This is a follow up to the question, “Are newer machines the key to older coins?" Online forum posters brought up operating frequencies and gold, so this addresses these two topics.

Looking at some online resources:  "Lower frequencies penetrate more deeply but higher frequencies are more sensitive to smaller targets." "Different metals respond better to different frequencies which is why all gold detectors run at 15 khz and up." "The lower the freq. such as 3 Khz will be sensitive in detecting copper and silver targets. Higher freq. such as 15 to 60 Khz will

be sensitive to gold targets. That's why most gold detectors sold have a freq. starting at 15 Khz and higher. The detectors sold with general hunting in mind have operating freq. starting from between 5 to 10 Khz." 

Minelab’s E-Trac and Explorer use FBS which simultaneously transmits, receives and processes 28 frequencies from 1.5 kHz to 100 kHz.
White’s V3 uses three frequencies 2.5 kHz, 7.5 kHz & 22.5 kHz and operates in the frequency domain only.
White's MXT is 14 kHz
White's XLT is 6.5
White's DFX is dual frequency 3 kHz and 15 kHz
Tesoro models use various single frequencies:
10kHz, 12kHz, 14.3 kHz, and 17.5 kHz. 
Tejon ranges 17.2-17.6 kHz.
Garrett Ace 250 uses a 6.5 kHz operating frequency.
Fisher CZ3D and Fisher CZ20 are both dual frequency, 5 kHz and 15 kHz
Fisher F5 - 7.8 kHz.
Fisher Gold Bug - 71 kHz

So, if you're looking for gold only you want a machine that handles the higher frequencies.  Hence, the Fisher Gold Bug at 71 kHz, and PI (pulse induction) units, but let's not get into PI units as most of us do not want to do old coin hunting in trashy sites on land with a PI. 

The multiple and dual frequency machines should always be able to turn up more targets than a single frequency machine.  Theoretically, if you have "cleaned out" a site with your 6.5 kHz White's XLT, and then come along with a 17.5 kHz Tesoro Lobo, you will find targets you missed and that were undetectable with the 6.5 kHz White's machine.

The result of this is that a newer multiple frequency machine will be able to find more targets than the single frequency machines (not necessarily older coins).  So the newer multiple frequency machines, including the old Fisher CZ and Minelab FBS machines will do better than a single frequency unit. 

This is where I start thinking about accuracy of target ID - beeping over metal is not enough, I need to know if it's worth digging or not.  How does the number of frequencies affect the target ID?  Is a dual frequency (or more) machine going to ID targets more accurately than a single frequency unit?  It seems like this would be the case.  Certainly in my experience I have found that my Minelab FBS machines are the most accurate ID machines I have ever used, and they are accurate at good depth as well, though any machine will start to drop off on target ID at the edge of it's detection range.  I have seen some reports that users of the White's V3 are also reporting more accurate target ID.

Now about finding gold.  How does operating frequency affects the detectability of lower conductive metals?  Gold is always difficult as it is alloyed with different metals.  10k gold is about 40% gold, so the detectability of a 10k ring is somewhat dependent on what the other 60% of the ring is made of.  Due to this variability in alloys, shapes and sizes of gold rings and jewelry, I do not think we can even predict accurate results for one frequency or brand or model of detector being able to find more gold while land hunting homes, parks and schools.  Thin gold rings are smaller targets and will be picked up better by a higher frequency, so a higher frequency may have a slight advantage there.  For purposes of this discussion, I'm keeping this focused on coinshooting and detecting at parks, schools and homes.  Nugget hunting and beach hunting would be different styles of detecting.

I think it comes down to what we have all been told in the metal detecting press and on online forums ad nauseam.  The only way to find more gold jewelry targets on land is by digging more junk and trash targets that fall in the pulltab range on ID machines.  If you do not have target ID, you will dig more junk, hence the potential is there for more gold.  So, do users of non-ID machines find more gold?  Maybe.  But their trash-to-treasure ratio is much higher than someone using a target ID machine.

And just a brief not about coils here too, as I feel these play a role as well.  The two current most expensive popular machines are the White's V3 and the Minelab E-Trac.  Both use DD (double D) coils.  In my experience the DD coil covers ground better than a concentric.  The Minelab I have found separates signals well, even penny size targets at depth.  Better ground coverage with good separation means you will be able to recover more targets and there will be fewer missed targets due to not overlapping sweeps or target masking.

So, why a newer machine?
1. Multiple frequencies = more detected targets
2. More accurate target ID = more signals that say "dig me"
3. DD coils = better coverage and separation

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Comments

Winkle Detector Sales
07/27/2009 12:12

This is a very good artical to have in one place. Showing the Frequencies of some differant Detectors.I have known this and a few other things about Detector's. As I am the Detector Dealer for the Black Swamp Detector Club. In business starting in 1970. Old Fellow 84
years young. Look under White's for my location.
You have some very nice artical's.
Robert D. Winkle. Where are you located?

