Impedance Matching Problem

[LarryG]

I’m attempting to acquire a signal, from a TDI board through a test fixture containing emulated CCD circuitry. The horizontal sync signals are 22.5 MHz, amplitude 0 to 6 V. They are routed to a NI 5112 scope card via HP 44472A VHF switch modules (50 ohm Z). On leaving the switch module they have been attenuated to apprx. 1 V P-P with a +3V offset. Simulated signal from function generator (50 ohm Z) works fine. Is this an impedance issue ? Any suggestions on how to match it ?

[Mike_T]

Larry,
The 5112 has two impedance modes which are software selectable. Which one are you using, the 1Mohm or the 50 Ohm input impedance? If you select the 50 Ohm input impedance does this solve the problem?

[LarryG]

Thank you for your response. Yes; I've tried both. It will only acquire the signal when set to 1 Mohm, not at 50 ohm