does the 100ma apply to home made metal detectors

[strike it rich]

just curious I read somewhere metal detectors had to be within the 100 ma range why is this and what would happen to performance if you increased output to say 150ma anyone ever constructed a home unit (in theory as it is against the law to have greater then 100ma output) in theory what would the gains be thanks

 

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[pgill]

Not sure of the answers, but would imagine greater power, maybe greater depth Here in South Africa I do not think anybody would care what power it is....

Be interesting to hear from the big guys here

God bless
Peter

 

[gallileo60]

just curious I read somewhere metal detectors had to be within the 100 ma range why is this and what would happen to performance if you increased output to say 150ma anyone ever constructed a home unit (in theory as it is against the law to have greater then 100ma output) in theory what would the gains be thanks

Think its 100 milliwatt, not 100 milliamp.....Yes it would be just like putting a linear amplifier on your radio...MORE RANGE.......There may be more to it than that tho...I never heard that MD's were limited to that small of an amount of power, but it could be....

 

[Ascholten]

In theory it should give you more depth. Afterall your detector works by the metal object intersecting a magnetic field your detector is putting out. More power = bigger field. You would probably have to scale your receiving circuitry as well if you are putting out greater power, lest you overload it with the increased field strength. Eventually you might expand the field to the point where it's picking up the electronics in the box as well and that will cause problems too.

I believe the rules are set by the FCC on the detector, they consider it a transmitter pretty much.

You could easily build your own metal detector but just like building your own CB radio, you really are supposed to keep it's output within the set limits.

Aaron

 

[gallileo60]

Yes, you would overload the reciever at some point...I bet if it was that easy to do you can be sure there would be "EXPORT" models, just like the CB Radios.....The Exports would not have to meet American Standards, and could run unlimited power...Therefore there must be some flaw in this idea.......Tom

 

[Ascholten]

gallileao that theory has some merit .. CB radios, there are millions of them out there, everyone has them. A metal detector, I do not know the numbers but it seems that it's still more of a 'niche' hobby. I don't see quite the circulation of MD's that a CB radio would have. Would it even be worth the manufacturers time to make one that is 'out of specs'? THey don't make that many to begin with.

On the CB's ... yes the radios are for 'export' only. Ie they have an increased range of frequency they can transmit on. Basically they are not 'locked out' like the US legal ones are. On the amplifiers, you can't use an amp in that freq range and power range period, while they will never admit it, the manufacturers know darned well the things are being used in the USA and there is a big market for the amps..

Another thing to take into consideration is, as power requirements increase, so does the need to store that power.. bigger batteries, which means more weight. Let's say I build a coil that puts out 10 watts. I have a choice, I can either change my batteries every 20 minutes now, or get a huge honker of a rechargeable battery that weighs 4 pounds alone to store the energy to run it for a few hours. Who want's to swing all that extra weight around?

Aaron

 

[gallileo60]

No there has to be a reason we dont have detectors that will get a penny at 1 foot...There has to be more to it..Im a ham, a cb'er, and swl'er..(Antennas are us) .Radios are my life..I might have even had an evil box, once, or twice....These coils, and recivers are so sensitive now, that you have to run them "desensed" as it is, or on alot of units you get chatter....I will think on this after I sleep..Wore out from coil swinging today, and just some clad to show for it.......At the very least we would have heard of some higher power units, or plans for them.....I've been detecting since the the early 80's..Built my first one in the 70's, it could detect the family car at 6 inches......Thats why I quit till the 80's...lol.....

 

[Ascholten]

gal, given everything is computer operated nowadays, that might account for the lower power, the pooter don't like the noise the coil would put out. Higher power and you start picking up EVERYTHING, every mineral shift you name it. It would probably be too much of a nightmare to try to squelch out the background noise then. Given a coil is really two coils, one the transmitter, the other the receiver it'd probably be like when the microphone is too close to a speaker and you get the feedback howl. If you were to build another 'old fashioned' detector that was not really computer driven but just an old transistor transmitter I wonder how it'd work.

Aaron

 

[Foilman]

On a concentric coil, the field is cone shaped and the pattern it sees is an upside down pyramid. There is no need for more power with that type of technology. It will never go deeper than the size of the coil allows. More power maybe of use on other technology. There are technologies out there that will go deeper, but you won't see them made for the hobby market. In my opinion metal detecting technology is in its infancy. At least in the hobby market. Who knows what is out there for somebody that has money to invest in expensive equipment. They are in fact transmitters and will always be legally limited.

 

[Ascholten]

foilman I have seen detectors and used them, who's coils are maybe a foot or two across, kind of a rectangle and can go 30 feet deep. They are called ground penetrating radars. the theory is essentially the same as a regular detector, just a bit higher frequency is all. Well yes they do 'transmit' in the sense of the word more but still, it sends out a signal and receives it.

The technology is there but few people have the $$$ to get one of these units.

Aaron