Voodoo Main Discussion

[SilverSurfer17]

Yeah ive done some checking around and it has problems im going to try a few things and see what happens maybe even make my own

[MartinB]

That mogami coax looks nice at least the connectors and the outside of the cable doesn't look like that cheap shiny plastic so then i assume just remove the ends and replace with 5 pin connectors [ATTACH]54234[/ATTACH]

Nice looking cable but it does have a conductive PVC sheath which may affect performance

[6666]

this will work, but it is true that for me the "discrimination" area is too small for the ocean range. the omega was my first test on the voodoo. after I did the dd and the super d. I have come to the conclusion that the pancake is the best idea. I tried .. I didn t succeed .. impossible to nulling .. I had no luck. so I persist on the super d, it is the only one that has a performance as good in PI as in hybrid on the voodoo circuit.
best compromise, surface, discri and depth ...

Which/what coil are you calling "pancake" ?

[MartinB]

While waiting for my PCB and PIC to arrive I decided to build a concentric except I went for a more conventional 360uH TX and 6.9mH RX coil. To test it I attached it to a modified Surf PI Pro with a split TX and RX. To my amazement it worked great for a disc channel but required reduced gain. So I figured why not just build a separate disc channel and have an analog version of the VooDoo? I am just using the existing PI channel as an equivalent GB channel and borrowed some of George?s idea from the VooDoo project. I am just merging the two channels just like the Raptor, TGSL or Whites classic with a pair of LM393s. The only real challenge was getting the frequency response of the GB and disc channels close to the same. Also.. Resonant frequency of the RX channel doesn?t seem to matter much as long as the sample delay and sample pulse can be adjusted to sample at the correct time.
Too many ideas from on George?s books to post here but I can show that it works.
https://youtu.be/9aqxGrFK9fo


So, here is a little demo of how it works. It deals with the ground signal quite well and can disc iron with an analogue meter.

Hi Surf
Which cable do you use for winding your coils?
I see that like me you have some interference before and after the signal. Is this capacitive from the coil?
Thanks

[ivconic]

this will work, but it is true that for me the "discrimination" area is too small for the ocean range. the omega was my first test on the voodoo. after I did the dd and the super d. I have come to the conclusion that the pancake is the best idea. I tried .. I didn t succeed .. impossible to nulling .. I had no luck. so I persist on the super d, it is the only one that has a performance as good in PI as in hybrid on the voodoo circuit.

I haven't tried such coil so far.
Balancing seems too complicated for me.
Even "CC" coil is too complicated to balance... in these conditions.
Truth is; the other day i prepared former for CC coil.
I had enclosure from before, i only 3D printed former for RX and former for bucking coil.
Enclosure is big enough to fit 25-27cm TX coil.
And dimensions of RX and bucking former are on the pics:

[lamoiz]

Omega type coils never were deep anyway.
What i am expecting from it is to be "comfortable" to experiment with in workshop.
Should be good for precise detection of smallest items, should be good in discrimination.
And yet... maybe i am just daydreaming, will see.
In the past i used larger room upstairs as my workshop, having lot of space and comfort for these kind of works.
Last several years situation has changed and now my workshop is 1x1 square meter, piled up with parts, tools and instruments.
Not to mention hums and interferences.
That's why i am forced to minimalize testing conditions, coils etc.
No harm done, this is just an attempt.

this will work, but it is true that for me the "discrimination" area is too small for the ocean range. the omega was my first test on the voodoo. after I did the dd and the super d. I have come to the conclusion that the pancake is the best idea. I tried .. I didn t succeed .. impossible to nulling .. I had no luck. so I persist on the super d, it is the only one that has a performance as good in PI as in hybrid on the voodoo circuit.
best compromise, surface, discri and depth ...

[ivconic]

maybe, but my tests with an omega give very poor results. I think the cancellation on the indoor loop limits the PI mode a lot. It works, but the detection area in hybrid mode is very small. In my application on the wet sand of the ocean, it is like looking on a small stretch of beach, it is not good for me.

Omega type coils never were deep anyway.
What i am expecting from it is to be "comfortable" to experiment with in workshop.
Should be good for precise detection of smallest items, should be good in discrimination.
And yet... maybe i am just daydreaming, will see.
In the past i used larger room upstairs as my workshop, having lot of space and comfort for these kind of works.
Last several years situation has changed and now my workshop is 1x1 square meter, piled up with parts, tools and instruments.
Not to mention hums and interferences.
That's why i am forced to minimalize testing conditions, coils etc.
No harm done, this is just an attempt.

[lamoiz]

Thanks!
I see.
...
Dunno... concentric coplanar coils were always hardest for me to make in my modest home made conditions.
Only because of the delicate balancing procedure.
"DD" were easiest.
Yet... "DD" is not most suitable coil arrangement for this kind of detectors.
What's next best trade off?
For experimental workbench purposes; i think the easiest would be "Omega" coil.
I draw 3D elements for it, for 3D printing. To make my life more easier while experimenting.
For those interested:

[ATTACH]54236[/ATTACH]
[ATTACH]54237[/ATTACH]
[ATTACH]54238[/ATTACH]
[ATTACH]54239[/ATTACH]

maybe, but my tests with an omega give very poor results. I think the cancellation on the indoor loop limits the PI mode a lot. It works, but the detection area in hybrid mode is very small. In my application on the wet sand of the ocean, it is like looking on a small stretch of beach, it is not good for me.

[ivconic]

I found it to be very important because the first couple of oscillations will go into saturation and will not be useful to sample there unless gain is decreased unnecessarily. You can get very good sensitivity even at very low gain if everything is nulled.

Thanks!
I see.
...
Dunno... concentric coplanar coils were always hardest for me to make in my modest home made conditions.
Only because of the delicate balancing procedure.
"DD" were easiest.
Yet... "DD" is not most suitable coil arrangement for this kind of detectors.
What's next best trade off?
For experimental workbench purposes; i think the easiest would be "Omega" coil.
I draw 3D elements for it, for 3D printing. To make my life more easier while experimenting.
For those interested:

[Altair]

I found it to be very important because the first couple of oscillations will go into saturation and will not be useful to sample there unless gain is decreased unnecessarily. You can get very good sensitivity even at very low gain if everything is nulled.

Do you test with deep null or not?

[SilverSurfer17]

That mogami coax looks nice at least the connectors and the outside of the cable doesn't look like that cheap shiny plastic so then i assume just remove the ends and replace with 5 pin connectors

[MartinB]

I saw the post on the three different types of cable to use ill have to order mine soon i was wondering anyone know what Minelab uses thanks or can narrow it down to whats best to use

Twin individually screened coax, but there are no markings on the cable to help identify it.

[dfbowers]

Question for Voodoo and DB experimental circuit:
how really important is to balance RX coil with TX coil?

I found it to be very important because the first couple of oscillations will go into saturation and will not be useful to sample there unless gain is decreased unnecessarily. You can get very good sensitivity even at very low gain if everything is nulled.

[6666]

RX coil is "VLF I/B" part of the detector. Expected to be in such range.
Although not sure how it would perform with lower inductance... the RX front end.

I am aiming for 1.2mH from table 6.1, about 60 turns on 5 inch former, be interesting to see what happens.

[ivconic]

but i will make 360-400uH TX coil and 7-12mH RX coil. why are you useing such a high inductance for the RX coil ?

Another thing I have been pondering Dave Emery says if making a PI conc then use a 22 ohm R between coil and mosfet, anybody doing that ?

RX coil is "VLF I/B" part of the detector. Expected to be in such range.
Although not sure how it would perform with lower inductance... the RX front end.