Coil Frequency Signal Transmision

[metaldigger]

I'm reading in my XTerra 705 Manual, Yeah I read the Manual, several Times over the past 2-1/2 months. Sucks JK. I like it a lot. Anyways I have the stock coil, and the Concentric 3kHx coil.
The manual on Page 2 The frequency of a detector is the number of times a signal is trasmitted into the ground per second (measured in Hertz- Hz). 1000Hz=1kHz
With a 3kHz coil does this mean the signal is transmitted 3 thousand times per second into the ground? if so the the 7.5 kHz consintric coil is 7.5 thousand times per sec, and so on to the 18.5?

If this is correct. Would not the detector have in reality more power to send the signal deeper with the 3 kHz coil? Than say the 7.5, or the 18.5?
How can the 3 kHz coil go deeper and be less sensitive?

Someone throw me a bone here. LOL

 

[Digger]

Lower frequency coils produce fewer electromagnetic lines of force / second = more spacing between those lines of force = less sensitivity to the smallest targets. As to depth, the theory is that lower frequencies do provide more depth of detection on larger objects. However, I've not been able to either prove or disprove that with my testing of the coils. I guess the question becomes "what is considered a larger target"? Is it a target larger than a coin or smaller than a 54 Buick? As I've said many times, the differences between 3 kHz - 7.5 kHz and 18.75 kHz is minimal. They are all within the range of 3 - 30 kHz, which is what many consider to be the optimum VLF range. And any of them will find coins. Coil size, design, shape and frequency do play a role in how well any coil will perform. But in my opinion, those factors are not as important as a good understanding of how to properly set up the X-Terra for a particular site. JMHO HH Randy

 

[David]

Very good explaination Randy, I recommend putting that on FAQFAQ.

The only time you will notice the difference and an advantage with an 18.75 (HF) kHz is better sensitivity than the MF and LF on small sub-gram gold nuggets(about less than 3/16" surface area) and small gold earing studs or a small fine gold ring on its edge.

As Randy said, yes how much more depth on what size larger target with a LF coil ?? I would also like to know ??

And as Randy said before many times (not a visual TID) an audio(audible sound being an iron grunt) advantage with the 3 kHz (LF) on iron ID'ing(identifying).

 

[Jackpine Savage]

The peak signal strength of targets occur at different frequencies based on their size, shape and conductivity. For instance silver dollars peak somewhere around 2.7 Khz and nickles around 19 Khz if memory serves. So no matter what coil you use it is almost always a compromise. Add in the ground mineralization signal which may require a completely different frequency to minimize and the compromise becomes even worse. Also, target ID detectors need to read both the ground and target signals to give a visual ID on the meter and that is why detectors give poor or no ID's in bad ground or on fringe depth targets.

As to the 3 KHZ frequency transmitting more power, I suppose thats possible. There might also be some slight gain given that lower frequencies travel farther. But since we hunt in ground and not air the difference is probably negligible.

Hope this helps and give you some food for thought.

With apologies to George Payne for my poor paraphrasing of his explanation.

Tom