RELIC HAWK

[Fred]

I don´t think there will be much inside the coil, we already have the oscillator and preamp on our schematic.
They could be on a separate board in the coil, but i doubt it will make much difference on discrimination.

Max, i asked before, but did you try to adjust you coil so there is a slight offset on null that will not give you a negative shift with iron far away?
regards,
Fred.

[Max]

I don´t think there will be much inside the coil, we already have the oscillator and preamp on our schematic.
They could be on a separate board in the coil, but i doubt it will make much difference on discrimination.

Max, i asked before, but did you try to adjust you coil so there is a slight offset on null that will not give you a negative shift with iron far away?
regards,
Fred.

Hi,
tryed so many times...but no success... the coil you can position in many different offsets/nulls also higher than usually and detector still works good but I put phase in a way I can then ground balance using the trimpot ot external 10turns pot.

When GEB balanced it ignores ferrite at 5cm and even less but not as smooth as in TGS and BandidoII ... it's a wildcat I think... don't like you near ferrite too much!

Anyway, using disc then... it ignores big iron stuff at few cms but then it sounds at far distance!

I had similar problem at BandidoII but that time was a wrong capacitor value... so wrong phase shift at demodulator... BUT our schematic is right, right ? Or I must expect some capacitor value is wrong there ???

Kind regards,
Max

[amtech2005]

RELIC HAWK

MAX , I do not own a Relic Hawk . But it would be nice if someone could test what models of Minelab have a low voltage dc on the RX coil wires. This will tell us if the Relic Hawk needs the Preamp circuit in the search-coil for proper discrimination , or not ????? I thought I saw a photo on this forum of a 15 inch minelab coil that did not have a pre-amp ???Anyway , I am still looking for a "Relic Hawk" to buy where I live , and then many of my questions will be answered..........Again Just some ideas , ......thanks........Eugene

[Max]

MAX , I do not own a Relic Hawk . But it would be nice if someone could test what models of Minelab have a low voltage dc on the RX coil wires. This will tell us if the Relic Hawk needs the Preamp circuit in the search-coil for proper discrimination , or not ????? I thought I saw a photo on this forum of a 15 inch minelab coil that did not have a pre-amp ???Anyway , I am still looking for a "Relic Hawk" to buy where I live , and then many of my questions will be answered..........Again Just some ideas , ......thanks........Eugene

Hi,
yes, it's what I think too... testing such kind of stuff is really easy for those who have it handy... just measure for dc voltage.

Now my puzzle of the day is about TX signal shape... cause I noticed a small... really small distortion at sine wave on tx signal... probably due to the oscillator itself or coil.

The distortion in a bit flattened part of sinus at top positive right end of signal... look at picture to have an idea of it... I didn't take a picture from scope but the distortion is similar to that from this bad simulation.

The question is: could this so small distortion cause such strange disc behaviour ?

Qiaozhi (and all) what do you think about ? Too distorted stuff can lead to disc fault ?

Kind regards,
Max

[Qiaozhi]

Hi,
yes, it's what I think too... testing such kind of stuff is really easy for those who have it handy... just measure for dc voltage.

Now my puzzle of the day is about TX signal shape... cause I noticed a small... really small distortion at sine wave on tx signal... probably due to the oscillator itself or coil.

The distortion in a bit flattened part of sinus at top positive right end of signal... look at picture to have an idea of it... I didn't take a picture from scope but the distortion is similar to that from this bad simulation.

The question is: could this so small distortion cause such strange disc behaviour ?

Qiaozhi (and all) what do you think about ? Too distorted stuff can lead to disc fault ?

Kind regards,
Max

The small distortion you have indicated in the TX waveform is really insignificant, and will have no effect whatsoever on the discrimination. The cause is most likely some nonlinearity in the oscillator. Nothing to worry about.

It is very difficult to debug this problem remotely. Have you probed the signal along the DISC channel, as you wave ferrous and non-ferrous targets in front of the coil? If you first try to monitor the output of the DISC sample switch with both target types, then you don't even need to move the target, as this will be a non-motion response at this point. The differentiating circuitry is further along in the channel. Try plotting the amplitude versus distance for both ferrous and non-ferrous.
If this looks ok , then we can eliminate the problem being located in the sampling circuitry.

[Max]

The small distortion you have indicated in the TX waveform is really insignificant, and will have no effect whatsoever on the discrimination. The cause is most likely some nonlinearity in the oscillator. Nothing to worry about.

It is very difficult to debug this problem remotely. Have you probed the signal along the DISC channel, as you wave ferrous and non-ferrous targets in front of the coil? If you first try to monitor the output of the DISC sample switch with both target types, then you don't even need to move the target, as this will be a non-motion response at this point. The differentiating circuitry is further along in the channel. Try plotting the amplitude versus distance for both ferrous and non-ferrous.
If this looks ok , then we can eliminate the problem being located in the sampling circuitry.

Hi,
ok...so we can exclude the small non-linearity at oscillator as cause of the problem with disc.

I'll do that way using scope on strategic points... then will report about results.

From what I see I will expect the signal will rise or fall with non-ferrous and ferrous metals there. I've checked before and seems it's ok... but I need look again at output of the sampling gate to report accurately.

Kind regards,
Max

[Max]

doing tests...

Hi Qiaozhi,
I'm doing tests... still seems everything nice... I will draw a plot of results when finish them and post here to see if everything is like expected or not.

