Jump to content

Why High Frequency? The Effects Of Different Frequencies On A Small Gold Target


Recommended Posts

Everyone needs to watch this video.

We talk all the time how lower frequencies ignore ground better and penetrate deeper on larger targets, but how high frequencies are better at getting small targets to respond. This video does a superb job of illustrating how high frequencies do a better job at "lighting up" a small gold target. The key is we are using one detector and coil with all the settings just the same - the only thing that changes is the frequency. This eliminates other extraneous factors that usually play into comparisons of this sort.

xp-deus-v4-frequency-selection-9-hf-coil.jpg

What this video does not show is how higher frequencies not only "light up" the target but also mineralized ground, creating difficulty with penetrating deeply in that ground. One of the great lessons in metal detecting is that there is no free lunch, and very often improving one thing comes at a cost somewhere else.

You can skip right to "the good part" at 2:45

 

  • Like 3
Link to comment
Share on other sites


It would be a lot more useful video if the sound track and video were better matched - made me wonder if it was filmed in French or something - even with swinging the coil over the target, the sound you hear and what he is doing seem to have little or no relation.

Still there is no question that a high frequency coil will see small targets better - including hotrocks and mineralized ground.

Link to comment
Share on other sites

Slow internet connection or some other issue caused by jumping ahead. Watch the video from the beginning if skipping ahead knocks it out of sync.

Link to comment
Share on other sites

The answer I have seen most often is that a detector running at a single frequency has an edge for technical reasons over machines running at multiple frequecncies. You will note that Minelab does not market their multifrequency machines for prospecting but instead offer machines running at single frequencies, though some Minelab models like the Eureka Gold do allow you to chose the frequency just like the Deus. Fisher sells the multifrequency CZ-3D but again does not market as a prospecting detector. Instead you are offered the single frequency Gold Bug Pro or Gold Bug 2. Note that Minelab's latest, the Gold Monster 1000, runs at a single frequency.

From the Tesoro website at http://www.tesoro.com/info/faq/generaldetecting/

"Tesoro detectors use an LC or tank circuit to generate operating frequency. A capacitor and an inductor are paired together and create a naturally occurring efficient frequency. Variation in the capacitor and inductor cause slight variations in the operating frequency, which reduces the likelihood of crosstalk with other Tesoro machines. The variation is small enough that it does not affect the performance of the detector.

The tank circuit described above generates a sinusoidal or SINE wave form. The SINE wave is efficient to generate and has no harmonics.

Two frequency machines may combine a pair of SINE waves but are more likely to use a square wave. Multi-frequency machines almost always use a square wave or modified square wave. Square waves are rich in harmonics and take more battery power to generate. Harmonics generated by a square wave can be counted as individual frequencies and can be used to give more information as to target type and depth."

From notes on using the White's V3i in mineralized ground http://forums.whiteselectronics.com/showthread.php?62484-Hunting-In-Mineralized-Ground-with-V3i

"3-Frequency: Uses all three frequencies to report data and audio information. This selection will be the best on target data reliability reported as it is using all three frequencies to classify the target. In mineralized ground this can be very useful as targets respond differently on signal strength at each of the different frequencies so that there is a better probability of calculating the correct VDI of the target. Not as sensitive as when using a single frequency but with turning the sensitivity gains up it can be almost as good as in mineralized ground, the ground usually will be the determination of how deep the detector will go. However, using single frequency of 22.5 kHz will do better on small targets (gold chains) than the 3 frequency mode and the 22.5 kHz will also make the small foil sound better as this is the trade off."

And finally, from Dave Johnson at https://www.tekneticst2.com/the-tek-files/the-history-of-metal-detectors-with-emphasis-on-gold-prospecting

"The 1990’s also saw the introduction of multiple frequency metal detectors.  This technology proved itself well for saltwater beach work, and for coinshooting and relic hunting requiring target identification and discrimination.  However multiple frequency technology is not by its nature particularly sensitive to small metal objects, and that kept it from having any impact on gold prospecting."

  • Like 4
Link to comment
Share on other sites

Hope it's ok to post this pic I pulled off the internet...it shows the differnece between frequency and image quality/depth using a ultrasound probe at 6,9,10,12 MHz. Notice that as the frequency increases shallower structures become more clearly visible but deeper structures start to blur or completely disappear. In Ultrasound the frequency of the probe is where it all starts...technology has become extremely advanced beyond that and I have always wondered if engineers in the two different fields (metal detectors/Ultrasound) use simular tecnology to achieve very different goals.

strick

 

F2.large.jpg

Link to comment
Share on other sites

Ultrasound is not unlike radar by bouncing sound off the target giving you an actual visual of the target. A metal detector works more like a transformer, using a current running through a coil to induce a current in another nearby conductive item. See Inductive Coupling

IMG_0391.PNG

  • Like 3
Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...