800 Detecting Coin Only On Outside Rhs Of Coil

[Mattjr]

When testing a coin on the 800, in an air test, I found that it only will detect on the right hand side of the coil, the side that the cable goes to but will not detect the coin in the middle or on the left-hand side.

The coin registers -5 to -6 solid on the display in all modes. Is this a problem ?.

I tested using lots of different coins and they would detect on left/ right and in middle of the coil. If you put sensitivity down to 10 or lower, on all coins  you can see that it is more sensitive  on RHS ( cable entry) of coil but still register on all other areas of coil. Could this be a problem or a design fault.

The coin is a sunday telegraph commemorative medal of queen Elizabeth and the queen mother.

[Steve Herschbach]

The only way to judge if the performance of a coil is acceptable or not is how it performs on targets buried in the ground, especially as directly compared to another make/model detector with a similar coil. Air testing DD coils will generate all sorts of complex signals on coins in air tests especially with a detector as fast as a Equinox.

What is the medal made of?

About Coils by Dave Johnson

Owners Manual Page 19:

[Mattjr]

This is a link of what the coin is -

Token - The Sunday Telegraph (The Queen Mother) - * Tokens ...
https://en.numista.com › ... › Tokens
 

The manual shows the most sensitive area on the coil is on the middle axis front to back. But i have found when testing and the sensitivity is turned right down that the area where the cable attaches to the coil and near by on RHS will pick up a target at greater distance than the rest of coil and with the above coin will only pick up on cable entry side.

When sensitivity is tuned up above 10 the coil will pick up any other targets any where over the coil the same distance no matter where it is.

 

[Randy Dee]

I think you have answered this minor problem yourself why would you want to use the detector with a "Sensitivity" set so low the general idea is to get the best detection depth performance from any detector is to operate it with as high a "Sensitivity" as possible without chattering and in land or sea usage not air testing.

 

[Steve Herschbach]

5 hours ago, Mattjr said:

The manual shows the most sensitive area on the coil is on the middle axis front to back.

They are attempting to illustrate in a very loose fashion how the detector performs related to items in the ground. Equinox is extremely sensitive and you can get the coils to do funny things air testing, just like you can with DD coils on other very sensitive detectors. I have observed what you are describing with other detectors, since one coil is the receive coil and the other the transmit coil. I have seen hot spots where cables enter coils. I have seen detectors exhibit sensitivity to items where the coil connects to the control box. Equinox magnifies all this in air tests due to it being extremely powerful. None of it is unusual on powerful machines with DD coils and not particularly relevant to whether the detector is properly working as designed detecting objects buried in the ground.

That's the best I can offer. If you really do think your coil or detector is defective I recommend you contact your dealer, and if they are unable to help you, Minelab directly. Minelab Service & Support

Coils Are More Complicated Than You Think

[Mattjr]

Thank you for explaining. The only other detector that i have owned in the last 20 years is a soverign XS. It did not have this issue when i tested it . I now understand what you talking about when you explain transmit and receive coils and will behave differently when burried underground. Thanks again.

[Jackpine]

23 hours ago, Steve Herschbach said:

The only way to judge if the performance of a coil is acceptable or not is how it performs on targets buried in the ground, especially as directly compared to another make/model detector with a similar coil. Air testing DD coils will generate all sorts of complex signals on coins in air tests especially with a detector as fast as a Equinox.

What is the medal made of?

About Coils by Dave Johnson

Owners Manual Page 19:

Steve

I wish ML would stop with the depiction of a blade shape detection pattern.  While it works to a given depth we all know on the deepest targets it behaves exactly like a concentric, having a definite sweep spot.  It's false hope thinking you have covered an area thoroughly unless you are using a Concentric coil type overlap with a DD coil.

[Steve Herschbach]

14 minutes ago, Jackpine said:

Steve

I wish ML would stop with the depiction of a blade shape detection pattern.  While it works to a given depth we all know on the deepest targets it behaves exactly like a concentric, having a definite sweep spot.  It's false hope thinking you have covered an area thoroughly unless you are using a Concentric coil type overlap with a DD coil.

I agree Tom, though it sure is not just Minelab. In my mind a round concentric has a field like a soccer ball cut in half, and the DD a field like a football cut lengthwise in half.

Best diagram I ever saw here from Jeff Fosters Digging Deeper With The DFX

[Jackpine]

Dave Johnson on search coil field shape

http://www.fisherlab.com/hobby/davejohnson/SearchcoilfieldshapeApril2012.pdf

note point 2 in his "fictions" re DD coils

[Steve Herschbach]

From https://www.kellycodetectors.com/catalog/how-metal-detectors-work