I think the plot kind is the best for giving such informations... but I'm a bit puzzled by target to use.

I'm using now a silver coin, an hammer head (soft iron) and a small gold ring but don't know if are good or consistent kind of targets ... I see amplitude variations there... will plot them soon.

Kind regards,
Max

[Max]

seems nice....

Hi Qiaozhi and all,
here some plots made with data collected for different targets.

First some values...

At 220nF - 1M6 joint at input of disc channel... just after the sampling gate and low pass I have a 0.22V level above the GND level.
Consider that GND is at about 5V over the negative rail... so the level at input is something 5.22V.

Now... I tryed retrieving from there the voltage variations... but was impossible task... too small variations and too offset to do it well... so I read them after the integrator.

At pin1 of U4 (integrator , disc channel) I have +3.5V above GND when no metal near coil. Coil was nulled at 15mVpp before tests.

All metals considered give positive response BUT iron that gives negative.
The values are respect the steady 3.5V so positive values for gold, silver etc... and negative (meaning less than 3.5V there respect GND) for iron... just when nearing iron very much you'll get invertion and rise variation, but always negative value.

So, consider I've reported in plots just variations respect to the steady state of no metal near. Also consider you'll see points with straight joints + poly interpolation I've added there to get better the picture.

Do you think something is wrong with them ?

Kind regards,
Max

[Fred]

Do you think something is wrong with them ?
Kind regards,
Max

Hi Max,
Nice work with the plots,
The invertion with the hammer is precisely what i was talking about some days ago.
I thought it was possible to cancel it by coil configuration?
I don´t understand why you cannot find a way to make coils without this invertion.
I didn´t make progress on my RH, i still have a few things i must do while weather allow it
Regards,
Fred.

[Max]

Hi Max,
Nice work with the plots,
The invertion with the hammer is precisely what i was talking about some days ago.
I thought it was possible to cancel it by coil configuration?
I don´t understand why you cannot find a way to make coils without this invertion.
I didn´t make progress on my RH, i still have a few things i must do while weather allow it
Regards,
Fred.

Hi,
I don't know... maybe is possible reduce the effect but I think that an iron mass at few cms from coil could give such an effect more or less.

The fact is that the signal goes down when with iron... no matter if there's the invertion or not and with other stuff like silver it goes well positive... and that's more and more confusing cause one would expect the total iron ignoring and there isn't!

Kind regards,
Max

[Qiaozhi]

Hi Qiaozhi and all,
here some plots made with data collected for different targets.

First some values...

At 220nF - 1M6 joint at input of disc channel... just after the sampling gate and low pass I have a 0.22V level above the GND level.
Consider that GND is at about 5V over the negative rail... so the level at input is something 5.22V.

Now... I tryed retrieving from there the voltage variations... but was impossible task... too small variations and too offset to do it well... so I read them after the integrator.

At pin1 of U4 (integrator , disc channel) I have +3.5V above GND when no metal near coil. Coil was nulled at 15mVpp before tests.

All metals considered give positive response BUT iron that gives negative.
The values are respect the steady 3.5V so positive values for gold, silver etc... and negative (meaning less than 3.5V there respect GND) for iron... just when nearing iron very much you'll get invertion and rise variation, but always negative value.

So, consider I've reported in plots just variations respect to the steady state of no metal near. Also consider you'll see points with straight joints + poly interpolation I've added there to get better the picture.

Do you think something is wrong with them ?

Kind regards,
Max

Hi Max,

Sorry for the delayed response.
These plots look exactly as I would expect. If DISC is not working correctly, then the problem must be located further along in the DISC channel. Can you now probe the output of the first differentiating stage (as before) and let us know the results?

The inversion with the large iron is quite simple to explain. Ferrous items cause the amplitude to decrease, but there is a limit on how much it can decrease. As the target gets closer to the coil, the signal will be inverted and start to increase. You should be able to confirm that the same thing happens with the TGSL.

[Max]

Hi Max,

Sorry for the delayed response.
These plots look exactly as I would expect. If DISC is not working correctly, then the problem must be located further along in the DISC channel. Can you now probe the output of the first differentiating stage (as before) and let us know the results?

The inversion with the large iron is quite simple to explain. Ferrous items cause the amplitude to decrease, but there is a limit on how much it can decrease. As the target gets closer to the coil, the signal will be inverted and start to increase. You should be able to confirm that the same thing happens with the TGSL.

Hi,
I will try... will test using same distances and report here.

Kind regards,
Max

[Geo]

Hi,
I don't know... maybe is possible reduce the effect but I think that an iron mass at few cms from coil could give such an effect more or less.

The fact is that the signal goes down when with iron... no matter if there's the invertion or not and with other stuff like silver it goes well positive... and that's more and more confusing cause one would expect the total iron ignoring and there isn't!

Kind regards,
Max

Max, I had the same problem with the PD when it was bad tunning. Also i had a similar problem at one LRL where the head was with ferrite.
Regards

[Fred]

Max, I had the same problem with the PD when it was bad tunning. Also i had a similar problem at one LRL where the head was with ferrite.
Regards

Hi Geo,
I suggest that if you want Max to stay calm , never mention LRL´s when talking seriously
Regards,
Fred.

[Geo]

Hi Geo,
I suggest that if you want Max to stay calm , never mention LRL´s when talking seriously
Regards,
Fred.

Hi Fred.
I will remember it
So i found the point that Max don't stay Calm
Regards