Inductance Reading ?

[thedigger]

Hi Lads
One thing that I have noticed over the years that those building DD coils are dropping the TX down from about 300uh to about 240 and on the RX from above 500uh to some where about 400uh.
Does any one have any thoughts on why this could be so.

[WM6]

Hi Lads
One thing that I have noticed over the years that those building DD coils are dropping the TX down from about 300uh to about 240 and on the RX from above 500uh to some where about 400uh.
Does any one have any thoughts on why this could be so.

Mean between starting non tighten coil windings and final tighten and glued coil?

[thedigger]

WM6
They could still space the wires,but could lift the inductance by putting a extra turn or two,which on the RX would not be much.

[Reg]

Hi Digger,

The only coils I know of that this is happening on are the ML PI coils. One idea of reducing the transmit windings is to increase the coil current. This is a common method used on VLF's and should work on PI coils also. This technique could lead to a little increase in depth. So, my guess is they were experimenting with this idea in hopes of gaining a slight amount of depth increase.

Now, what I don't know is if it really provided any real benefit that could be readily measured. When it comes to PI's, there so many variables that it is really hard to determine just why something happens.

Keep in mind the DD coil is like an air transformer, so by increasing the RX winding inductance greater than the transmit inductance, you should get a step up in signal somewhat like what happens on a regular transformer. Since it is a very low value signal, this inductance increase can be done without requiring an increase in delay because there isn't much signal to decay to begin with. If one were to try to increase the transmit inductance significantly, then the time to decay would increase thus not allowing for sampling at the shorter times. Also, the ML is extremely sensitive to the inductance that will work. Fortunately, it appears, this condition is eased when working with DD coils.

Reg