GARRETT XL500 coil help needed

[Micheal]

hello guys..the garrett xl 500 8inch coil is not sheilded and measures 1.2 ohms...so I have cut the coil cover and opened it up and did some investigating, yep there was no sheilding on the wires ,so I covered the wires with the plastic spiral stuff then with scotch sheilding mesh on top of that and ran a wire to connect the scotch sheilding to the external braided sheilding on the coax as shown on the forum ...On completion I then measured the ohms and it has now dropped to 1.0 ohms ...so it has dropped by 0.2ohms ,this now changes the whole scenario do I changed the damping resistor which is 1k standard from the factory at the moment and what value damping resistor will I have to put in place (I dont have a scope I am thinking a 1.2k resistor but im only guessing) and will it be more sensitive.
Or do I add more wire so that it measures back up to 1.2ohms...what is the best solution in this case...all help is greatly appreciated thank you

[kt315]

yep there was no sheilding on the wires

there was shield wire in a cable?

[Qiaozhi]

hello guys..the garrett xl 500 8inch coil is not sheilded and measures 1.2 ohms...so I have cut the coil cover and opened it up and did some investigating, yep there was no sheilding on the wires ,so I covered the wires with the plastic spiral stuff then with scotch sheilding mesh on top of that and ran a wire to connect the scotch sheilding to the external braided sheilding on the coax as shown on the forum ...On completion I then measured the ohms and it has now dropped to 1.0 ohms ...so it has dropped by 0.2ohms ,this now changes the whole scenario do I changed the damping resistor which is 1k standard from the factory at the moment and what value damping resistor will I have to put in place (I dont have a scope I am thinking a 1.2k resistor but im only guessing) and will it be more sensitive.
Or do I add more wire so that it measures back up to 1.2ohms...what is the best solution in this case...all help is greatly appreciated thank you

This is curious. Why do you think the dc resistance of the coil would be affected by adding shielding to the wires? Could this just be a measurement error?

[Micheal]

HUH nice...no its not a measurement error (I have measured it before and after).It is showing 1.0hms

[Qiaozhi]

HUH nice...no its not a measurement error (I have measured it before and after).It is showing 1.0hms

Since the shielding is only connected to circuit ground, then how can the dc resistance of the coil wiring have been changed?

[Micheal]

I dont know but I am assuming the sheilding has created some efficiency...and actually it seems that the coil is a little weaker in sensitivity but I have to do tests to confirm this ...but compared to the 33cm large coil which is fairly sensitive this 8 inch coil is very weak and I use it on the beach in wet sand and there is not much depth at all but the large coil has depth but is very difficult to pinpoint targets ,so I am trying to make this small coil more sensitive

[Qiaozhi]

I dont know but I am assuming the sheilding has created some efficiency...and actually it seems that the coil is a little weaker in sensitivity but I have to do tests to consirm this ...but compared to the 33cm large coil which is fairly sensitive this 8 inch coil is very weak and I use it on the beach in wet sand and there is not much depth at all but the large coil has depth but is very difficult to pinpoint targets ,so I am trying to make this small coil more sensitive

The only change that I would have expected is a small increase in coil inductance, caused by adding the shielding, which could squeeze the coil windings together. The inter-winding capacitance may also be slightly affected.

[kt315]

you do not wish to share a photo... can not able to see what you try to say... may be the cover is the shield itself? standart practice of brands is that coil cover has a conductive layer inside (I had pointered on that many times). this graphite layer IS THE SHIELD.

[Micheal]

well the plastic spiral wrap which I put on first is fairly tight the I wound the scotch sheild on in a spiral formation rather than the trditional wrap over style and its not really that tight but its all nice and neat and experimantal at the moment...the other thing I am thinking of if I cant achieve a decent result is to wind a totally new coil altogether to achieve the 1.2 ohm but the wires that I have at present I am not really confident of a better result for this size coil.

[Micheal]

there is no graphite sheilding of any kind ...its just the wire coil inside the housing ,and the housing is just made of plastic ...and the coil is measuring 1.0 ohms when I measure the with the multimeter( I will put a picture )

[Micheal]

anyway the other thing I would like to ask is is 1.0 ohms a good thing because compared to many other detectors this value is fairly low and why have the manufacturer made it so low resistance.

[Micheal]

Here is what I mean

[Micheal]

wire from scotch sheilding to coax sheild...by the way it has 22 turns approximately 18cm diamatre

[Micheal]

my xl500

[kt315]

wire from scotch sheilding to coax sheild...by the way it has 22 turns approximately 18cm diamatre

do not clearly see the coax shield has a gap... look at this.