Wausau pilot. [volume] (Wausau, Wis.) 1896-1940, 1922-12-28
RADIO COLUMN
TELEPHONE THEORY

the ordinary line telephony and the
analogy is very close. 1t consists of
modifying current of electricity ac-
cording to the vibrations of the voice
or of the musical instrument.
The important fact to bear in mind
| is that there is an actual transfer of
electrical energy from the transmit
ting station to the receiving station
both in line telephony and in radio
telephony. In the first case it is
current flowing along the wire con-
| Meeting the two stations; in the sec
ond case it is a continuous flow of
electrostatic, or radio waves between
the stations. This transferred ener-
| gy is modified by the vibrations of the
voice impressed on the microphone,
or mouthpiece, and these modifica-
lions are reproduced at the receiving
end.
Consider a simple wire telephone
| first. An electric current flows
through the sending apparatus and
| through the receiving apparatus. To
modify this current, use is made of
| the fact that voice sets up vibrations
in the air, (Which are translated into
sound by the human earl. These VII
/ VI sttlOilo are ulIGClGu dSdiuSl Il UlSIdl
| diaphram in the mouthpiece of the
telephone. Behind this diaphram and
| bearing against it, is a little metal
j cup filled with fine granules of car
bon lit is characteristic of a group
of carbon granules that it's resistance
to electrical current varies accord
ing to the pressure exerted upon it..
The greater the pressure the lower
the. resistance, and more current can
flow through. When the vibrations of
the voice strike the diaphram they
cause it to vibrate, and these vibra-
tons cause a varying pressure on the
cup of carbon granules, which, in turn
causes variation of the current
flowing through it.
This current also flows through the
| earpiece of the receiver In the re-
ceiver is another metal diaphram sim
liar to that in the mouthpiece. Be-
hind the diaphram is a coil magnet,
with the polepieces permanently mag
netized, really a miniature horse
shoe magnet. The magnetic force of
this magnet exerts a pull on the metal
diaphram. The current from the
tranmitting instrument flows through
the coils of the magnet and any varia-
-tion in this current causes a cores
ponding variation in the strengts. of
the magnet which is pulling on the
diaphram. 1t will be seen that this
variation will cause the diaphram to
! vibrate. The important point to re-
member is Mat the current VARIES
| exactly in accordance with the vibra-
tions of the voice; the pull of the
magnet in the receiver varies exactly
as does the diaphram in the trans
mitter. This in turn causes sound
waves in the air between the dia-
phram and the listening ear which
thus hears the speakers voice repro
duced
i The same thing happens in the case
of radio telephony, except, as has
been stated, that the transfer of en-
ergy from one station to another lis
accomplished by means of radio
waves. While the transmitting sta
ton is sending out waves, there is
current flowing in the circuit of the
receiving station which is electrically
turned to the same frequency. BY
means of apparatus somewhat more
complicated than that of the ordinary
telephone, but using exactly the same
kind of mouthpiece to speak into.
these waves are modified, or varied
in strength, as the current is in the
line telephone wire. At the receiv-
/ ing end the waves are made to vibrate
the diaphram of the receiving phones
| which translate the vibrations into
| sound waves audible 10 the ear.
/ Translating these waves into sound
is the function of the detector, crys-
| tai or tube.
LOOP ANTENNAE
| Every enthusiast who has had diff
Guilty in figuring out a place to put
up an outdoor antenna has thought
more or less of the indoor types, and
doubtless especially of the loop. The
loop antenna has several very def
mite advantages: it takes compare
lively little room, it is very selective,
and it makes the receiving set porta-
Bile. These advantages are largely
outweighed by it's disadvantages, par
| ticularly for receivers in this section.
removed by several hundred miles
from the broadcasting stations.
A loop antenna is made by winding
about 100 feet Of stranded antenna
wire-Litzendraht is very good-on
| a wooden frame five or six feet
|
| with the grid and filament of the first
vacuum tube and shunted by varia-
Bile condenser to permit tuning. The
reason for its great selectivity lies in
a popularity it possesses of picking
up more energy from a transmitting
station lying in the same plane than
from one situated at right angles to
| it.
The handicaps are that the loop
| picks up very little energy in con-
trast to the outdoor antenna which
extends over a larger space. With
the average receiver a loop would not
pick up sufficient energy to operate
the set at all. 1t is possible. by the
use of radio frequency amplification,
to build up the little energy picked
up to point where signals may be
heard. This complexities the set con-
siderably and adds much to the ex-
pense. II would be wise for the anna
teur in this district to wait until
broadcasting stations Of large power
i - AMmHG