New-York tribune. [volume] (New York [N.Y.]) 1866-1924, 1922-08-13
Engineer Discusses Methods
by Which Distant Signals
Can Be Increased So That
Detecfor Will Function
Regeneration and Cascade
Are the Two Means; He Says
Efficient Transformers
Are. Available for Use
By B. Bradbury
Radio En0fneer G.. L.

When receiving very weak radio |
signals from distant stations it is
found that application of the audible |
tones as heard in the telephone re-
ceivers is of little or no benefit, since |
the strength of tube noises, static, or
)tker interference is increased in |
greater proportion than the signal
strength. Under these conditions the
most satisfactory signals viii often be !
obtained directly in the output from |
he detector without additional ampli-
ication, since the signal, although |
weaker, is much more distinct in the |
telephones than when amplified.
To secure louder signal with good |
quality, or to receive more distant sta |
tions, some other means of amplifica
tion must therefore be adopted. This |
other means is the amplifcation of the
signal frequency as it is received on
the antenna, before its reaches the
with a decrease in the energy re-
ceived, so that if we can increase this
energy before it reaches thaA detector
better efficiency will result,
One of the most common meth DDS
of obtaining radio frequency amplili-
cation is the utilization of regenera-
ton in the detector tube itself. Since
perfect rectification does not take
place IN the detector, certain amount
of radio frequency flows in its plate
circuit, so that by coupling this circuit
back to the grid or input of the tube,
the amplified signal frequency is made
to re-energize the grid and cause a
still greater change in the variations
of the plate current.
Two Methods of Regeneration
Regeneration may be accomplished
by means of capacitive or inductive
| back coupling, or combination of
both. Short-wave receivers are often
constructed with variable inductance
In the plate circuit, which can be
tuned 80 the signal frequency Suf-
ficlent voltage is thus built up across
the plate circuit to feed a small amount
of energy back to the grid through
the capacity between the grid and
plate within the tube itself. For long
wave lengths the tube capacity becomes
insufficient for good regeneration, and |
some additional means must be pro-
vided, such as inductive coupling be-
tween the grid and plate circuits. This
| consists of placing & coil of wire in
the plate circuit and coupling it back
to the input or grid circuit of the tube
Another method Of obtaining radio
| frequency amplihcation is to use one
or more vacuum tubes ahead of the |
| detector tube with suitable coupling
between them to transfer the energy
from one tube to the next at the signal
frequency. AS with audio frequency,
the coupling between tubes may be
resistances, inductances or transform
ers, but they cannot, Of course, have
the VHIuog q for anSia
quency coupling. Just as it is some
what Of problem to build trans
| former which will transfer voltages
uniformly over wide range of audo
tones, 80 is it difficult to build trans
formers which will operate we'll over
broad range of radio frequencies
Since there is such a great difference
in the frequeneies of the various wave
lengths in use, 1t is necessary to change
transformers to receive all of the Diff
ferent classes Of communication.
Back Coupling Oscillation
At short wave lengths amplifcation
is accompanied by more or less regen-
GRAFTON through the grid and plate
capacities Of the tubes, as mentioned
in connection with detector regenera-
coupling Is sufficient to cause oscilla-
tions In the amplifer tubes, and to
overcome this tendency some special
means must be provided, such as an
| adjustable grid voltage which can be
made positive and thus secure stable |
operation.
Resistance coupling has the disad-
vantage Of letting through tube noises
| and other audible frequencies, SO that
it is sometimes difficult to use it with
| advantage in addition to the regular
audio stages following the detector. 1t
mas, however, the advantage of being
effective over wide range of freouen- |
cles and will therefore give uniform
amplitication over broader wave length |
band than inductive coupling.
Several Stages Can Be Used
Inductlve or transformer coupling. as |
previously mentioned, will transfer en-
ergy at limited range of freouencies.
For this reason inductances and trans |
formers made for use In the amplifca
ton Of the high frequencies of short |
wave lengths will not transfer tube
noises or disturbances which are limit |
ed to audible 9requencies. Several
stages may thus be connected In cas-
cade TO amplify the signal without
distortion before 1t reaches the detec- !
added as desired to obtain whatever
volume OF sound is found necessary.
Three or four states Of radio fire.
quency. application make it possible to |
use loop antenna with good results. |
For receiving broadcast signals loop
made by winding ten turns Of wire,
spaced three-eighths of an inch apart,
on frame three feet square, Is about |
the right size to use. There are now
transformers on the market which will
give good signals in conjunction with
a loop, and the construction of such a |
set Will produce very gratifying re.