5 posts in this topic
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
Regardless of the "Machine" your swingin' now! What coil was your favorite?
My Favorite is below .Nugget Finder Advantage 3 spoke's the whole range...
."What a Ya Reckon....1:57 "Only Fools Reckon" and at 3:58
"Oooooo! How good is that Coil"
"Are you Downgrading your Optimism? 2:33 I hope you Enjoy this "dig" as much as I do!