开云体育

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:


?
73,
Woody