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Optimal Frequency For Coin Hunting - Teknetics 7.7 Khz Omega 8500 Vs 13 Khz Patriot


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There are two recent, active threads elsewhere on this site discussing detector frequency.  I've started a new topic here because this is specific -- frequency for coin hunting.  It probably has an impact on both relic and jewelry detecting as well, but only peripherally (I think) with native gold.

To frame up my concern, I first should disclaim that, as with most detecting, there is no simple answer that treats all conditions.  Ground mineralization, electro-magnetic interference (EMI) background, and goal target size, shape, composition and expected depth can all be variables (and usually are) in finding the optimal solution.

For my situation the local mineralization is typically mild to at worst moderate.  Living in a city, EMI background is certainly a concern although I haven't noticed severe cases and often it's unnoticeable.  Target size, shape, composition (coins), and depths of a few inches to deep, since I want old coins, are my parameters.

Now that I've laid the groundwork, I'll narrow the choices -- high single digit frequencies (6-10 kHz) vs. midrange frequencies (13-15 kHz).  The former has the advantage of less susceptibility to mineralization (probably not an issue in my ground) but higher response to EMI.  Lower frequencies favor high conductors (copper and silver and most of their alloys) compared to higher frequencies which cater to the lower conductivity metals, especially gold, lead, and nickel and most of their alloys.  Higher frequency also gives better response to small items (e.g. small jewelry and the smallest coins).

Iron is the enemy of just about every type of modern metal detecting.  It's plentiful, easily corroded, and most items made of it are nearly worthless, unless you're talking very large stuff (cars, trains, bridges,...).  Iron (I think) is more of an issue with higher frequencies, just like mineralization which is usually some kind of iron oxide, but lower frequencies see iron quite well, too.  On top of that there is a hidden disadvantage at lower frequencies -- wraparound.  My experience combined with quite of bit of reading has come up with an explanation for this unexpected weakness.  The conductivity (ID-) scale is non-uniform at low and high frequencies.  High frequencies expand the low conductivity range (especially iron) and compress the high conductivity range.  Low frequencies do just the opposite.  On the surface this sounds like another advantage for low frequencies.  But the devil in the detail is that the compressed iron range causes more spillover, in this case wraparound to the highest frequencies where the high conductors live!  I found this out the hard way using a 3 kHz coil on my Minelab X-Terra 705.  The wraparound can be so severe that iron IDs as large silver alloy coins (such as US silver dollars and even in some cases half dollars) and smaller (e.g. rounds and bars of) pure silver.  Yes, this isn't a steady ID but rather jumpy between iron and silver, but when you are in trashy ground (just about any site that has seen building construction or simply fences) you'd like to discriminate out the iron range.  With discrimination on and you just hear high conductor and can get fooled, at a minimum having to go back into all-metal mode to see if there is a significant iron signal.  This can be tedious and time consuming.

Back to the two chosen frequency ranges: most modern detectors in the 6-10 kHz range are less expensive (<$400) devices, with an accompanying paucity of features and possibly other cut corners.  Most of the 13-15 kHz detectors ("all around detectors") are of better quality, have more features, typically go deeper, and come at costs in the mid-range -- $400 - $1000.  For me the cost isn't too much of an issue, at least between these two.  (Minelab CTX 3030 is a different story.)

For specific examples, the Teknetics Omega 8500 is low frequency (7.7 kHz) but has features no other detector currently selling under $400 can touch.  At least that's my observation.  For a limited time you can find it for $379 new -- it's usually about $650.  Compare it to the new Teknetics Patriot (rebranded Fisher F70) at a current featured price of $400 new.  By all accounts it's nearly equivalent to the First Texas 'black' flagships -- F75 Limited and T2 Special Edition.  The Patriot/F70 is a true jack-of-all trades (i.e. coin, jewelry, relic, and even gold nugget) detector.  But concerning old coin hunting, is it a match for the lower frequency advantages(?) that the 8500 has?  Yes, finally a question.  :smile:

 

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On 5/30/2017 at 6:21 PM, GB_Amateur said:

To frame up my concern, I first should disclaim that, as with most detecting, there is no simple answer that treats all conditions.  Ground mineralization, electromagnetic interference (EMI) background, and goal target size, shape, composition and expected depth can all be variables (and usually are) in finding the optimal solution.

