My uBITX has always been a little deaf (couldn't figure out why) so I built a RX front-end addition. Also wanted AGC so it became an amplifier followed by an attenuator. As with prior AGC / RF Gain mods, it inserted in the RX antenna trace (Ripley, et.al.). As built, it provides a maximum gain of ~ 8 db (+12db from mmic - 4 db from atten) with a 3.5 db NF, which can then be attenuated to more than (about) 50 db down. Have not measured exactly... It really wakes up the RX!
Attenuator Control: >5 volts for minimum attenuation, approaching zero volts for maximum attenuation (at 22 to 5 ma, depending on attenuation setting). For manual control would use a potentiometer and voltage follower for current buffer...
I made no attempt to minimize current draw. It is a bit of a pig, consuming 70 ma + control current (22ma).
Also, no attempt was made to minimize the board physical size...
It uses a MAR3 SM mmic followed by a HSMP-3816 pin diode array attenuator.
If anyone is interested, I have a to-scale PDF for the board layout, a parts placement image, full resolution schematic, etc. I can ZIP up a package...
Currently working on an audio derived AGC amp/controller for this thing. Have it sort of working, but not happy with the performance yet. Sure would like to have some Plessey SL621C ICs. I have an ancient homebrew rig that uses one and it is great!
So far, It looks like this: