RELIC HAWK

[eclipse]

This is sovereign coil, not the coil I've seen.
Perpahs wasnt on this forum it was long time ago.
But hey there it is - the small coil.
Also you've seen RH original board, have you noticed that
there isn't a coil on the board.

[Max]

Max,
The more I research this, the more that I believe this is a common problem with all totally analog VLFs. Some models get around this by not being so sensitive. I think the reason for this can be understood by studying Whites patent for their VDI. In the patent information, it finds that the weak iron (iron at a distance) 'smears' (is not consistant phase angle) across the VDI. Looking at the code for the VDI, the phase angle is determined each time the GND channel is sampled and is above the threshold. In weak iron, the phase angle varies randomly over 180 degrees. The way that Whites Spectrum Eagle, XLT, DFX discriminate this is by the inconsistancy of the phase response. They can do this because they are uPC controlled and maintain a response level (maintained within the fade window time period) for every 9 degrees of phase angle. I am not sure that you can totally eliminate/discriminate this with current analog circuitry.

Regards,
J. L. King

Hi,
I think you're probably right about that. All my efforts to give no weak iron detection give just reduction of the problem but not complete solution of it.

Maybe an optimized coil could only partially solve that but, cause device is so sensitive, it's nearly impossible eliminate totally that behaviour in that analog design.

It will be easy know about that... cause people who had/have RH can try with a piece of soft iron (an cheap ... bad hammer) and see if detector see that when it's at e.g. 30cm or more... it's kind of cracked response but confusing in real search.

At less depth they will see no detection at all of the hammer.

If it's so, they must also know that cause must be infrequent they dig soft iron stuff at 30-40cm range, when in disc mode.

This do not apply to e.g. horseshoes cause they're actually of steel , not soft iron.

I hope someone could tell us what's real behaviour on soil... and if soft iron stuff is picked up at deep from time to time.

Kind regards,
Max

[kt315]

...

[nakky]

... or coins, no matter what - everything which would effect phase shift there so you can adjust it more precise, ML are using this small coil for that purpose.

I've seen X-ray of such coil somewhere, small coil inside the search coil, nothing else

Eclipse,do you mean this.Grt Nakky.

[KingJL]

Hi,
Also, apart the iron detection at far... the detector works as expected... and is also about deep about detection... so it's only a small thing... maybe related to a schematic mistake or to something strange at ML design.

Max,
The more I research this, the more that I believe this is a common problem with all totally analog VLFs. Some models get around this by not being so sensitive. I think the reason for this can be understood by studying Whites patent for their VDI. In the patent information, it finds that the weak iron (iron at a distance) 'smears' (is not consistant phase angle) across the VDI. Looking at the code for the VDI, the phase angle is determined each time the GND channel is sampled and is above the threshold. In weak iron, the phase angle varies randomly over 180 degrees. The way that Whites Spectrum Eagle, XLT, DFX discriminate this is by the inconsistancy of the phase response. They can do this because they are uPC controlled and maintain a response level (maintained within the fade window time period) for every 9 degrees of phase angle. I am not sure that you can totally eliminate/discriminate this with current analog circuitry.

Regards,
J. L. King

[Fred]

... or coins, no matter what - everything which would effect phase shift there so you can adjust it more precise, ML are using this small coil for that purpose.

I've seen X-ray of such coil somewhere, small coil inside the search coil, nothing else

Hi,
That´s interesting,if Max used a 1mh it could explain the problems he encountered.
What would be the purpose to use a separate small coil instead of the main one and adjust phase shift with a loop of wire like in other MD´s ?
regards,
Fred.

[eclipse]

... or coins, no matter what - everything which would effect phase shift there so you can adjust it more precise, ML are using this small coil for that purpose.

I've seen X-ray of such coil somewhere, small coil inside the search coil, nothing else

[Max]

1 micro (1uH) it is. It work both ways on board or inside the coil. If it is on your pcb you can adjust the phase shift the way ivconic does - with small pieces of metal inside the coil.

Do you mean aluminium foil pieces ?

[eclipse]

1 micro (1uH) it is. It work both ways on board or inside the coil. If it is on your pcb you can adjust the phase shift the way ivconic does - with small pieces of metal inside the coil.

[Max]

I am guessing that RH does not have any circuit inside the coil just a small round (25mm) winded coil which is 1uH on the schematic. If i remember right its used for adjust phase shift. No other components used

Hi,
yes, seems so. But we have it on PCB ???

So maybe the problem with disc is there!

Maybe that is a compensating small coil used for phase alignment and must be inside coil housing... not on PCB!

Hell, this is an important detail!

Do you mean the "102K" stuff there ??? But it's 1mH not 1uH ! Mistake in schematic ?

