WEATHER SATELLITE FAQ
                     (Frequently Asked Questions)

                               by Tom Glembocki

Send additions/corrections to Tom Glembocki, tomgle@cybernetics.com

Thanks to powerful computers on our desktops and the relative
abundance of radios available to receive the VHF weather satellite
frequencies, many individuals are now inquiring into how to break into
the fascinating hobby of receiving live weather satellite pictures for
display on their home PC. Equipment needs today are fairly
modest and all equipment required is available "off the shelf". The
purpose of this guide is to point the weather satellite beginner in
the right direction to successfully receive, display and use weather
satellite images.

                           WHAT'S UP THERE?

There are two type of weather satellites available for amateur
reception:
     1.Polar orbiting satellites circling the earth every 90
        minutes.
     2.Geo-stationary satellites situated at fixed locations
        in the sky.

The Polar Orbiting satellites, so named because they travel in a
North-South orbit that takes them almost over the North and South
poles, are the easiest to receive.  The plane of their orbit forms a
constant angle to the sun, thus these satellite orbits are also
referred to as being sun-synchronous.  One reason for a
sun-synchronous orbit is that the light illuminating the scene below
the satellite is constant for a particular geographic region at a
particular time of day.  The satellite passes over a particular region
at almost exactly the same time each day.  As the earth rotates under
the satellite orbit we end up with a satellite pass ascending from the
South and a later pass in that 24 hour period descending from the
North.  Currently there are four US and two active Soviet satellites
providing us with picture gathering opportunities.  The polar orbiting
satellites are in low earth orbit, typically 300 - 800 miles up.  This
orbit height limits the width of the image swathe they are able to
capture.  The images returned by these picture takers show about a
1700 mile width of ground and clouds below.  As a polar orbiting
satellite travels in its orbit it is scanning the earth below with a
radiometer consisting of a mirror, telescope and both infrared and
visible image sensors.  As each 1700 mile wide line is scanned by the
radiometer, the line is transmitted to the ground below on VHF
frequencies in the 137 Mhz band.  The lines are sent at a relatively
slow 2 lines per second.  To receive a complete viewable picture on a
computer requires that several minutes of the satellite orbit be
received.  A typical overhead satellite pass usually lasts 10 to 15
minutes depending on how good the antenna and radio are.  Even a poor
antenna and radio are able to receive enough of an overhead pass to
get a viewable picture.

The second type of Satellite is the Geo-stationary weather satellite.
This bird is parked in the "Clarke belt" 22,500 miles out and orbits
in synch with the Earth - one rotation every 24 hours.  This satellite
is available 24 hours per day providing the amateur community with 24
hour a day weather imaging.  The image these satellites cover is fully
the whole earth disk from edge to edge, top to bottom.  Because the
geo-stationary satellites are so far away (23,000 miles) their signals
are weak and consequently they are more difficult to receive.  This
tutorial will concentrate on the easy to receive polar orbiter weather
pictures.

       WHAT EQUIPMENT DO I NEED TO RECEIVE WEATHER SATELLITES?

An APT (Automatic Picture Taking) ground station consists of the
following components: Antenna, Receiver, PC Facsimile Card, Personal
Computer with VGA or SuperVGA display.

                             THE ANTENNA

This is the most visible component.  An Amateur Radio 2 meter
omnidirectional antenna works well here.  There are other commercially
available antennas specifically for weather satellite use.  Vanguard
Labs carries an omnidirectional turnstile for under $100 and Satellite
Data Systems carries the omnidirectional quadrifilar for around $300.
The Weather Satellite handbook shows how to build a simple antenna.
The June 1992 issue of WeatherSat Ink carried an article on how to build an
excellent performing Lindenblad Antenna, "The Twirler I" by Richard Emerson,
for only a few dollars using hardware store PVC fittings.
WeatherSat Ink Fourth quarter 1993 has a construction article for the
Quadrifilar antenna.
Addresses for the above companies are found elsewhere in this FAQ.


                           ANTENNA CABLE

This is a length of RG/58U coaxial cable that runs from the
omnidirectional antenna usually outdoors to the receiver usually
located indoors. For long runs of cable (over 25 feet) it is beneficial to
mount a preamp at the antenna. Most preamps require a source of 12 volts DC,
in some cases supplied through the coax receiving cable, and other cases
as a separate pair of wires.

                WHAT FREQUENCIES AND FORMATS ARE USED?

There are two frequency bands used by the weather satellites
- the VHF band of 137 - 138 Mhz and the S band frequencies around
1691 Mhz. The polar orbiters use both VHF and S band, while the
Geo-stationary orbiters only use S band for their image transmission.
There are several formats of image transmission used by the
satellites, both analog and digital. The polar orbiters transmit an
analog audio picture format referred to as APT (Automatic Picture
Transmission), a very easy to receive
and demodulate signal format. Their other image product is the digital
data transmitted at 675 Kbps called HRPT.  It is possible to receive
APT in your kitchen with a radio and a computer.  HRPT is much more
involved.

