18" Goldquest coil

[Anonymous]

I was hopeing one of you pulse techs. might be able to help me out. I was wanting to build a 18" coil for my Goldquest SS. I am looking for cannonballs that are from 4-6ft. deep. The 11" coil should get some of the targets, but I am wanting to get better signals on the deeper targets. If anyone can supply me with the proper wire gauge and number of turns I would need to build this coil I would be very greatful. Thanks, Mark L.

 

[Anonymous]

I believe 11" is the largest that can be done on the Goldquest because of inductance problem with a coil that size running at such low Usec.

 

[Anonymous]

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[Anonymous]

Hi Mark,
Don is right, in that the primary design criteria for the Goldquest was to have a high sensitivity to small targets, particularly Gold. It was not anticipated that coils larger than 11in would be used with this detector. However, there is nothing to stop you experimenting with larger coils. The transmitter current is limited by an internal resistor so even coils which are way out of spec will do no harm. You can go up to 1mH inductance without generating excessive flyback voltage. What you won't be able to do however is sample at 10uS. You will have to turn the delay(reject) back to just past the point where the detector responds to a metal target i.e. running a large coil at 10uS will just cause the receiver to saturate, maybe for 20uS or more. As you are wanting to detect large targets, this should not be a problem, and also the transmitter and sample pulses will be proportionately wider, which is what you want. Use stranded wire 10/0.1mm preferably.
Eric.