ter you have completed this series of experiments you will be
something of an adept at radio and are in a position to plan your final
set. For this set you will need to purchase certain parts complete from
reputable dealers because many of the circuits which I have described
are patented and should not be used except as rights to use are obtained
by the purchase of licensed apparatus which embodies the patented
circuits. Knowing how radio receivers operate and why, you are now in a
good condition to discuss with dealers the relative merits and costs of
receiving sets.

[Illustration: Fig 119]

Before you actually buy a completed set you may want to increase the
range of frequency over which you are carrying out your experiments. To
receive at longer wave-lengths you will need to increase the inductance
of your antenna so that it will be tuned to a lower frequency. This is
usually called "loading" and can be done by inserting a coil in the
antenna. To obtain smaller wave-lengths decrease the effective capacity
of the antenna circuit by putting another condenser in series with the
antenna. Usually, therefore, one connects into his antenna circuit both
a condenser and a loading coil. By using a variable condenser the
effective capacity of the antenna system may be easily changed. The
result is that this series condenser method becomes the easiest method
of tuning and the slide wire tuner is not needed. Fig. 119 shows the
circuit.

For quite a range of wave-lengths we may use the same loading coil and
tune the antenna circuit entirely by this series condenser. For some
other range of wave-lengths we shall then need a different loading coil.
In a well-designed set the wave-length ranges overlap. The calculation
of the size of loading coil is quite easy but requires more arithmetic
than I care to impose on you at present. I shall therefore merely give
you illustrations based on the assumption that your antenna has a
capacity of 0.0001 or of 0.0002 mf. and that the condensers which you
have bought are 0.0005 and 0.001 for their maxima.

In Table I there is given, for each of several values of the inductance
of the primary coil, the shortest and the longest wave-lengths which you
can expect to receive. The table is in two parts, the first for an
antenna of capacity 0.0001 mf. and the second for one of 0.0002 mf.
Yours will be somewhere between these two limits. The shortest
wave-length depends upon the antenna and not upon