Measuring bandwidth - Video transmitter Saw filter upgrade

[Teklock]

Guys, I'm completely new to this so take it easy...   I'm about to upgrade the saw filter in a 900MHz-1.3GHz wireless video receiver, but I want to take measurements to see if it actually improves anything.   The saw filter mod is a popular one with the FPV folks.  Unlike the 2.4GHz and 5.8GHz A/V systems that were purposely designed for A/V applications, the 900MHz - 1.3GHz models are older designs that use a baseband RF tuner developed for the satellite receiver industry.  So swapping the 27MHz filter for the 17MHz gains some performance.

I can get the RSSI voltage np, but I would like to get the bandwidth and sensitivity before and after.  I Have a 75 ohm resistor across an RCA jack as a terminator to fine tune with my SDS7102.  I'm just shining a flashlight at the camera to try to get a fully saturated white level.  I have access to a AG2052F waveform generator.  Is there a way to use that instead to get a "reference" instead of using my transmitter?  I also have access to a USRP B210 SDR, so I can get some gain info, but I still don't feel like i''m getting the correct sensitivity.