Frequencies and depth

[coin hunter]

Does everyone know that The FCC regulates The power output of metal detectors. I read this somewhere,couldn't find it again on the internet so I called Garrett its true. Just like CB , Walkie- talkie, Portable phone etc, they become limited almost toy like I think. I have a 2500 Garrett with adjustable frequencies . I was told they where sideband frequencies. SO what are the frequencies ? Back to the FCC regulation. Power output regulations where started in 70's on metal detectors. So what ever metal detector we buy it is limited in the depth capability, how many inches it goes. I know everyone is going to say my goes deeper than this brand and that brand. The fact its 5 inches to one is 7 inches to another and so on. Of course i"m talking about coin targets. I put a coin on the ground put bags of soil on top [still in the plastic] and measured with a ruler. Try this you won't like the results and use a ruler please.

 

[Bence]

I heard that they're all limited to 12v, as to not interfere planes, millitary bases etc. This is why when a new detector x model comes out, there's hardly or no improvement in depth, because it's already been pushed to the limit so companies have to find their way around making detectors go deeper. People with HAM radio lisences can use instruments with greater output. I heard it in layman's terms so I can only explain it in layman's terms.

I know what you mean about depth claims, the first time I stuck a pick in a dig hole...

 

[Bugar In. USA]

On your depth, and sensitivity, It is all governed by the design of the circuit, the design of the coil=how they work together, the frequency, moisture of the soil, mineralization of the soil, how long the target has been in the soil, and if it has corroded and made a halo like area around it which would affect the conductivity, soooo many things,if the coin is on edge or flat, silver or copper, i have some detectors with 6 -9v batteries, some with 1, some with AA batteries, and from what i'm told and have seen on some, the detectors have a regulator type device that lets them run on around 5 or 6 volts, the regulator cuts it back to operating voltage, some detectors will air test very poorly, but when detecting over soil will go to very extreme depths, If you want facts on a certain detector try that particular one out, or talk to users of that one, field tests in magazines are influnced by advertising dollars.
And the VLF frequencies are regulated by the FCC

 

[R-n-R Magnolia SpringsAla]

I wonder if someone would make a detector you had to get a license for would it sell.......like hotcakes, they could not build em fast enough! Hmmmmmm.......

 

[SteveP(NH)]

Don't forget that VLF detectors are transmitter-receiver designs and so the depth that the machine can pick up a signal is also influenced by how sensitive and how good the signal to noise ratio of the receiver circuit is. More expensive and newer designs can use more expensive components with better technology than cheaper or older designs. Therefore those detectors will be able to pick the signal out of the noise at the limits of their detection depth and so they will be able to find deeper targets even with the same limit on the transmitter power.

Also the effective radiated power of any transmitter is also determined by the size of the antenna or in metal detectors the search coil. That is why a bigger search coil gets you more depth. Some of the new machines have bigger search coils that are lighter in weight than older, smaller coils.

Another thing to consider is that newer and better electronics can also reduce power consumption and the use of state of the art electronics and composite materials can make for significantly lighter detectors which for some of us older folks can mean longer duration in the field and so more opportunity to find stuff. The newer designs can run at the same transmit power for 30 to 40 hours on 4 AA batteries instead of the 8 that older designs use which not only saves weight but also makes it cheaper to power the machine.

Finally and perhaps most importantly newer and faster electronics can improve a detector's recovery time. Here is a little test for you to try next time you have your detector out. Put a nail down on ground that doesn't have any other targets near it, then put a coin down about 6 inches away from the nail. Next sweep your coil so that it goes over the nail first and then the coin. Most of today's detectors, even the newest, fastest ones won't be able to right up the coin because they haven't yet recovered from the nail target. Keep moving the coin away from the nail until you get a solid target response each time when swinging over the nail first. Older and slower designs won't be able to ring up the coin until it is over a foot away from the nail!

Given how hunted many public sites are nowadays most of the good targets left are there because they are in the recovery time shadow of larger or less deep pieces of trash.

So there is still a lot of room for metal detector design engineers to improve the performance of detectors and this is why it is important for the detector manufacturers to keep their detector designs up to date and to use the latest and best electronic components in their high end machines.

I hope someone from Garrett reads this post and thinks about it when they are thinking about whether or not to come out with a new machine - the GTI line is getting to be pretty long in the tooth, and its past time for a major overhaul.

 

[coin hunter]

I agree with everything that has been said .I just remember in the old day of CB's if you new a man that dab in electronics he could peak the watts output with turn of a little screw driver . Bang more transmitting power. Just an idea. FCC please do not read.

 

[Uncle Willy]

Depth is as variable as the ground conditions one is detecting in. There is no universal depth for any detector anywhere in the world. Coil size also plays a big part in depth as does wet or dry ground and many other variables. One can run as many tests as they like but the results only apply to their specific area, conditions, settings, operator expertise, etc.

If the manufacturers would come out with a detector with variable operating frequencies like from 0 to 100 khz or whatever then the coil's attraction to different metals would be vastly improved and the detector could be adjusted to hunt for each.. There's still a lot of room for improvements if the makers would just do it.

Bill

 

[Uncle Willy]

Yeah there's still plenty of room left for major improvements in today's detectors if the manufacturers would just get off the pot and implement them and cease trying to make them all easy and simple to operate. That's fine for newbies but us oldtimers would like something we could sink our teeth into.

Bill.

 

[Onus]

Mr. Garrett, are you listening? Many of your fans are starting to defect because you haven't kept up with modern profiles on your equipment. C'mon now give us something to crow about. Onus

 

[Delaware Bill]

Not positive, but I seem to remember a post by the Fisher head engineer Dave Johnson where he stated that the FCC does not limit metal detector frequency or power out put. But like I said, not positive.

 

[NM5K]

"12v" is the voltage that the machine runs on. That has nothing to do with the power
output. I imagine the power output of most detectors is in the milliwatt range.
With most non licensed emitters, 100 mw is the maximum output.
And 100 mw is 1/10 of a watt. Many might not actually output that much, but I've
never looked into it. Being a ham would not allow one to use a higher power level
because they still have to follow the rules of the service being used.
Our power rules only apply to the ham bands. IE: my maximum output power on
most bands is 1500 watts or 1500000 milliwatts.. :/
Back when CB's had licenses, they had the same levels for the unlicensed
walkie talkies. 100 mw was the maximum output, and many of the cheaper
ones only did 50 mw or so. Where as a licensed CB could do 5 watts input
power, which would give you about 4 watts max output to the antenna under the
best conditions.
You never get out all that you put in. In general with radio transmitters, it
will vary to the type transmitter, but with most linear amps, if you get
60% out of what you put in, you are doing pretty well.
The current ham power regulations only deal with output, and don't take
input under consideration.
But years ago, hams were regulated by input power. When they changed
the rules, it actually gave most a power boost.
If I remember right, 2000 watts input used to be the old rule, which might
give you 1000-1200 watts out or so.
Being you can run 1500w out now, that is generally over 2500 watts input.