Garrett Groundhog

[Qiaozhi]

Please note - I have already posted this question in the Coils Forum.
Does anyone here know the internal coil configuration of the Garrett Groundhog?
This is a 1970s VLF/TR detector that was the machine for finding gold. Its frequency of operation is 15KHz.
In particular, I would like to know the inductance of the TX and RX coils, and whether the tuning capacitors are contained within the search head or on the PCB.

[digital logic]

I have the diagram from cscope 330. It transmits at 115 kHz and the transmitter is inside the disk, near to the coils.
Do you need this?

[Qiaozhi]

Originally Posted by digital logic

I have the diagram from cscope 330. It transmits at 115 kHz and the transmitter is inside the disk, near to the coils.
Do you need this?

The reason I'm asking about the Garrett Groundhog coil is related to our investigations into the pistol detector, which is either using a Groundhog coil, or maybe just the casing. We're not sure at the moment.

However, if you have the circuit diagram for the Cscope 330, then please post it on the schematics forum. I'm sure there are many people here who would welcome this addition to their collection.

Thanks.

[J_Player]

You be interested in doing some research of posts made during the past year on pistol type detectors in this forum. From what I have read, I might speculate that there is indeed a coil in the pistol that does not use a shield. From what I recall, an unshielded IB coil has some unusual distance properties if you are using it in an area far away from electrical interference. The use of IR has been explained as a method to augment the extremely weak signals received by means of imparting heat energy to the target area. But even without the IR, these unshielded coils were said to pick up weak signals at much greater distance providing the sensing circuits were very finely tuned in a different manner than a conventional detector is tuned. I also noted the early IB method was said to work, but as other standard metal detector technologies were developed, it was found they also worked as well or surpassed the performance of the IB circuits. I recall a large frequency range could be used, but a certain range worked better (I assume the circuit you are investigating uses the best frequency found by the experimenters).

Best wishes,
J_P

[Qiaozhi]

Originally Posted by J_Player

You be interested in doing some research of posts made during the past year on pistol type detectors in this forum. From what I have read, I might speculate that there is indeed a coil in the pistol that does not use a shield. From what I recall, an unshielded IB coil has some unusual distance properties if you are using it in an area far away from electrical interference. The use of IR has been explained as a method to augment the extremely weak signals received by means of imparting heat energy to the target area. But even without the IR, these unshielded coils were said to pick up weak signals at much greater distance providing the sensing circuits were very finely tuned in a different manner than a conventional detector is tuned. I also noted the early IB method was said to work, but as other standard metal detector technologies were developed, it was found they also worked as well or surpassed the performance of the IB circuits. I recall a large frequency range could be used, but a certain range worked better (I assume the circuit you are investigating uses the best frequency found by the experimenters).

Best wishes,
J_P

Hi J_P,

Have a look at the Remote Sensing Forum, in the thread "Mineoro 2-Box -- 492 feet range? ", which (incidently) you started!
Any input welcome.

[J_Player]

Hi Quiaozhi,

I have been following that thread. Strange as it seems, the project they are discussing probably began as one of Alonso's early experiments with a 2-box detector, and we are probably reading about a model based on one of the many off-shoots of his earlier experiments.

From what I have read, it appears that Alonso experimented early on with the old 2-box detectors, making modifications and exploring many of the ways to use this detector that most people considered of little use. Apparently he refined a number of the features of a standard 2-box detector so it would perform better than standard in certain conditions. We see Morgan's report that it finds shallow treasures for him in mineralized ground where the competitors give no signal. I did not expect to hear this kind of response from a user, but I believe it is true, considering all the extra controls on the Mineoro 2 box detectors. It appears Alonso decided to install lots of extra controls for the user with the understanding that this detector would need be adjusted for optimum performance depending on the hunting conditions. This is a typical design strategy used by metal detector manufacturers when they make special purpose machines designed for advanced users. Also note Morgan did not experience any great depth from this detector. From what I can tell it gives similar depth readings as other competing detectors, but is much more sensitive in mineralized ground.

As near as I can tell the pistol style detectors followed when Alonso decided to make a compact version of the IB. This is where the discovery that the distance could be enhanced by removing the shield started in the pistols. But the circuits were also modified to optimize the non-shielded small coil. From that point on, it seems the circuitry changed as new metal detector technologies were developed, and as the experiments showed promise in using little used or known properties of these detectors.

If you go back and read through Esteban's posts in the past year and even earlier, you will see he describes several different style pistols he has used. When we eliminate the Zahori style static detectors, he has described a general class of coil pistols which use an unshielded coil which is connected to circuitry that seeks a variation in the balance between several finely tuned circuits. These "finely tuned circuits" have taken the form of IB as well as a number of variations that no longer fall in the IB class. Of particular interest is the IR circuits he used which were connected integrally with the coil assembly, so a portion of the IR feedback signal passed through the coil and supposedly caused a variance when a target was scanned with the IR/coil assembly. There are also telescopic antenna versions which are said to work not so well as the IR versions.

The whole antenna assembly does not seem very difficult, but adjusting the coil windings and component values must take a lot of time with trial and error methods until the best performance is found. The information is here in the forum in Esteban's posts. It takes time to research because it came in bits and pieces. You must scan through hundreds of clown photos to read half of the details he gave, and the other half came before the advent of the clown war.

Best wishes,
J_P