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Subject: SPACE Digest V11 #523

SPACE Digest                                     Volume 11 : Issue 523

Today's Topics:
          Sorry state of US Space Program...
             Re: Weather Satellite Photos

Administrivia:

    Submissions to the SPACE Digest/sci.space should be mailed to
  [e-mail].  Other mail, esp. [un]subscription notices,
  should be sent to [e-mail], or, if urgent, to
             [e-mail]

----------------------------------------------------------------------

Date: 12 Jun 90 00:52:40 GMT
From: nsc!pyramid!infmx![e-mail]  (William Daul)
Subject: Sorry state of US Space Program...

First, let me say I MISS having the country and leaders
being interested in the the Space Program...

We should stick with what we do best...spend money on
the Defense Department, cut the budgets of everything
else, hide our head in the sand ignoring the National
Debt.  No other country can come close to us in these
areas.

--Bi((

------------------------------

Date: 12 Jun 90 13:56:10 GMT
From: swrinde!emory!sol.ctr.columbia.edu!IDA.ORG![e-mail]  (Eric Roskos)
Subject: Re: Weather Satellite Photos

[e-mail] (Henry Spencer) writes:

>US weather-satellite pictures are free to anyone who feels like receiving
>them; there are a good many amateurs doing so.  Unfortunately, to do this
>you need special electronics -- it's not in the commercial comsat frequency
>bands -- and there's a fair bit of hardware involved.  For the low-orbit
>birds (I forget where NOAA 6 is), you also need tracking programs and
>a computer-controlled antenna.

Well...  actually that depends on which kind of photos you want to
receive.  During the hurricane season (and sporadically at other times)
I put satellite photos from NOAA-9, NOAA-10, NOAA-11, and occasionally
the Soviet Meteor satellites, on VMD.CSO.UIUC.EDU in the directory
PHIL.515.  NOAA-6 is not operating any more.  NOAA-9 has mostly failed,
but still has some working parts, including the visible and near
infrared sensors of the AVHRR (Advanced Very High Resolution Radiometer)
used to produce the familiar satellite pictures.  NOAA-10 and NOAA-11
are still working well.  NOAA-10 goes by in the mornings around 8-9AM
local time, NOAA-11 around 2PM local time, NOAA-9 in the evenings around
5:30PM local time.  (These times are for daylight savings time.)

I receive these pictures at home using a home-made "turnstile-reflector"
antenna, which is fixed in position (omnidirectional), a PC, and a small
crystal-controlled VHF receiver.  As you can see if you look at some of
the pictures in the above directory, I tend to have trouble with signal
fading, but that is mostly because the antenna is located on the balcony
of a brick and concrete apartment building, which gets in the way of the
satellite as it is going overhead.  (The apartment complex doesn't allow
visible outside antennas.)

The cost of the overall system varies depending on what it does, but is
very inexpensive compared to most satellite equipment.  In my case I
built a lot of it myself to reduce the cost further, although buying
ready-made equipment is not that bad (about the same price range as a
good VCR.)

These pictures are in the "APT" (Automatic Picture Transmission) format,
a very slow-scan analog raster format developed in the early 1960s for
use with simple drum-type mechanical recorders.  Since it is so simple,
it also works well with PCs.

There are other digital services from these same satellites, though,
which give higher-resolution pictures.  Those do require a tracking
antenna, as well as hardware to receive and decode the digital
transmissions.  For the slight difference in picture quality I've seen
in examples of PC-based equipment for these digital pictures, it's
better just to use the APT service and enhance the image with
conventional image enhancement techniques.  The major advantage from the
digital services is that you can get a lot of other information (sensors
that detect the ozone layer, incoming radiation from space, etc.  are
all encoded in the telemetry frames, along with all four of the
downward-looking image sensors).  I don't have any equipment for that so
I don't know how well it works for home use, although some people do
have home stations for this service (called HRPT, High Resolution
Picture Transmission).  Stations for that service cost in the thousands
of dollars.

You can also receive occasional pictures rebroadcast on shortwave (HF)
from NOAA's "GOES TAP" wire service by various stations on the east and
west coast, but the quality of the pictures is not as good as normal
GOES images (though it tends to be better than the ones shown on TV).  I
find I can rarely receive the shortwave pictures during the summer,
though, due to my location.  If you are in the California area it is
supposed to be much better, since NOAA runs a station there (NMC) with a
directional antenna; its primary lobe goes out across the Pacific, aimed
at Hawaii, but the two side lobes go up and down the west coast.  There
are some pictures put in the same directory (above) by someone else who
has a GOES station (that also requires a dish antenna, but a fixed one)
fairly regularly at present.  Several universities have said they are
going to put together an automated system to make GOES pictures
available on the Internet, but none have gotten it working yet.

