5 posts in this topic
By Steve Herschbach
I have a White's DFX that is perhaps my favorite park jewelry detector, though my Minelab CTX 3030 threatens to change that. The trump card for the DFX still is that I have a rare and highly sought after Big Foot coil. The Big Foot is a 3" x 18" coil specially wound internally in a figure 8 pattern that eliminates electrical interference and allows the use of the front half of the coil for pinpointing with the DFX, which was designed with the coil in mind. The coils were hand made by Jim Karbowski who called his company Applied Creativity. Jim unfortunately passed away in 2007 and the coils now go for far more used on eBay than they ever did new. http://www.gazettetimes.com/news/local/obituaries/james-karbowski/article_c8505ae6-50ec-5639-8a21-33a96b718ad4.html The coils are labor intensive and despite lots if lobbying I never could get White's to make them.
When White's announced the V3 I was excited by what I see as a "Super DFX". The DFX allows you to run either 3 kHz or 15 kHz or both together. It is highly programmable, too much so for many people but for me it pretty much turned into a 15 kHz detector to drive my Big Foot coil. The Big Foot is not made for depth, but at 18" long it is great for sweeping large parks or sports fields cherry picking targets. Here is my Big Foot attached to my old MXT in the UK, sitting next to a friends unit similarly outfitted. Huge fields like that in the photo is where the Big Foot shines.
The V3i runs at 2.5 kHz, 7.5 kHz, and 22.5 kHz, all together or each separately. It can do all sorts of frequency comparison tricks and has the best color display on the market, that can be programmed to show an amazing array of target response and information. Again, maybe too many settings for some people - this set of note by V3i engineer Bob Canaday will give you an idea of how complex adjusting the V3i can get http://www.metaldetectingintheusa.com/files/bob-canaday.pdf A tweakers dream however, and it works with the Big Foot, but not perfectly, as some target VDI information is skewed at different frequencies. Good enough though.
I really wanted to love the V3i!
The problem is with two different units I ran into serious electrical interference issues with the V3i in Anchorage, Alaska, my old home town. The same places where my Fisher F75 would shut down. The main culprit was buried power lines, which in Anchorage meant nearly all parks, school yards, and other places I might want to use a metal detector. I worked with White's on the issue to no avail, my main suggestion being that a figure 8 wound EMI coil be made specifically for the V3i, but it never came to pass. Sadly for me, I just finally gave up on the V3i.
Then I ran into a guy named Marko at Ganes Creek in two different years. He was running the V3i in the 22.5 kHz Prospecting Mode with a Detech 10" x 12" SEF coil. Marko killed it at Ganes Creek two years in a row with the V3i finding many nuggets large and small. Everyone gets lucky now and then but Marko consistently did well, and I always pay attention when I see results like that. You can see pictures of Markos 2011 finds at http://www.whiteselectronics.com/finds/?view=gainesgold
Fast forward to my moving to Reno, Nevada. It has crossed my mind now and then whether the V3i might behave better here. I still am intrigued by the 22 kHz mode, perhaps for hunting the miles of cobble piles around here looking for that big gold filled cobble. You need something with a combination of depth and good ferrous discrimination for that, and Markos results still intrigue me. The kicker however is that I have a new XP DEUS detector on the way. The Deus has many of the programmable aspects of the V3i and can run at 4, 8, 12, or 18 kHz, though only one of those at any one time. The V3i offers more ability to actually identify targets, but the Deus is reputed to be much better at target separation.
So I have a V3i on the way. People may wonder how I can afford to load up on detectors like this. Well, being in the industry for 35 years has advantages, and one if them is I get my detectors nearly always for less than I can sell them for later. I do have money tied up in them but it basically rotates as I sell one and get another. I am not pouring money into detectors. That being the case, I find it worthwhile strictly from the aspect of satisfying my own curiosity and continuing my never ending education in all things metal detecting.
The fact is though I will be selling a bunch of detectors and accessories this winter. I will be doing lots of testing and comparisons and then deciding eventually what goes and what stays. That in itself ends up being the most important test of all. The good news is you all get some of the benefit I derive from all this craziness!
White's V3i Advanced Users Guide http://www.metaldetectingintheusa.com/files/advanced-users-guide.pdf
This was posted in the Find's forum as well but no answer yet. So I am planning on getting a 18 or 15" DD coil for my GPX 5000 for relic hunting. I am looking at ML and Detech coils. I am unsure if I should go ahead and get the ML 18" DD or rather the Detech one, or maybe even the 15" Spiral DD by Detech. Which one gives more depth on relics? Which one is more quiet? Any suggestions?
By Ridge Runner
I myself when I get something new like a coil for one of my detectors I think all is well. Well my thinking has just been shot down. I've had this 7 inch coil from Detech not too long but never really checked it over but I won't do that again. What I found was the nut at the coil didn't have maybe but one turn on it. I know that this could come from any coil company and I was lucky that it hadn't gotten wet.