The Geo-stationary satellites transmit an analog audio format very
similar to APT but named WEFAX.  The biggest difference between APT
and WEFAX is that APT is transmitted at 120 picture lines per minute
while WEFAX is transmitted at 240 lines per minute.  In either case,
decoding is very simple because we're dealing with audio frequencies
that change amplitude in proportion to picture black/white/gray area.
In addition, the Geo-stationary satellites also transmit digital data
that is more involved in the equipment required to decode - a 2.11
Mbps data stream named VAS (Visible and infrared spin scan radiometer
Atmospheric Sounder).  The following chart lists the currently
available weather satellites with frequency, format and products
available.

               WHAT SATELLITES ARE ON WHAT FREQUENCIES?

             POLAR Orbiters
             ==============
             NOAA-9:     APT 137.62 Mhz
             NOAA-10:    APT 137.50 Mhz
             NOAA-11:    APT 137.62 Mhz
             NOAA-12:    APT 137.50 Mhz
             METEOR 2-20: APT 137.85 Mhz
             METEOR 2-21: APT 137.40 Mhz
             METEOR 3-3:  APT 137.40 Mhz
             METEOR 3-4:  APT 137.30 Mhz
             METEOR 3-5:  APT 137.30 Mhz
             METEOR 3-6:  APT 137.30 Mhz

              Geostationary
              ==============
             GOES-2     78 degrees long   WEFAX 1691 Mhz
             GOES-6    135 degrees long   WEFAX 1691 Mhz
             GOES-7    112 degrees long   WEFAX 1691 Mhz
             Meteosat-3 75 degrees long   WEFAX 1691 Mhz

        WHAT KIND OF RECEIVER DO I NEED FOR THESE FREQUENCIES?

After you get your tracking program up and running you should be able
to predict a satellite pass and tune it in on your VHF receiver.  NOAA
9 and 11 will be on 137.62 Mhz, NOAA 10 and 12 will be at 137.500 Mhz.
On 137.300 Mhz, 137.400 Mhz, and 137.850 Mhz are the METEOR series of
Soviet Meteorological Satellites.

Many popular "police" scanner radios are available from Uniden
Bearcat, Radio Shack and others that cover the 136 to 137 Mhz
satellite band.  If you use a scanner receiver the regular
communications I.F.  bandwidth of the scanner is probably not optimum.
The ideal I.F.  bandwidth of your receiver needs to be about 42 khz.
A wide bandwidth will mean the signal will be weak and there may be
too much background noise to see the picture.  If the bandwidth is too
narrow, the white areas of the picture may come out gray or noisy.

March 1991, '73 Magazine' has an article by John Hoots on page 12
with a description of modifications that can be made to some scanners
to improve the I.F. bandwidth.

Ready made satellite receivers are available from several sources
with the correct I.F. bandwidth. They are:

   Vanguard Labs, 196-23 Jamaica, Hollis, NY 11423, tel 718-468-2720
   Hamtronics, Inc.,65-D Moul Road, Hilton, NY 14468-9535,
     tel 716-392-9430
   Quorum, 1020 S. Main St. Suite A, Grapevine, TX 76051,
     tel 817-488-4861
   Spectrum International, PO Box 1084, Concord, Massachussets 01742
     tel 508-263-2145

              HOW MUCH WILL A WEATHER SATELLITE SYSTEM COST ME?

You can pay over $2,000 for some APT systems.
A brand new do it yourself system will run between
$600 and $1500, with $1000 about average.  HOWEVER, if you are
resourceful, you can set up a system for $200-$500 which will provide
excellent pictures. Several individuals
have put together systems for less than $100, even FREE. My first
system cost $140 complete. It was primitive but was a start, and got
me hooked pretty quickly. A good starter is the "WEFAX Explorer"
from Quorum Communications. This consists of a VHF scanning radio
and a demodulator on a single PC card for $645. Plug it into
your computer, add an antenna and you have an instant ground station.

A Geostationary system uses much of the same hardware as the APT
ground station, but in addition requires a dish antenna and microwave
downconverter. This naturally adds to your cost. Dish antennas start
at about $200 while downconverters begin at $200. Old TV satellite dishes
can sometimes be obtained for low or no cost - they provide excellent
microwave antenna's for the Geostationary satellites.
A simple kit downconverter was featured in WeatherSat Ink, fourth quarter
1993 for $150 in parts.

