Arizona state miner., 1925-07-11
BY CARLTON z. BUTLER

BY CARLTON {. BUTLER
Associate Member Institute Of Radio
Engineers and American Institute Of
Electrical Engineers.
The tuned radio frequency type of
receiving set employing two stages of
tuned radiO-frequency, detectOr, and
two stages Of low ratio audio-fre
quency amplifcation, is going to be
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-freGuency transformers and
cOuplers, has now reached the ad-
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-
Ceivers. Generally this consisted of
high losses in the coil itself, that null
lifted the coed effects gained by the
peculiar shape of winding. This diff
ficulty has now been overcome in the
new low-loss doUghnut coil designed
by Frank Reichmann, one of the pio-
neers in the radio engineering fed,
by the use of stagger winding.
Shows Lowest Loss.
The stagger-wOund doughnut coil
not only has the advantage of an en-
closed magnetic field, which prevents
intercoupling, but it also shows the
lowest loss of any coil now on the
market The enclosed field practical
ly 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
doughnut coils will produce a receiver
that possesses tremendous volume,
amazing selectivity, and a much bet
ter tone quality than is usually OBJ
tanned with a set Of this type.
Until the Introduction of the torOid
coil into the construction of tuned
radio-frequency receivers, most ali of
the sets were built along the same
lines, with great stress laid on the ad-
vantage Of different methods of MAX
ing the receiver stable in operation. by
preventing oscillation. Some circuits
used small balancing condenser be-
tween the grid of one tube and the
plate of the preceding tube, others
used a pOtentiOmeter or balancing re-
sistance of some sort in the plate cir
cult Of the radiO-frequency tubes.
Without stabilizing condensers or
reSistances of some sort, the average
f1ve-tube set Of this type is practically
useless, bringing III distortion and
whistles when the receiver is tuned to
the wave length Of a station. The sole
function of the auxiliary apparatus is
to add sufficient losses, or resistance,
to the circuit to bring the total amount
of energy down below the oscillating
point of the receiver.
If the same circuit could be so ar
ranged that the fields Of the coils
could be balanced and located in a
manner that no inter-acting of the
magnetic fields Of the coils would take
place, the volume and range of the re-
ceiver would increase wonderfully.
The tone quality would also improve
with the absence of the auxiliary Qp-
paratus. This is exactly what is done
in the receiver described in this
article, through the use of Iow-loss
dOughnut coils which have self-con-
tanned magnetic fields, and so prevent
fnter-actiOn of the coils and circuits.
1t is for this reason that it is unneces-
sary to mount the coils at critical
angles to avoid whistling and bowling.
In practice the coils may be placed
side by side without any noticeable
effects.
AS the magnetic field is entirely
closed, no pickup effect is noticed
without the aerial and ground and no
static or signals will be received ex-
cept on the exact wave to which the
receiving aerial is tuned This makes
it an ideal summer radio receiver,
and 1t can be used near a powerful
brOadcasting station without interfer-
ence
Parts Needed.
To build the receiver you will need
the following parts: