What is the proper way to use an external 10 MHz clock signal for an HP/Agilent signal generator (in my case: 8648C)?
With my Tektronix, Rohde & Schwarz devices, internal/external reference has to be selected which makes sense.
But the manual for 8648C is just totally silent: How to activate it, how to ensure that is is actually used and locked?
Is it activated automatically? On powerup? When the external clock is connected? 5s after it is connected? ... ?
According to the manual:
10 MHz REF INPUT and OUTPUT These connectors provide the input and output ports for the instrument's timebase reference. The instrument will lock to a 2 MHz, 5 MHz, or 10 MHz external reference source connected to the input that is within ±5 ppm. When the internal timebase is being used, the output connector provides a 10 MHz, 1 Vrms level signal.
But with the scope I can see the 10 MHz signal at the REF INPUT always. Sure enough, the manual also doesn't say how to deactivate the "internal timebase".
I am not sure if the device actually uses the external reference because the measurements suggest I have some frequency mismatch.