The Challis messenger. (Challis, Idaho) 1912-current, 1925-07-08
BY CARLTON e. BUTLER

Associate Member Institute of Radi
Engineers and American Institute o
Electrical Engineers
The tuned radio frequency type o
receiving set employing two stages o
tuned radio-frequency, detecfor. ant
two stages of low ratio audio-fre
quency application. Is going to b.
far and away the most popular broad
casting receiver for the coming sea
son
This is due largely TO the fact that
the development OF the toroid coil. for
both radio-frequency transformers and
coupIers, has now reached the adj
vanced stage, where practically all OF
the bad features Of the tuned radio
frequency receiver are eliminated with
their use.
Toroids are not new. Some Of the
best engineering talent in the United
States and Europe has been working
on them for three or four years. There
always seemed TO be some fault that
could not be overcome. that prevented
their successful application in radio re-
celvers. Generally this consisted of
high losses In the coil Itself. that null
Lifted the good effects gained by the
peculiar shape OF winding. This diff
ficulty has now been overcome In the
new low-ioss doughnut coil designed
By Frank Reichmann, one Of the pio-
neers In the radio engineering field,
by the use of stagger winding.
Shows Lowest Loss.
The staggerwound doughnnt coil
not only has the advantage of an en-
closed magnetic field. which prevents
intercoupling. but 1t also shows the
lowest loss of any coil now on the
market The enclosed field practical
iy eliminates the pickup of stray sig
nails and static by the set itself. These
factors combined mean that the con-
struction OF radio-frequency set with
doughDut coils will produce receiver
that possesses tremendous volume,
amazing selectlyity, and a much bet
ter tone quality than Is usually OBJ
tanned with set Of this type
Until the introduction OF the toroid
coil into the construction of tuned
receivers most all of
the sets were built along the same
lines. with great stress laid on the adj |
OF different methods of max |
Ing the receiver stable In operation by |
oscillation. Some circuits 4
used small balancing condenser be-
tween the grid of one tube and the
plate OF the preceding tube, others
used potentiometer or balancing re-
sistance of some sort in the plate cir
,uit Of, the radlofrequency tubes.
Without stabilizing condensers or
-esistances OF some sort, the average
ive-tube set of this type is practically
iseIess. bringing in distortion and
Whistles when the receiver Is tuned to
he wave length of a station. The sole
JUNCTION of the auxiliary apparatus is
D add sufficient losses. or resistance.
3 the circuit to bring the total amount
energy down below the oscillating
olnt of the receiver
II the same circuit could be so ar. '
lnged that the fields of the coils
'uId be balanced and located In a
amer that no inter-acting of the I
agnetic fields of the coils would take
ace. the volume and range of the re-
liver would increase wonderfully.
ne tone quality would also improve
it'll the absence of the auxiliary APP
ratus- This Is exactly what is done I
the receiver described in this o
ticle, through the use of low-loss y
ughnut coils which have self-con- s
med magnetic fields. and so prevent 9
ter-action Of the coils and circuits 8
Is for this reason that Ii is unneces- n
ry to mount the coils at critical RI
giles to avoid whistiing and bowling. n
practice the coils may be placed q
lie by side without any noticeable a
ects. .,
AS the magnetic field is entirely Ia
'sed. no pickup effect is noticed OF
thout the aerial and ground and no II
'tic or signals will be received ex- to
II on the exact wave to which the te
'etving aerial is tuned. This makes OF
an ideal summer radio receiver. Ia
II can be used near a powerful
station without interfer- 7
e.
Parts Needed.
% build the receiver you will need
following parts: oil.
ntenna coupler. low-loss doughnut nd
coil. NJ,
'w-loss doHghnut radio-frequency OF,
transformers. 90
traIghtIine frequency low-loss vari- Of
able condensers Of OOO5 mid. ca sis
pacity. nm
toll ratio audio-frequency trans SUI
formers. sill
andard tube sockets with five 25- 70:
ohm rheostats, If the c 3O1-A type eel
OF tube is to be used. This combi- ca
nation is recommended. Operation me
can be sjmpiified by using q 25- sot