Reply
Robert Barnett
11/22/2009 18:57

I tend to disagree about newer machines being able to find more. I have an old schoolyard in back of my house thats been detected over the years. I've checked with guys I've seen detecting there the past 5 years some with the newest machines including minelabs and I've never seen any find any old coins. My friend has a new whites dfx and we've compared signals between his dfx and my old qxt and see little difference between the 2.
Bob Barnett

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Neil in West Jersey link
02/16/2010 13:23

I have doing extensive bench testing regarding target VDI the White's V3 white using using different frequencies. Once of the most surprising results of the research is the significant loss of sensitivity to gold while using the V3 in low (2.5 KHz) frequency. No question about it, while searching for gold or small jewelry, high frequency means higher sensitivity.

Reply
TC
03/10/2010 20:45

Nick I found this article pretty interesting and ran across the info below via White's. What's your take on this .....even though I know your a Minelab guy already.....

There is much confusion - some of it deliberate - over how many
frequencies a detector actually uses, and whether multiple frequencies
are truly better than a single frequency. What defines a multi-frequency
detector? What do multiple frequencies really do for depth and discrimination?
A multi-frequency detector is defined as one that simultaneously--
or, in automated sequence—transmits, receives, and processes
more than one frequency. Some detectors have the ability to operate at
one of several selectable frequencies, but they still are single frequency
detectors because during operation they can only transmit and process
a single frequency. The same is true of detectors that have a control to
slightly vary their operating frequency to minimize interference; even
though they have the ability to operate at many (slightly) different frequencies,
they are fundamentally single frequency designs. Currently, all
multi-frequency hobby detectors run their multiple frequencies simultaneously
as opposed to sequentially; they are all characterized by having
multiple processing channels in the receive circuitry. Therefore, a 2-frequency
detector will have two processing channels. Spectra V3 has three
independent processing channels; it is a true 3-frequency detector.
This all sounds easy, so where is the confusion? It turns out
that (currently) all multi-frequency detectors create a transmit signal that
is composed of digital waveforms which are designed to produce peak
energies at the desired frequencies. As a side-effect, these digital waveforms
also produce undesired harmonic frequencies. Lots and lots of harmonic
frequencies, 10’s or even 100’s of them. These harmonics have no
useful energy and are not part of the signal processing. So while we can
claim to transmit many, many frequencies, we cannot claim to process
or use them. Therefore, we could easily claim the Spectra V3 transmits
17 frequencies, or 28, or 39, or 55—we could get plain silly with this. And
such a claim would be true, technically speaking, but since all those extra
frequencies are not actually used, it would be misleading to make such
V3 - the story
3 Frequencies “why not 28?” ...
3 Frequencies “why not 28?” ...
a claim. White’s chooses, instead, to claim the number of frequencies we
are actually using and processing. It may not sound as impressive as a
55-frequency detector, but it’s honest and accurate.
Pulse Induction (PI) detectors also utilize a digital (pulse) transmit
waveform, so they transmit a tremendous number of harmonic frequencies
as well. So is it fair to include pulse induction as a multi-frequency technique?
Not really, because PI detectors process in the time domain, not
the frequency domain. So even though they use broad-band signals, they
are not frequency-based detectors at all. Calling them “multi-frequency” is
simply another attempt to confuse the consumer.
Once we get beyond the marketing hype, the real question is:
What does multi-frequency do for depth and discrimination? The truth is,
any time a detector is simultaneously transmitting more than one frequency,
the transmit energy must be divided amongst the frequencies. Therefore,
a single frequency detector can usually squeeze out slightly more
depth than a multi-frequency design at that certain frequency. But this is
an advantage only at one frequency, which tends to favor only a narrow
range of targets.
This is where a multi-frequency detector such as the Spectra V3
really shines. V3 transmits at 2.5kHz, 7.5kHz, and 22.5kHz, making it
simultaneously “hot” on silver, relics, and gold. Single frequency detectors
are unable to have peak performance over such a wide range of targets.
This is an advantage not only in detecting desirable targets, but also in
discriminating out undesirable targets. So multi-frequency detectors get
excellent depth over a much wider range of targets, and do a better job of
identifying targets. But Spectra V3 can also beat single frequency detectors
at their own game: V3 has the ability to run in single frequency mode
using any of its three frequencies, and the transmit waveform is optimized
to put all the energy into that one frequency. So if you want to hunt for only
deep silver or only gold jewelry, V3 can be optimized for these tasks.

Reply
Dan Huffstatler
04/20/2010 11:25

You have some really good information here. Thanks for explaining the differnt types of frequencys used for different types of metals and great
comment by TC on the whites V3.

Reply
eve isk link
01/24/2011 19:21

You have some very good information here. Thank you for your explanation frequencys different types of metal and a great use of differnt types
Comment by the TC white v3.

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