NOTES

1.It may be possible to place the 700 turns in four layers. However, as subsequent layers are added it becomes more difficult to maintain close spacing. Most likely it will take five layers. Actual turns count is not critical. If you have 700 turns before reaching the end of the bottle, continue winding to complete the final layer.

2. Coil constructed as shown will provide an inductance of about 10 millihenries. An approximate formula (neglects a small multilayer correction factor of about negative 5 percent) for calculating the inductance is:

                            L=(r²n²)/(10(r+l))

where: r=one half the bottle diameter in inches   n= number of turns  l= coil length (inches)

3. A coil tuning capacitor for two sensor bottles as shown, connected in series, will be about 0.25 microfarads.

4. After winding, fill the bottle with a "proton rich" fluid. Distilled water, kerosene, methanol have been used. Common isopropyl alcohol will work.

5. Spice bottles are not designed to hold liquids. The lids may have a paper inner liner that should be discarded. If needed to stop leaking, try making a gasket from bicycle inner tube or similar material.

In my backyard environment, for the best signal to noise ratio, I found that two identical coils were useful. These were connected in series and oriented for minimizing the level of power line harmonics. An orientation with the coil axes in line and electrically series opposing provided a degree of cancellation of common-mode power line noise pick up.