Low frequency vs Higher for Relic Hunting

[Canewrap]

If low frequency (say 5khz)works well in good ground (and bad) and a higher frequency (say 18khz) only works well in good ground. Why not have most of the relic hunting machines at a low frequency? Afterall, most of the relics being sought are at least dime size or larger. What would be the advantage of using an 18khz machine in good ground over a 5khz? Is there better separation or disc with the 18khz?

 

[BarberBill]

Good question - I'm thinking that part of the answer is that most of the detectors are designed to be more general purpose than specifically relic hunting. Curious too, now that I think of it, most of the machines reputed to be among the best for relics are generally higher frequency, but they have either auto ground tracking or manual ground balance. Hopefully some of the more tech oriented members will jump in.
HH
BB

 

[BarnacleBill]

If only it were that simple! There are many compromises made as nothing turns out to be ideal. Lower frequencies tend to penetrate mineralized ground better, but also tend to respond less well to lower and mid-conductive metals, with smaller sized items also being a factor. Which leaves the designer with some choices to be made to optimize the detector. Ideally it would be switching frequencies to match the ground conditions and the targets sought. Two recent examples are the Minelab X-Terra series where each coil is optimized to a given frequency, and the White's V3 where a broadband coil approach is used to effect the change. Note that both of these designs have higher frequencies with Prospecting in mind and that Prospecting is usually done in areas with high mineralization. But if you are looking for small low conductivity items like gold you need to use an appropriate frequency.

There has been several attempts to also overcome the problem by driving the detector receive gain to the limits with a higher frequency design to overcome the depth loss. Examples would be the Shadow X5, Tesoro Tejon, First Texas T2, and F75. But in Physics there ain't no free lunch! These detectors can be very twitchy; ground noise, EMI etc. Oddly enough none of those designs has an automatic ground track to deal with quickly varying ground.

HH
BarnacleBill

 

[Canewrap]

Ok, I understood what you said BarnacleBill. But, with relic hunting in mind, I guess the only thing that, say a Minelab Advantage (5khz) wouldn't get optimal depth on, would be camp lead and bullets? I know somebody that uses an X-terra with a 3khz coil and he does fantastic on Indian heads, so I gotta assume that a low frequency coil does ok on copper and probably will do ok on brass, maybe not as well as it does on silver. So, when we're talking about how low frequency does well with silver and high frequency does well on low conductors, how much of a difference are we talking about? Rough percentage wise? Like will a low frequency machine add about an inch in depth on high conductors over high freq in good ground? I know this probably tough to quantify, but what is your feel for the difference? I've just picked up an Advantage to relic hunt and probably will add a high freq concentric to my X-terra 705, in order to have the bases covered.

 

[crazyman]

Bill, to many people get hung up on the frequency thing. There are other factors besides the frequency alone that come into play. I've had low frequency detectors that hit on low conductors like small gold better than some high frequency detectors. For relic hunting on targets the size of buttons and bullets I doubt whether you would see any difference. Lower frequency detectors like the Whites 5900/6000, Blue&Gray, Eagle, Spectrum and XLT have probably pulled more relics out of the ground than any of the higher frequency detectors through the years in both good and bad ground. I would only consider the frequency of a detector first in my decision based on the type of ground I would be hunting more so than the conductivity of the targets.

 

[BarnacleBill]

In the FAQ of the Terra forum I have a couple of posts that are more "visual" rather than text and can show the "tendencies" of frequency effect.

This first link has some animated GIF's that present in a nomograph type of form a little slide show for optimizing coil/frequency selection when you have that kind of choice available.

http://www.findmall.com/read.php?55,745158,745158#msg-745158

The first table in this review of the X50 shows air tests with the X50 against a variety of targets.

The good:

1. The tests are done with the same type/size of coil at two different frequencies on the same detector, therefore more apples to apples with frequency being the dominant variable.

The bad:

1. It's in the air, and ground can skew the results, you would have to bury or mark targets in your ground to develop better data.

2. Coils can be wound with greater or less sensitivity, therefore even though the coils are the same size, one design might be wound "hotter".

http://www.findmall.com/read.php?55,290751,290751#msg-290751

And as crazyman mentions there are a whole host of other factors of individual detector designs that come into play. And perception is one of those factors. If you look at the the forums of the Minelab BBS/FBS detectors you will find that they are noted as being Silver killers. The posts of the coin/Silver finds dwarf any of the other forums. And by the way this seems to greatly agitate the U.S. based manufacturers to no end. You will from time to time even see on those forums the complaint that the BBS/FBS detectors don't do well against low conductive targets like Nickles and Gold. Yet if you go look at the Beach & Water forum, which are the dominant(and have been for a long time) detectors for finding Gold rings? Lo & Behold the BBS/FBS based detectors rule the saltwater beaches. Are they good at finding small(fine) gold items? Apparently not as good as a more specific tool like an X-Terra with a high frequency coil, but they will certainly find gold rings without a doubt.

Keep in mind much of what I've posted has to do with "tendencies". There are very few absolutes, which is what makes the hobby interesting in figuring out what works best for what you are trying to accomplish. And yes you can spend a ton of money and time in figuring that out(Lawd knows I have)!

And I'll leave you with a vision. Picture a hunter with the latest greatest most expensive detector(we'll pick on the White's V3) at a trash filled city park. He is proudly sporting some heavy artillery and adjusting his life away as the Sun moves across the sky. Meanwhile in the same park is an Old Codger with a beat to death Tesoro Compadre he bought used for $89 that is just killing the guy with the V3. You should be a little more concerned with Bruce Lee holding a mop handle than me holding a mop handle.

