Detecting in South Africa

Homie, That was the first I had heard of that too. I found that in the legal notification section. Probably for the FCC or for some foreign equivalent. It said " The following statement is not relevant to metal detectors but is printed here to satisfy legal notification.  'Tho reduce potential radio interference to other users, the antenna type and its gain should be.....bla bla bla. '  It says the machine is allowed free movement in Finland, Sweden, Latvia, SUI and BIH what ever that is.

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Homfire, Yes I think that FCC spurious radiation thing is a joke. There are so many sources now, many made in foreign countries FCC can't test them all. I have a Tracphone that transmitts its location to every FM radio and TV within a 30 foot radius. When I'm driving my car the signal is strong enough to interrupt the music I'm listening to. My computer even picks up the signal.  How many millions of cells are there like that?

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		Quote:			Posted by gambol1
	GD, Reading through the Fisher Manual I found a statement that the machine " required antenna impedance is 53 ohms." and the antenna has a maximum gain of 3 db. The Operating freq is 13 khz. Knowing this would it be possible to design a coil for the machine?

Absolutely. Within limits, that is. You are told, in this case, the power gain inherent in the antenna which is really a combined inversion of how much is required to build the field during the transmit and the sensitivity during the receive cycle. They are easily plugged into a Smith Chart after you determine the field size and shape.

The subsequent discussion of FCC rules, etc., regarding the word "antenna" is not relevant in this case since this is a magnetic field only in the audio range. The frequency of 13khz is within the normal range of hearing for a human being yet you can't hear your coil emitting anything. This is because there is no sound pressure being created, just a magnetic field. There is also no radio frequency component so there won't be any long range effects.

As a point of interest, this is a very good question and one often misunderstood by the users of metal detectors. The DIY crowd often don't consider the power required to drive the circuitry and the receiver sensitivity needed to sense the returning signal. It is of great importance and really should have its own topic started.

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		Quote:			Posted by gambol1
	GD, good to know. Too bad I'm getting too old to get my head around new complex systems like that. I'll concentrate on getting the best results with my coil and spend the time in the field before the weather turns bad. gambol Wise

Homefire has echoed my sentiments. Learn your machine and tweak it in your head for its best performance. I've learned to listen for those whispers of deep metal. That has boosted my finds of high value items by 10 times my previous finds. No joking. I can actually tell what I'm going to dig just by hearing it. I'm correct more than 75% of the time. For the rest, I can clearly "see" why an item fooled my ears. For example, if it sounds like a deep half dollar, it often turns out to be a deeply buried aluminum disk or a flattened piece of foil. I still count that as a successful target because in the past, before I learned my machines, they would be passed over along with the good stuff.

Karl Von Meuller, one of our treasure hunting giants, once said that the best machine to use is your head. He was right. He advocated learning your detector by using it everywhere that you could. People have strong opinions on old Karl but the truth is, he died a happy man not having to work for a living but living off his finds instead. We shared camp fire coffee in the Mohave Desert many moons ago. Too many. He moved on in the morning but the evening was full of good talk.

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		Quote:			Posted by homefire
	Hard to do that with most of the New machines.       Constant Threshold tones are a Good thing.    It talks to you like RADAR!

But they still whisper on the deeper targets when they flutter from diminished signal return. Slicing up that tone is the same as the whispered tones of the older machines. My brand new Tiger Shark claims to have constant threshold but it still gives up gold and silver beyond its estimated depth.

Look at my list of detectors, mate. I can't bring myself to part with any of them. They all have their uses and best conditions under which to use them. I always bring one back up machine along. Before I leave on a trip, I feel like a golfer choosing his next club.

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