Now that I've got your attention ...
One interesting alternative I've seen to traditional walkin' 'n swingin' metal detecting is called the Hot Foot Rug. I'm sure many reading this have heard of it. Basically, from the looks of it it's a search coil apparently embedded into a flexible, rectangular carpet-like piece of material measuring from 18" to 6'. The carpet must, of course, be attached to a box, which the user can keep by their side or clip to a belt. The carpet itself can either be attached to a harness and pulled while walking or dragged behind a vehicle, enabling detectorists to cover a lot more ground -- and with less walking required -- than traditional "stick" detecting. The only thing that makes me not even consider buying one is what I consider to be the excessively-high price (then again, in my opinion MOST metal detectors and search coils are way overpriced.)
Especially when dragging the carpet behind a vehicle I would assume the user absolutely must use a good set of noise-canceling headphones.
I'm very surprised that the device mentioned above is about the only one of its type I've seen for sale. In my opinion -- and especially with so many detectorists being middle-aged and/or retired folks who aren't as mobile as they used to be -- you'd think there'd be quite a variety of such carpet-like search coils available.
Does anyone here prospect with such metal-detecting rugs? My main interest is in prospecting for large, deep nuggets and this technique -- especially with my bad knee -- really appeals to me, as the rug search coil can be several feet wide, which dwarfs even the largest traditional round/oval coils. Any feedback or information on such carpet-type detectors would be appreciated.
I was reading the Australian Electronic Gold Prospecting Forum today and noticed a post about detector depth. I was wondering what others think about today's detectors compared to what was available 25 years ago. I read somewhere that (Woody) the guy that does mods to detectors thinks that for outright depth the sd2000 still goes the deepest. I wouldn't know as I've never owned a sd2000 or a gpz7000. Anyway, i found the comments at AEGPF interesting and wonder if anyone here has actually done a depth comparison between the zed and sd2000. Heres the snippet from AEGPF
Quote from AEGPF: "The deepest Pi detector ever developed in my opinion was a prototype SD2000 that BC modified for the late Jim Stewart.BC slowed down the clock speed to give a very long pulse and made some other unknown changes to the circuit to cope with higher currents etc. At the time the SD2000 came out BC stated that it was at about 95% of the maximum potential depth that any handheld PI could ever achieve (and still pass emission standards). However, the deepest PI that has ever been made for gold was Corybns detector which detected a nugget of around 10oz? at 3 feet in depth in WA. Somewhere on the forum is a reference to it and I will try and find the link when I have time.
"What is interesting is that the deepest nuggets ever detected by a Pi was by a detector used in the early 1980's in WA-Corbyn's wheeled detector! Pictures of it and the depths of some of nuggets he found with it can be seen in Mike Wattones book: Quest for gold.NO Pi detector today could match the depths Corby got on at least one nugget! (4cm nugget at over 36" in mineralized ground)"
First, I want to say this is one of the best forums I have ever seen. Steve has put together a GREAT website. The knowledge base on the forum is just phenomenal. I have learned so so much more about metal detectors from all of you.
So let me explain assumed.
White's and Garret were the best metal detectors.
Carl Moreland was still working for White's
Metal detectors were 10 years behind technology of today. (just my thought)
After making the assumptions, I realized how wrong I was thanks to this forum. I realized White' and Garrett have been a sleep. Carl Moreland either quit or was fired. White's and Garrett detector are whats 10 behind.
When I got back into metal detecting last year. I was looking for a new machine. I looked at White's and Garrett with the assumptions. I thought about building my own detector. So I read Carl Moreland's book. (Great book) I realized that it would take me 2 to 5 years to develop my own detector. So I scrapped this idea. I could not understand why White's or Garrett had not built a detector with what I expected. I thought that with today's technology there should be a sweep frequency oscillator for the coil-s and an easy to read display. That being said, White's closest model was the V3i. Garrett had nothing. I quickly realized that I needed to look at everything. Because of the forum, I found Minelab was being discussed. When I found the Minelad Safari, I quickly realized it had what I was thinking of building. I don't like their LCD display. It does not look clear a crisp to me. However the machine looks promising. Then I looked at the E-track and CTX-3030. These also look to be very promising machines. Just the price is higher that I want to pay for a -2 times a month hobby. I really wish the best for White's and Garrett. They have their work cut out for them.
I want to thank John, Chuck, Tom and Terry and many others I do not know their names for the knowledge your provided and a special thank you to Steve H for his superior knowledge and the wonderful website he has provided.
By Steve Herschbach
The latest issue of the ICMJ is out, and I have an article in it titled Selectable Frequency vs Multi Frequency Detectors. Those of you with a digital subscription can read it online.
The ICMJ has a policy against mentioning brand names in articles so I wanted to post this as a supplement to the article.
