Evening star., 1923-02-18
NATIONWIDE BROADCAST :
SUBDUINC INTERFERENCE
Radio Stations Disturbing Each Other
Must End, Is Clamor of Fan, Pointing to
Many Difficulties Being Faced.

leaps and bounds and without waiting
for desirable refinements in the ra-
do art.
Coincident with the advent OF ra-
diophone broadcasting and its subse-
quent rapid growth. very great i'm
petus was given to the investigation
OF the problem of selective transmits
carried on by the Navy. AS a result
or these Investigations. effective and
economical methods have been de-
Vlsed, by the employment of which
the most troublesome interference
given off by transmitting stations, es-
peclally that on the short broadcast
waves, can now be neutralized at the
transmitting stations them selves and
therefore eliminated at the distant re-
ceiving stations.
Important Brondcastink.
Thus the broadcast service, how
ever indirectly, has been instrumental
IN eXpedittng an important advance
in the development of 1.-THE radio art
as regards interference elimination
which will ultimately prove to be as
beneficial to the radio services which
must function continuously as to the
services which are at liberty to suS-
pend operations at will.
If the broadcast service should
likewise expedite or cause to be
static. or the complete naturalization
of its effects. then its fame would in
deed be assured.
One of the measures taken by the
Navy to reduce or. eliminate interfer-
ence Is the modiftca ton of it's many
spark" transmitters (Which gives
off comparatively broad" work in &
wave as we'll as superfluous harmonic
Waves), into vacuum tube transmit
ters. The working wave OF the vac
uum tube sets is very much sharper"
than that given off by the spark sets,
, but vacuum tube sets likewise give
off superfluous harmonic waves.
These harmonic waves will be sup
pressed at the stations, however. by
the use Of special filter circuits asso-
ciated with the transnitters so as to
dissipate the energy of the harmonic
waves at the stations and thereby
prevent their being radiated in space.
The modification of the spark sets
is being made only gradually as
funds become available for the pur-
pose. because several hundred of the
spark sets are in daily use on board
ship and on shore and the total ag-
gregate cost is therefore considera-
| BILE. The average cost for making
these notifications is about $4,000 per
set, but this procedure enables the
prising the existing spark sets and
obviates the purchase of complete
vacuum tube sets with the resulting
expenditures Of huge sums OF public
funds which otherwise would be nee
eSSary.
en- by the Navy to eliminate interfer-
ence Is the modification Of it's exist
ing arc" transmitters.
This type OF transmitter is installed
on ships of the Navy (and also on
merchant shipsl and likewise at vir-
N,ta 1lsE
widely extended chain of stations on
shore, including the high power sta
tions ranging in locations from An
napolis, Nd, to Manila, 4 the Phil
ippineS.
Rangt Of Arc Transmitter.
The arc type OF transn,itter in
stalled at these stations ranges in
power from 2 kilowatts to 500 k3lo-
watts.
arc type Of tran smitter has been one
of the worst offenders in radio S re-
CARDS the creation of superfiuous in
terferring waves In the ether. It not
only gave off numerous harmonic
| waves, but also other superfiuous
waves which have been designated as
"mush,' and the working wave had
associated with 1t a distinctive Corn
; pensating' wave differing in length
from the working wave by about 200
meters.
| Methods have been devised by the
Navy radio whereby filtering circuits
| may also be associated with the arc
| transmitting equipment to suppress
| the harmonic. "mush," and "compen-
| sating" waves directly at the trans
| mitting stations and thereby prevent
! their radiation in space.
ModihcationS to several of the
Nays low and medium power arc
{ stations have already been made, as
have also the San Francisco l00-kilo-
watt high power station and the San
| Diego, Calf. 200-kilowatt station
thereby eliminating interference from
these sources in these areas Of large
population.
Similar notifications are now being
made at the Sayville, L. T., 2oo-kiIo-
watt station and preparations are be-
ing made to apply this method to the
Annapolis 500-kilowatt station.