NF patch 30x7" or NF 24x12" ? advice

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Post  bikehe on Sun Aug 11, 2013 8:06 pm

Hi, hoping to get some knowledge from those that have used either coil or both and what would be your choice. All my coils are NF which consist of the 17x11" solid, great coil, 14" spoked and an 18" solid, great coils as well along with the ML 11". Trying to maximise my ground coverage in the short times I'm able to get out bush in some open ground. I mostly use the 17"x11" but feel I'm losing time in the day using this coil on mostly flat slopinjg country. From what I've researched to date the 24x12 will go to similar depths as my 18" round and picks up small pieces as well with good coverage between swings. The 30"x7" has better coverage but wont go as deep and suspect it will find smaller bits perhaps due to the tighter tips. The weight difference is only about 40 grams so this isnt a problem for me. Is it best to have the little extra depth of the 24x12" and sacrifice the length or sacrifice depth and get more coverage. Any help or advice much appreciated

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Post  kon61 on Sun Aug 11, 2013 10:19 pm



G'day Bikehe.

You're pretty much right in your evaluation of both coils.The answer here lies in the depths of ground you intend on scouring over and the average size of nuggets to be encountered. If your intentions are to hover over ground that has a cover of less than say 8 inches of top soil,before reaching your gold bearing wash layer,then the 30x7 will more than suffice for gold that averages bellow the 5 gram mark.If your gold bearing wash layer lies deeper than that stated above and your gold is greater than 5 grams in weight or size then Id go with the 24x12. Both coils will pick up half a gram at a few inches depth,but you already have a good selection of coils to contend with,so why go for either,for no one coil does all? Find gold with your 17x11 then come back and hammer the ground with the rest. Smile 

Cheers Kon.What a Face 
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Post  bikehe on Mon Aug 12, 2013 10:07 am

Hi Kon,
Thanks for your input mate much appreciated. I just got back from a 3 week trip in the WA gold fields and its getting harder and harder to find pieces. We found some nice pieces totalling just over 5 grams but there are alot of quads, caravans and generally more people out there now where I use to go and places are getting hammered even though its a big country out there and plenty more to look over. Spent alot of time with the 17x11" searching for new patches and thought I need a longer coil to cover more ground in the day. The 17x11 is my choice around shrub and spinifex country but there is a lot of promising pen country to detect so I'm leaning towards the 24x12 as some of the ground can be deep and having that extra depth would be nice.

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Post  Guest on Mon Aug 12, 2013 3:32 pm

another point that you are probably aware of is that all mono coils have a cone effect (funnel) under them so they go deaper in middle than edges. So still have to cover 1/3 (approx) of sweep area on next sweep to get those deeper targets that are on limit of being detected.
I might be wrong but was under belief that the longer narrower coils at the end of the day were not covering much more ground than the smaller round detectors. - some one out there may be able to clarify this

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Post  kon61 on Mon Aug 12, 2013 10:29 pm

G'day Travelergold.

          Your pretty much correct on the so called cone effect and that by overlapping monos x at least a third of each swing will safely say you've covered the ground quite thoroughly,but the greatest depth on a particular size nugget is not always achieved via the centre of a mono coil.An example of this can be seen with the smaller sub gram gold which tends to kick in clearly,a quarter of the way down from the tip of the coil and then tends to fade when swinging over the same target directly over the centre of coil.The larger the nugget or positive target is,that's where the centre of coil plays its greatest role towards exceeding and excelling on depth from any other section of coil length or width.
Lets not get confused here with ground coverage of a coil,as compared to coil field strength on a particular size target,at a certain depth.The longer narrower coils do cover more ground than the smaller coils do,but with less concentrated coil field strength on the same size target at depth,than a coil half its size or length unless again the positive targets encountered,tend to increase in size. I believe this happens because larger coils have a much broader coil field strength over their entire length than the more concentrated field strength given off by the smaller coils over the same size target. That's also why the larger the coil,the slower the swing speed should be for the picking up of faint positive signals.
Anybody else out there confused on what I'v said above,cause I know I am.scratch study elephant albino afro 

          Cheers Kon.What a Face
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Post  bikehe on Tue Aug 13, 2013 3:52 am

Hi Kon great info mate and yes was a bit confusing but I know what youre trying to say. I thought also that as the coils increase in size the number of windings decrease to keep the impedance in spec with what the circuitry in the magic box requires . When the tx is turned off on the mono and the coil recieves, having less windings makes them a little less sensitive but they work well on the larger deeper targets as those targets hold their EMF longer also. Thats my understanding of it anyway

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Post  kon61 on Tue Aug 13, 2013 9:57 am

G'day Bikehe

Yep and your not wrong there either. Density,size,surface area of and how a target is found to be sitting in relation to being picked up by the receive end of coil windings,also plays a major role as to the targets signal strength at any given depth as does the larger diameter of a coils receive end wiring.The length of coil wiring as coils get larger in size,remains pretty much the same specs,as that on a smaller wound coil,so as to match or keep in line with the impedance of the machines output frequency,maintaining ground balance and coil stability,but the smaller the coil,the more coil windings it will have in order to maintain similar results,with the difference being greater density in field strength,hence sensitivity.That is why smaller coils have a more denser or concentrated field strength leading to greater sensitivity to targets,within its capable depth range,than a larger coil using pretty much the same length of coil winding.
Now I'v had it,I'm more confused than ever.affraid Shocked What a Face 

      Cheers Kon.
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Post  bikehe on Tue Aug 13, 2013 9:57 pm

Kon61 thanks mate and appreciate the more detailed explanation. Ok have decided to bite the bullet and bought a NF24X12 from Reeds, as this coil seems to be a happy compromise for my needs. Hopefully will get out and try it soon.

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Post  rc62burke on Tue Aug 13, 2013 10:26 pm

kon61 wrote:G'day Bikehe

Yep and your not wrong there either. Density,size,surface area of and how a target is found to be sitting in relation to being picked up by the receive end of coil windings,also plays a major role as to the targets signal strength at any given depth as does the larger diameter of a coils receive end wiring.The length of coil wiring as coils get larger in size,remains pretty much the same specs,as that on a smaller wound coil,so as to match or keep in line with the impedance of the machines output frequency,maintaining ground balance and coil stability,but the smaller the coil,the more coil windings it will have in order to maintain similar results,with the difference being greater density in field strength,hence sensitivity.That is why smaller coils have a more denser or concentrated field strength leading to greater sensitivity to targets,within its capable depth range,than a larger coil using pretty much the same length of coil winding.
Now I'v had it,I'm more confused than ever.affraid Shocked What a Face 

      Cheers Kon.
Hey Kon
Thank you for your well informed explanation, something I have not read before & explains a thing or 2, awesome info at this house of learning
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