Sovereign Coil.

[Geo]

Hi bbsailor.
I have this schematic, but the coil has amplifier with the AD797.
I believe that AD797 it is about the same with LT1028. So if i find the schematic, i will add the resistor that i lost and i will connect the pcb in the new coil,so no need to construct a new small pcb . Amplifier is shielded at Tornado coil, what will hapend if i will not shield it??

Regards

[bbsailor]

Hi bbsailor.
I have this schematic, but the coil has amplifier with the AD797.
I believe that AD797 it is about the same with LT1028. So if i find the schematic, i will add the resistor that i lost and i will connect the pcb in the new coil,so no need to construct a new small pcb . Amplifier is shielded at Tornado coil, what will hapend if i will not shield it??

Regards

Geo,

Shielding accomplishes two important things.

1. Maintains a fixed capacitance relative to the ground so the RX signal stays the same as the coil height above the ground is varied slightly when sweeping the coil. Both the TX and RX coils should be shielded.

2. Helps to shield the RX coil from external noise.

Think about using Scotch 24 mesh as a shield. It works very well on PI coils but I have not tried it on a Sovereign coil but it should work. The key to making a stable IB coils is to maintain coil stability so there is no movement of the coils relative to the shield and no movement of either coil relative to each other.

Once you put the amplifier in the coil housing and the filler sets you will need to use the RX small balancing loop to null out any response caused by the circuit board and it's components.

bbsailor

[Geo]

Geo,

Shielding accomplishes two important things.

1. Maintains a fixed capacitance relative to the ground so the RX signal stays the same as the coil height above the ground is varied slightly when sweeping the coil. Both the TX and RX coils should be shielded.

2. Helps to shield the RX coil from external noise.

Think about using Scotch 24 mesh as a shield. It works very well on PI coils but I have not tried it on a Sovereign coil but it should work. The key to making a stable IB coils is to maintain coil stability so there is no movement of the coils relative to the shield and no movement of either coil relative to each other.

Once you put the amplifier in the coil housing and the filler sets you will need to use the RX small balancing loop to null out any response caused by the circuit board and it's components.

bbsailor

I asked about the shield of amplifier . If it is not important, i will put it outside of the housing shield so to have the ability to play with the gain....

Regards

[Geo]

Yesterday i measured the coil.
The Tx is 1010uH.... 0.65mm wire diameter (i don't remember now the DC resistance but about 1.8 R).
The Rx is 404 uH ..... 5R dc resistance and 0.3mm wire diameter.
Tx diameter is very bad for me @#$%#@. I must winding again the Tx coil because i used 0.4mm wire. But there is another problem i have not so thick wire, so i must looking for to buy it.
As i see i will spend all the winter with this coil

[Geo]

.... and some photos from the old blasted coil...

[Geo]

At the attached schematic there is a capacitor 0.6uF parallel with the Tx coil. Inside the coil of my Sovereign there is not this capacitor. Sovereign is a 17 frequencies detector, so i believe that the capacitor must not be parallel with the tx coil????
Who is your opinion????

Regards

[Qiaozhi]

I do not think it makes sense to have a 600nF capacitor across the coil ... and worse than that, it's shown as a polarized cap.

[Geo]

I do not think it makes sense to have a 600nF capacitor across the coil ... and worse than that, it's shown as a polarized cap.

Tx is 1mH. 1mH with 600nF tune at 6.5 Khz.
My coil had not capacitor so i will not connect one at the new coil (if i will finish it )

[Qiaozhi]

Tx is 1mH. 1mH with 600nF tune at 6.5 Khz.
My coil had not capacitor so i will not connect one at the new coil (if i will finish it )

When I said it doesn't makes sense, I was meaning for a multi-frequency design like the Sovereign.

[Geo]

When I said it doesn't makes sense, I was meaning for a multi-frequency design like the Sovereign.

I understood it

[Geo]

Here is the schematic of the coil amplifier with AD797. Small differences from the LT1028. Also on this schematic there is more gain....
I destroyed the resistor that connecting parallel to the coil. As the Rx inductance is the same (400uH) i painted it with the same value 560R as it is at the LT1028 schematic.
Any comment ????

[plumabob]

Hi Geo,

Sorry I did not spot this sooner. That mystery resistor is 750 ohms. I have built many sovereign coils and pre-amps. Keep the TX at 1.01uH-1.02uH with a resistance less then 2 ohms. Wind the RX to .440.uH to .460uH with a R of around 5 ohms. Little more or less does not matter. This will give you a very hot coil. If you can find some nylon / polyester copper/nickel tape, this works the best for your shielding. I also do use the graphite spray with good results but the tape will give more consistant results.

Bob

[Geo]

Hi Bob,
Thank you. I wait to receive Graphit 33 spray. What op.amplifiers did you used for the coil amplifier??? LT1028 or AD797???
I did not try the old ampl yet, if it has problem i will construct one bigger, not SMD.
My Tx coil is 1002uH 1.6R and the Rx is 398uh. When i will shield them the inductance will increase 10...30uh so it will be perfect.
What resin did you use??

Regards

[plumabob]

Hi Geo,

I have built both, but the AD797 op-amp is far superior. Your R value on your TX is a bit low. You should be closer to 2 ohms. Even slightly above is better then too low. Maybe drop 1 wire size and rewind. I found performance was reduced when resistance dropped too much on the TX. Wish I knew why but that was what I observed.

I keep my coils very light, my 15 x 12 is 15 ounces. I use expandable foam, then sand it down close to the windings, then epoxy on a bottom. So I end up with a light weight sealed coil.

Hey I thought metal detecting was against the law in greece???

Bob

[Geo]

Hi Bob,
I used exactly what the original coil had. I measured it and it is 0.63mm diameter with varnish, so i put the same. My multimeter reads 2.2R but if i will dismount 0.6R who it is the resistance from multimeter terminals, i have 1.6R clear.
Did you checked the phase betwen Tx and Rx coil??? When i move the terminals then the phase change very much. So i will put the pcb ampl near to coil terminals and also i will use some turns to null the phase.... not the amplitube.

At Greece metal detecting was against the law

regards