Well, that about sums it up. There is a lot more to a detector than frequency. Frequency sets some basic parameters, but the sensitivity of the receiver circuit (how high gain is it?), transmit power,  and the efficiency of the ground balance and discrimination filtering methods employed are every bit as important. Even such basic items as what type of coil is stock with the detector matter a lot, as does the visual display/control layout and audio characteristics. I pay attention to frequency but it is only one factor among many when choosing a detector. In general, single digits (1 - 9 khz) are coin detectors, and models in the teens (10 - 19 khz) are multi use. The 7.7 khz Omega 8500 comes stock with a concentric coil and is designed as a coin detector and the Patriot at 13 khz with a DD coil is a more general purpose unit. Both however will probably find most of the items that the other will. In the end you have to just look at the features and make a choice.

If all you ever do is coin hunt the Omega 8500 is a fine choice. I have to admit to being a bit biased to concentric coils myself when it comes to dealing with bottle caps. Running with wide open tones is usually the solution to your ferrous wrap problem. Many ferrous items generate both ferrous and non-ferrous responses, and when you suppress the ferrous response via discrimination you make the item appear non-ferrous. Running with full tones allows you to hear both components of the target signal.

The Teknetics Patriot at 13 kHz and with the DD coil is going to handle tougher ground conditions better.

teknetics-omega-8500-metal-detector.jpg

  • Adjustable Backlight
  • Waterproof Elliptical Searchcoil
  • Notching Controls – Discrimination & Variable Volume by Category
  • Independent Gain & Threshold Control
  • Ground Mineralization Readout
  • Ground Phase Error Readout
  • 2 Modes of Operation:
  • Discrimination All Metal
  • Selectable V.C.O. Base Tone
  • Choice of 3 Tones plus V.C.O
  • Digital Target-ID System
  • Ground Grab® Computerized Ground Balancing with Manual Override
  • Frequency Shift to Eliminate Electromagnetic Interference (EMI)
  • Visual Background Iron-ID
  • Enhanced Multi-Level Depth Boost
  • Static Pinpoint with Numerical Depth Indicator
  • Large Target Overload Alarm
  • Quick-Switch Mode Control – Discrimination to All Metal Mode
  • Multiple Audio Tone ID Options
  • Expanded Iron ID Range, 1-39
  • Unique, Intuitive Interface & Display
  • Standard Coil 10” (25 cm) Concentric Open Frame
  • Waterproof Coil Yes
  • Batteries 9-Volt Alkaline (not included)
  • Battery Indicator Yes
  • Battery Life Yes
  • Pinpoint Mode Yes
  • Target ID 1-99 Target-ID Numbers
  • Audio 3-Tone plus V.C.O
  • Volume Control Yes 0-10
  • Discrimination Modes 8 Categories + Notch
  • Discrimination Adjustment 1 - 65
  • Sensitivity Adjustable 1 - 99
  • Operating Frequency 7.69 kHz
  • Depth Indicator Digital, 1" increments
  • Weight 2.5 lbs. (1.1 kg)
  • Length 43” - 53”
  • Headphone Jack Yes, ¼” (6.3 mm)
  • Ground Balance Ground Grab® Computerized Ground Balancing
  • Backlight Yes
  • More information on Omega 8500