       The following are sources and prices for downconverters:
               Spectrum International          $450
               Quorum Communications           $550
               WeatherSat Ink kit              $200

                    WHAT IS THE BOTTOM LINE HERE?

The easiest way to begin receiving weather satellite pictures on your
PC is to tune into the Polar Orbiters operating at 137.5 and 137.62
Mhz. A simple omnidirectional antenna and police scanner will get you
started. Several public domain tracking programs will tell you when a
satellite is passing overhead so you know when to tune it in. The
audio from the earphone jack of your scanner needs to go to a weather
satellite facsimile card in your PC. The software that comes with the
PC card does the rest. For best results you need a VGA or SuperVGA
monitor on the PC. Thats all there is!

Price range for various weather facsmile PC cards:

Multifax  $300.
OFS WeatherFAX $395.
Timestep ProSat $399.
Satellite Data Systems $799.
Quorum Communications $695.

An example of a package deal is the one from Quorum Communications.
For $695 they have a combination receiver and demodulator card that
plugs into your PC.  The addition of an omnidirectional VHF antenna
such as the ones from Quorum, Vanguard or Spectrum International for
around $150 is the only other piece of equipment you need (in addition
to your computer).

          WHAT ABOUT SHORTWAVE FAX BROADCASTS?

Many have sucessfully received images and weather charts rebroadcast
by Naval facilities around the world. Reception is relatively easy
requiring just a general coverage shortwave receiver such as the
battery operated portable Sony 2010. Antenna consists of mainly a long
length of wire or a dipole cut for the specific frequency. The
headphone output of the receiver goes to a demodulator sold by AEA,
Software System Consulting and others, or to a Packet Radio TNC
designed to demodulate HF Fax, such as the PK232 or MFJ 1278.
Results are generally disappointing because of the large amounts of
noise, especially in the atmospherically charged summer months.
Typical demodulators only offer 16 shades of gray - far below the 256
shades offered by APT and WEFAX systems. However, the system costs are
low and good results can be obtained at times.

        WHAT IS GOESTAP AND HOW CAN I RECEIVE IT ON MY SYSTEM?

On the C band TVRO satellites, the images from the NOAA GOES
spacecraft are retransmitted. This product is known as GOESTAP and is
available on SpaceNet 3 transponder 17. The GOES West images are on
1.885 Mhz and the East images are on 1.930 Mhz. You need to hook to
the unclamped base band video out with a shortwave reciever or scanner
that has FM reception ability. Another way is to use a $39 mixer
available from Monitoring Times that will move signals in the 0 to 4
mhz range up to 137 mhz where an ordinary weather satellite receiver
will receiver and demodulate the FM, giving you an audio signal for
your PC weather facsimile card. This signal has a 120 line per minute
rate similar to the polar orbiter signals.
Swagur enterprises has created a device called the Swagursat GT which
allows the TVRO receiver output to be decoded with the proper bandwidth.
The output of the Swagursat GT is an audio signal which can then be decoded
by the weather fax card.

                 HOW DO I CONTACT EQUIPMENT VENDORS??

   GTI Electronics
   1541 Fritz Valley Road
   Lehighton, PA.  18235
     tel (717) 386-4032.

   LONE EAGLE Systems
   Mr. Dave Peres
   5968 Wenninghoff Road
   Omaha, NE.  68134
     tel 402-571-0102

   MultiFAX
   143 Rollin Irish Road
   Milton, VT 05468

   OFS WeatherFAX
   6404 Lakerest Ct
   Raleigh NC
     tel 919-847-4545

   Quorum
   8304 Esters Blvd Suite 850
   Irving, TX 75063
     tel 800-982-9614

   Satellite Data Systems
   PO Box 219
   Cleveland, MN 56017
     tel 507-931-4849

    SSC/Software Systems Consulting
    150 Avenida Cabrillo, Suite C
    San Clemente, CA 92672
      tel 714-498-5784

   Swagur Enterprises
   Box 35
   Middleton, WI 53562
     tel 608-592-7409

   Timestep (dist by Spectrum International)
   Spectrum International
   PO Box 1084
   Concord, Massachussets 01742
     tel 508-263-2145

   Vanguard Electronics
   196-23 Jamaica
   Hollis, NY 11423
     tel 718-468-2720

   WHAT DIGITAL IMAGES ARE AVAILABLE ON SATELLITE AND HOW DO I GET
   THEM?

The NOAA polar orbiters output a digital image using a format called
HRPT. The resolution of HRPT is 1.1 Km per screen pixel and consists
of image information in 4 or 5 spectral bands - usually one
picture in the visible spectrum and several IR images. Receiving HRPT
requires a small tracking dish antenna to follow the bird as it
crosses the sky, a specialized receiver and PC demodulator card. As
the HRPT signal is received, it typically is saved to disk. All 5
channels for a complete pass occupies 80 megabytes of disk space.