Most metal detectors run at a single frequency. Low frequencies, that is single digit frequencies under 10 kHz, react well to high conductive targets, like coins, or large items, even if those items are of low conductivity. If you look at this typical metal detector target scale below you will note that non-ferrous items read higher not just based on conductivity but size also.
Low frequency detectors also do not "light up" the ground or hot rocks as much as detectors operating at higher frequencies. Many do not even offer ground balance controls because a factory preset level works well enough for some uses. Low frequency machines under 10 khz therefore tend to be aimed at the coin detecting market. There are too many models to list but most people have heard of the 6.5 khz Garrett Ace 250 as a perfect example.
High frequencies 30 khz and over have extreme sensitivity to low conductive and small items, but also struggle more with ground penetration and hot rocks. Their extreme sensitivity to tiny trash items like aluminum bits do not make them very practical for any detecting except gold prospecting. Machines 30 khz and higher tend to be dedicated prospecting machines. Examples would be the 48 khz White's GMT, 71 kHz Fisher Gold Bug 2, 56 kHz Makro Gold Racer, and 45 khz Minelab Gold Monster 1000.
In 2002 White's introduced the White's MXT at 14 kHz, and it is a perfect example of how detectors running in the "teens" make excellent "do-it-all" detectors. Since then everyone and their brother has jumped on that bandwagon, and there are too many machines running in the 10 kHz - 20 khz region to mention. Prospectors in particular would recognize the 19 khz Fisher Gold Bug Pro, but few know it is also sold in slightly different versions as the Teknetics G2, Fisher F19, and Teknetics G2+, all 19 kHz detectors sold to the general coin and relic market. Garrett has the 15 kHz AT Pro and 18 khz AT Gold to name a couple more popular metal detectors.
Well if low frequencies are good for coins and high frequencies good for gold, why not make machines that can do both? Or both at once?
Selectable frequency refers to machines that can select from one of several possible frequencies, but analyze the signal from only one frequency at a time. These may also be referred to as switchable frequency detectors. Multiple or multi frequency detectors analyze the signal from two or more frequencies at once. In theory this multifrequency analysis can be done simultaneously or sequentially at a very high speed. The end resultant is the same - the results from two or more frequencies are compared to derive information that cannot be had by analyzing a single frequency alone.
Multiple frequency detectors usually have a fundamental frequency, and then other "harmonic" or secondary frequencies they also use, but the power (amplitude) fades with distance from the primary frequency. From page 9 of Minelab's Metal Detecting Terminology:
You can find more information on harmonic frequencies at http://www.ni.com/white-paper/3359/en/ and here also.
Coils normally must be wound specifically to make use of any given frequency or set of harmonic frequencies. A coil will usually work best at the given fundamental frequency making it difficult to get the best possible performance at all frequencies using one coil. The Minelab X-Terra series specifically requires a coil change to achieve a frequency change for this very reason. People who own them know 3 kHz coils weigh more than 18.75 kHz coils. Why? Because heavier windings are used at 3 khz for optimum performance at that frequency.
Here is what is probably an incomplete list of selectable frequency detectors and year of release:
1989 Minelab Eureka Ace Dual 8 kHz 19.5 kHz
1993 Minelab XT 17000 6.4 kHz 32 kHz
1994 Compass X-200 6 kHz 14 khz
1997 Minelab XT 18000 6.4 kHz 20 kHz 60 kHz
1999 Minelab Golden Hawk 6.4 kHz 20 kHz 60 kHz
2002 Minelab Eureka Gold 6.4 kHz 20 kHz 60 kHz
2005 Minelab X-TERRA 50 7.5 kHz 18.75 kHz
2006 Minelab X-TERRA 70 3 kHz 7.5 kHz 18.75 kHz
2009 Minelab X-TERRA 305 7.5 kHz 18.75 kHz
2009 Minelab X-TERRA 505 3 kHz 7.5 kHz 18.75 kHz
2009 Minelab X-TERRA 705 3 kHz 7.5 kHz 18.75 kHz
2009 XP DEUS 4 kHz 8 kHz 12 kHz 18 kHz
2016 Rutus Alter 71 Variable 4 - 18 kHz
2017 Nokta Impact 5 kHz 14 kHz 20 kHz
Multiple frequency or multi frequency machines have become very confusing, as a lot of marketing material has focused on the number of frequencies transmitted. What really matters is what frequencies a detector receives, and how the information is compared and processed for results. Some commentary here. Many people look at the marketing material and assume that a machine processing multiple frequencies is somehow working across the board to deliver the best possible results at all frequencies. However, the two issues outlined above do apply. The machines are employing harmonic frequencies, and so cannot compete with a machine optimized at a single frequency as opposed to one of the distant harmonics running at less amplitude. Second, making one coil run perfectly at all frequencies is extremely difficult, again giving the dedicated machine an edge.
