The GPX4000 & Electrical Interference

As a newbie - I just started detecting 2 month ago - I have a question, please.
So far I have been detecting in the area around Dunolly and Wehla in the Victorian Goldfields. A month ago I got some support from a friendly member of this forum during a field trip and found my first nugget. Ever since I used the same settings or close to the same and managed to find a few more small pieces in the same area. However, last weekend I went out again and it seemed whatever I tried, I couldn't get the machine balanced. Remembering the JP GPX video, he made a remark regarding the weather without going into detail. My question now: was this overcast weekend with rain and wind creating interference which made my detector going made or was it my lack of experience muddling up the settings? I was running a 18" elliptical Commader Monoloop and 8" round Minelab monoloop, Gain 11, man tune 110, Ground balance in tracking and fixed (no difference) everything else as per factory settings or very close to those presets.

Thanks for your help.

Ralph

Your Gain might be a little high if you're having trouble balancing. Something too many people seem to do is to run the Gain and Sensitivity a little too high thinking they'll be sensing deeper with it... and they do that will all sorts of detectors too. Not just the GPXs.

Think carefully about what you were wearing on your body the last time you went out that was different to the previous trips out that you made. It may simply have been a set of keys down low in a front pocket or different shoes or even (as I myself discovered) a knife sitting on the belt rather than on my backpack. This turned out to be the reason why I wasn't able to properly balance on one particular trip (when on all previous trips out with the same gear had been uneventful in relation to GB problems).

The GPXs are certainly susceptible to atmospheric conditions like a distant thunderstorm and I have even heard that aircraft chatter between pilots may be a concern for minor interference if the aircraft flight paths are low and the GPX is not correctly tuned to accommodate this. Your 8" Monoloop would be more prone to ground noise than a larger coil or a DD coil. Moisture in the ground can sometimes be desirable but if you are on pockets of saturated mineralization clays, they could possibly have added to your problem.

hi out4fun,
yep your gain a bit high try around 8, if on quiet ground you can go up
a little.

if there is interferance coming from somewhere try this,
put tracking in fixed
turn gain to 15
point coil in the direction of interferance
then hit auto tune
make sure you don't forget to lower your gain back down when finished tuning
you may have to fine tune manualy, just a couple of numbers eitherway
to get it perfect,

if that fails have a look at your target volume you may have to lower that a little
but i would leave that as a last resort.

hope this helps a little
cheers fencejumper

Hi nero_design and fencejumper,

Thanks a lot for your help. Out of all the different aspects mentioned there were quite a few which were different to my previous trips, e.g. this time I wore clothing with metal buttons just above knee height, stormy weather, moist ground and obviously settings which weren't suitable for these conditions. I am looking forward to getting out again and apply this new knowledge.

Cheers
Ralph

Nero is correct, because a small mono is more sensitive it technically would also be more prone to hot rocks and some hot ground noises compared to a larger coil. Larger monos are less sensitive so therefore less prone to some ground noises (and also some smaller nuggets) but are more prone to EMI because they are effectively a larger antenna.

JP

Post Note for Marshall's benefit: Obviously don't try to run a large Mono too close to the ground especially in Normal timings as ground effect will cause noise, however even a complete ninny would soon suss out the detector is noisy and either lift the coil or change over to a DD. With the GPX-4000 (and previous machines to some extent) there was the potential to generate an Anomalous type response if the ground held small magnet type rocks however thanks to SETA with the 4500 this has now been completely dealt with. The best way to test this is find an Anomalous response with the 4000 and then check it with the 4500.

thanks JP... somedays (mostly afternoons) it gets too noisey for a larger mono and the only way I can seem to get anywhere is to switch to the standard DD...but yeah that's EMI

Typically this time of year the monsoon thunderstorms are building up in the tropics, well within the range of our detectors especially in the afternoons, plus the local weather then becomes more unsettled as the temps build up which then exacerbates the problem. I should also point out here moving the Gain by 2 points from FP (8 ) to 10 increases the susceptibility to EMI by far more than the sensitivity increases on good targets, my suggestion especially when using the Enhance timings is keep the Gain at or near FP (General Search Mode option) to maintain stability along with sensible levels of Motion (less or equal to FP (Slow)) and the Stabilizer (less or equal to FP or 10).

JP

Out4Fun wrote:As a newbie - I just started detecting 2 month ago - I have a question, please.
So far I have been detecting in the area around Dunolly and Wehla in the Victorian Goldfields. A month ago I got some support from a friendly member of this forum during a field trip and found my first nugget. Ever since I used the same settings or close to the same and managed to find a few more small pieces in the same area. However, last weekend I went out again and it seemed whatever I tried, I couldn't get the machine balanced. Remembering the JP GPX video, he made a remark regarding the weather without going into detail. My question now: was this overcast weekend with rain and wind creating interference which made my detector going made or was it my lack of experience muddling up the settings? I was running a 18" elliptical Commader Monoloop and 8" round Minelab monoloop, Gain 11, man tune 110, Ground balance in tracking and fixed (no difference) everything else as per factory settings or very close to those presets.

Thanks for your help.

Ralph

Hi Ralph,
Last weekend was particularly bad weather with electrical storms right across the state of Victoria. These machines are capable of picking up a lightening strike hundreds of kilometers away. I would say that just about anyone detecting would have had trouble with atmospheric conditions last weekend. Lightning will come through the detector as a false target. If you swing over the same spot that you heard the noise then you will most likely get silence when you thought you had a sure thing. During these conditions it is quite normal to struggle with trying to get the machine to run smoothly.
Brett.

Just to let you know my mate (no not dwt) was out last Saturday in Vic doing some tests and said the air was very electrically charged due to the weather so before you change your settings permanently, although the advice offered is correct, to answer your question, the weather will change the settings required and as I said last weekend definitely that was the problem...

Hi guys,

Thanks for all the information.
It seems the weather played a role in my unsuccessful attempts last weekend, however the other information will help me to fine tune my settings under any conditions. Next time I get the chance to get out I will be testing different settings as suggested. After all I am still learning and so far my knowledge is only based on a small detecting area of the Goldfields and basically two weather settings - sunny/hot and wet/stormy.

.....can't wait to get out again.

Cheers
Ralph