Thoughts on compairing detectors

[EZrider]

Information on compairing detectors
On many fourm sites compairing detectors seems to be a hot topic. What is deper,faster lighter ect. I am writing this to give everyone some food for thought. As well as to inform new people. I will also cut and paste some clips from different areas of information.

Two names that should be well known are Dave Johnson and John Gardner. These two people are the direct result of what we detectorest swing today. Here is a clip from a interview on what thay had a hand in developeing.

Dave: "Old Fisher: 1260, 1220, 1210, 1225, 1235, 1265, 1266, 1280, Impulse, CZ6, CZ5, CZ20, Gold Bug, Gold Bug II, TW6/Gemini, FX-3, and several industrial products.
Tesoro: Diablo MicroMax, Lobo Supertraq.
White

 

[dobbie]

very interesting never knew about the sensitivity. i was to think that it became more powerful...well now i know...thanks for the input of info..much appreciated.

 

[JB(MS)]

If it hasn't been reinstated in the last year or so there's no longer a 100 milliwatt restriction on the transmit power of metal detectors. At one time that was true, in fact all unlicensed radio transmitters, which includes metal detectors, were restricted to 100 milliwatts output.. The text books when I was taking an electronic course in the early 1960's qouted the FCC regulations and made it very plain that to exceed 100 milliwatts would be a violation. But after a discussion a few years ago with Carl Moreland, who has the Geotec forum, both of us went through the FCC regulations and found no reference to a 100 miliwatt restriction. I contacted the FCC and asked where I would find the info and they directed me to Section 15 of the Regulations. According to Section 15 there is no restriction on power output for transmit frequencies below 9 khz. From 9 khz to 90 khz it's it's based on e-field strength at a distance, basically 2400 divided by the frequency.<br /><br />There's a lot more involved in making a detector go deeper than just the transmit power. The text below is from C-Scope's Plain Truth articles on their website and explains the effect of increasing transmit power, or gain, and why VLF detectors have been restricted to pretty much the same depth levels for years, and also why we keep getting new models with more bells and whistles but little to no improvement in performance..<br /><br /><i><b>"It is in the fundamentals of electromagnetics where the laws of physics establish limits which cannot be exceeded. Metal detector R&D engineers all understand these laws very well and they all have to develop their detectors within the same constraints. To demonstrate the point furher.......it is possible to put the cheapest metal detector in a controlled laboratory situation and you can tune it to detect a coin in air at one metre! However, if you take that machine outside and try to use it on the ground it is absolutely useless and won't detect a thing. This is because the huge amount of energy in the search coil is simply detecting the ground<p>Doubling the gain of the detector doesn't give you twice the depth but it does give twice the ground signal! (The magnetic field from the transmit coil to the target diminishes as a cube law. This magnetic field induces circulating eddy currents in the target and these eddy currents produce an opposing magnetic field, which also diminishes as a cube law. It is these which are detected by the receive coil. - So we are talking of a 6th power law of signal against distance (3rd power out and 3rd power back) . So to double the depth of detection requires a transmit current (or receive gain) increase of 2 to the power 6 (that's 64 times as much!). Resonating the receive coil gives free gain and a filtering , but requires more stringent temperature drift measures ".<p>This also explains why you cannot get more depth out of a metal detector. Any detector manufacturer who tells you that they have a new development which gives dramatic increase in depth has to be treated with a lot of suspicion. You CANNOT get around the laws of physics!"</b></i>

 

[tabdog]

On a simpler note.

Power is all well and good.

But what puts the most money in my pocket is my

$70 Compadre.

It seems to be my least powerful machine.

But it is a money making fool.

HH,

 

[JB(MS)]

You're right Tabdog. I've been involved with detectors for almost 40 years, have had more detectors than I can remember and always have 7 or 8 that includes at least one of the deeper detectors available. I've found thousands of coins, a good many nice relics and a lot more jewelry than I ever thought I would, but I don't doubt for a second that a Compadre would have found at least 98% of everything I've found. I know for a certainty that when we hunt together my hunting buddy Jim always kicks my butt with his Compadre regardless of what detector I'm using, even though all of them but two will go a lot deeper than his Compadre.

 

[clondike clad]

Also on the thought yes the FCC have s 100MW max.
BUT AND A BIG BUT IS HOW THE receiving circuit is set up.
A hi end detector with a very sensitive receiving circuit can pick up very weak signal (deep coins etc) and process them.
example is are the XL PRO from Whites or the Fisher 1266 and others

 

[Sunny Jim]

My 2cents is what is done with the recieved signal is what counts and how fast it does it.

 

[rifleman]

[quote Sunny Jim]My 2cents is what is done with the recieved signal is what counts and how fast it does it.[/quote]

I don't claim to be an engineer but what you said makes good sense to me. An example would be the V-Flex technology in the Minelab X-Terra detectors. The cleaner the signal is to process, the better the detector can determine what the signal it is receiving is.

Good hunting, John K

 

[BarberBill]

Has always seemed to me that the discussions over power and depth much overshadow the (to me) more important features. Such as, weight, balance and easy handling, quick retune, good discrimination, a true, all metal threshold mode and a good selection of various coils. My two bits.
HH
BB