I highly recommend people not go down the technical rabbit hole but instead focus on what the machines do, on how they act. Two things are very apparent.
First, the big market for a long time was coin detectors, and the goal always was to identify coins as deep as possible while ignoring trash as well as possible. Processing two or more frequencies simultaneously gives the detector engineer more information to work with. All the focus was on developing great coin detectors and guess what, the multi frequency machines for all intents and purposes act just like very good lower frequency coin detecting machines. Good ground rejection, and great discrimination on coins for as deep as it can be achieved. The multi frequency machines don't really go deeper than single frequency coin detectors, they just do a better job delivering clean discrimination results to depth.
Here is a list of introductory models of multi frequency detectors and year of introduction. I am not listing all the derivative models to reduce clutter. I will post that later.
1991 Fisher CZ-6 5 & 15 kHz
1991 Minelab Sovereign BBS
1999 Minelab Explorer S/XS FBS
2001 White's DFX 3 kHz & 15 kHz (Simulates single frequency by ignoring half the dual frequency signal)
2012 Minelab CTX 3030 FBS2
Second, single frequency detectors have a ground balance problem. They can ground balance to mineralized soil, OR they can ground balance to salt water. Multi frequency machines can reduce signals from both mineralized beaches and salt water simultaneously, making them ideal for saltwater use.
1993 Minelab Excalibur BBS (Sovereign in waterproof housing)
1995 Fisher CZ-20 5 & 15 kHz (CZ-6 in waterproof housing)
2001 White's Beach Hunter ID 3 & 15 kHz (DFX in waterproof housing)
There is a third class of machine that can run either as selectable frequency OR multi frequency detectors. Quite rare at this time.
2009 White's Spectra Vision 2.5 Khz or 7.5 kHz or 22.5 kHz or all three at once
2017 Minelab Equinox 5 kHz or 10 kHz or 15 kHz or 20 kHz or 40 kHz plus multi frequency options
In my opinion multi frequency has delivered well on its promise. The Minelab BBS and FBS machines are renowned for their ability to discriminate trash and detect coins due to their sophisticated processing. Again, focus on what they do. Not even Minelab in their marketing tells anyone these are prospecting detectors. Second, the Fisher CZ-20/21 and various Minelab Excalibur models are without a doubt the most popular and successful non-PI saltwater beach detectors made.
I have a DFX and I think it is a fantastic jewelry machine in particular. A good coin machine but lacks a bit of punch. The Vision/V3i upped the ante but while amazing on paper suffers from interface overload. The Minelab units are simple by comparison and a lesson on how people in general just want the detector to get the job done. Feature overload is not a plus. However, I think White's has the right idea. The ability to run either separate frequencies or multiple frequencies at once is very compelling. I just think nobody has really done it right yet in a properly configured package. The V3i has the ingredients, but needs to be stuffed in something like an MX Sport with a simplified interface and improved ground balance system. It really never did beat the MXT in some ways and many people when "upgrading" to the V3i end up going back to the MXT.
Selectable frequency has yet to really deliver on its promise in my opinion. So far it has been difficult to produce a selectable frequency machine that truly performs at all frequencies on par with a dedicated single frequency machine. The Minelab Eureka Gold at 60 kHz just never gets mentioned in the same breath as the White's Goldmasters/GMT or Fisher Gold Bug 2. Also, most selectable frequency machines in the past have been very feature limited prospecting machines, restricting their overall market appeal.
I personally think we have seen enough variations of single frequency detectors. I do not believe much can be done to exceed the performance of the dedicated single frequency VLF type machines we currently have. What can obviously be done is a better job of packaging machines that deliver true punch at different frequencies, or multi frequency machines that bring across the board performance closer to what is expected of PI detectors. I do think we are seeing this happen now. The new Nokta Impact and the new DEUS V4 update are expanding the available options in selectable frequency in more usable packages. The Minelab GPZ and other hybrid platforms blur the line between what is traditionally considered PI and VLF and simply need the addition of discrimination to go to the next level. There is still a lot of potential to deliver machines that might reduce the number of machines many of us feel compelled to own by delivering more across the board performance in a single machine that would now take several detectors. Exciting days ahead.
For those who want to try and get their head around selectable frequency and multi frequency technology, Minelab and White's have a gold mine of information in a few of their references. Dig into the following for some great explanations and diagrams.
Minelab - Metal Detector Basics and Theory
Minelab - Understanding Your X-Terra
White's - Spectra V3i Owners Guide
White's - V3i Advanced Users Guide
Better yet are the last three parts of the DFX instructional video by White's featuring engineer Mark Rowan explaining frequency and multi frequency methods: