The L'Anse sentinel., 1923-02-02
interference OF
RECEIVING SETS
Each, When Tuning for Distant
Station, Acts as a Continuous
Wave Transmitter.

We have explained that the contlnu-
Gus, fairly steady whistles, usually
heard while tuning for the distant sta
tions, was due to a combination OF
the carrier waves of two stations
which were very nearly on the same
wave length. There is another series
of whistles always present which very
much resemble the whine of mos
quito both in tone and amount Of an
noyance produced. These are caused
by the receiving sets of other listen
ers. Every receiver using a vacuum
tube detector with regenerative cir
cult Is a potential transmitter. In
fact 1t contains all the essentials of
radiophone transmitte- on small
scale.
The detector tube when oscillating
produces oscillation exactly similar to
the carrier wave of the radiophone
stations. The frequency or wave
length of this wave can be varied by
changing the tuning of the receiving
tuner
The usual procedure In tuning for
a distant phone station Is as follows:
Put the detector tube in an osciliating
condition after the tuner has been ad-
1usted near the point where expert
ence has taught us to look for the
broadcasting stations, then move the
dial slowly across the approximate
point where the stations are usually
heard. The carrier waves are located
by whistle which starts at the upper
limit of audibllity and goes down the
scale until 1t becomes so low that 1t is
no longer a note. At this point the
set Is In exact resonance, and IL the
ticker. coupling, or plate tuning in
ductance is decreased until the detec-
tor tube stops oscillating. the very
best adjustment Is obtained for recep-
ton of that particular station.
Unfortunately while this listener Is
going through this operation his re-
ceiving set is acting as continuous
wave transmitter, and is producing.
some inharmonious walls In the
phones of his nei,hbors who happen
to be already on the wave of the same
station. The continuous wave sent
out by the receiver combines with the
carrier wave of the transmitting sta
tion, producing an audible note. If
the operator could tune his set as sim
ply as was described above there
would be very little interference, but
he usually whistles back and forth
across the wave Of the transmitting
station several times. Often several
listeners who have been getting the
concert perfectly will get restless be-
tween selections and get their tubes
to oscillating and whistle up and down
few times.
All listeners should be very careful
to keep their directors in non-oscil-
lating condition as much as possible
to reduce this annoyance of interfer-
ence between receivers.
Opinions seem to vary considerably
In regard to the comparativ amounts
of energy inducted into the antenna by
the f"single circuit" or conductively
coupled. and the "three circuit" or
lnductively coupled receiving set.
Previous to the Introduction of the
single circuit very little trouble had
been experienced with beat notes
from receiving stations. This was no
doubt due to the fact that receiving
sets were rather few and far between /;
also up until few years ago there
was a very small percentage of c. W.
| telegraph and phone stations so that
there was no reason why an amateur
should keep his tube in oscillation
condition. On the contrary, he was
very careful to keep II just below the
oscillatlng point, that being the most
sensitive adjustment for spark signals.
With the telephone and C. W. tele-
graph transmitting stations, 1. O., tube
transmitters, came the single circuit
tuner with its extreme simplicity of
| adjustment, which was so well adapt
ed to the very sharp tuning Of the
new transmitters. And with the ad-
vent of these new transmitters came
the necessity for making the detector
| tube oscillate In order TO locate a sta
tion on the scale of q receiving tuner.
Naturally then the interference be-
tween receiving sets became notice
able at about the time that the single
circuit sets became numerous. and this
helped to prejudice the minds OF the
radio public against this type of re-
ceiver. However. the fact that the
single circuit arrived at about the
,ame time with the Interference was by
no means the only reason for believing
this tuner to be the main cause OF
the trouble.
For instance in constructing a single
circuit or conductively coupled tuner
the difficulty is in obtaining regenera.
ton NJ all Doints on the scale. This
For Evenjno Wear.