Need help on making VLF DD coil

[robbor]

For a whites goldmaster VLF 50K hertz. I wanted to make it on a piece of flat fiberglass and would like the coil to be 16-18" DD. I lost all the info I used to have.
As I recall I need a Tx, Rx, and nulling or bucking coil. Is the bucking coil part of the Tx or Rx?

I need info on wire size and type?

Number of turns? How do I figure?

Sources for a 3/16" sheet of fiberglass? Will ant plastics store carry it? I had trouble hinding some a long time back.

Im planning on epoxying the coils down with no cover. I saw nickle spray listed but could use more info on shielding.

Any new info on large empty housings.

Lastly I dont have use of a Oscilliscope, I should be able to use 2 DMM's correct?

Thank you all, Rob Olling

[robbor]

Wow, nobody around huh? It just dawned on me that I needed to measure my coils inductance and I have to dig out the inductance ciucuit adapter I made.
Any idea of the formula for figuring the number of turns??? Thanks

[Reg]

Hi Robbor,

I do not have the specific information about the transmit or receive coils for the Whites, so I can't help you there. Hopefully, there is some information posted on this site that will help you.

Now, as for coil housings, you might look at Bill Hay's website, www.hayselectronics.com and see if one of his housings would work. He does have one large DD housing that might be what you would want.

Also, you might contact Charles (NY) and ask him what size coil form he makes that might work also. Just check for more information about Charles on this site.

There are a couple of different sites that will help you with building coils. I personally use the following: http://my.athenet.net/~multiplx/cgi-bin/airind.main.cgi

You can change to inches for your measurements if you so desire. Once the calculation is done, I use the .1% value and have found it to be quite accurate for my purposes. However, I normally build PI coils.

Hope this helps some.

Reg

[Geo]

Hi Robbor,

Now, as for coil housings, you might look at Bill Hay's website, www.hayselectronics.com and see if one of his housings would work. He does have one large DD housing that might be what you would want.

Reg

Hi Reg. As i see at Hays page the housings for large coils are open, so how to make a good shielding? Who other is the difference between housing for PI coil and for VLF coil?
Regards

[Reg]

Hi Geo,

The most common form of shielding used on VLF coils is the use of conductive paint. Normally, this is a carbon or graphite based paint of some type.

Now, when using an open coil form such as those made by Bill Hays or Charles of NY, you can simply paint the inside of the housings with the appropriate type of shielding paint. I personally paint the entire inside plus the inside sides but do tape off the areas where the two halves will connect so they can be sealed properly. A ground connection is then either glued on to the painted surface with conductive glue or taped to the painted surface with a good quality tape. I personally just tape the connection by stripping about 2 inches of insulation off two pieces and taping the bare amount of each piece to either the top or bottom half of the coil form. The other end of these two wires are then soldered to the ground connection of the either the transmit or the receive coax ground.

There are several types of paint that have been used and mentioned on other threads on this forum. Here is a link to some info. http://thunting.com/geotech/forums/s...ad.php?t=11164

Now, I have recently tried using a graphite lubricating paint for shielding and it appeared to work just fine. I used a paint I got from P&R Supply. Here is a link to that site.
http://pandrsupply.com/SearchResult.aspx?CategoryID=24

A single coat of paint has a resistance of about 6K ohms which is well within the range recommended by George Payne.

Hope this helps.

Reg

[Geo]

Hi Geo,


Now, when using an open coil form such as those made by Bill Hays....

Hope this helps.

Reg

Hi Reg. Thank you . But at Bill Hays page i read "11" O.D. Open search coil housing with liquid tight pigtail, for P.I. Detectors".
What is this who make the coil house suitable for PI only ??
Regards

[Reg]

Hi Geo,

The coil housings made by Bill Hays can be used for any type of detector design, not just PI's. It just happens that more and more people are building PI's now. So, it was listed that way.

The center width of the coil housing was built wider than necessary so one could experiment with the overlap. This overlap is very critical on a TR or a VLF type detector but not as critical on a PI. On a PI, one doesn't have to be as exact in "nulling" the coil. As such, one can have a wider center overlap area. This helps a little when trying to detect real small gold.

Reg

[Geo]

Thanks Reg

Thanks
Regards