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201.3 Description of Recorders
The vertical~incidence ionosphere recorder (C2 or C-3) is a
device which measures and records virtual heights and critical frequencies of the layers of the ionosphere. Transmitted pulses of
radio-frequency energy are reflected from the ionosphere and received
by the equipment on their return, the travel time indicating the
height of the reflecting layer.
The frequency is swept through the
range of 1 to 25 megacycles. The critical freyuency of a layer is ine
dicated by the frequency above which the signal penetrates the layer,
thus producing no return, and is a measure of the maximum electrcn
density. The received signal is displayed as an intensity-modulsted
oscilloscope trace, showing layer height as a function of frequency.
The presentation is photographed automatically. A more detailed dis~
cussion of the method and of the interpretation of the photographs
may be found in Reference 3.
Rel
Antennas
The antennas used with the ionosphere recorders in the Marshall
Islands were single-wire, vertical-delta type ("balf-rhombice"),
50 ft high, with the slanting legs 78 ft long, the transmitting and
receiving antennas and the ground plane being in mutually perpendicular planes. The antennas at existing stations are sinilar, but are
multiewire to provide better impedance match throughout the range,
and are longer, the slanting legs being about 90 ft long. 41°. are
designed to radiate and receive principally in
over the entire band of frequencies. However,
the beam is wide, and at others there are sice
returns are received under certain ionospheric
2e2
2Ze2e
the vertical direction
at scme frequencies
lobes; hence, oblique
conditions.
OPERATING PROCEDURE
In the Marshall Islands
Scheduled operatim of the recorders at both Marshall Islands
stations began several days prior to the first shot.
It continued in
accordance with the planned program (which appears below) except that
fallout after the first shot curtailed operations at Rongerik,
Aftere
wards, the recorder at Rongerik had to be started prior to each shot
and left to operate wmattended, at one sweep per minute, until the
film or the gasoline in the power mit ran out. At both stations, a
sweep time of 15 sec was used, the entire range of frequencies from
1 to 25 megacycles being covered in that time. In the program which
follows, “normal" indicates five sweeps an hour (on the hour, and at
15, 30, 45, and 59 minutes past). "D" and "H" respectively, represent
the day and hour of each shot, and minus (-) or plus (+) indicates
time before or after the shot, respectively.
(Additional data were
obtained in the courses of test and maintenance runs.)
2l
SECRET