HH
BarnacleBill

 

[UK Brian]

I did some test with Sean a few years back using silver bars and bags of gold coins. We concluded that low frequencies would give the best depth but only on larger and thicker targets in higher levels of ground mineralization. Sensitivity lost on smaller/thin targets.

Higher frequencies go deeper for any target as long as there's little or no mineralization.

But then you have to take into account the effect discrimination has on what you decide to dig. Each metal has a specific frequency at which the I.D. is optimised. I think it was George Payne who produced the information that optimal frequencies for silver was 0.8 kHz, copper 2.7 kHz and nickel 17 kHz. This is for discrimination, not depth, so if you stick to all metal its not such a problem.

The lower frequencies have the effect of increasing the surface area of the target if its thicker metal by penetrating the item to an 1/8th of an inch or more (but not much more) whilst the higher frequencies that have much less penetration can generate a greater signal on small or thin items because they need less surface area to generate a large signal.

 

[Canewrap]

Thanks Mike, I know it seems I'm hung up on frequency. I just wanted to make sure (as much as one can) that I'm backing the right horse in picking up the Advantage. Everything you great guys have posted reinforces that I picked up the right machine for the job. I'm adding hunting old homesites this year and this machine looks like the perfect choice for that and what was said about larger masses of precious metal helps because I'm getting into cache hunting and I know I can get a 15" WOT coil for this detector that my other choices just didn't have. Occasionally I run into areas of bad ground around here and it will help to have a machine that can tackle that. I really appreciate the help you guys have been and with any luck I'll have some good stuff to post in the coming year.

 

[crazyman]

I think when talking about the frequency range of detectors used for most coin, jewelry or relic hunting today the size of the object and the detectors sensitivity to small objects comes into play more so than the conductance of the same object. When it comes to sensitivity to small targets one factor that can make a difference outside of just the frequency is the discrimination range of the detector. In the case of the Minelab Sovereigns it's discrimination range at it's lowest setting has to much bias in the iron range. If they expanded the discrimination range it would increase the sensitivity even more on small to medium gold. One detector I'll use as an example was a Mr Bill's modified Whites IDX Pro. Using the small gold ring pictured below which ID's in the small foil range the ring was tested at different depths in wet mineralized sand at the beach. Setting up the detector at the preset mark on the discrimination range which knocks out small iron and with the black sand switch set to normal I buried the the ring at a depth just below where the detector would respond. I then lowered the discrimination to it's lowest setting and got a hit on the ring. I then set the switch to black sand which expands the discrimination range even lower and was hitting the ring even with the coil an inch or a bit more above the sand. So in this case a low frequency detector with the expanded discrimination range might outperform a higher frequency detector with a more limited discrimination range on the same size target.

 

[BarberBill]

I've detected with different machine's frequencies from 5.6 to 15Khz though most of my detectors have been around 10Khz. I haven't done any serious testing or comparisons to the capabilities as regards the different frequencies, nor do I want to start any arguments on the subject. Anyway, that said, for all practical purposes actual in the field, park, fairground or whatever, I haven't seen any real plus or minus on any of these machines for the targets we generally hunt that would be directly traceable to the machine's frequency. Please note I'm talking PRACTICAL differences in the field, not specific, special instances where the theoretical differences might make a bit of difference. As mentioned several times in this thread, there are numerous variables that come into play. Anyway, as long as it goes beep, I'll keep digging.
HH
BB

 

[silversmith]

My comment, no matter what you have, you just can't beat plain old good luck. Loosers can run around yelling "there's no such thing" while some pimple face'd dude, with a old junk detector he found in a dumpster, will go home with 3 or 4 big gold rings he found in a worked out park, in a 2007 Caddy he won in a raffle, sporting a gorgeous blond under each arm. So don't discount this in your equations. The same guy has to do all the testing. Joe with a Super Dilithium Cross Polarized V73 Tesoro's finds, that runs on 32 mhz, has nothing to do with Ellan's Silver Grabber Whites find's that runs at 10 khz. I've seen this over and over. Just my opinion.

Who I'm I ? I got junk detetors, ain't much to look at, drive a Chevvy that I made payments on for 25 years, but I did go home with ONE blond under my arm. That ain't bad......

 

[BarberBill]

I agree. When it's all said and done, the coil has to pass over a good target and the operator has to dig. If that doesn't come together, doesn't matter what detector is used. Knowing your machine and persistence is way more important than frequencies, TIDs and other bells and whistles IMHO.
HH
BB

 

[Canewrap]

While everything you guys said is valid, I do believe luck is usually opportunity meeting preparedness. The only reason I get hung up on such minute aspects of this hobby is that a lot of the better relic sites around here and up into Tennessee have been pounded to the point that you're lucky if you can find camp lead at 10". However, I know that if I can eek out an inch or two deeper than the those machines that hunted through here through the late 80's and the 90's I can make some good finds that have sunk to the bottom of the plowzone. You wouldn't believe the kinds of stuff we used to find at the bottom of the plowzone when I was an Archy in a past life and we dug 5-foot squares that we systematically removed layers of dirt from. At the bottom of the plowzone, resting on the hardpan was frequenty an assortment of farm junk that had been plowed in deep when farmers were still plowing that deep. Due to soft soil and changing plowing methods, not a lot of the deep stuff would be brought to the surface anymore. Have you noticed how deep a lot of the belt plates are coming from that last few years? So, yeah there are a lot of other factors more important than the frequency of your machine, but as in all hobbies that are obsessive, its easy to want to know everything you can to improve your preparedness when the opportunity arises.