DD coil and scope drawings

[Rick S]

http://www.thunting.com/geotech/forum/tech/images/scope_drawings.JPG


I am close but still can't get any use of the GEB. I can't ground balance with the coil. I am using the op-amp 4053 which gives disortions when metal is pasted over the coil and a some what of a square wave pattern to tune the coil to. At least I can seen a signal now. I have set up the stock DD coil on the scope connected to the detector and looked at the proper wave form that I am trying to match the pattern. My coils are balanced to resonant at 50khz with capacitance in parallel to each coil. A Small pot has been added parallel with the Tx coil in a effort to shape the wave form. My coil has a stretched 'S' shape form and the stock is more of a square wave shape. Do you think there is an impedanced problem? What would be the best way to attack this situation?
I hope the drawings will help. I wish I owned a digital camera. It would make things alot easier. Rick S

[Reg]

Rick,
Looks like you have a phase shift problem. What you see isn't distortion but a difference in sampling time. My guess is that you are off by about 30 degrees or so.

You said you have a capacitor across the receive? Try removing it.

The 4053 is an analog switch used to sample the receive signal. What you are seing is a sample of the receive signal and the differences you see are caused by the sine wave being sampled at a different time.

Do you have a dual trace scope?

Reg