we have to realize that nothing is 'perfect.' No 'perfect' detector, no 'perfect' search coil, and no 'perfect' conditions that we can count on because there are so many variables.
frankj3 said:
I've been using my 4" coil on my Legacy 3500 a lot lately while working an old city park that has nearly 80 years of hidden trash. For the most part this coil has been EXACT....except with dimes.
Working in trash it's always helpful to use a smaller-size search coil, sweep a little slower, and try to pick the targets out of the junk. I have preferred smaller size coils for almost all of the detecting I've done since March of '65, unless it was a model with a fixed search coil that wasn't as small as I liked. I keep some accessory coils in my back-pack detector bag, all mounted on a lower rod for quick changes afield, but usually have a smaller coil mounted on my detectors all the time, unless 'bigger' is more practical for an open site.
frankj3 said:
Here's my problem:
I get a signal that looks to be a dime by the sound and by the display on my Legacy 3500 when swinging one direction. When I swing the opposite direction to help pin point, I get the display signal of a Zinc penny. The depth tends to stay the same for either indication. When I dig the find, probably 99% of the time it is a penny. If the unit gives me the indication it's a dime in both directions, then it will be a dime.
When you say it "looks to be a dime," are you referring to the numeric VDI read-out or to the 11 TID segments?
When you hope for a dime but recover a penny, is it an older Copper-based penny or a more modern Zinc 1¢?
Have you made sure the Ground Balance is set? Are you checking to see if there are any trash targets close to the recovered coin that could have been masking it and causing the unstable TID?
frankj3 said:
So why do I get 2 different signals?
Why? Because nothing is perfect. You might already know, but in case you don't (and I guarantee you many people don't) the 1¢ TID segment has 'Zinc' over it and that suggests a reading to be a lower-conductive Zinc 1¢
The 10¢ TID segment has a Cu over it, and that is representing the older, copper-based 1¢ coins which have a conductivity closer to that of a dime. Thus, most 1¢ Memorial and latter Wheat-back coins will
usually respond similar to a clad or silver 10¢ read-out. Note that I said '
usually' because through the years our USA 1¢ coins have been made of different metal mixtures. Also, even though the coin books tell us that the Indian Head 1¢ from 1865 and some with the change-over in 1864, as well as most Wheat-Ear and Memorial 1¢ coins were the same size and shape and alloy content [size=small](usually 95& Copper and 5% a mix of Tin and Zinc)[/size], they do not all have the same metal quality and read-out or conductivity.
Most, not all but most, Indian Head cents and early Wheat-Back cents from 1909 to about ±1920 will read a little lower. Often they have conductivity readings similar to a modern Zinc 1¢ or aluminum Screw Cap. Some newer pennies that are still pre-Zinc mintage can also 'read' just slightly lower due to impurities in the ore processing or from wear. This can cause a 1¢ coin to have a slightly lower conductivity, and with the 11-segment TID of your 3500, it isn't a very precise read-out. Well, actually it is, because the target might not be 100% like a 10¢ or 100% like a Zinc 1¢, so the TID can jump between the two segments.
frankj3 said:
Am I doing something wrong? It's starting to frustrate me!
Probably not, except hoping the TID to be 100% accurate and it never will be, not when you're dealing with a lot of different trash. Learning all we can about metal detectors and metal detecting can be, at times, a little frustrating.
Monte
