VLF Eldorado

		Quote:			Posted by Eugene52
	For advanced builders , files are in zip folder  : HH.............Eugene

I simply changed the Eugene's word "builders" with "designers", but should add "the circuits are in WEB"
Every amateur designer should copy the best foreign solulutions, but a professional designer should avoid to copy patented solutions.
To reduce the parasitic AM of TX caused by change of distance coil-ground and change of soil properties, Bob Podhrasky (designer of GARRETT) created in 1978 the amplitude stabilized TX. For stabilization he uses P.-I. controller. This kind controller is not the best solution when the amplitude of TX changes very fast at coil swinging. For maximal fast "dismodulation" of TX amplitude modulation, should be used P.-I.-D. controller. The attached picture of Bob is taken from a video in YouTube and the attached circuit diagram of stabilized TX is taken from a patent.
I'm not designer of metal detectors. My hobby is to design TXs, RXs and antennas for QRP amateur radio. Reading information in WEB, I can recognize good design solutions and copy them.
Tesoro introduced Eldorado with TX amplitude stabilisation in 1986. This is 8 years after amplitude stabilisation used in metal detector Marksman of GARRETT.
Eldorado is designed by Jack Gifford.  He writes for this design: "The Eldorado was a simple detector with a manual ground balance, but with a new style of circuitry that worked incredibly well in the highly mineralized soil". This is correct. The metal detector works well in such soil. In metal detecting terminology the term "highly mineralized soil" means magnetic (the correct term is ferromagnetic), but not means conductive soil or salty beach.
If the mineralised soil is nonconductive, it acts as ferrite core for TX coil. In this case the change of distance TX coil - mineralized ground not changes the amplitude of TX oscillation because in practice the ferrite core not absorbs energy.
The problem arises with  the conductivity of soil because in this case there are eddy currents flowing through soils resistance; the oscillating energy in TX tank dissipates as heat in the soil, ie there is energy loss (the correct term is "soil absorbs energy"). The result is that the amplitude of oscillation diminishes when TX coil approaches to soil.
Jack uses proportional controller for "dismodulation of TX, but this is not so effective as PID controller.
The picture of Jack is extracted from WEB site of TESORO.

Linkback:

You are not allowed to view links.
Please Register or Login

http://www.thunting.com/smf/index.php/topic,15858.msg103184.html#msg103184

		Quote:			Posted by Eugene52
	It will be cool to see these circuit revisions soon on our Forum Here  . Great Topic mikebg started !! Best Regards................Eugene

Eugene,
This topic was not started by me, but by you. It can be titled "Eldorado for advanced builders". My postings are only replies and their abstract is:
"Eldorado is not properly designed. Please copy better TX and RX blocks from other circuit diagrams". In the postings I'm trying to explain IMNHO what is not properly designed and how it SHOULD be designed. Note the term SHOULD. We should use it often because after it is attached an information for discussion.
I'm quite a newbie to this forum and despite MNHO (my not humble opinion), I do not intend to start soon any topic unless you as Global Moderator not come up with some intriguing title as: "How should MD (metal detector) work" or "How should be MD designed ". This is no joke. Participants in this forum taught me "How should BFO MD work", "How should be designed the best search oscillator for BFO MD", "How should work the reference oscillator in motion BFO MD" and "How should be designed the best TX for a MD ".
But let's continue reasoning on the topic: What should be done by Jack Gifford starting in 1986  the design of Eldorado?
1. He should have theoretical knowledge or should analyze "How should MD (metal detector) work?",
2. To explore everything designed and patented recently in this area in order to copy the good decisions.
If Jack Gifford is now monitoring this forum, he would hardly dare to publicly answer the first question, but should analyze it for themselves because the correct answer will give of his company advantage over competitors. For the second task I can say with certainty that creating Eldorado in 1986, Jack has not read carefully patents of Garrett. If this was done, he would have noticed that the TX circuit of Bob exists in several patents of Garrett, but in none of them no patent claims on it. Can not and should have, because in all textbooks on Automatic control writes that are used generally three types of controllers to stabilize the amplitude:
P (proportional), which gives a significant error in the established regime
PI (proportional-integral), which has no error, but acts more slowly and
PID (proportional-integral-derivative) controller having best performance and speed.
The designed by Bob amplitude stabilized TX did not contain any significant innovation for which he could have a patent claim. Any producer can use with impunity to such a design, but it is not the best design solution. Best TX for MD must contain amplitude stabilization with PID controller and a separate driving oscillator.
What follows here in our topic "VLF Eldorado"? We should examine the shortcomings of the RX preamp in the circuit, but before that let those who follow the topic to see  preamp circuits in other designs and to establish whether they contain so high ohm resistors connected to the input of opamp and how they amplify the induced voltage in RX coil having AC mains frequency and its harmonics.
Yours Mike-BG

Linkback:

You are not allowed to view links.
Please Register or Login

http://www.thunting.com/smf/index.php/topic,15858.msg103369.html#msg103369