Low Versus High Frequency

[CTidwell]

Just watching a vid of a guy showing the difference of low, mid, and high freqs on the same targets (all natural finds, not buried plants).
Was demonstrating how 40 kHz was slamming these nickels and pulltabs, but 4 and sometimes 7 wouldn't touch them.  It got me wondering.
I've heard that if you run low freqs you will likely miss gold, especially small gold, but does the pendulum swing the other way?
Lower freqs should hit silver better, right?  Does that mean that in high freqs you are likely to miss silver?
Just my musings on a typhoon filled day...

[phrunt]

You may find this informative.

Selectable Frequency And Multiple Frequency - Metal Detector Advice & Comparisons - DetectorProspector.com

Why High Frequency? The Effects Of Different Frequencies On A Small Gold Target - Metal Detector Advice & Comparisons - DetectorProspector.com

VLF Punching Deeper - Metal Detector Advice & Comparisons - DetectorProspector.com

A short answer is high conductors like silver coins at depth benefit from low frequencies while small low conductors like gold nuggets favour higher frequencies.  Many manufacturers of single frequency detectors for do it all general-purpose type detectors went for the middle ground of the 10 to 20 kHz range usually around 14kHz until multi frequency came along.

I've found some of the best detectors for silver coins in milder ground in the single frequency detectors are the sub 10kHz detectors regardless of price range.  

[CTidwell]

Thanks for all the links!  Just getting over the bad weather today. 🙂
I knew high for gold low for silver, but was mostly curious about the statement

"If you run low freqs you are missing gold.  Especially small gold."
and if it is also true the other way
"If you run high freqs you are missing silver, especially small silver."
I figure there's more silver in parks, for example, than gold.

[phrunt]

That statement is correct, you wouldn't want to run a 40kHz detector in a park looking for silver coins, you'll leave plenty behind, just like you wouldn't want to run a 5kHz detector looking for small gold nuggets, you'll leave most behind, that's partly why multi frequency detectors have become so popular.

[CTidwell]

Thank you so much.  That's pretty much what I was assuming. Good to hear it from someone who actually knows what they're talking about. hehehe

[JCR]

My rule of thumb centers around the US 5 Cent Nickel coin & common Aluminum trash.

If where I am hunting holds the possibility of older Nickels, buttons, old jewelry or a US Gold coin, I will use M1 or M2 or at least 15 kHz single frequency. These all give a good response at depth on a Nickel.  M3 or 4kHz lose that good hit with any depth.  10 kHz is not much better.  I prefer M1 because any iron trash will be better behaved & it seems to punch through mineralization better than M2, M3 or single frequency.

If where I am hunting holds the possibility of Silver or other higher conductors, I will again choose M1.  If EMI or conductive ground is a problem then M3.  If Aluminum trash is a problem I will choose 4 kHz as it really dulls the Al response. M3 will also but not as well.

[CTidwell]

Super helpful.  Thank you!

[Zaj56]

On 11/2/2024 at 3:38 AM, phrunt said:

You may find this informative.

Selectable Frequency And Multiple Frequency - Metal Detector Advice & Comparisons - DetectorProspector.com

Why High Frequency? The Effects Of Different Frequencies On A Small Gold Target - Metal Detector Advice & Comparisons - DetectorProspector.com

VLF Punching Deeper - Metal Detector Advice & Comparisons - DetectorProspector.com

A short answer is high conductors like silver coins at depth benefit from low frequencies while small low conductors like gold nuggets favour higher frequencies.  Many manufacturers of single frequency detectors for do it all general-purpose type detectors went for the middle ground of the 10 to 20 kHz range usually around 14kHz until multi frequency came along.

I've found some of the best detectors for silver coins in milder ground in the single frequency detectors are the sub 10kHz detectors regardless of price range.  

Excellent! Are there any charts showing what metals are low conductors  and what metals are high conductors?

[GB_Amateur]

45 minutes ago, Zaj56 said:

Are there any charts showing what metals are low conductors  and what metals are high conductors?

Well, yes and no.  If it were only that simple.  Here's an example:  I was in a schoolyard and got a 36 (out of max 40) digital target ID (dTID) on the Minelab Equinox.  That's high and I was rewarded with a sterling silver ring.  (Well, actually it was my wife who received the reward.  🙂  Some time later I was in a ghost town and got a 12-13 signal, expecting a USA 5 cent 'nickel'.  This time another sterling silver ring, likely for a child.  So size really matters.

Shape also matters.  A ring and a coin of the same composition and weight will read differently due to how efficiently eddy currents (which create the return magnetic signal) are generated in the target.  Annular (aka 'ring') shape leads to a more efficient eddy current and thus a higher dTID than a disk (e.g. coin).

Gold (alloy) is the big exhibitor of this principle.  Small rings can show up low, in the foil range, and large rings can be up with the mid-conductors (like zinc cents and aluminum screw caps).  Serious jewelry detectorists tend to dig a wide range of dTID's and just live with having to dig lots of aluminum alloy, again which can be all over the scale depending upon its size, shape, and alloy composition.

P.S. I'm sure Steve has a good writeup on all this stashed on the website somewhere.