Following are some notes I put together some time ago on how to receive
APT pictures directly from the satellite.  These notes were originally
put together for a group of amateur meteorological satellite users.
I did some cursory editing just now to update a few things, but it is
basically unchanged from the original November 1989 posting date.

Some notes on weather satellite reception
E. Roskos  11/7/89

There are three sources of weather satellite imagery that are easily
accessible by amateur users.  These are HF (shortwave) broadcasts from
NOAA's NMC radio station in San Francisco and the Navy's NAM radio
station in Norfolk, VA; direct reception from polar orbiting satellites;
and direct reception from geostationary satellites.

All these sources use variations of the APT (automatic picture
transmission) format developed in the 1960s for use with fairly simple
mechanical recording equipment.  Surplus equipment from the 60s and 70s
is available to record these images, but it is much more cost-effective
to use a computer to record the images.  The image quality is also
usually better, except with the highest-cost equipment (surplus
equipment which records on photographic film, and typically costs
$1000-$2000, gives better pictures but also requires a lot of
maintenance).  The lower-priced (~$600) equipment either records on wet
electolytic paper, which has limited contrast and limited resolution, or
on plain paper using a carbon transfer process, which only gives solid
black / solid white images, and is only suited to weather maps.

The APT format transmits in a raster image similar to that used by a
television, but transmitted at a much slower rate: the HF and polar
satellite transmissions send 2 scan lines per second, while the
geostationary satellites send 4 scan lines per second.  Because the data
is transmitted so slowly, it is relatively easy to decode and display on
a personal computer.

The following equipment is needed to receive these images:

1) An antenna.  For HF transmissions, a regular long wire shortwave
   antenna, or a directional "beam" antenna, is used.

   For polar orbiting satellites, a "turnstile-reflector" antenna is
   the most economical; people wanting to receive a strong signal for
   the longest time possible sometimes build much more elaborate,
   rotatable antennas, but when starting out a turnstile-reflector
   (T-R) antenna is adequate.  It consists of four pieces of wire of
   a specific length, mounted parallel to the ground in an X shape a
   specific distance above a reflector made of "hardware cloth" wire
   screen.  This antenna actually consists of two dipole antennas
   mounted at 90 degrees to each other.  The only difficult part of
   building this antenna is that these two dipoles must be connected
   by a length of cable that will serve to delay the signal from one
   of the dipoles by 90 degrees relative to the other antenna.  In
   reality, even this T-R antenna is not strictly necessary; a simple
   dipole antenna can be used, although periodic signal fading results.
   Another alternative is to use a discone antenna (about $90) made to
   receive VHF (police, fire, etc.) communications, or a VHF active
   antenna (about $300) if space is very limited.

   For geostationary satellites, the best antenna is a dish antenna.
   "Loop yagi" antennas are also available that consist of a long rod
   with loops of aluminum spaced at specific intervals along it; I don't
   have any experience with these antennas, so I don't know 1sthand how well
   they work, but it's claimed they work reasonably well.  The geostationary
   satellites are generally harder to receive and require more equipment,
   though, and the images produced by them are of relatively large areas,
   so polar satellites tend to be better for starting out, since they also
   give "close up" images of the local area.

2) A receiver.  A high-end VHF scanner can be used if it provides at least
   a 30 MHz bandwidth, but only the higher-priced scanners provide this,
   since police and fire (and amateur) VHF communications use a much narrower
   bandwidth.  A receiver with a bandwidth that is too narrow will not
   give usable pictures; most of the picture will have "snow" in it rather
   than an image.  The best alternative is to buy a crystal-controlled
   receiver made specifically for the purpose; these are available for
   around $180 (plus crystals, which are around $15).  I currently use
   a modified 2-meter amateur radio receiver, but it is not really adequate
   since it only has a 20 KHz bandwidth, and costs much more that a
   WEFAX receiver.  Unless you have a receiver already that has the proper
   bandwidth, it is a good idea to buy one of the specifically-made
   WEFAX ones.  In any case, the receiver must be able to receive the
   137-138 MHz range; not all VHF receivers will receive this range, since
   it is specifically for weather satellites rather than voice.
   [NOTE: the above crystal-controlled receivers have been discontinued
   by the manufacturer.  The company now produces a tunable receiver for
   about $100 more in place of it which is reported to be much better.]

   For receiving HF images, a conventional shortwave that can receive
   single sideband is sufficient.  The $300-range receivers work reasonably
   well if they are fairly stable and can be tuned precisely enough,
   but reception of single sideband is required.

