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Reception...
An introdution to receiving imagery. RIG can supply
many of the items required for DIY applications.
Please check out the links page for commercial
suppliers for 'turnkey' applications.
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Polar
APT
Most members start by receiving images from
the `Polar orbiting satellites', which transmit Automatic
Picture Transmission (APT) signals in the 137MHz band. Current
satellites include the American NOAA series and Russian Meteor
or Sich series. These tend to be sun-synchronous, with two
orbits passing at or near overhead at the same times each
day, 12 hours apart. APT resolution is about 4km per pixel
and two channels are usually transmitted, Visible and Infra
Red. |
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| The 137MHz band is
a fairly easy band in which to build your own equipment and
is relatively inexpensive as a band to start with. Provided
you own a PC then it is possible to get started receiving APT
signals for a little as Receiver kit and antenna for less than
80 Pounds sterling, by using shareware to decode the signal,
using the power of your computer sound card. |
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Geostationary
The next stage tends to be reception from
one of the geostationary satellites over the equator e.g.
Meteosat 7 on the Greenwich Meridian , GOES East & West
over America, Meteosat 5 over the Indian Ocean and GMS the
Japanese satellite imaging over the Far East. |
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| WEFAX images
can be received either using a prime focus dish linked to a
1.69 GHz receiver or it is possible to use a off-set dish (ex
Satellite TV type) with an active feed, linked through a downconverter
connected to your existing 137MHz polar receiver. For those
with site difficulties, then both a long yagi or there is even
a small 9 inch (22.5cm) micropatch flat antenna available commercially
at at approximately 120 Pounds Sterling, can be used instead
of a dish.
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High
Resolution Picture Transmissions (HRPT and CHRPT)
For the really keen and requiring either
more experience in construction or a bit more savings, there
are the highest resolution images available, namely HRPT or
CHRPT. These transmission are from the Polar Orbitting satellites,
about 1.7 GHz, and comprise either 5 (HRPT) or 10 channels
(Chinese HRPT) of spectral information, giving resolution
down to 1.1km pixels. It is necessary to track the satellite
with your antenna and image files can be as large as 120MB. |
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| The equipment is
more specialised and due to the high frequencies and data rates
involved, HRPT is more for the experienced amateur. Equipment
can be purchased from the suppliers on the links page and RIG
offers DIY kits for those who wish to build rather than buy.
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Meteosat
second Generation (MSG)
The current series of EUMETSAT geostationary
satellites at 0 deg. longitude - analogue WEFAX and digital
HRI (PDUS) will end with Meteosat-7 when the new MSG-1 all
digital satellite takes over at 0 deg. between mid and end
of 2003.
When operational MSG-1 will be known as Meteosat-8 and will
transmit LRIT (Low Rate Image Transmission) and HRIT (High
Rate Image Transmission). |
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Due to operational
problems. Eumetsat is relaying the signal via Hotbird and this
can be received using a TechniSat SkyStar 2 PCI DVB receiver
card. This is a digital satellite TV 'free to air' satellite
receiver that is installed inside your computer.
Please see the article on the MSG page
for more details. |
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