Step attenuator

As there is no way of changing the amplitude of the signal produced electronically I've decided to add a "step attenuator". This is basically a box of switches that allow you to switch in a bunch of circuits to reduce the signal getting out.

I'd like to be able to get down to about 0.1uV so worked out that about 150dB should do the trick. I've ended up with a circuit with the following attenuators 1db,2,2,5,10,20,20,20,40,40. Anything bigger than 40dB would probably be too difficult!

Anyway I designed up a PCB and bought a bag of switches and last night knocked the thing up. The box is roughly made up out of PCB stock. It doesn't need to be too pretty as this will all sit inside another housing when its finished, it's really just for shielding.

It seems to work as expected (after a lot of working out resistor values). Anyway here's a few pics of the thing. I really need to take it to somebody else to tell me if it is working correctly as all my test gear is pretty ropey!

I decided to use F-connectors for this as BNC connectors are starting to get a bit too expensive, the front panel connectors will still all be BNC.