Evening star. [volume] (Washington, D.C.) 1854-1972, 1929-02-24
STATIONS MAY TRY
USING SAME WAVE
Synchronization Believed So
luton for Problems of
Facilities.

With stations WPCH and WCCO and
b proposed large network of chain sta
tions contemplating experiments with
synchroni5ed operation on the same
wave length, there seems some likeli-
hood that a successful system will be
Forthcoming within the next IL months
The development of such system of
simultaneous operation would solve the
ALLEGATION problems of radio regulatory
bodies once and for ALL Such
scheme would allow chain broadcaSterS
transmitting the same programs to OPP
crate on the same wave length and
thereby reduce the number OF channels
in the broadcasting spectrum to half
of those required under the present ar
rangement. Where now there are $50
licensed stations, of which more than
70 per cent share their wave channel or
a part-time basis, the number could be
increased approximately 80 per cent
and without causing interference. This
would take care of the 100-odd applica-
tions now pending before the Federal
Radio Commission and still leave some
to spare.
Problem of Synchronization.
To the layman there is apparently no
reason why stations transmitting the
same programs cannot employ the same
frequency simultaneously AS matter
of fact, they can, providing the fire.
quencies of the two stations using the
channel are precisely the same. There
in, however, lies the explanation OF why
it presents such problem to radio
engineers-that of operating on identi-
cal wave lengths
An analogy of what takes place when
two stations operating on the same
channel vary in frequency readily
reveals why accuracy is so potent. AS
sumo station in New York and an
other in Chicago, both having a power
of 500 watts, attempting to operate on
a frequency of 1000 kilocycles stimuli
taneously. Both would have a reliable
service range of at least within a 100
mile radius of each point. However,
their carrier waves would be capable
of reaching points 1000 miles distant.
Science has discovered that sounds
vibrating at more than 10000 times a
second, or at 10000 cycles, are not
audible to the human ear, and has
designated all frequencies above this
point as radio frequencies and below
as audio. The radio transmitter operat-
ing. 1000 kilocycles would be emit
ting radio frequency of 100000
cycles, well above the range of the hu-
man ear.
Beat" Not Troubles.
Assuming the stations in Chicago and
1000, 900 cycles there would be no trou-
BILE. However should the Chicago sta
ton drift off the million cycle frequency
as little as 200 cycles, beat note effect,
or heterodyne, would be set up between
the two stations. The So-called beat"
would be caused by frequencies falling
In and out of resonance, the number Of
which would be determined by the
difference In cycles. A difference of 200
cycles would make audible on any radio
receiver within the range of the carrier
waves pitch slightly below middle &C"
on the piano. Ee
Obviously, unless the frequencies of
the two stations were maintained pre-
CiSely the same, 1t would be impossible
to use the same wave channel stimuli
taneously. Thus far, a. practical means
of accurately controlling the frequency
of two or more stations has not been
developed.
Used at WBZ and WBZA.
However, it has been tried, and in
some cases has been quite successful.
Possibly the only case where such a
system has been developed tosthe point
where it is performing satisfactorily Is
in the case of WBZ, Springfield, and
WBZA, at Boston. Several years ago
engineers discovered that it was i'm
possible to receive the signals of WBZ
in a certain section of Boston. Experts
working ON the problem decided that
- %aa1Nv L. l.. - =
S00-watt plant in the heart of Boston
and synchronize it with the Springfield
station. BY means of crystal oscillators
and a method of controlling the tenn
perature of the two oscillating units and
the use of several pairs of wires between
the control rooms of the two stations
It was possible to operate them stimuli
taneously without interference. This
scheme has been functioning for a
period OF two years, and 1t Is seldom, If
ever, that the two transmitters deviate
m frequency or cause heterodyne,
Crystal May Be Solution.
When engineers solve the problem of
controlling the frequency of a broad
casting station it will be possible for
stations to synchroniZe. The piezo elec-
trio crystal oscillator has been prob
n1AS VAC AIOob QCFSlOpIIlGIlU
toward that end. Engineers and experts
look to this system of controlling fire.
quency as the only means through
which synchronization will be realized.
Although far more constant than any
ether means of controlling wave-length
OF transmitting set, the crystal oscil-
lator is subject to a certain amount of
variation caused by changes In tenn
perature and humidity A quartz
crystal may vary as much as 500 cycles
when subject to temperature change
OF two or three degrees in temperature
In order that two stations may operate
on the same channel it first will be
necessary for engineers to develop a
means OF not only controlling frequency.
but methods of maintaining the crystal
oscillators at exactly the same tenn
perature. In order to accomplish this
purpose 1t may be necessary to erect a
receiving station at least five miles from
each transmitting set and link them
70 the two control rooms and together.
Such stations, designated as monitors.
would check the frequencies of the
Two sets and make the necessary adj
Justments when deviations are recorded.
Another system of using wires for
the controlling of frequency has been
suggested, but not tried, because of the
tremendous expense involved, it might
also be possible to employ the newly
developed wired wireless system of
transmission. At any rate, engineers
and broadcasting station owners and