Shoshone journal. [volume] (Shoshone, Idaho) 1884-1931, 1924-01-11


: simplicity Of operation In a multi
@ stage radio frequency amplifier hav,
S caused many a broadcast enthusiasts
no end OF trouble, according to r. +
0 Humphreys In the New York Evening
A Mail. OF course the greatest selectiv-
ity obtainable in an ampIiier of this
type, consisting of two or more stages.
is afforded by the use of tuned or semi
tuned transformers as interstage COUP
lings. On the other hand, this method
or linking up the successive tubes of
radio frequency amplifier involves
such a multiplicity of tuning controls
and Is generally so selective that II
lacks all operating hexibility. and
therefore is of no practical value
either to the novice or to the listener
IN who abhors knob winding sets" Gas
they have appropriately been called.
Permanent Tuning.
Primary and secondary windings of
tuned radio frequency transformer
are commonly shunted by small voria- |
bic condensers of equal capacity.
which must be progressively rotated in
unison to the left or right in the
course OF hunting a station. It is
necessary that the primary and sec
ondary circuits Of this transformer
always be in tune or very nearly so.
II the signals amplified by the first
tube are to be passed on to the Sec
ond, etc. The semi-tuned transformer
comprises one tuned winding usually
the secondary, and this is controlled
Dy small variable condenser. Trans
FORMERS Of the foregoing types have :.
air cores.
with the advent of the so-caIled e
untuned radio frequency transform o.
~ an instrument designed to respond
over band of wave lengths with .,
'arying degrees of efficiency has come N
INTO widespread use In the broadcast w
'eceiying field. These transformers E,
liner essentially in their operation A
rom those previously described in m
nat they require no tuning adjust n,
nents and lack selectivity. Some q,
Of this order have q
range of from ITO to $50 G
ieters, while others possess a range y
from approximately 200 to $50
letters.
the band Of wave lengths over %
hich interstage radio frequency COUP fo
ngs Of this type will respond de- bo
snds on their construction entirely m,
ne core used in certain efficient nc
ansformers of this character con- IF
SIS OF thin laminae of silicon steel. Va
mere are also air core untuned radio th.
equency transformers in popular use 70,
broadcast reception, but while ve,
csc are generally more efficient I'm,
an those of the steel core type at ind
me particular wave length, their for
'rking range is considerably limited dia
struments of this type may operate col
lclently over wave band of $50
tiers, giving their strongest response the
wave length at about the middle of
this band. ,n
Tuned Importance. arc
Tuned impedance, as a form of in is
stage radio frequency counling hoe pos
ne into vogue with some promi- r
Ice during the past year. 1t affords
ectivity with simplicity of control
] takes the form of a varlometer
coil comprising few turns of
e with a low capacity variable
denser In shunt. This coupling Is
listed to the wave length desired
manipulation OF the controlling
ID. The windings OF the variome-
or the coil. depending on which Is
o. are common to the output cir
OF one tube and the input circuit
The tube which follows. Great Sc
WITTY is obtained with the tuned 4
edance by employing II consistent 4
throughout the ampliier and be-
en- the last ampider tube and the
'ctor
ne circuit herewith illustrated en-. ,yor,
res TWO stages Of radio frequency III.
''ihea'lon and a defector. The hras'
pug circuits ~ the first and second sold.
'es of ihe almpllher are oquipnea dlo i
hp pniuned iron core Transform. ,,,,,,
'pH tuned impedanco respective. M
since me nnienpa tuning porilon M,
n.s ni'ui does noe AFFORD very End
,p}f tuning as b trur of mosi MI ,
pa 'oN iunefs Hhen usod ID thle I'M.
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