Kind regards,
Max

[Max]

I spent a few hours Today "again" digging in the Geotech archive Dungeon !! Anyway , I did not get the answers I was looking for. On this forum a few years back were several photos of assorted minelab coils , some were an X-ray image and some were torn a part. Charles of upstate New york had some great posts about 3 years ago , but no photos anymore !!! I found some posts that had a little red-x in the corner that means they have been removed , which is ok to me . All I want to find out is , why some minelab coils have the little circuit board inside the coil and why some do not . I guess it might be a Pre-amp or used for some kind of impedance matching or even some kind of EQ "equilizer board" for Broadband BBS . Maybe this little board can be used in several minelab detectors , and if there is a minelab detector that needs just the search coil and doesn't need the little boards function , it will not send a low dc voltage to the little boards switching transistor , and then it will act as just a high impedance load and do nothing more. I wish I can find all those photos . Another Unsolved Mystery on Geotech !!! I am still searching till I get all the answers / Specs that I need , or find all those great missing photos..................Take Care Everyone ..................Eugene

Hi Eugene,
I think there are 4 main reasons for having the PCB inside the coill housing.

1. mechanical stiffness: if you connect the coil with a long cable to the preamp, any movement of cable could create problems.
The cable is part of the LC tank circuit and an e.g. variation in inductance of the cable (e.g. when it moves) could trigger a false signal.
If you, instead use a preamp board inside coil you'll be sure the cable will only carry an output signal to the main PCB, not being part of the resonating stuff. This will also prevent detuning by thermal... cause preamp board, bucking coil and main coils are all epoxied togheter... so thermal effects will cancel is all tuning if made on that elements only.

2. noise reduction: if the cable is part of LC circuit the turns of cable... the more it's long etc are all good params to increase noise at preamp. If you, e.g. shield coils and use e.g. shielded cable you're theorically proof to external noise... but it isn't: a few will enter by cable cause no cable shield is perfect... expecially if you have it to be flexible (like in MD case). This for E field noise. For B field noise... the stuff is really different... you simply have no protection about induced noise cause magnetic flux will chain with cable too.... picking up more noise voltage: the cable shield is totally useless about that.

3. calibration and precision required: if coil/cable must match a very strict set of params you'll probably prefer the preamp inside solution. That way you can do all the tuning at coil, including bucking stuff and preamp board position inside housing... then you'll use the cable just to receive power and send back output. That way you're not required tuning the coil considering the cable also... and an operator will only tune a coil+preamp stuff... and the cable will not introduce important tolerances in that.
Is more reliable way... cause you eliminate the cable influence from any tuning operation, and this apply also to connectors that often are quite different pieces and could introduce e.g. inductance variations if in series in the LC tank.

4. PS... forget this one... another is phase due to preamp: if you tune for a special phase shift the preamp could influence that. If you made coil+preamp you'll tune just for output phase shift of preamp... thus compensating eventual unwanted phase shifts due to different ics.

Kind regards,
Max

[eclipse]

I am guessing that RH does not have any circuit inside the coil just a small round (25mm) winded coil which is 1uH on the schematic. If i remember right its used for adjust phase shift. No other components used

[amtech2005]

RELIC HAWK

I spent a few hours Today "again" digging in the Geotech archive Dungeon !! Anyway , I did not get the answers I was looking for. On this forum a few years back were several photos of assorted minelab coils , some were an X-ray image and some were torn a part. Charles of upstate New york had some great posts about 3 years ago , but no photos anymore !!! I found some posts that had a little red-x in the corner that means they have been removed , which is ok to me . All I want to find out is , why some minelab coils have the little circuit board inside the coil and why some do not . I guess it might be a Pre-amp or used for some kind of impedance matching or even some kind of EQ "equilizer board" for Broadband BBS . Maybe this little board can be used in several minelab detectors , and if there is a minelab detector that needs just the search coil and doesn't need the little boards function , it will not send a low dc voltage to the little boards switching transistor , and then it will act as just a high impedance load and do nothing more. I wish I can find all those photos . Another Unsolved Mystery on Geotech !!! I am still searching till I get all the answers / Specs that I need , or find all those great missing photos..................Take Care Everyone ..................Eugene

[Fred]

1. the Search- Coil , and if the search-coil pre-amp or Minelabs little circuit inside the coil is required ?

Hi Eugene,
There is already a preamp in the schematic, so if it must be located in the search coil it should be removed from the main board.I don´think it is the case here, but it should be easy to verify counting the wires connecting to the coil...

Hi,
Fred.
Can you post latest PCB look.

Here it is, last version.I did not made the last mods from Max.
Regards,
Fred.

[amtech2005]

RELIC HAWK

Hi,
I will be glad if this happen BUT HOW YOU calculate this?
Please share your calculator

Hello Tiktak , I calculate on how "SLOW" I am , in relation to my Age !!!
I'm sure it won't take that long ........Once everyone is done with summer Vacation and is back on the Forum . I remember someone here on this Forum saying they had just bought a Relic Hawk , and said they would post the little bits of missing information when they had time , this was 2 months ago !!!!......Anyway , I think the Relic Hawk project is about 95% completed !!!!...Thanks to Max , Fred and Everyone ....Eugene