n the
primary circuit. A certain amount you will need to couple the antenna
and the secondary circuit. The coil which you wound at the beginning of
your experiments will do well for that. Anything more in the way of
inductance, which the antenna circuit requires to give a desired
wave-length, you may consider as loading. In Table II are some data as
to winding coils on straight cores to obtain various values of
inductance. Your 26 s. s. c. wire will wind about 54 turns to the inch.
I have assumed that you will have this number of turns per inch on your
coils and calculated the inductance which you should get for various
numbers of total turns. The first part of the table is for a core of 3.5
inches in diameter and the second part for one of 5 inches. The first
column gives the inductance in mil-henries. The second gives number of
turns. The third and fourth are merely for convenience and give the
approximate length in inches of the coil and the approximate total
length of wire which is required to wind it. I have allowed for bringing
out taps. In other words 550 feet of the wire will wind a coil of 10.2
inches with an inductance of 8.00 mil-henries, and permit you to bring
out taps at all the lower values of inductance which are given in the
table.

Table II

Part 1. (For a core of 3.5 in. diam.)

Inductance in Number Length Feet of wire
mil-henries. of turns. in inches. required.
0.10 25 0.46 25
0.16 34 0.63 36
0.20 39 0.72 42
0.25 44 0.81 49
0.40 58 1.07 63
0.60 75 1.38 80
0.80 92 1.70 100
0.85 96 1.78 104
1.00 108 2.00 118
1.20 123 2.28 133
1.80 164 3.03 176
2.00 180 3.33 190
3.00 242 4.48 250
4.00 304 5.62 310
5.00