RELIC HAWK

[amtech2005]

RELIC HAWK

Eclipse , It will be interesting to see what the final "winning bid" is !!! And yes the U.S. Dollar will be getting worse and that's being optimistic. Anyway , I get the feeling that the Relic Hawk we see posted has had some "Heavy Use". Just from Looking at the photos , the detector housing front plate is very dirty . What is wrapped around the discrimination Knob ?? "Excellent Condition" ???????.....I see dirt on the search-coil also. There will be other Minelab Relic Hawks ,maybe perfect condition with a better starting price. If you blow up the pictures a little you will see the dirt. I never noticed that earlier today !!.....Eugene

[Max]

Max,
What does the output from the Discriminator gate (U2 pin 7) look like? In simulations, I see that it is unbalanced for some settings of GB/DISC. Seems to come from DC offset at U6 pin 7. The gate shout be equal in on off times. If it is not, that play tremendouse havoc with discrimination.

Still researching!

Regards,
J. L. King

Hi,
I've checked at pin7 U2, it gives 50% duty cycle always when rotating geb pot.

When rotating disc pot I get about 5° on state increase in tON time.

Kind regards,
Max

[Max]

I'm afraid that this is true for some detectors. For instance, some of the Fisher's have this problem. They can be great for finding really deep nails!

Hi,
this is a really sad news... do you belive the problem I'm experiencing at disc is related to the smaller coil I'm employing at now or enhanced by it? (it's 11'' DD)

I hope the RH isn't part of that scenario of "deep nail finders"...

Kind regards,
Max

[Max]

TGSL and recent Spectrum can also be fooled ocassionally with deep iron .
Luckilly not often case, but sometimes they do.
At Spectrum problem is less due nice VDI bars. When this occurs i get bars at both sides of zero, usually highest and lowest bars are rising.So there is good base for doubts. But with TGSL situation is worse, lot of doubts about detected item. Yet it is not so oftenly. Usually medium sized iron item at more than 30cm deep in ground will fool out TGSl easilly. Large iron item is easilly recognizable by specific sound, even when it break through discrimination. It's got "metalic", flat "bang" instead soft "beep" usuall for good metals.
But medium sized iron items are nightmare, almost identical "bleep" as on good coin! Again, all these only on metal under 30cm in ground...
Small iron items are totally rejected from coil surface up to full range of detection, no problems with those at all....rusty nail...joke for TGSL as well as for Spectrum...
I think this is mostly due uneprfect coil we made...? Or...?

Hi Ivconic,
you're right... but all this happens on soil.

When testing on the bench... my TGS or TGSL run ignoring any soft iron in size of a 200gr hammer head... both from near and from far.

The RH clone I've made, instead, behave bad way with same iron stuff on distances starting from about 15cm: that's really impressive that a piece of iron sound like a copper coin at such distance... and sure it's a really worse problem that could make cloned device totally unreliable about disc on real soil.

I'm sure problem could not be so big at real, original ML RH but this happens in cloned and coinseeker too as I read.

Mistake in schematic ? Special components involved ?

I don't know...

Kind regards,
Max

[tiktak]

Hi,

Hi,
Max how are you?
U3 and U4 are still both 4066 on the schematic!!!
We can see clearly on Musketeer that there are two TL074!Could this be a lead?
And I dont see TS27m2?

[KingJL]

Hi,
I've checked at pin7 U2, it gives 50% duty cycle always when rotating geb pot.

When rotating disc pot I get about 5° on state increase in tON time.

Kind regards,
Max

That's about what I see in simulation. The variance I see at the DISC is toward the maximum DISC setting. Toward the mid to lower settings, I see 50% duty cycle.

Could this imbalance at the higher DISC setting be causing your anomallies?

I have found that a little fine tuning of the R & C values in this phase shifting circuit can minimize the variances. As yet, I have not found the 'perfect' combination. A lot depends on the amount of phase shift needed to achieve GB. The quality and tolerance of the capacitor and resistor used in the pre-amp (2.2n & 470 ohm in the high pass filter network of the inverting input circuit) can affect the phase shift of the pre-amp and thus the phase shift required for GB.

Regards,
J. L. King

[Ultimate_Haze]

Hi,

Hi,
Max and all folks.
I am londering why you use NE5532?I can see on musketeer NE5534!!!

[KingJL]

The quality and tolerance of the capacitor and resistor used in the pre-amp (2.2n & 470 ohm in the high pass filter network of the inverting input circuit) can affect the phase shift of the pre-amp and thus the phase shift required for GB.

Sorry, that was 220n & 470 ohm!!!

Regards,
J. L. King

[KingJL]

Max,
I have found a resistor combination in the phase shift circuit that exhibits a bit more linearity of duty cycle to the gates, and gives a better GB & DISC range.

You might want to try the following:
Change the GB & GEB pots to 25k (multi turn of course) and change the 30K that is between the GB/GEB and U6 pin 5, to 27K. Change the DISC pot to 25K and the 18K between the DISC and U6 pin 7 to 12K.

With this combination, I get less than 1% deviation in duty cycle at the DISC gate throughout the DISC range. Also you get a little better range in the GB (86 deg - 113 deg).

Regards,
J. L. King

[Max]

Hi,
Max and all folks.
I am londering why you use NE5532?I can see on musketeer NE5534!!!

Hi,
I'm using NE5534 at preamp, but I've found that, in some cases, NE5532 (that's the dual op amp version of it) could be used also instead of 27M2 or 27M7 stuff.

I stay really strict to specs but so far with not great success about disc...

Kind regards,
Max

[Fred]

I have used single turn pots in the PCB layout,i guess i should change them all to multi turn, even if it is not a priority right now....probably the long (horizontal) ones.
Fred.

[Max]

I have used single turn pots in the PCB layout,i guess i should change them all to multi turn, even if it is not a priority right now....probably the long (horizontal) ones.
Fred.

Hi,
yes , it would be nice having all them as multiturn like in original RH... though I noticed they are useful also 1 turn kind... with a bit of practice you find the right spot...

For now I'm just using a 10turns pot for external GEB.

Kind regards,
Max

[ivconic]

Hi Ivconic,
you're right... but all this happens on soil.

When testing on the bench... my TGS or TGSL run ignoring any soft iron in size of a 200gr hammer head... both from near and from far.

The RH clone I've made, instead, behave bad way with same iron stuff on distances starting from about 15cm: that's really impressive that a piece of iron sound like a copper coin at such distance... and sure it's a really worse problem that could make cloned device totally unreliable about disc on real soil.

I'm sure problem could not be so big at real, original ML RH but this happens in cloned and coinseeker too as I read.

Mistake in schematic ? Special components involved ?

I don't know...

Kind regards,
Max

Yes...only in ground. When testing on bench my devices also acts by the book - perfect.
So...ground DO shift phase more than we expected!? Along with phase ground DO affects amplitude also...hmmmm! What to do ?
I am tempted to take some scope with me outdoor and perform all kinds of measurements "in vivo"...damn! Lot of hard labour!

[tiktak]

Hi,

Hi,
Max,
Yes this is the setup for RH.Only Man GB is multiturn!Maybe and fixed but its trimer.

[tiktak]

Hi,

Hi,
Max.
As I look the pictures posted from Ivconics RH.I see 9 transistors and in ower parts list there are 4!!!Why?3 normal+6 smd.Hum..........Cutted schematic again.But it works?!