WRAASE electronic WRX-137 Operating Manual

Operating Manual

WRX-137 Weather Satellite Receiver

WRAASE electronic GmbH, Germany

General

The WRX-137 weather satellite receiver covers all polar orbiting weather satellites which
transmit in the analog APT mode. Beside the 5 fixed frequency channels any other frequency
between 134 and 141 MHz can be manually selected in 10kHz steps. Additional fixed
channels can be added by firmware-updates, if required. All modes and functions can be
manually selected by the front panel controls.

For unattended automatic operation and/or if the receiver shall be located at a remote location,
frequency selection can be remote controlled by software, either by the supplied program
"WRX137" or the actual satellite receive software “WxToImg” or Timestep “PROsat”. The
WRX-137 receiver can feed the PC sound input for use with any popular soundcard-based
APT satellite image decoding software like "WXTOIMG". For this, the rear panel audio
output supplies an especially filtered subcarrier output signal with constant, but adjustable
level, independent of the front panel volume control.

The WRX-137P also supports “PROsat” and “JVComm” decoding software with its built-in
microprocessor controlled APT decoder and serial RS232 data output. “PROsat” and
“JVComm” allow full multitasking (receive images while processing and displaying other
stored images and/or running other software). Soundcard based software often has none or
only very limited mulitasking capability and suffers under time- and memory-consuming
processing. The WRX-137 was originally designed to also receive the WEFAX signals from
geostationary satellites. Since this is obsolete now, the second “CONV.” marked BNC
connector is now used as a second input for passive VHF antennas (no DC on that socket).

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CONNECTIONS AND SETUP

Power supply

Power requirement is 12 to 16 V DC @ 200 mA. Voltage stability is not critical because it is
internally stabilized.
If you do not use the supplied AC power supply, carefully check the correct polarity: Center
pin is (-) . The unit is fully protected against wrong power polarization: An internal fuse will
immediately blow. To reach the fuse for replacement you must remove the 4 screws on the
bottom and pull the chassis out of the main case. It is a standard 20mm radio fuse (250 to 500
mA).

Antenna Connection

It is strongly recommended to use a special weather satellite antenna with righthand circular
polarisation (KX-137 or MX-137). Only with such antennas an interruption-free satellite pass
and a coverage range of 4000 or more kilometers can be expected. If the antenna cable length
is in the range of 20 to 30 m, an antenna preamplifier may not be necessary. Our preamplifier
AA-137 or the active antennas KX-137 or MX-137, however, will in most cases improve
reception-quality and -range as well as immunity against strong terrestric signals because of the
integrated high-Q-filters and the extremely low-noise transistors.

In order to dc-supply a preamplifier or an active antenna without the need of an additional
cable, DC-voltage of 10 V is always present at the antenna input socket. This is not needed
when using the passive antenna model KX-137P but does on the other hand not represent a
problem. There exist, however, other antenna constructions which represent a DC-short-circuit
which would cause an immediate fuse-blow inside the receiver.

Antenna Considerations

As the satellites circulate in a polar orbit, the antenna should have a free line-of-sight at least to
north and south. Mounting the antenna under the roof is not recommended (althought in some
cases acceptable results are achieved). The height above ground is only critical with respect to
the lowest possible line-of-sight elevation angle to the horizon and possible reduction of the
shadowing effect of surrounding buildings. As a rule of thumb a line of sight to the horizon at
an elevation angle of 10 to 15 degrees is sufficient. This only applies for buildings, trees are
not so critical.
For good reception performance it is extremelyimportant that the antenna is mounted in a safe
distance to any possible radiation sources of broadband radio noise. Such sources of
interference are computers and all devices which contain microprocessors or switching power
supplies. The broad noise floor created by such devices (nowerdays most electrical household
equipment is suspicious) can easily cover the weak satellite signal. Noise reduction regulations
keep such noise low but do not eliminate it in a close distance. Keeping the antenna in a
distance of several meters from such devices will normally avoid such interference problems.

Connection to the PC

Received satellite data are output as analog audio throught the „AF OUT“ marked rear panel
socket and as digital serial data stream through the 9-pin D-sub connector “COMPUTER”.

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