Eric, GQ Ground Filter

[Wirechief]

Hi Eric, I was wondering if the ground filter in the GQ is some sort of ground balancing circuit? CU later! Wirechief.

 

[Eric Foster]

Hi Wirechief,

The switched filter helps, but it is not true ground balance. The normal filter in the GQ, is what is known as a 1st order high pass filter. This has a variable time constant, by means of a pot. Ground variations are usually slow compared to the rate of signal change for a nugget, ring or coin. These ground signals can be either conductivity generated, as on a salt wet beach, or magnetically generated, as on iron mineralised ground. The 1st order filter can compensate for most wet beach signals, but does not roll off fast enough to zero out strong magnetic ground. You could shorten the time constant of a 1st order still further, but you would start losing sensitivity to wanted signals. A second order filter, with its steeper roll off at low freqencies, helps maintain object sensitivity, while speeding up the zeroing out of ground signals. This is switched in as an option, by means of a toggle switch.

This type of filter responds to the rate of amplitude variations, while a true ground cancel circuit rejects the ground time constant, irrespective of the amplitude.

Eric.

 

[Wirechief]

Hi Eric and thank you for the explanation of the ground filter cicuit. Every time I read one of your explanations I realize how little I know but at the same time I am learning. I don't know how you find time to help us but thank you Eric. You can bet that I'm also building up quite a folder of notes from this forum.CU later Eric and God Bless. Wirechief.