I do find that the Detech 7" coil works great on my MX Sport and I don't regret buying it.
This is just to let you know when you think you know everything you really don't.
I had been running my threshold setting at 7 to get the slight hum in my phones and it finally dawned on me this is not an optimum setting for picking up deeper fainter signals since a setting closer to 0 should be best. Having always ran the detector volume control in the upper ranges and using the headphones to control the audio level, I decided to switch it around by setting the headphones to max and using the detectors volume control to set the overall audio level. This made a huge difference, now I can get that same slight hum with a threshold setting of 2. Subjectively there seems to be much less modulation on the deeper targets where now coins in the 10"+ range are much louder hits. I'm also running the detector volume control at 4 to 5 to get the same audio volume I was getting before with it set in the mid 20's.
OK so I decided to do some air tests to see what difference there is in audio modulation and on coin size targets there is a difference in audio the last few inches.
First number is a full audio report distance (or as close as my ears perceive it), second number is the distance target lost. The difference between is the amount of audio modulation where the target volume decreases to the point the signal is lost.
The first column is with the headphone volume at max and threshold audible at 1 setting (0 is silent), second column is detector volume at max with threshold at 7 (6 silent)
Headphones max......................-... Detector max dime............. .............9" /10" ...- ..7" / 10" Buff nickel......9-1/2" / 10-1/2" ...-.. 8" / 10-1/2" IH penney..........10" / 10-1/2"....-....9" / 10-1/2" As we see there is no difference in detection distance between the 2 settings but a more modulated audio response with the detector volume at max.
I also tried the dime with the detector volume at max with a 0 threshold setting and the results were a full volume report to 6" with a max detectable distance of 9", for a 1" loss. Because of this it is apparent that ML has designed the threshold level to follow the volume setting (7 equals 1) which would allow max sensitivity when the detector is used without headphones in cases where a high volume setting is needed to overcome ambient noise. The loss of response on the dime indicating a negative threshold setting because at this volume setting 6 is actually zero.
Since these were coin sized targets and not tiny nuggets the difference could be even bigger when nugget hunting.
By Steve Herschbach
The Gold Bug Pro had turned into one of my favorite prospecting machines, especially for trashy areas. Ray Mills and I have been bugging (get it?) Fisher to put the machine out with the 10" elliptical coil as stock. In my opinion it is the best all around coil for the detector and also makes it look like it should as a prospecting detector and cousin to the Gold Bug 2. Right now you can only get the coil as part of a package or as an after purchase accessory. The coil works on the Fisher F5, Gold Bug, Gold Bug Pro, and Teknetics G2.
By Steve Herschbach
VLF detectors can come with DD or concentric coils. This is similar to but not quite the same thing as DD versus mono on a pulse induction detector.
VLF detectors are more alike than different these days. One thing that can make a real difference is what coil the detector comes with. Two very similar models will be quite different if one comes with a 12" round mono, and another an 11" x 7" DD.
In this case the very same detector can be turned into two different detectors by changing coils. Here are a couple rarely seen on the F75 - the 10" x 5" DD and 10" elliptical concentric. A big difference between the Teknetics T2 and Fisher F75 was that the F75 came later and the ability to use concentric coils was added. The T2 can only use DD coils
Why DD or concentric? DD coils are all the rage these days. However, concentrics have more consistent detection patterns with less dead spots up close. Every notice how that DD coil goes wacky on shallow targets? And concentric coils are much better at identifying flat ferrous targets like bottle caps. Here it is from the guy that should know best, Dave Johnson, lead designer on the F75.
About Search Coils http://www.fisherlab.com/hobby/davejohnson/searchcoilsessayrevised.htm
Search Coil Field Shape http://www.fisherlab.com/hobby/davejohnson/SearchcoilfieldshapeApril2012.pdf
I like the 10" DD for the solid design, better for working in stubble or other locations where an open coil might hang up. The concentric just for being better behaved. The DD is the better prospecting coil for bad ground. Concentrics do well on milder ground.
A note on coils. The blade like knife edged detecting pattern depicted in DD marketing ads is largely myth. Electromagnetic fields radiate and simple coils cannot focus them into beams. A round concentric coil has a search field shaped like a soccer ball cut in half. A similar size DD coil will have a search field more like a football cut in half lengthwise. If you ever doubt this, just fire up your detector with a DD coil, flip it over, and run a coin under the coil noting where the signal fades at different locations under the coil.
Finally, depth is more related to coil width than coil length. Think of a 5" x 10" coil as a stretched out 5" coil, not as a skinny 10" coil. That is why when listing elliptical coil sizes you will often see me putting the small number first. Marketers do it the other way around so you tend to think you are getting more than you are.
Fisher F75 with 10" Elliptical DD Coil
Fisher F75 with 10" Elliptical Concentric Coil