seperate ground for coil shield?

[grungymike]

Reading Moodz's thread on the full differential PI front end reminded me of a question that occured to me while reading bbsailors article on building a fast mono coil.

In that design the coil shield is grounded thru the coax cable shield, adding noise to that ground path and any components connected to it.

On the board I'm working on I've made a real effort to create 4 different ground nets (power supply, xmt, analog rcv and digital rcv), connected at the main cap (C1 on the hammerhead), in order to minimize noise.

Taking that idea a step further, what I'm thinking of is a seperate path for the coil shield ground, running all the way back to the same cap.
The idea is to dump the noise into the cap before it can get into the 1st op amp and cause problems.

This would make the unit incompatible with Minelab's or others' coil assemblies, but I'm about ready to build my own coils anyway, after hearing of all of the recent quality problems that seem to be cropping up.

I'm already on rev G on that sucker, so if this idea isn't valid, somebody please just shoot me now...

gm

[hobbes_lives]

It sounds like something that would be fairly straightforward to test. If you have a working unit with a coil that is not sealed, you could measure the noise at the output of the preamp, then disconnect the coax from the coil shield, run a separate ground to the coil shield, and then measure the noise again.

It's a good idea to try, but my guess is that you won't see much difference in the noise.