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Since Jackpine Savage is almost always right....almost.
Posted by: BarnacleBill
Date: June 08, 2008 09:18AM
He recently touched on a coil selection factor that is not taken into account in the coil selection table in the FAQFAQ. And that is that size matters. :lol: It does, but the intent of the chart was to give a rule of thumb for equally sized targets. When looking at the table, strict attention should be paid to the use of the word "favored" as was chosen carefully and meant to convey a "bias" or "trend". It is not meant to convey "absolutely deterministic". As high conductivity items that are small or thin, can sometimes be better found with a high frequency coil.

Aside from what is in the table, there are several other factors that should be taken into account, and their weighting is determined by each individuals circumstances. But trying to include all of that information would make for a very complex and difficult to read table, and possibly be more confusing.

1. How mineralized is the ground, as a lower frequency will go deeper.
2. Am I hunting in iron, as lower frequencies and concentric coils tend to disc out iron better.
3. Am I hunting in stubble, as spoked coils tend to catch and hang up.
4. How is my health, as even though not optimized for a particular target, a lighter coil may allow me to hunt longer. So I trade off a little less target bias for a longer time in the field.

There is a lot of gray area, even though it's much easier when the choices are black & white.

In order to try to address the point brought up by Jackpine, which I have kind of avoided for fear of causing more confusion, I have taken a stab at trying to present some useful information. This may not work as intended, since once again it is meant to show a "trend" or "bias". I can tell you right now that it is no where near being mathematically nor geometrically correct. First looking at the diagram below the black diagonal line is the "trend" line and will be the focal point in the examples presented. A vertically oriented line is drawn between coil size & frequency. Then a horizontal line at the point the trend & vertical lines meet, to show the size & conductivity bias.

First a static version of the nomograph for your use if you desire. Then the examples are animated GIF's that you need to click on and watch like a short slide show that repeats itself.

Example 1:

Example 2:


The next step...
Posted by: Jackpine Savage
Date: June 08, 2008 09:33AM
Most excellent!!! Never seen it done this way before and hey it woiks!! nyuck nyuck

Sorry to cause you all the hard work Bill but, it was worth it!

Now anyone can plot their coil size, frequency, desired target and presto!

Now how would you plot out those first order targets for me? :wink: :rofl:

HH Tom

Hey Digger I think this post deserves to be in FAQFAQ :smile:N/T
Posted by: Jackpine Savage
Date: June 19, 2008 05:16PM

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Thanks Tom. (and Bill) Consider it done! :thumbup:N/T
Posted by: Digger
Date: June 19, 2008 08:26PM

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You'll never know for sure......unless you dig it! HH "Digger"
After 40+ years of detecting, and having owned dozens of different detectors, I've come to the conclusion that maintaining success in the field is largely dependent on three things..... choice of site, acquiring a proper skill set for the detector and the detector itself..... in that order. Research, practice and persistence. There are no substitutes.
Edited 1 time(s). Last edit at 06/19/2008 09:35PM by Digger.

Got to have a new coil.
Posted by: bfodnes
Date: June 21, 2008 07:28AM
The 10.5" DD @ 18.75.

the red line will follow the black line, indicating hot on any target....

Gotta be something to it, whats long time users of that coil have to say.



Hi Bjorn
Posted by: Jackpine Savage
Date: October 25, 2008 05:36AM
Good point on the HF 10.5 DD. I never used one but IMO opinion your thoughts are pretty close. Perhaps a bit of sensitivity loss in the small low conductive (tiny bits of foil) and large high conductive (large US silver coins) regions and you would have a pretty general idea of the coil. I would think it would be a very good general purpose coil for when a higher frequency is desired.


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