New-York tribune., 1922-04-02
First Aid to Radio Fans
How Heterodyne Is Worked:
An Indoor Aerial With Crystal:
Guarding Against Lightning
III. Y. T Troy n Y


word is other power In its applica-
ton to radio, the heterodyne effect is
used IN continuous wave telegraphy-
the modern form of signaling NV
means of wireless. The theory Of
heterodyne can perhaps be best ex-
planned in the following manner: The
transmitting station will be sending
out electromagnetic waves of a cer-
tain specific frequency, which for the
purposes of illustration we may saw
is $4,000 cycles per second.
Now this frequency is far too high
for the human car to respond to and
1t is also too high for the telephone
RECEIVERS to record. The problem that
had to be solved before continuous
wave telegraphy became success was
how to reduce this frequency so that
the telephones would record the sig
nails and make them audible to the
ears.
The heteroayne method has been
found the most efficient and it consists
of pitting one set of high freouencies
against another. In our supposititious
case the incoming frequency is at the
rate of $4,000 cycles per second. In
order to obtain results in the tele-
phones the operator causes his receiv-
ing set to oscillate or, in other words,
he turns 1t into miniature transmit
ting set. He adjusts these oscillations
until they are about 49,5o0 cycles per
second in frequency.
Controlling the Frequency
The condition that now exists in his
receiving apparatus is this: The two
sets of frequencies clash with each
other 500 times every second, or to put
it into electrical phraseology, they are
out of phase with each other 500 times
each second. Now, every time they
clash the two sets Of frequences cause
a click in the telephone receiver and
second produce very musical note. 1t
will be readily seen that the operator.
being able to control the oscillations
of his receiving set, can produce any
musical note he pleases, because all he
! has to do is to vary his own set to
make the number of clashes per second
anything he chooses. He can, for in
stance, make it 10 per second or 1000
per second.
Another advantage of this system is
that in the event Of his being inter
fered with by ordinary spark signals
he has good opportunity to overcome
this interference by simply making his
own set produce higher frcquencies
than the incoming wave, and still get
the same results. In other words, in
stead of producing oscillations at a
frequency of 49,5O0 cycles a second,
he can go to $4,000 cycles second
How the Squeal Is Caused
This heterodyne effect is very puz-
cling one to the radio novice who has
just Joined the ranks Of the fans since
the introduction of broadcast music,
because with his regcnerative vacuum
| tube set he often causes his set to
oscillate and heterodyne upon the car
rier wave of the broadcastng station.
This accounts for the squeal he often
gets when he is adjusting his set.
For the purpose of receiving music
it is much better, after getting this
squeal, to reduce the filament current
until the squealing stops. 1t is at this
point that your receiving set is in the
best condition to receive speech and
music.
I have consistently advised against
the use Of an indoor aerial with a
crystal detector, except where the ap-
paratus is being used in a city very
close to the broadcasting station. |
have also repeatedly stated that crys-
tai detector cannot receive music cf-
hciently at greater distances than
twenty-five miles. In this connection
the following letter from H. v, Of
Brooklyn, is interesting:
"It will interest you to know, how
, ever, that with an indoor antenna--150
feet Of bell wire strung around my
rooms, ground floor of an apartment,
get WIZ as clear as bell. That is,
of course, with crystal detector, and
while reception is not loud enough to
bother my eardrums it still is good
and absolutely clear"
Careful Adjustment Needed
! r. P, Montclair, N. ].
Q.-I have regenerativc receiver,
type RAG, and q vacuum tube detector
1t consists of vario-couplcr and two
! yariometers. I want to know why
can't get any stations but WIZ. My
aerial is 100 feet long and about so
feet high.
A.-You should get the small broad
casting stations in and around Jersey
City. You should also be able to hear
Springfield, Mass, Schenectady and
Pittsburgh. The tuning of this set is
very sharp. In other words, the slight
est adjustment of the different dials
will throw a station out. I would
advise you to tune it as slowly as