High Frequency (16 Mhz-48 MHz) Peak Hold/Envelope Detector Circuit?
Opamp + diode based peak detectors are useful for narrow band and low frequencies only. This is mainly due to the reverse recovery time of the diodes and the opamp bandwidth + slew rate considerations. Such peak detectors might be good at giving you a relative measure of signal strengths at various frequencies, but will not give you true absolute accurate dynamic range. 

Furthermore,as you need a bleed resistor on your peak detect capacitor, this essentially limits the bandwidth you can detect accurately because you have a fixed RC time constant to work with. You need to look into other ways of detecting a signals magnitude, power etc, depending on the dynamic range, accuracy and frequency you need.

Your choice of diode is also not ideal, you need to use schottky types

Check out: AD8307, this is a broadband Log detector, it uses a completely different topology to achieve good dynamic range and bandwidth!