I need to use something to control the power of a 90MHz rf signal output from a VCO. I have tried to use a VCA(Voltage controlled Attennuater) before, but then I found it will introduce some noise while attenuating. Then I notice this VGA (AD603) uses a passive way to attenuate the rf signal, which won't introduce any noise. I just went over the datasheet. One thing I didn't understand is it seems the input and output impedance of this VGA is not 50 ohm. But all of my other components have a 50ohm impedance. I think I will just buy an evaluation board and connect it to my VCO with a SMA cable. Can I still use this AD603 in my circuit? Thanks for the help.