Why is "OVERLOAD" message sometimes displayed in Network Analyzer mode of the 4395A? How can I avoid this error message?

The OVERLOAD message on the 4395A Network Analyzer mode is often displayed when Sweep Start frequency is lower than 5 kHz and a wide IFBW is selected. A local signal leakage (local oscillator feedthrough) of IF mixer falls in the IF bandwidth and causes OVERLOAD message to be displayed. Changing the input attenuator setting has no effect on this phenomenon because the local signal leakage is generated after the input attenuator. The OVERLOAD due to a local signal leakage is a particular phenomenon of low frequency network analyzers.

In order to avoid the OVERLOAD display, set the IF bandwidth equal to or less than 1/5 of the start frequency when the 4395A makes a swept measurement in low frequency region. If the IF bandwidth is set to auto mode, the IFBW is automatically set equal to or less than 1/5 of each measurement frequency. For more details, refer to Page 6-26 of the 4395A Operation Manual.