3) A downconverter, if you are receiving geostationary images.  This
   converts the geostationary satellite's signal from its frequency
   of 1691 MHz, to the 137 MHz range which WEFAX and VHF receivers receive.
   You don't need a downconverter for anything but the geostationary
   satellites (this is one of the reasons the geostationary satellites
   could be considered a "more advanced" satellite to receive).

4) A preamplifier.  This is only necessary if your signal from your
   VHF antenna is not strong enough without it.  If you use one, you
   should get one that can be mounted out at the antenna end of the
   transmission line, so it should be waterproof.

5) A demodulator.  For polar and geostationary satellites, you need
   an AM demodulator; the AM refers to the fact that the audio tone
   produced by the receiver is a 2400 Hz amplitude modulated signal,
   rather than referring to an amplitude modulated carrier signal --
   the RF signals from these satellites are FM.  For receiving images
   from one of the HF stations, you need an FM demodulator, because
   these stations send an audio signal which varies in frequency from
   1500 Hz to 2300 Hz, rather than varying in amplitude.  Some of the
   FM demodulators you can buy (such as the A&A demodulator I use)
   really are just filters that convert the FM signal to an AM signal;
   you then have to input this to an AM demodulator to get the data
   you need to display the image.  Thus to receive HF images you may
   need both an FM and AM demodulator.

6) Software to display the images on the screen.  One of the better
   starter packages is from Elmer Schwittek in Florida; see below for
   his address.  You can also write your own software if you are good
   at "real time" software.

7) A computer with a display capable of displaying at least 16 distinct
   shades of grey with at least a 640x480 pixel resolution; higher
   resolutions (720x540, 800x600, etc.) are better.

8) For the polar satellites, software for calculating when the satellite
   is coming by.  The "ORBIT23" program on SIMTEL20 is the one I use
   for this, since it is public-domain.

That's basically all you need, although getting it all working, eliminating
RF interference from the computer, etc., may require some general experience
with radio.  Receiving the HF images are the easiest, and require the least
equipment and expertise, although depending on where you are and how
good your antenna is, you may find the image quality is limited due to
a weak signal.  The signal for WEFAX images needs to be considerably better
than is required simply to receive human-readable shortwave broadcasts,
since the machine will interpret the noise as part of the image.  I find
that much of the time I only get a marginal image here, although I have
only a very small antenna, and am not in the best location for receiving
the nearby station.

Here is a typical station in terms of cost:

    Antenna         $35 (build-it-yourself variety)
    Receiver      180
    Demodulators      85 (for both FM & AM together)
    Software      50
            ====
    Total        $350

This doesn't include the computer, VGA board, and monitor.  You can also
use an EGA, but you have to have a monochrome display since an EGA can't
display 16 shades of grey.  There are also programs available for the
CGA, but the CGA doesn't really have adequate resolution.  If you are
buying a new display adapter, it's best to pay the extra $100 and buy a
VGA rather than an EGA; you get a lot more flexibility, and can still
buy a monochrome VGA monitor for it for $120 if you need to cut costs
somewhere.  This is much better than buying an EGA and a color monitor,
in my opinion, at least for the purpose of WEFAX images.

Following are some references and sources of equipment; I don't have
experience with all the companies listed below, but they all sell
equipment for WEFAX, and have been recommended by others in the past.

Books:

Martin R. Davidoff, The Satellite Experimenter's Handbook, published by
the ARRL.  This book is essential; it tells how to build the T-R antenna,
tells about weather satellites, gives addresses to write for more
information, and generally has the technical information you need to
get started.  Buy this book first.

Larry Van Horn, Communications Satellites, published by Grove Enterprises.
This book is much less essential, but has a chapter on weather satellites
that gives a lot of "vital statistics" about the satellites for those
interested.

Georg Klingenfuss, Klingenfuss Facsimile Guide.  A loose collection of
facts about radio facsimile, particularly weather, but geared more towards
European users.  Klingenfuss's English is sometimes very hard to understand,
and the data isn't very up-to-date compared to the other sources, but it
does have some technical details not found in other books, as well as
pictures -- most of the book is pictures of images from various stations,
though many of them are in Europe.  The equipment listed in the book tends
to be high-end, expensive equipment, and isn't always the best available,
so it's best not to rely too heavily on that part.

All the above books are available from most of the mail-order shortwave
companies, and most are available from local ham radio dealers.

Sources:

    Software Systems Consulting
    1303 S. Ola Vista
    San Clemente, CA 92672
    [phone]

This company sells a complete package, including hardware, for $99.00.
I have never used it, but it gets enthusiastic reviews from time to time
on the Usenet.  It seems to simply connect to the RS232 port of the PC,
so I am not sure it gives grey-scale images -- maybe just black and white
weather maps.  It might be a good starter system for someone with a limited
budget, however.  [Note: I have since seen good grey-scale pictures from one
of their packages, so this one is worth looking into.]

