User's Guide ______________________________________________________________________
Construction
Vaisala Telemetry Antenna RB31 consists of the directional antenna
segments, Antenna Amplifier and Switch RBD121, radome, antenna
base, and antenna cable.
Antenna Segments
The antenna consists of six antenna segments for horizontal reception
and one segment for upwards direction.
Each horizontal segment is a folded ground plane antenna with a 60°
corner reflector. This type of antenna provides a favorable front-to-
back ratio and directivity. Maximum gain direction is towards the
horizon, where the distance between the radiosonde and the receiver is
at its greatest and the field intensity at its weakest. The gain of an
antenna element, at 0° elevation angle, is 12 dB (over 1/2 wave
antenna).
For the upwards direction - or high elevation angles - the antenna is
equipped with a cross dipole. The cross dipole has radiators bent down
to enable the antenna to receive transmissions having extensive
polarization fluctuation.
One antenna segment at a time is connected for the reception. The
antenna switch is controlled to make the selection between seven
directions: North (N), North-East (NE), South-East (SE), South (S),
South-West (SW), North-West (NW) and Upwards (90°).
Cross dipole
Reflector
plate
Switching unit
Radiation element
0211-101
Figure 1
Antenna Elements
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