Evening star. [volume] (Washington, D.C.) 1854-1972, 1923-11-18
RADIO GOSSIP AND NEWS

ton was in operation. However, al
present this Is the case only with GER
tam stations, and because 1t Is
matter of difficulty to maintain ex-
also because this Is of great I'M
portance, the bureau has been collect
ing some interesting data on the sub
1ect. AS a result of these measure
ments. 1T Is possible to give out IN
formation, from time to time, on sta
lions which maintain n sufficiency
accuracy to be useful as frequency
standards. Several stations. which
use special means for maintaining
constant frequency, have very nearly
attained the goal of remaining within
two kilocycles of the assigned fire.
quency, as recommended by the
second national radio conference
Transmissions from seven stations
may be used in standardizing APP
paratus, by the methods given in
bureau of standards letter circular 50.
Radio signals of. standard frequency
and their utilization"
Crystal Set Interesting.
The crystal detectors are the
simplest of all radio detectors used
at the present time. Unlike the
vacuum tube, it does not, in most
cases, require a local battery for Its
operation. and the initial cost is
practically the last cost. The crystals
are inexpensive. easily obtained, and
can easily be replaced with little
trouble. should the old ones become
imperative or dirty. Their disad-
yantages are threefold. They are
critical to adjust; they are not as
sensitive vacuum tubes. and.
thirdly, they cannot be made to
fo, st1 -
continuous wave signals.
Essentially the crystal detector,
sometimes known as a mineral de-
tector, consists of a crystal upon
which a contact of copper or steel
wire is made. 1t Is this contact that
inasmuch as this contact Is a rectifier
of the radio frequency currents.
Crystal detectors consist in the COM
mercial form of base. a metal cup
in which the crystal Is mounted, a
wire contact, known as the cat
whisker, a holder for the wire, and
binding posts for convenient con-
nectfons. The crystals used most
commonly at the present are: Galena,
radiocite, silicon, carborundum, and
bornite. in the order named. The
hrst two require a light copper or
phosphor bronze contact, while the
rest work better with a heavier steel,
needle point contact.
The radio frequency energy in the
receiving set. before II reaches the
detector. is weak alternating cur
rent. similar to the house lighting
current. but where the house lighting
current alternates it's polarity 40
times per second. this radio frequency
current alternates its polarity 1,O00.-
oo0 times Tor more) per second,
namely. where the house lighting
current has a frequency of sixty
cycles. the radio frequency currents
nave a frequency of 100000 cycles per
second.
A curren6of this frequency cannot
be heard for several reasons. When
one or the groups of alterations acts
on the telephone receiver 1t causes
no motion of the diaphragm, because
each variation of the current in one
direction is followed by the current
Moving In the opposite direction. so
that the telephone diaphragm has not
enough time to start moving and
resulting effect Is no motion at all.
something that allows the current
to now through It in one direction
and stops the current from flowing
In the opposite direction is needed in
the circuit, to actuate the diaphragm.
The detector does this
AT the contact between the crystal
and the cat whisker. current can flow
through In one direction, but not in
the other. Such oscillations pass
lut utleCtOT, winch sup
presses half of these oscillations.
This current is still vibrating much
too fast for the telephone diaphragm
to follow. but the successive impulses
of current flow through the telephone
receiver, and the impulses in any one
group are all in the same direction,
SO that their effects add and produce
motion OF the diaphragm. The mo-
ton of this diaphragm causes sound
waves which vary in pitch and in
m he \