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]

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]

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

[Fred]

Hi JP,

I have precisely been reading Esteban´s posts for some time now,and as you said we can find only small bits of partial information.But interesting anyway.
from one side it looks like this Pistol is a mixing of BFO and totally tuned unscreened IB,but other info leads to a "magneto-electric" detector
Anyway i really cannot understand the role of IR beam, that aparently should be modulated, nor the (non-existent)HV generator.
I also believe in Morgan, and even if the detection distance he reports is not so great, it if far better than regular MD,and extremely interesting.
I hope that by finishing reverse-engineering and possibly simulating the circuit we will be able to understand more about its function.
Best regards,
Fred.

[J_Player]

I hope that by finishing reverse-engineering and possibly simulating the circuit we will be able to understand more about its function.

There isn't much to reverse engineer. When you have an accurate circuit diagram, you can make a clean schematic that will be easy to understand. The hard part is the missing search head design. There are two problems with this:

1. You don't have a clue what components are in the search head, or the values of those components.

2. If you did know the components and their values, I would think you could not build a copy that works unless you are lucky. The reason is because I suspect there is a tuning procedure needed in order to make the circuitry operational. With any luck, if you had the components for the search head connected to a working circuit, the pistol may give some sort of reading. If it does, then you can further tune some of the components for better response, or even use test equipment if you know what you are trying to tune for. I have a feeling the physical positioning of the coil and other apparatus in the search head may be critical, similar to how the physical positioning of some conventional search coils is (ie: DD coils).

The real missing info is about the theory of circuit and how it interacts with the coil and other search head parts. It would be good to to first have an understanding of what property of the target you are basically searching for, and how the search head components respond to these properties. If you first know these things, then you will find it much easier to tune a similar pistol detector. At present you are playing with a puzzle even if you have all the circuit data.

In any case it looks like an interesting project to experiment with. I have also read other reports of some of these pistols getting some medium range signals which are better than a conventional metal detector.

Best wishes,
J_P

[J_Player]

Here are some more thoughts about the pistol style detector from the Mineoro 2-box thread:

I see Max has posted a very nice schematic of the pistol detector that shows all the parts except the search head. If the search head is finally added to the circuit, then we will have a full diagram to experiment with. I suspect that once the full diagram is posted, several forum members will build pistols to experiment with, and may get them to work as well as the unit that Morgan tested. But if we reach this stage, I expect we will see further improvements in the pistol.

If you consider the pistol coil designs have been pioneered by a small handful of people and have been kept out of the mainstream, it is unlike other metal detectors that have been improved by hundreds of experimenters with different approaches and ideas. The current pistol designs have only the refinements that a small number of people were able to make. If the design is studied by more people with diverse experience in building coils and other circuitry, we may see some improvements in the design, construction methods and calibration of this pistol. Look at the long history of improvements in conventional metal detector technology that happened in the decades after the first consumer models became popular. This would not have happened if it were not for so many people involved in independent experimenting. I suspect some of the forum members with strong conventional metal detector experience will find ways to improve the pistol if they come to fully understand the principles that cause the circuits to respond to targets.

Another thought is about the general usability of this kind of detector. I suspect this detector has limitations mostly concerned with electrical noise, and operates best away from civilization. But in conditions where noise is not a problem, the pistol could be a very nice tool to use that would eliminate much of the work involved in scouring the ground with a conventional search coil. I doubt it could replace a conventional metal detector because there are certain things I expect a conventional detector does better. If I were hunting in an area where I suspected a treasure, I would certainly search the ground with a conventional detector if the pistol did not produce a target signal. But I might make the preliminary search with the pistol, because of the time-saving implications.

Best wishes,
J_P