Evening star. [volume] (Washington, D.C.) 1854-1972, 1924-11-16

Is obtained from a 1,50o-voit direct
current dynamotor driven by bank
Of storage batteries totaling "a volts
and 320 amperes. The discharGlnE
rate Is Il amperes for this dynamo
tor. Tho filament supply Is from two
6-volt batteries. Five microfarads Of
condenser are connected across the
motor commutator and Is microfarads
across the generator comnautator to
reduce commutator ripple. 50
Henry choke Is used. the single choke
accomplishing two purposes, that OF
eliminating commutator ripple and
also that Of acting Is q familiar Hei-
sing choke.
A two.stase push-pull anplifier is
used. which Is combined with . micro
phone control keyboard, with its famil-
lar switchboard keys and lights. and
this is placed In the announcing posi-
ton. Two microphones are ordinarily
used. one for announcing and the
, other for performance. a shielded
cable Is conducted from this line am
plifer to the truck. where 1t passes
through q flve-watt speech amplifler,
the plate voltage Of which Is supplied
by a 3o0-volt storage battery and
from there into the incubator tubes.
The entire apparatus is panel
mounted and very compact, as Is shown
III inc luClOScQ pnOtOs.
The antenna, Of course. varies with
different conditions, and. in fact, It ia
| a rather complicated process to put
the truck into operation each night
at a different locality, as this entails
| practically the erection OF broad
ca sting station every day. the condi-
lions never being the same twice,
especially with respect to ground ana
antenna. Wherever possible, connec-
~
| as this has been found In general the
best ground connection available, and
also, wherever possible, the high
| end Of the antenna has been sup
ported by a flag pole. building or 9TH
! err structure if one OF sufficient height
was available. If not, then the So
| foot sectional Army type mast was
called into service. although this Is a
rather complicated and difficult thing
| for the three men comprising the
| truck crew TO put up without outside
assistance. It has been found that In
general the antenna should be run
/ at right angles or in the opposite d.
rection from the limo between the
| truck and the line amplifler or micro
! phone position. 1t has also deem
found absolutely necessary TO ground
the shielding OF the line amplifier
| cable at every conceivable point to
avoid the presence OF high-freQuency
current which distorts the meditation.
and It is in the eliminating OF these
high frequency currents from the mi
| crophone and line amplifler that the
! special set has become necessary In
each case and which has made the OPP
| Grafton OF this truck broadcastin
station so interesting.
AS the transrnitter Is working very
close to the fundamental wave length
| OF the antenna through the use Of a
| series condenser, the antenna current
Is not very great. II being on the av-
| erage Of two amperes. The modula-
ton, however, is at a maximum and
! therefore WJAZ does not have the
| loud carrier and weak modulation
| characteristics Of many stations, but
| its meditation IL very nearly as loud
as the carrier wave itself.
The truck has been moved about to
\ a number Of towns within hundred
miles Of Chicago and two-hour pro-
| grams on the average broadcast from
| each town at about the same place.
| The same antenna has been used In
| every case, although. OF course, the
supports have been different, and the
| capacities and resistances different
| but the antenna itself has consisted
| Of a four-wire, fat top, los feet In
length, provided with clip connectors
| for easy and quick assembly. Tele-
| phone calls have been arranged for In
as many cases as possible, and as An
example Of the interest OF the listen
Ing public in this project over 100
| calls were actually received at the
| town of Sycamore. ILL.,. and the tele-
phone company later reported that
| 400 calls were Cancelled because OF
f! improper facilities in the telephone
| exchange for handling them fast
| enough. There were calls from Min.
nesota. Ohio, Pennsylvania, New
| York, Indiana and Wisconsin.