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Chet

X Coil Cable Modification

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I did the Minelab cable cutting and soldering differently than specified by the manufacturer.

Instead of cutting the cable near the Minelab connector I cut it below the Minelab curled cord and installed the 5 pin connector at that location.

After the connector was installed and marine grade shrink tubing was applied a plastic tie wrap was attached with another piece of shrink tubing. This is used to pull the cable out of the lower end of the upper shaft since the Minelab curled cord retracts it out of reach.

I then used a heat gun to soften and straighten approximately 8 inches of the lower X Coil curled cord. Cut it at that point and attached a new connector at 8” above the lower shaft.

I have all three X Coils setup with three new lower shafts attached. This modification allows quick easy change of coils in couple of minutes.

It is reasonable to be concerned about interference from the two connectors being located so close to the coil. This is not a problem since the detector only detects motion change relative to the coil.

A simple experiment will demonstrate how the detector nulls out metal that is not changing position relative to the coil.

Place a small test target on the ground with an aluminum soda or beer can about 2 feet from it. Swing the detector over the small test target. You will only hear the response from the large can.

Now tape the can on top of the detector shaft 2 feet from the center of the coil. Now swing the coil over the test target and it will be detected.

With the can attached the detector it will sound off as you lift and lower the detector to the ground since the coil is remaining flat while the shaft and can are changing position relative to the coil.

In normal detecting when setting the detector down or lifting it I hear this sound-off with the 17” x 12” coil but not with the 10” or the 17” round coils.

There is no effect during normal detecting since the coil is not tilting or changing position relative to the shaft.

Have a good day,
Chet
 

Cable modification1.jpg

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It's an interesting concept Chet, I am yet to try that method over here but I am planning to do just that.

 There are the obvious benefits of being able to change the coils at the lower shaft instead of in the narrow gap up where the ML plug connects to the box.  Also being able to utilize the curly part of the Minelab cable itself. 

I will be comparing the new "Chet" way against the original "patch lead" way for depth on same targets, sure it will involve some time consuming swapping back and forth but worth while doing I reckon.

Thanks again Chet for trying different ways of doing the same thing.

cheers dave

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I would not recommend using this method, that is an awful lot of metal and potential stray RF to have so near to the coil. Even the slightest movement could make its way to the RX.

Just my 2C and not wanting any future X coil discussions to become heated, have moved on from all the emotive debates there's more than enough information out there for people to make informed decisions now.

A more mellow these days😇
JP 

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Interesting concept.  I do like it better, so long as you are not balancing out that connector, making it less sensitive to gold.  I like metal as far away from the coil as possible.

 

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Just now, Andyy said:

Interesting concept.  I do like it better, so long as you are not balancing out that connector, making it less sensitive to gold.  I like metal as far away from the coil as possible.

 

The coil would have to be seeing that connector that close to the coil, so it has to be impacting on the GB and X balance even if it is held completely motionless.

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I agree that the coil is seeing the connectors at a close distance. I will do some more testing on this but the results of my depth comparison testing did not show any noticeable performance problems.

The coils magnetic field has fixed disturbance at all times from the copper cable through the copper and solder in the control box to the battery.

I used the GPZ 19 cable for the X Coil adapter cable.
The two new connectors were in place on all three X Coils when I compiled the coil depth comparison chart data.

Each coil was successfully balanced on the ferrite core before testing. 

The GPZ 14 coil that was used in the test has the original cable with no new connectors installed.

The smallest nugget tested was a 0.06 gram.

I will do some performance testing on this next month while in Arizona. I will start with the can taped onto the shaft as a worst case condition.   

Have a good day,
Chet
 

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Often wondered about all that copper in the coil cable, from the external cable wound round shaft, whether on PIs or VLFs if not fixed properly the movement would cause falsing. Thus if it`s fixed and not allowed to move in relation to the coil why not lower down connectors too? We often are blinded by blinkers and then a bit of thinking outside the box can simplify something, I`ll be following your performance tests keenly. Many thanks for sharing this with us.

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Don't even concern yourself about EMI from the coil adapter, twin ferrite chokes inside the control pod are there for that very reason.  The outside metal of the adapter is shielding, hence connecting the shield wire to it.   I guess if it's just if the GPZ cares about seeing the adapter, as well as the pre-existing coil wires that it was already seeing.  I don't know how you'll ever know unless the impact was significant which it clearly isn't.  I guess you can reverse what you've done if you end up not liking it with some gel filled cable clamps or something or just solder and heatshink.

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I put together some checks to help when you first fire up the GPZ 7000 after the cable modification. This procedure comes with no guarantee! But is better than having no procedure. 

To safeguard the detector; time the following steps with a watch.

1. Fire up the WM12; with a Minelab coil attached to the GPZ 7000. 

Push the GPZ power on button and verify and record the elapsed times for the following events;

The full operating Screen Display should appear at approximately 20 seconds;

EMI noise from the receiver coil should occur at approximately 30 seconds.

Important note! 

As you proceed with the rest of the testing keep time in mind. The transmit power transistors are very rugged and have good heat sinks to draw the heat away and keep them within a safe temperature range. 

If there is a short in the cable or coil transmit connections it will overheat the transmit transistors within several seconds and cause catastrophic failures. 

So the thing to do is monitor the elapsed seconds for an event to occur. In the following procedures substitute your recorded times for the 20 sec and 30 sec times. 
If an event doesn’t occur within 5 seconds of the expected time power down the detector quickly to avoid the heat buildup within the power transistors.

2. Now repeat the above test with the new adapter cable connected to the detector without the a coil connected to the adapter.

If there is a short within a new installed connector transmit connections it should display an overload alert shortly after the full display screen appears and should shut the detector down automatically. If this alert occurs be prepared to immediately shut it down in case the automatic shutdown doesn’t! 

Otherwise with no coil attached there will be no EMI noise at 30 seconds and at approximately 60 seconds there will be a No Coil Detected Alert and the detector will shut down automatically.

3. Now connect the Minelab donor coil to the adapter. Power up and the full display should appear at 20 sec and EMI noise from the receiver coil should be at 30 seconds.

If there is a short in the new Minelab donor coil connector transmit pins it should give an overload alert and shut down.

If there is a short or open in the receiver pins there will be no EMI or there may be abnormal EMI noise.

Wave a coin over the coil to see that the transmitter coil is working. 

4. Connect the new X-Coil and power up again. The full display should appear at 20 sec and EMI noise from the receiver coil should be at 30 seconds. 

If there is a short in the new X-Coil coil connector transmit pins it should give an overload alert and shut down. 

If there is a short or open in the receiver pins there will be no EMI or there may be abnormal EMI noise.

Wave a coin over the coil to see that the transmitter coil is working. 

Have a good day,
Chet

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So Chet what your basically saying is if the 7000 has no coil attached, (like you forgot) in your haste changing coils even from a GPZ14 to the GPZ19 to actually connect the plug to the box then the detector won't fry itself, there is a built in safety mechanism in the GPZ7000

So then knowing this, the safety checks you mention can be undertaken carefully with measured time increments.  Very interesting.

cheers dave 

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