Hi there!
I need to rectify a 3MHz signal, with 30mVpp. I tried with an opamp LM318, but the bandwidth is not enough. I tried with a transistor 2n3904, in a common emiter configuration but I almost got an unity gain. I did this on a protoboard. Can I still use protoboard at this frequencies?. Any advice will be appreciated.
Thanks

joc,

use two npns hooked as a differential pair tie one base to a voltage reference (AC short)  then apply your 3 MHz signal to the other base (bias it correctly of course)  your rectified signal will be at the emitter.  

2n3904 will work at these frequencies.

Can I still use protoboard at this frequencies?  Probably not an issue unless your trace is a meter or more.
Jeremy