Best GPX with DD regarding Iron reject and power-line stability.

Hello guys and girls hoping you're all well.

Just a quick question regarding EMI and whether the GPX detector line running DD's have improved in this area as the models have progressed.

Thinking about grabbing an old second hand GPX and DD/AI coil for around and under big power lines.
The ZED does around small power lines and house feed lines ok with threshold off and sensitivity up with success but these big lines make it a little cranky.

Would one see any difference running a DD/AI on a GPX4000,4500,4800 or 5000?

Cheers,

Hoff.

Hi Hoff, Iv'e used a DD only a few times so I cannot really comment much apart from they're great on noisy ground.
I run a little 8" mono coil when around power lines with good results.
I turn down the rx a little and run the audio in quiet,seems to work,but if you're talking about the high voltage/70 metre high towers, they may cause problems when close.
Also the time of the day makes a difference to power line that are pulling current,I find in the afternoon/evenings when people are home with more electrical devices on creates current drag on the lines that increases EMI
Some sparky out there may have a better explanation than me?


cheers   moredeep
ps i'm running a 5000

Thanks Moredeep,

Funny you talk about detecting when the power demand is low as CostasDee told me something very much the same many years back, god bless him. Agree 100% on the coil size having a major affect on EMI going from the 17" X-coil to the 12" Z-Search is heavenly on the ears.

Thanks for the reply mate.

Cheers,

Hoff.

G’day H G,

We have the 11” & 14” Coiltek AI coils and they worked very well on/around the salt lakes in WA. Sorry we never tried them near the power lines, but they are very sensitive on small gold in the salty ground. We were using them on 4500 & 5000.


Cheers.


Mike.

Thanks for that Mike.

Hoff.

moredeep wrote:Hi Hoff, Iv'e used a DD only a few times so I cannot really comment much apart from they're great on noisy ground.
I run a little 8" mono coil when around power lines with good results.
I turn down the rx a little and run the audio in quiet,seems to work,but if you're talking about the high voltage/70 metre high towers, they may cause problems when close.
Also the time of the day makes a difference to power line that are pulling current,I find in the afternoon/evenings when people are home with more electrical devices on creates current drag on the lines that increases EMI
Some sparky out there may have a better explanation than me?


cheers   moredeep
ps i'm running a 5000

I find also wind velocity/direction if high can also heighten the EMI near power lines. I am usually out of range of the lines but have found the winds to make a big difference. On days of no wind I have no issues unless real close to the lines.

G'day Hoff

Things have stayed pretty much the same in regards to using a GPX close to, or under power lines Hoff. Salt coils or AI coils are more user friendly or less prone to EMI than both mono or DD coils when run near/close to, or under power lines, but at a slight cost to depth advantage over targets. The thing to keep in mind here, is that the smaller the coil diameter, the less EMI one is likely to encounter, with DD coils being less prone to EMI than the same in size mono.  
Now if you can get your hands on a small in size concentric coil, made to suit the GPX (say between 11 or 15 inches in diameter) would just about wipe away EMI altogether, whilst maintaining good sensitivity & maximum depth capabilities, over in ground targets lying close to major power lines. Same thing now applies to the GPZ 7000 when using concentric coils.
Hot Northerly winds, depending on wind direction, can be a nuisance by increasing the effects of nearby EMI, when blowing in the direction of detector operator.
Cheers Kon

The higher the humidity the higher the corona discharge. If it is windy detect up wind of the HV power lines and let the wind blow the ions away.

I hate telling a tradesman how to do his job so don't take this the wrong way.

I hope you're running in cancel, that's what it's for...

....BINGO....

I'm curious butch what was your bingo moment?


cheers moredeep

moredeep wrote:I'm curious butch what was your bingo moment?


cheers    moredeep

Put your Minelab in cancel and you can walk right up to an electric fence, that's what it's for. Try it.

Just trying to help the newbies 'moredeep'.

now I get you, yep it's a handy switch alright.
It's also handy when one has dug a whopping deep hole and your not sure how much further you have to dig.
flip machine into cancel and if you can detect the target you are getting very close.


cheers moredeep

It only works with a DD coil.
Here's a clipping from the manual.

I tried this again today just to reassure myself.. In my back yard , plenty of EMI, the detector went crazy until i switched it to 'cancel' a DD coil.. Just brilliant. As i said earlier, i have detected right up to an electric fence pulsing away in the goldfields, like normal response in cancel.

How about Bruce Candy..

The lesson here is we should not only read our manual but to comprehend it.

I hope this helps 'Hoffs Gold'.

The Coiltek 11" AI Coil is awesome in high EMI areas.  It is a shame they discontinued it.

These are high voltage power lines from a windmill farm near my house.



I can run it in my house quiet as a mouse not affected by EMI at all even on high gain.



This video is mucking around with it on various settings on a shotgun pellet in my house on a GPX 4500.

Thanks for all the info guys its been awesome,

Very interesting point you make about Concentric coils managing EMI Kon, wish you had of told me that before I sold my X-Coil Patch lead with the Spiral 17"

I haven't tried Cancel no Butch as I haven't had my GPX5000 for 10 years now, but if I grab another unit I will definitely try it. But given they make concentric coils for the ZED now I doubt I will.

There's some very interesting thoughts about the wind playing a part in EMI around powerline, I'll definitely keep that in mind.

Cheers for sharing the video's Phrunt.

I hope all you guys have been finding a few nugs and are fit and well.

Cheers Hoff.

G'day Hoff

My apologies Hoff, but I did  put up a post on the workings of the new 17 inch Concentric coil (by X-Coils) in the All about coils section, within the X-Coil section itself. Post reads "Concentric X-Coils for GPZ 7000") on the 7th of Feb 2021.

Cheers Kon.

Breathing life back into this post as it covers the heading and my current question,

Buy another GPX5000

Looking to do some Iron Reject work with the 5k in a couple iron filled trashy spots at good old Ophir the sh#t hole.
With interference resistance aside, does anyone know if the standard Terracotta Coiltek DD will complete the "Iron Reject Campaign" any different to using the Anti-Interference version?

Yes, I'm well aware we should dig everything, and I've lived by that rule for 15 years but in this instance I'm happy to take the risk.
I've busted my ass at this spot with the NF 17x13 Mono for the last few months without success so looking to push the odds in to my favour a little with a change of tactics.

Cheers,

Hoff.