teknetics-patriot-13-khz-metal-detector.jpg

  • 13 kHz frequency – good for coin shooting, relic hunting and gold prospecting
  • Frequency shift for eliminating electrical interference
  • Visual Target-ID by category and 0-99 numerical indication
  • Target-ID confidence bar
  • Continuous ground mineral concentration readout
  • Push-button static pinpoint
  • Speed selection – normal for most conditions, slow for deep coins in non-trashy areas
  • 11-inch waterproof DD searchcoil
  • 40 hours of battery life (4 AA batteries)
  • Standard Coil 11-inch Open Frame Bi-Axial™
  • Waterproof Coil Yes
  • Batteries 4x AA (not included)
  • Battery Indicator Yes
  • Battery Life 20-25 hrs.
  • Pinpoint Mode Yes
  • Target ID Yes
  • Audio 8 audio tone options
  • Volume Control Yes
  • Discrimination Adjustment Yes
  • Sensitivity Adjustable
  • Operating Frequency 13 kHz
  • Depth Indicator Yes, 4-segment
  • Weight 2.9lbs (1.3 kg)
  • Length Length 43.5” to 52.5” (110 cm to 133 cm)
  • Headphone Jack Yes
  • Ground Balance Yes
  • Backlight No
  • More information on Patriot

 

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  • 3 weeks later...
On ‎5‎/‎30‎/‎2017 at 7:21 PM, GB_Amateur said:

There are two recent, active threads elsewhere on this site discussing detector frequency.  I've started a new topic here because this is specific -- frequency for coin hunting.  It probably has an impact on both relic and jewelry detecting as well, but only peripherally (I think) with native gold.

 

Now that I've laid the groundwork, I'll narrow the choices -- high single digit frequencies (6-10 kHz) vs. midrange frequencies (13-15 kHz).  The former has the advantage of less susceptibility to mineralization (probably not an issue in my ground) but higher response to EMI.  Lower frequencies favor high conductors (copper and silver and most of their alloys) compared to higher frequencies which cater to the lower conductivity metals, especially gold, lead, and nickel and most of their alloys.  Higher frequency also gives better response to small items (e.g. small jewelry and the smallest coins).

Coin Hunting as well as Coin & Jewelry Hunting as well as Relic Hunting can involve searches for targets spanning a wide range of conductivities.  Some might be more responsive to a higher or lower operating frequency, but if we want to find all the potentially desirable targets that could range from a very low-conductive gold chain or baby's ring or a US $1 or $2½ coin or common 5¢ 'nickel' on up through some interesting conducive coinage to the larger to smaller 90% silver dollars to silver half-dimes, then it might be logical to select a very good 'universal-range' operating frequency.

The VLF range is from 1 kHz to 30 kHz and you sectioned off two subjective categories of 6-10 kHz and 13-15 kHz.  I can tell you that through the years I have seen and handled models, or prototypes of models, that operated at either end of the VLF range and both showed very weak points when it came to all-purpose versatility ... considering only the operating frequency at this point.

By the latter '70s I found that I was quite comfortable with several detector models, and my personal interest in finding a very good, general-purpose operating frequency continued throughout the next 15-20 years.   The more I bought, sold and traded to get all sorts of makes and models working at different frequencies, I would use them afield and put in ample time ... then sit back and think through how they worked, what their strengths and weaknesses were, and compare them with other units I had used or currently owned.

I would make changes along the way to my personal-use detector battery so that I retained the detectors that worked the best for me, handled various challenges well, and produced desired in-the-field results.    In short, I kept the best of the best when it came to performance.  Now, I am more of a very devoted detectorist and use them a lot of over 52 years now, but I am not the schooled and educated design engineer.  Therefore, I do read a lot, when it is available, from detector engineers who I have come to respect because sometimes, just maybe they have something to say that makes a lot of sense.

One such notable character is George Payne, credited with designing the first VLF ground cancelling hobby-based detector.  Also the first VLF-Disc. or ground-cancelling motion-based discriminating detector.  He brought us the first visual Target ID detector design, soon adding Tone ID to the circuitry.  After the demise of the original Teknetics/Bounty Hunter company he teamed up with other former industry figures and started Discovery Electronics.

About that time George did an excellent write-up regarding conductivities and frequencies in an explanation of how he decided on an "optimum frequency" for designing the Discovery Treasure Baron.   What was that optimum frequency?  It was 12.5 kHz.

