw@stanford.edu
Model: 7265
Date: 10 Mar 2005

Comments

Good day, I'm running a frequency response experiment with a 7265 (S/W Version 8.6) lock-in amplifier. When the start frequency is set below 1KHz and the stop frequency is above 65KHz, the input sensitivity switches to microvolts when the oscillator frequency reaches about 63KHZ and the signal is not measured (it appears to be disconnected or severly attenuated). However, the signal is actually present and the gain has not changed. If the start frequency is set at 1000Hz or above, the problem does not manifest itself. Try this: Connect Osc. Out to Input A. Osc. amplitude = 10mV Sens. = 10mV, Gain = 30dB Freq. Resp. Experiment Start Freq. = 500 Hz Stop Freq. = 100 KHz No. Points = 201 Law = Lin Start At around 63KHz, the displayed signal drops from 10mV into the noise floor at the microvolt level. Returning to the main display, the input sensitivity is set very low, and only a noisy signal is displayed, even thought the input signal has not changed. The "SET" button has to be pressed to reset the input to achieve a correct display of the signal. Any help with this would be appreciated. Regards, James Wallace Stanford University