New-York tribune., 1922-07-09

Amplification
Is Discussed
Advantages Radio Frcquen-
cy AmPlification Pointed
Out and Its Drawbacks
Are Considered i'm Detail
Capacity in Vacuum Tube
Important Factor on Short
Wave Work Because of
Extra High Frequencies

Within the last two months the sub
ject Of radio-frequeney amplihcation
has been considered by an eyer-grow-
ing number Of radio fans. This in
creased interest has been caused by the
new types Of apparatus that have been
placed on the market and the somewhat
vague discussions Of the principle in
volved. Under the circumstances,
therefore. propose this week 70 out
line what the advantages OF radio
frequency ampliheation are, and what
arc the drawbacks 10 its application.
In the first place. as is we'll known
by this time, there are two types Of
amplifcation. First, radio amplifea-
tion; and second, audio ampliheation.
The first consists Of amplifying very
high frequency oscillating electrical
currents. which act as carrier waves In
radio communication. The second ap-
plies 20 the voice currents that are
carried along upon oscillating currents
For all practical purposes no more
than two stages Of sudio-freqGeney
modification can be successfully used
because OF the fact that this type Of
amplifcation, dealing with audible
sounds, amplihes all Of the inherent
noises existing in the apparatus ITSELF
and when more than two stages are
attempted, these extraneous noises be-
come Objectionable and seriously in
terfere with the quality Of the repro
duced speech and music.
VIII Build Up Signals
The advantages Of radio-frequency
Amplhcation are the following; With
this system il is possible, by the use
Of multi-stage amplihers, to build up
high-frequency oscillating currents, no
matter how weak they may be before
these currents are passed through the
detector tube for reetiheation. The de-
tector tube itself cannot operate on
electrical oscillations that are below a
certain value in strength. Under the
circumstances, therefore, II is quite
possible 70 receive over vast distances
by means OF radio-frequency amplih-
cation, through the simple expedient OF
building up weak currents received by
the aerial until they are strong enough
TO be passed through the detector
There are several drawbacks 20 this
system when we deal with short-wave
reception. These drawbacks do not AZ
feet long-wave radio, and II is for that
reason that we know just what the ad-
vantages Of radio-frequency amplihca-
ton really are. When we come to
short waves. however, an entirely diff
ferent situation exists. This IS due 20
| the fact that on short waves the oseil-
+ lnting currents alternate with terrihc
freouencies. ranging anywhere from
100000 cycles q second upward. AZ
/ this frequency capacity effect becomes
very pronounced, and IS one OF the
main causes Of trouble In applying am
plihcation on short waves.
Vacuum Tube Acts as Condenser
Take. for instance. the vacuum tube.
The wires connecting the grid and
plate elements in the tube itself are
insulated from each other through the
glass holder az the bottom Of the tube.
Glass is a material that has very high
dielectric constant, and consequently
/ there is a very definite amount OF ca
pacitv in the vacuum tube itself. which
/ varies considerably in different vacuum
tubes. despite the fact that they are
all manufactured on a quantity pro-
/ duction basis.
From this. IL will be readily seen
/ that even where we get radio-fre-
quency transformer, which is excel
/ lently designed, il will operate better
with one tube than IL will with an
other, and as a result Of this extreme
care must be taken in controlling a
set composed OF radio-frequency am
plhcation.
Z on the short waves, theoretically
speaking, il would be necessary TO tune
each stage OF radio-frequency amplih'
cation into resonance with the incom'
ing wave. In other words, there should
/ be A circuit OF inductance and capacity
between each radio-frequency amplify'
ing vacuum tube, so arranged that II
can be varied and put into resonance
with the signals II is desired TO re-
ceiye.
In a subsequent article I intend tc
90 into further detail about this inter
esting phase Of radio reception, giving
some particular pointers with regard
10 its use for the guidance Of those
fans who have the time and opportu'
nifty 10 carry out experiments with IL.