I found that quite interesting because while I had a model or two that operated at a lower or higher frequency range, usually for specialty applications, I had already long settled on an established personal detector battery that operated from 10 kHz to 15 kHz ... all models that were ± 2.5 kHz of George's perceived 'optimum' general purpose operating frequency.

Since '83 the vast majority of all my coins, be it modern 'flash money' or the early era coinage I prefer to find, has come my way using detectors that operate from 10 kHz to 15 kHz.  My all-time favorite Utah ghost town kicked out hundreds of coins that I filled four binders of 2X2 carded oldies ... using my favorite detectors in that frequency range.

Today, my Regular-Use Detector Battery is comprised of 2 Nokta Impacts (and I mainly use the default 14 kHz), 2 Nokta Relic's (19 kHz and used for select, challenging Relic Hunting sites), 2 Nokta CoRe's (another great general-purpose device at 15 kHz), and four favorite Tesoro's: a Bandido II µMAX, Silver Sabre µMAX, Mojave and Vaquero (all operating at 10 kHz, 12 kHz or 14.5 kHz) and I don't feel a need for any regular-use detectors of a different frequency extreme from these.

Those early days in this wonderful 'hobby' from '65 thru the '70s are sadly gone, but very memorable when I reflect back on 60K-70k coins a year, but when not working overtime or extra work I got into the ± 120K range a year.  When I made a shift to more Relic Hunting of older sites during the '75-'83 period I was still singling out favorite detector models and most were in the 10 kHz to 15 kHz range and I continue this favored preference today.

Models in this range include most general use Tesoro's, the Teknetics T2 and Fisher F75 at 13 kHz, White's MXT Pro, M6 and MX5 at about 14 kHz, the Makro Racer and Racer 2 at 14 kHz, and as mentioned the Nokta FORS CoRe which captured my attention two-and-a-half years ago operating at 15 kHz.

Other than my analog-based Tesoro's, my more digitally-based circuitry CoRe has been my primary-use unit complemented by the Relic for certain touch applications in very iron littered sites.  Today, they still get a big share of use when I am out hunting, but the new Nokta Impact has become my first-grabbed TID model at most sites.

The Impact has a default start-up at 14 kHz yet allows the operator to make on-the-fly frequency changes to 5 kHz or 20 kHz, and I do that on occasion as needed/desired.  But most of the time I have ample mode and settings controlled to gain me great all-around performance at that 'all-purpose' 14 kHz frequency.

Sorry to ramble on about the frequency part of your question, but my own field work and selection process seems to be in agreement with a frequency choice by one of the most notable detector engineers we have had, and I am quite comfortable with the array of makes and models I carry with me and rely on daily.  But making a detector selection calls for more than just picking an operating frequency.

As Steve H. mentioned, there are a number of other variables we have to consider.  The ground mineral make-up; presence of masking trash to deal with; the size and type of search coil(s) we use for different site conditions; and the differences in how each make and model detector is engineered to handle filtering unwanted targets and the processing and recovery speed they provide.

I feel one big mistake we can make is trying to be too selective and settle on owning only one single detector and expect it to provide us with exceptional performance in all circumstances.   Since the early '70s I learned there was no such thing as a 'perfect' detector and I have maintained a regular set-up of 2 to 4 detectors minimum that can complement each other to best provide needed performance.

So my suggestion is to narrow your detector search to models that fall within the 10 kHz to 15 kHz range, then check out as many as you possibly can.  I am sure you will find two or thee that will impress you and that can be the start of how you establish your own new detector arsenal.

Monte

 

 

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On 6/17/2017 at 3:10 AM, Monte said:

So my suggestion is to narrow your detector search to models that fall within the 10 kHz to 15 kHz range, then check out as many as you possibly can.  I am sure you will find two or thee that will impress you and that can be the start of how you establish your own new detector arsenal.

These are real words of wisdom! I have been searching for that one detector and never found it. Thought of building one and found so many variables that you could not answer all the needed questions. I am glad every one has put forth the energy to write all this information about frequencies, I was about to write something and really did not know where to begin. Thanks to all you that have contributed. This has helped me a lot.

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