Evening star., 1927-05-29
ALL TRANSM|TTERS
WILL Be MEASURED
Commission Adopts Plan as
Means of Solving
Chief Issues.

The Federal Radio Commission ir
seeking a means to determine how
much power a broadcast station needs
what its service area is and whether
mr. not It is correctly located to serve
its community, has decided to have
the field strength OF all broadcast
transmitters measured by the various
Offices of the supervisors OF radio
This Is going to be big Jop' re
ouiring considerable time and money
and the training of personnel for radio
test car crews, not to mention the
perfection and construction OF stand
ardized measuring apparatus. Spe-
cial receiving apparatus and standard
measuring instruments are required
Tor this undertaking. which Is
Unless the many observations taken on
stations are comparable. and radio-test
ears adaptable to cross-country serv-
f,eA are needed. At least nine COM
riete sets of apparatus and as many
test cars are desired At present
there is bu- one test car and one
set of the experimental necessary
equipment available. This is located
in the Detroit, or eighth. radio super.
visory district. Plans for the con-
struction of several more are ready,
however. when funds permit. The
cost of the new apparatus above is
estimated at $4,000 per set, even If
the engineers and experts of the de.
partment assemble it themselves, buy
ing the parts from commercial radio
supply houses.
Measurement Need Cited.
It was not until the advent of
broadcasting that any attention was
paid to the emmissions or power from
radio transmitter; existing COM
nercial stations were satisfied If their
messages went in the general direc-
ton desired, since most Of the sta.
tions were operating from pointto-
point. Antenna power was roughly
figured as half the total input and
usually is today.
The need for service area measure
ments was pointed out by Secretary
of Commerce Hoover during the third
radio conference in Washington in
1924, when he expressed a desire to
know in what directions and to what
distances broadcast stations served the
public. His idea was that If the serv-
ice area was irregular. in the shape
OF figure eight, for example. instead
Of the ideal circle, other stations
territory not served, or that lying near
the shorter radius of the first trans
mitter.
Following his suggestion the radio
experts of the Department of Com
merce, the radio supervisors in the
field, with the cooperation of the Blu.
reau Of Standards, undertook to learn
something about the laws of radio
broadcasting, so as to work with them
instead of fighting them, and thereby
solve one Of the major problems
Gel
sion. Considerable research was car
ried on by Supervisor S. w. Edwards
or Detroit. Even the first expert.
mental apparatus designed to measure
the Held strength or the value Of the
received signals from stations made
the vagaries of radio less mysterious.
Today the radio engineers are able
to state positively I'm most cases why
q broadcast station radiates well in
one direction and is not heard in an.
other. Previous to these tests the
matter was one Of pure conjecture.
Area OF Service Mapped.
The value OF this type of measure.
rleDts cannot be- overestimated in
securing the best possible service and
emciency from broadcast station, for
by such measurements the area a
station actually serves may be &C,
curately mapped and thus its value to
the public determined. Public serv.
ice. 1t VIII be recalled, is the prime
requisite for authorizations to broad.
cast issued by the Federal Radio Com.
mission. 1t is desired to- have the
whole country adequately covered
wiln as Few stations as possible. This
sort OF DATA 10 not only necessary to
the commission but most desirable to
Lhe station owners who want to cover
as much territory as they can, in
keeping with satisfactory signal
strength throughout the area. There
are many broadcast stations, orig.
InalV intended to serve a certain
community, which are covering other
areas much better. but interferine
with stations located therein. Such
conditions have been shown in the
Isw neld-strength measurements al.
ready made by Supervisor Edwar
ana also by the engineers OF the
american Telegraph & Telephone Co
Nho nave conducted similar exneri.
menus with certain New York stations.
IN Undertaking to show what hap-
pens 70 broadcast programs after they
,vase the Iransmitters, standard units
sno standard means OF measurement
nad TO be worked out, so that results
could be compared. The ordinary
unit OF field strength or fntensitv
measurements is volts per meter, but
oeing large unit, it is reduced IN
practice to nnillivoits per meter. But
Tor the general reader, rnfllivoIts
aIone WIZ be used. A millivolt is the
unit employed to designate the
strength of the incoming radio signal
as we get it on our receivers: IL is the
uny traction of the power emitted
from the broadcast station antenna
Wnicn reaches our receiving antenna
Hno mas to be amplified materially be-
Lore we can transform 1t into an au.
Inc strength Of this received signal
varies from to 30 milliyoIts even on
standard receivers, depending unon
tnelr distance and angle from the
senong station. as well as the ioca
uon OF the station and the interyen-
ing terrain. To determine the service
area or single station Something
IKE $50 observations must be taken
on SIX or more radiating lines from
Lhe station and at many different dis
tances. A minimum of four DAYS is
ordinarily required to make such a
survey. Other data to be ACQUIRED
from this type of test include the de.
termination of whether or not the To-
catlon or the broadcast station is
!oea! or whether some neighborine
buildings throw a radio shadow" over
a part of the territory supposed to
pc served, weakening the signal SO as
70 make 1t of little value to the lis
teher living in that shaded area,