Problem with VNA

Hi There
we use 8720ES HP Agilent Vector Network Analyzer but we see this error message on its display: "caution: phase lock cal fail" recently. we did some tests but the error is reminding. Can anyone help us. it's very urgently
thnx a lot

Well, the measurements are not going to be accurate if you have error messages like that. Make sure there is nothing connected to the "external reference", or whatever it is called, on the back panel. I am not sure there is a way in the software to make sure the external reference port is disabled.

What type of devices are you measuring? Passive or active?
You can try increasing the power of the VNA

Hi there
Before any testing and after power on the VNA this message appears and it's like that the VNA calibrate always after power on and it's prevents any testing

this problem is probably related to the phase locked loop of the VNA.

Send this VNA to Agilent to fix it.