Question for Ralph, or Beachcomber......

[Anonymous]

Years ago, when the CB radio was popular, many people would add a "linear" so that they could increase the power of their CB radio, thus attaining long distance communication...this was not legal, but was often done.
Would it be possible to adapt some type of apparatus, like the "linear" concept, to an older metal detector to enhance it's performance, performance equal to the latest detectors on the market? If so, could it be done in a legal manner? Has it ever been tried? Please have a great day! Kelley (Texas) <img src="/metal/html/smile.gif" border=0 width=15 height=15 alt="">

 

[Anonymous]

Pi machines concentrate their power on the 'on' cycle. The transmiter then turns off to listen for the decaying eddy currents.
VLF machines are different. They have 2 coils which are always 'on'. One transmit and one receive. If you put too much power through the transmit coil it will overload the receive coil, which is right next to the transmit coil. That's why they are called 'Induction Balance' machines.
Additionally, increasing power is not very efficient. I read somewhere that it would take 8 times the power to double detection depth.
Because of this 2 coil design, the upper practical limit on powering transmit coils has probably been reached. The latest VLF designs try to take advantage of newer and more stable and sensitive components to extract the most info from the power at hand.
Please jump in here Bill and/or Ralph. I'm sure you can add some good info.
Hope this helps !
John

 

[Anonymous]

I don't know if it's been done or not. I have thought about it myself. One of my favorite detectors of all time was the Teknetics Mark Iand if such an amplifier could be made that would bring the Mark I's depth capabilities in line with today's machines it would be a worthwhile project. Some of today's machines are just starting to catch up with George's techniques. He was one of or psosibly the first person to put into production a detector using a much higher transmit coil voltage in his detector. This was first done in the Teknetics ST which I believe had between 40 and 50 volts on the Transmit winding. This is part of the reason the Tek ST had such great depth. Years later Nautilus adopted the concept in thier DMC-IIB which also uses around 50 volts on the transmit coil. The most recent entires into the high voltage transmit arena were Troy with the introduction of the X-5 and X-3 and now this year Tesoro has decided to take that route with the new Tejon. Yet this is a design that George Payne introduced around 15 years ago. So to answer your question I would assume that you can increase the depth of older machines by either building an add-on transmit linear amplifier or by modifying the original transmitter section to use a higher voltage transitor or FET and building the additional DC to DC Converter necessary to supply power to the circuit. As I said it is something that I have been thinking about for awhile. I have a Mark I that I am thinking about doing it to over the Winter. As far as the legality of it I would think that you can go up to at least 500mw of transmit power now. Years ago when these older machines were made any transmitter over 100mw had to be licensed by the FCC so everyone kept the transmitters at or below 100mw so that no special licensing would be required. Today we are allowed transmitters of 500mw without a need for special licensing by the FCC. Sorry for the long Post.
HH
Beachcomber

 

[Anonymous]

from 100mw to 500mw? That would partially explain the claims of increased depth of detection of the newer detectors now hitting the market place...bottom line, increased power with some refinement of present known technology, not really any new technology. Please have a great day! Kelley (Texas) <img src="/metal/html/smile.gif" border=0 width=15 height=15 alt="">

 

[Anonymous]

Somewhere in a closet, I have an old book written by Charles Garrett that explains the theory of how a metal detector works...guess it may be time to read and study, this is interesting to me. Thanks for the reply, please have a great day! Kelley (Texas) <img src="/metal/html/smile.gif" border=0 width=15 height=15 alt="">

 

[Anonymous]

As the power of any machine is increased, there are issues to deal with other than just "going deeper". As you increase the signal, you might get better depth response to good targets, but you also get better response to the junk, the ground signal, external interferrence, and internal circuit noise. If "more depth" is over-ridden by alot of added noise (regardless of the source), you are somewhat defeating the purpose to begin with.
Any detector, assuming that it is working at it's "optimum" capabilities, is still limited in depth by it's coil size. That is just a matter of physics. If you increase power at the coil, there are still limitations as to the size of electromagnetic field any particular coil can produce..... i.e. limitations in depth. You then also have to take into consideration the receive end of the circuits, the added noise and "feedback" created by the added power at the coil, having to balance the TX signal to the RX side, added ground signal, etc. etc. It's all really a very delicate balancing act.

 

[Anonymous]

Actually increasing the transmit power doesn't increase electrical interference or circuit noise. It does however increase target signal strength, junk target strength, and ground noise. Youa re right about it all being a delicate balance. George Payne just had a little discussion about this very subject over on Carl's Forum earlier this week. When someone asked him about the Deep Hunter Module for the Treasure Baron.
HH
Beachcomber

 

[Anonymous]

....that increasing transmit power doesn't increase electrical interferrence. That is an external factor, and would only increase via tweaking the RX end of things, not the TX. Increasing the transmit power could cause some instability in the RX side in the form of "noise" though if the added power were not otherwise compensated for on the RX side. Just increasing the voltage at the coil is not always the best way of increasing range (depth), but it obviously helps on some machines (the Nautilus IIb for instance). If I remember right, the X5 puts out only 14 volts at the coil compared to a maximum of 44 volts on the DMC-IIb. Thats quite a difference, but you won't see the relative depth to coil voltage ratio of the Nautilus and X5 increasing by anything close to the percentage difference in the two machines. If that were the case, the Nautilus would be detecting about 315% deeper than the X5. When you throw in the limitations of the coil (by mean diameter), it's more a matter of increasing target perception by producing a stronger target response than it is in any great increase in raw depth. You could increase the TX power to make all of those fringe targets put out a much stronger signal, but if the stronger TX power is overloading or causing too much feedback on the RX side, then you've still defeated the purpose of increasing the TX power in the first place. The same can be said for increasing target response "reception" on the RX side by turning up the gain or threshold too high. If it causes more noise or more ground or junk "masking" problems, then you're forced to adjust back to a "useable" level. Too often we tend to forget that few of todays machines work at their "optimum" theoretical levels of performance. There are recent introductions that are a definate improvement compared to some earlier machines, but still others (the Nautilus for example) that have been around for years, and have long been regarded as the real "depth-masters" of the detecting world. But then we're back to factoring in all of the other considerations and preferrences in some of the more "modern" machines such as weight, size, simplicity in operation, etc. One day that optimized level of performance and all of the other factors will come together into one fantastic machine. But right now, it seems more of a matter of guys like George Payne, Dave Johnson, and other excellent engineers making small strides in squeezing out every last bit of performance in todays designs. I personally still believe that the next great advance in detectors will be in the realms of pulse induction technology where things operate in a more quiet environment in comparison to induction balance, even though the basics of what they can do at their own level of optimization is still restricted by the same basic laws of physics.
Then again, there is always GPR....... <img src="/metal/html/wink.gif" border=0 width=15 height=15 alt="">