Evening star., 1922-05-19
Expert Advice on Radio
10. 5.-Working of Crystal Detectors.

is adjusted and the cat whisker is
moved about over the crystal until
the most sensitive spot is found and
the crystals come clear and loud.
A simple Detector.
But defector which will work may
be made much simpler, for all that
is necessary is some sort of a cp,,-
cat whisker on one side and the
I wires and the crystal on the other.
| and a small coiled wire supported
| by a bit Of brass and a clip or clamp
| serve. However, such makeshifts are
never satisfactory, for the efficiency
Of a detector depends largely upon
the variety of motions which may De
obtained by means of the adjustable
arm carrying the cat whisker and
the upright which holds 1t.
Moreover, the affair must be rigid
and perfect contact must be made
between the crystal and wires. In
order to accomplish this the crystal
of fusible metal or composition OF
mercury and tin, but far better
method is to wrap the lower part of
the crystal in tinfoil and then clamp
It in the cup, if necessary. packing
the cup and crystal. The arm which
holds the cat whisker should be pro-
Vided with an insulated tip or knob
to prevent ones fingers from carry
ing off portion of the electrical cur
rents and to avoid the necessity of
touching or handling the crystal: the
cup should also be adjustable to va
rious positions. II crystal is touched
with the fingers 1t will soon lose its
from the skin. This may be removed
and the sensitiveness restored by
washing in alcohol or ether
But even the best crystal detectors
have their faults and their limitations.
In the first place. considerable time
and trouble must be used in adjust
ing the contacts and, even when this
is done, the contact may be altered
or broken by the slightest jar or vi
bration. This adjusting must be done
as it next to impossible to And the
exact spot on the crystal twice the
results are never twice alike More
over, a crystal detector set Is very
limited in the distance at which it
can receive music and messages, the
dinary conditions being about twenty
five miles, although loud spark sig
nails. may be heard for many times
that distance.
Faults of Crystal Set.
Another fault which many persons
unfamiliar with radio do not realize
and which causes much disappoint-
satisfactorily amplif1ed or it's sound
niagnified SO that the sounds coming
! through it are audible without using
head telephone receivers.
Although by attaching a megap phone
or photograph horn to the receivers
! tie sounds may be increased some
what, they cannot be built up until
I they may be heard all over a room or
! hall.
But despite all this. thousands of
| crystal sets are in daily use and are
giving immense satisfaction and in
! calculable pleasure and enjoyment to
| their users.
If near a breadcasting station they
! give good reception and. as they are
very simple cheap and require no bat
(, teries, they will always be favorites
! with many people. Moreover, they
| are the best sets for beginners, as
with them one may learn the hrst
principles of radio telephony. while
any one with the least mechanical
| ability may make a set which will do
as good work as any ready made
set costing several times as much.
Copyright. 1927
| ACKNOWLEDGEMENTS Of Head Phones.")