The Winslow mail., 1926-01-15

Smith is one of those rare per-
sons who always manages to take
advantage of disadvantage. There
are some nights when reception IS
not so good, or times when he does
not like what he can get over the
air, but instead of grumbling he
recognizes the chance to learn
something more about how the set
works.
It was on one of these eventful
occasions that | happened to find
him trying to trace the radio cir
cults from input to output. The
various basic units of the set were
becoming as familiar to him as the
ARRANGEMENT of engine, clutch,
transmission and differential in his
car. He had formed definite
mental picture of the order from
aerial to tuner, to radio frequency
amplifier tubes, to detector, to aud
10 amplifier tubes and to loud
speaker, but it was that change
over from radio to audio that still
puzzled him.
81 don't blame you for being
puzzled" l cheered him a bit.
There is probably no part OF radio
theory that is more carelessly eX-
planned than the change from radio
to audio. l think you've got it pref
ty well fixed in your mind that the
original sound variations or values
are carried on electromagnetic
waves oscillating anywhere from
10000 to 100000 cycles per sec
ond, and you recognize this as al
ternating current, but from the talk
you hear it is certainly difficult
to know whether the current is
alternating or direct after the de-
tector tube has rectified it.
"That's just my problem" he ad-
mitted. 81 can visualize the radio
frequency-those high speed oscll-
lations ns-reaching the grid OF the
detector tube. l can see the mega
tive electrons being attracted
across the gap to the plate OF the
tube which is positively charged
with the current from the "B" bat
terry. l can clearly understand that
this arrangement means that the
current from the plate to the ear
phones can go only in one direc-
| ton because it has been rectlfled
by the tube. But then why do they
| talk about this rectifed current as
'audio frequency? | thought ire
uuency' was the term used to de-
fine the number of cycles OF any
! oscillation. And after the current
is converted into the audlo type
it's supposed to go in just one dl-
rectiOni"
Here he pointed to contradictory
statements which he had picked
from various sources, which GER
tainly left doubt as to just what
did happen after the detector got
through with the radio frequency
form of the current.
"I've been puzzled over just the
same point" l told Smith, but I've
finally got it straight from practl-
cal electricians It's a pretty big
story, and l guess there's much
that has to be taken for granted
but it will ease you considerably
to know that the current is nc
longer alternating after it has pas
sed through the detector, whether
you use a crystal for this purpose
or a detector tube"
"Fine!' Smith exclaimed. But
then why speak of audio frequency
when the current in audio form Is
not alternating? How can there be
oscillations in direct currentY
That's just where they confuse
us" ! explained. "You see, al
electrical circuits are oscillations
: 1t is the basis upon which radl'
stands. But the term is rathe
t vaguely used. First they are us
= ing it to mean alterations, thel
y to mean pulsations. This is con
: fusing. and unnecessary.
t "Just picture the current comm
f in over the antenna as alternatin
= current. Picture it changing its d
rection thousands of times a set