Here's a little reading material.
It'll help you understand why using terminators and matching impedance, plus using attenuators, is a good thing.
Basically to keep "ringing" from distorting your signal the transmission (coax) needs to have the same impedance(ohms)on both ends, the input and at the end connected to the DUT. Otherwise you will get part of the signal you sent from your signal generator reflected back to it which will affect the waveforms. Same as having too much SWR on a CB radio.
You can build your own pads to match the impedance and attenuators.
Here's an attenuator, with pads, that I built, along with some links to the information behind it.
