Big foot style for a PI

[green]

I tried the coils in reply #27. Without shielding and making rigid it's hard to get good numbers. I didn't see anything yet that would make me want to make a finished coil with them. The double race track did look it might discriminate. Maybe I'll try one with the two race track coils. I think I like the big foot style better since it cancels EF,reduces noise and ground. Think I'll try a larger double round next. Charted a 4 and 6 inch round mono coil with the gold nuggets to see if a certain size might be better for nugget detection. The spiderweb coils wind a lower inductance than I expected so the signal strength would be a little higher with more turns. 4 inch(220uh) 6 inch(230uh). Don't know what uvolt level can expect to detect on the ground. If 10uvolts the 6 inch coil might be a good. If 1uvolt, should try a larger coil. 1 amp peak current, higher current might help.

[6666]

Green is it possible to add a few more turns on that 4inch and retest ?

[6666]

Here is one way to make bigfoot, easily adapted for 3:1 PI, and former made from cardboard made in few minutes.

[green]

Green is it possible to add a few more turns on that 4inch and retest ?

No, it's potted. When I do another one I will try to get 300uh+. Looking at the chart in reply#31 I would have to almost double the turns to gain .5 inch in detection distance. 1000uh coil. I am curious what a few turns would do. After looking at it I think not much. Another thought. The added turns would increase the diameter with the spiderweb coil, maybe more change than I was thinking>

[6666]

No, it's potted. When I do another one I will try to get 300uh+. Looking at the chart in reply#31 I would have to almost double the turns to gain .5 inch in detection distance. 1000uh coil. I am curious what a few turns would do. After looking at it I think not much. Another thought. The added turns would increase the diameter with the spiderweb coil, maybe more change than I was thinking>

Thanks.

[Chet]

Here is one way to make bigfoot, easily adapted for 3:1 PI, and former made from cardboard made in few minutes.

Hi 6666

Are the numbers 48 - 0.35 and 85 - 0.22 the number of turns and the size of wire?

Thank you,
Chet

[6666]

Hi Chet disregard the wire information the text on the picture is of a bigfoot for a whites S2-S3,
the former could be used to make a 3:1 PI bigfoot, just wind the tx and wind the RX 8.
I guess the word bigfoot has become a bit generic.
Its just the shape I was showing, a bigfoot is a large TX and the smaller RX wound or twisted in an 8 shape
and this former makes it easy to make.

ALA fig #16
http://www.geotech1.com/pages/metdet/info/coils.pdf

[green]

Hi Chet disregard the wire information the text on the picture is of a bigfoot for a whites S2-S3,
the former could be used to make a 3:1 PI bigfoot, just wind the tx and wind the RX 8.
I guess the word bigfoot has become a bit generic.
Its just the shape I was showing, a bigfoot is a large TX and the smaller RX wound or twisted in an 8 shape
and this former makes it easy to make.

ALA fig #16
http://www.geotech1.com/pages/metdet/info/coils.pdf

Thanks for the picture of the big foot coil. It would make it easier to make. I've been using magnet wire and for me the bundle wind doesn't allow fast enough sampling. I started calling it a big foot style because somewhere in the forum I saw to make a figure 8 coil, make a round and twist it into a figure 8. No mention of a Tx and Rx.

[Chet]

Hi Chet disregard the wire information the text on the picture is of a bigfoot for a whites S2-S3,
the former could be used to make a 3:1 PI bigfoot, just wind the tx and wind the RX 8.
I guess the word bigfoot has become a bit generic.
Its just the shape I was showing, a bigfoot is a large TX and the smaller RX wound or twisted in an 8 shape
and this former makes it easy to make.

ALA fig #16
http://www.geotech1.com/pages/metdet/info/coils.pdf

Hi 6666


Thank you for the reply and Carl's paper on coils. It has been some time since I had read it. It has some really good information for me to mull over.


Best Regards,
Chet

[Chet]

Possible advantages of the DODd or Double DD coil arrangement.


1. The two receiver coils wired in opposite polarities should cancel most of the external interference since it is received by the two coils from distance noise sources equally.


2. The two receiver coils wired in opposite polarities should cancel/balance most of the ground signals that are generated directly under the two coils.


3. The separately nulling of each receiver coil over opposite sides of the transmit coil will prevent direct air transformer coupling of the high voltage flyback pulse into the receiver coils. Little or no damping/loading should be needed across the two separately nulled receiver coils since they will not be carrying high voltage or high current.


4. The residual signals from the balanced and nulled coils wired in opposite polarities should be very low level. This should greatly reduce or remove opamp saturation time and should allow higher opamp gain to be used and earlier target sampling time for small gold should be possible.


5. The direct air transformer decoupling of the nulled receiver coils from the transmitter coil should allow slower coils with many more turns to be used. Basket or Spider coils should not be necessary for the nulled receiver coils. Standard or bunch winding methods should work fine for the two receiver coils. Adding more turns will allow more signal strength to be developed from the weak eddy currents circulating in the detected target. The transmit coil still needs to be a fast coil to provide the greatest flyback/target energy.


6. The field pattern under this configuration will be two sensitive detection points were the coils overlap for targets at shallow depths. A double beep should be heard for shallow targets. At deeper depths the coil patterns should converge similar to a conventional Double D coil except balanced better from side to side. Added receive turns should provide performance similar to a Mono coil.


7. Figure 8 coil considerations: The separately nulling of each receiver coil over the transmit coil may be better than the Figure 8 coil configuration. The Figure 8 has direct air transformer coupling of the high voltage spikes into the two halves of the receiver coil. This may require more precise nulling to cancel the high voltage spikes. The achieved null may be more sensitive to temperature changes and the coil bumping into surface irregularities. The direct air transformer coupling requires fast wound receiver coils and heavy damping resistors. Little or no coil gain is allowed by the limited number of turns in the faster receiver coils.

Best regards,
Chet


http://www.geotech1.com/forums/attac...0&d=1423900787

[green]

Made another 4 inch coil. The first had 30T, the second 36T. still not enough for 300uh. The 4 and 6 inch are ID. Got a a higher increase in signal than I expected. Have to use a higher turn increase than I've been using for the spiderweb coils. Hi Chet, thanks for the reply. Some things to think about and try.

[6666]

Green is this calc any help ? to update the calculated info make changes then click any other box
did a rough clac on 4 inch , it gave about 39 turns for 300uH, but make it 40
are you winding these coils on tooth picks ?
http://www.deepfriedneon.com/tesla_f_calcspiral.html

[green]

Green is this calc any help ? to update the calculated info make changes then click any other box
did a rough clac on 4 inch , it gave about 39 turns for 300uH, but make it 40
are you winding these coils on tooth picks ?
http://www.deepfriedneon.com/tesla_f_calcspiral.html

Thanks. Think 40 turns would be about right. Yes they are wound on toothpicks.

[Qiaozhi]

Made another 4 inch coil. The first had 30T, the second 36T. still not enough for 300uh. The 4 and 6 inch are ID. Got a a higher increase in signal than I expected. Have to use a higher turn increase than I've been using for the spiderweb coils. Hi Chet, thanks for the reply. Some things to think about and try.

If this is a flat spiral coil, then 36 turns will not be enough for 300uH. The Coil Calculator estimates 36 turns will give 310uH, but that is for a tightly bound circular coil with 0.56mm wire.

[6666]

Yes they are wound on toothpicks.

Are you useing foam to stick in the tooth picks ?