The GOES Geostationary satellites transmit a digital signal called VAS
which has a resolution of .8 km per pixel. Because the satellite is
higher up than the polar orbiters, it sees a lot more of the earth and
consequently generates a lot of image data. Its great not having to
track the satellite, but because the data rate is over 2 million bits
per second, a large dish is required, typically 12 feet
diameter minimum. VAS, like HRPT, requires a specialized receiver and
PC demodulator card. In addition, because the full earth is 15,000
pixels wide and 15,000 pixels tall, the full image requires 225
megabytes of storage. VAS images are transmitted continuously 24 hours
per day every half hour.

               HOW DIFFICULT IS IT TO INSTALL A SYSTEM?

You should be be able to assemble, install and track your
satellites in one day, even if you know NOTHING about the
technology involved.  You need only know how to install an antenna in
your yard or on your roof and know how to install an adapter card in
your PC.


    I LIVE ON A WOODED LOT WITH LOTS OF TREES.  IS THIS A PROBLEM?

Not for VHF reception of the polar orbiters in the 137 MHZ VHF band.
Excellent pictures can be received on the VHF frequencies under a
heavy canopy of trees.  A chain saw is needed for Geo-stationary
reception.  Geo-stationary signals from GOES and METEOSAT are in the
low microvave S band.  Trees in the way mean you don't get a picture,
at least in the summer time.  Trees have a tendancy to block the
microwave signals.  Usually you can find SOME place to put the dish to
see the satellites. Mounting on a pole or your roof may help the
situation.

         WHAT DIALUP BBS SYSTEMS ARE THERE FOR FURTHER INFORMATION?

VAS-DAS BBS - 804 525 5202 is a live online provider of VAS imagery,
and has the last 24 hours of VAS from GOES-7 online for downloading.

SAT-TRACKER BBS - 714 590 4382 has files and satellite images,
NASA news, and educator lesson plans.  Sysop is Kermit Allen, a Los
Angeles educator and faculty advisor for the student organization
"Sat-Trackers"

Vanguard BBS - 718 468 2720 has files and information on antennas,
converters, receivers, demodulators, and video equipment. Vanguard is
a commercial vendor of systems.

Dallas Remote Imaging Group BBS - 214 394 7438 has thousands
of files and satellite images, latest NASA news, astronomy, educator
lesson plans, information on NOAA satellites, etc.

     WHAT PUBLICATIONS ARE AVAILABLE FOR FURTHER READING?

WeatherSat Ink, 4821 Jessie Drive, Apex, NC 27502 fax:  (919)-362-5822
publishes a quarterly magazine ($18 per year US, $23 foreign, US funds) that
has the latest news, technical developments, operating status of active
satellites, educational activities, equipment reports and more.

Remote Imaging Group, RIG-SUB, PO Box 142, Rickmansworth, HERTS, WD3 4Rq,
England Is a quarterly journal published by the UK based RIG that is the best
in the field.  It contains many articles and construction projects by RIG
members. A unique feature is high quality centerfolds of satellite imagery.

The ARRL, 225 Main St., Newington, CT, publishes several amateur
radio satellite publications and The Weather Satellite Handbook. All
are well done excellent publications for theory and formats.
Unfortunately, time and technology marches on and The Weather
Satellite Handbook is not up to date on image capture equipment or the
digital modes of HRPT and VAS. It is useful to have, however as a
reference.

Spec Com Journal, RR 2 Box 86, Clarence Iowa 52216
has a lot of weather satellite coverage and a regular
WeatherFax column by Ralph Taggart, author of the Weather Satellite
Handbook.

R. Myers Communications, PO BOX 17108, Fountain Hills, AZ.  85269 tel
602-837-6492 publishes The Weather Satellite Report with up to the
minute news on weather satellite imaging and excellent photographs.

Space Technology Education Program (STEP-Environmental Research
Institute of Michigan - PO BOX 134001, Ann Arbor, MI 48113) publishes
another nice newsletter for educators on direct readout programs.

National Air and Space Musuem
7th Street and Independence
SW
Washington DC
202 357-1300
The NASM has an Educators Resource Center at 202 786-2109 for teachers
from K-12, and can provide educational materials, slides, videotapes,
etc. on the space program.

I HAVE A QUESTION THAT WAS NOT ON THIS LIST.  HOW DO I GET AN ANSWER?

Ask.  You can post your question to the WXSAT mailing list -
wxsat@ssg.com on the Internet, via EMAIL to tomgle@cybernetics.com or send a
self addressed stamped envelope to Tom Glembocki at WeatherSat Ink,
4821 Jessie Dr, Apex NC 27502.