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Offline Eugene52Topic starter
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« on: June 08, 2011, 02:56:20 pm »
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We may now have "new help" on a recent unsolved problem !!

The last problems that I remember on this project were :

1. Discrimination circuit was never correct , no full range .
2. 5 Khz TX[transmit] oscillator circuit problems , wrong transistors ?
3. PCB original layout was surface mount , a "through hole" design was requested by everyone . So when the original design was changed from "surface mount" to "through hole"  there were new power and grounding issues created with the new board . Do we Construct a dual using [2 boards] ?

4. What would be the correct search coil to make for proper 5 khz output and discrimination , a DD or a concentric with nulling coil ?

Here should be the last posted project files below .

UPDATE: 06-10-11 Forum Member LUC already posted everything in the Download area of our Forum !!   Great

Best Regards................Eugene

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« Last Edit: June 10, 2011, 11:59:52 am by Eugene52 »
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« Reply #1 on: June 13, 2011, 01:32:54 pm »
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I made detector using this schematic. Work very bad .

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Offline mikebg
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« Reply #2 on: June 13, 2011, 03:40:31 pm »
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I think the drawbacks of Relic Hawk family are fixed by Minelab designers in the next family with similar schematics - Musketeer. Here is the circuit diagram of a Musketeer (unknown model).
We need to do some tests and measurements to understand what Minelab has imroved and modifyed. Who of the participants in this forum have an original Relic Hawk or Musketeer (manufactured by Minelab), to make some tests of main parameters?

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Offline dr.jare
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« Reply #3 on: June 14, 2011, 01:18:36 pm »
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Quote:Posted by mikebg
I think the drawbacks of Relic Hawk family are fixed by Minelab designers in the next family with similar schematics - Musketeer. Here is the circuit diagram of a Musketeer (unknown model).
We need to do some tests and measurements to understand what Minelab has imroved and modifyed. Who of the participants in this forum have an original Relic Hawk or Musketeer (manufactured by Minelab), to make some tests of main parameters?
Hi mikebg.Your scheme is from Serbian forum (

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) and to the Minelab Musketeer XS. Here is the correct scheme Minelab Relic Hawk:

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Offline mikebg
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« Reply #4 on: June 14, 2011, 03:39:20 pm »
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Dr. jare, thanks!
I have several questions:
1. If there is a ferrite core in the 1mH inductor,
2. If this inductor is inside sensing head, ie where to sign cable connector in the circuit diagram and
3. Why preamp U1 operates with low gain (only 32 times)?

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« Reply #5 on: June 15, 2011, 12:55:04 am »
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I tried only  rx and one filter section..very very important U1 gain.
15k  must be variable resistor..

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Offline dr.jare
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« Reply #6 on: June 15, 2011, 01:42:38 pm »
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Hi mikebg. I have not made these detectors (Minelab Musketeer XS and Relic Hawk). This is the reverse engineering of IVCONIC (Geotech Forum). Register on his forum "Hobi Detektori"

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and there ask questions in English, his nickname is Stevan and will gladly answer.

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Offline mikebg
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« Reply #7 on: June 17, 2011, 01:17:09 am »
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Quote:Posted by errol
I tried only  rx and one filter section..very very important U1 gain.
15k  must be variable resistor..

Errol, the 15k is not suitable for gain control for two reasons:
1. A potentiometer in front panel adds stray capacitances and receive interferences. Opamps hate stray capacitances in output and in feedback.
2. The change of 15k will change phase shift of preamp, ie it will change discrimination setting.
The phase shift is formed by timeconstant of resistor 15k and capacitor 1nF. They form the upper cutoff frequency fc of amplifier, which is 10.7 kHz. The fc is calculated with formula fc=0.16/(R*C)
fc=0.16/(15k*1n)=10.7 kHz
The amplifier makes phase shift 45 deg at cutoff frequency.
The operating frequency 5kHz is only two times different from the upper cutoff frequency. That means there is significant phase shift.

More suitable for gain control is resistor 470 ohm. It forms with 220nF the lower cutoff frequency, which according the above formula is
fc=0.16/(470*220n)=1.5 kHz
This fc is more than 3 times different from operating frequency 5 kHz. That means, if we decrease gain with 470 ohm resistor (as shown below), the change of phase shift will be insignificant and in practice this wont change discrimination.
Note that in this circuit, the potentiometer involves minimal interference because its wiper and one lead are grounded. Now we can put the potentiometer SENS in front panel and operator can reduce gain at bad ground.


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« Last Edit: June 17, 2011, 01:20:55 am by mikebg »
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« Reply #8 on: June 17, 2011, 06:09:04 am »
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hi mikebg. you totally agree.
 I mean, opamp output level very important.
if level is high.  filter not work
regards

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« Reply #9 on: June 18, 2011, 11:35:43 am »
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Dr. Jare, Registration in the Serbian forum requires too much data for me:

Fill in the form with Facebook, Associate your Facebook account
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Mesto boravka *: ,Pol *: Male Female
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I wont register because the questions in the last row I do not want to share.

You helped for this thread with posting reply #3.
Now you can help again seeking in the Serbian forum answers for questions in reply #4.

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