New-York tribune., 1922-07-23
High Frequency
AmPlification
Working Tips
Hints for Those Wishing TO
Experiment With Cascade
System Radio Frequency
Ampliiication of Signals
System Net Perfect Yet
But Offers Scope for Those
With Time and Means
to Carry Out Experiments

w ~
In nm article last Sunday the adj
vantaeos and drawbacks of ra1io-fre-
auency application were outlined and
The reasons given why mp 90 Tho present
time 10 has not been universally sue
cessful on short wave signals.
There difficulties have been over
come in a different way by the genius
o. r. n. Armstrong through tho inven-
tion Of the super hcterocyne and super
rsccnerativc systems which function
far beyond all expectations on short
waves
There is. however. quite romantic
interest In the use of radi0-frequcncy
nmnlifcation. and its development has
been greatly forced In England, where
the British amateurs are very much
hnmpcrcd by stringent government
regulations. but has only recently been
taken up here.
Tuned system Tedious
II tie experimenter wishes 20 install
tuned circuits between each tube IN
/ the radio-frequcncy section of his re-
ceiver, and then carefully and patiently
tune each stage into resonance with the
/ incoming signal, there Is no problem
/ DO solve in using this foru of amplih-
cation on short waves. This system.
however. is extremely laborlous and,
moreover. very tricky. 10 requires the
most delicate touch and cxper. adjust
ment. which come only after months
% experience.
Since the development Of tho radio
broadcasting system. however the
great growth o. public interest in radio
has given the necessary stimulus to
seek a solution OF the problems in
volved. and number 81 engineers
throughout the country have been
stcadfnstly experimenting with trans
formers which will function success
fully without adjustment with any or
the types % vacuum tubes now on tho
market.
Some of these have been brought
down 90 o fairly fine point OF efficiency,
but they still require that the operator
shall observe certain fundamental
facts In order that successful results
cap be achieved.
In all radio-frequeney ampiifying
circuits 10 Is absolutely necessary that
a potentiometer should be used across
the A battery which lights the nlaments
Of the tubes. This stabilizes the entire
circuit and enables the operator 20 put
the proper amount OF negative bias on
the grids of the radio-frcqucncy tubes.
This function will be further assisted
by placing a bypass condenser Of AZ
least .u0l MID capacity across tho grid
lead and negative side OF the poten-
tiometcr. One potentiomctcr and by
pass condenser can be used for all
OF the radio-frcquency amplifying
stages used IN the set.
While it is possible 20 use a rcgen-
eratiye circuit In connection with
radio-frequency amplifcation. this is
not advised because 10 only adds 10 the
difficulty Of adjusting and balancing
the receiver. 10 must not be forgot
ten that on short waves the phenome-
non OF regeneration is actually present
IN radio-frequeney application.
Beware Of "All Wave" Transformers
This Is due 10 the capacity effect
which exists in the grid and plate leads
in the vacuum tube and the winding
Of the transformers. In fact. By care
fully adjusting the potentiometer The
entire set can be put into an oscillat-
ing condition just in the same manner
a. regenerative set oscillatcs.
The radio ian who is intent In ex-
per.menting with radio-frequency am
plifcation is warned against the radio
q frequency transformers which claim %
cover too wide p band Of wave lengths
IL simply cannot be done.
The following are a few hints Of GER
tain fundamentals that should be OBJ
served: First Of all, radio frequency
amplihcation IN short waves Is Tor the
. experimental who has time and means
+ 90 work with H. Only hard tubes can
be used in connection with 10. These
tubes, Of course, are not critical as 70
plate voltage, and at least IS volts
. should be used IN the plate circuits.
The potentiometer should be varied
very carefully until the best signal
+ results are obtained. The more the
/ potentIomctcr is varied toward the
/ positive side the more stable tho set
f will operate, but the signals will be
weaker. The more negative bias nut
on the rrids by the potcntiomcter the
stronger the signals will be until the
osciilating point is reached. The set
shoua be- kept below this point.