    Elmer W. Schwittek
    2347 Coach House Lane
    Naples, FL 33942
    [phone]

A good place to start; Schwittek sells three different compiled BASIC
programs (object code only) for the IBM PC: one for the CGA, one for the
EGA, and recently has added one for the VGA, each of which is around
$50.  The programs work with the demodulators from A&A Engineering (see
below).  The manual, though short, gives a good introduction to WEFAX,
gives diagrams for the A&A boards in case you really want to build them
from scratch (it's much better just to buy the board kits from A&A), and
gives sources for equipment.  The program is kind of primitive; it has
the usual BASIC limitations (images are written directly into RAM, then
dumped to disk after you finish recording an image; you have to specify
the RAM buffer via hardware addresses, since it doesn't use the DOS
memory allocation routines, and it's possible to overwrite DOS until you
figure out the proper addresses; etc.) but it's a very good program for
the price, and the manual and hardware gets you started fairly easily.
He also seems to be very helpful in terms of answering questions.

    A&A Engineering
    Stas J. Andrzewski, W6UCM
    2521 W. La Palma, Unit K
    Anaheim, CA 92801
    [phone]

This company sells good, low-cost demodulator boards that aren't
specific to a given PC.  The AM board has an A/D converter on it which
is necessary to use with the FM board as well, since the FM board only
has a 1-bit digital interface if used on its own.  The AM board's A/D
converter is an 8 bit converter, and the documentation claims it gives 8
bits of data, but in fact the A/D converter is too slow to produce 8
bits of data, so only the high-order 4 bits are usable.  This is OK,
since the PC only can display 4 bits worth of data at once, but if you
want 8 bits you have to build your own A/D converter.  Nevertheless,
it's a good board for the price, and is what I currently use, myself.
You can get the FM and AM boards and a power supply for a discount over
buying each separately; it's a good idea to buy all 3 since the boards
require 3 different power supply voltages.  The board without the power
supply are around $85; I'm not sure what the price with the power supply
is, but it's not a lot more than that.  They don't come with a case, so
you have to buy one of the experimenter's cases from Radio Shack or
something similar.  I piggybacked mine onto an IBM PC prototype board,
got the power from the PC's power supply, and built the new A/D
converter on the prototype board, but I don't recommend that unless you
feel comfortable building boards to plug into your PC.  The easiest way
(and the way Schwittek recommends) is to interface it to the four button
inputs of the game adapter, and have all the demodulator hardware
external to the PC.

    Spectrum International
    PO Box 1084
    Concord, MA 01752
    [phone]

Sells loop yagi antenna kits (you have to bend the aluminum elements
into loops, etc., so some work is required), downconverters, etc.  I've
seen other companies that advertise already-built loop yagi antennas
instead, but don't have their addresses.  The antennas are fairly
expensive, I think around $300.  Again, it's best to save this for
later and work on receiving polar satellites first.

    Hamtronics, Inc.
    65-D Moul Road
    Hilton, NY 14468-9535

Sells WEFAX VHF receivers.

    Vanguard Labs
    196-23 Jamaica Ave.
    Hollos, NY 11423

Sells WEFAX VHF receivers and related equipment.  Used to sell the above
$180 receiver, but discontinued it around April of 1990, replacing it
with a new continuously-tunable receiver (called the WEPIX, I believe).
They have a bulletin board at [phone] which includes
advertisements and prices for their products, although they don't seem
to read it often, so leaving messages on it doesn't seem to do much
good.  Their equipment which I've seen is excellent, designed by an
elderly engineer named Andre Calatayud who has been building the
equipment since 1956.  Their delays between ordering and delivery varies
widely, from a week or so to 1-1/2 months; they apparently redesign the
products from time to time, and if a new design is in process will not
ship until the new version is done.

    Atlantic Surplus Sales
    Ed Bienstock
    3730 Nautilus Ave.
    Brooklyn, NY 11224
    [phone]

Sells surplus WEFAX recorders, VHF receivers, surplus test equipment,
dish antennas, downconverters, etc.  Has a wide variety of equipment,
all of it either surplus or from one of the companies listed above; I
bought a surplus Alden WEFAX recorder from him back before I found I
could do it much better with a computer.  "Caveat emptor" is a good rule
of thumb with this company; it seems to be run by one person, who seems
to have a virtual monopoly on some types surplus WEFAX recorders, and
who seems to have a sort of "old fashoned" way of doing business.  It
took me *months* to get him to ship the machine, and the shipping was
very expensive ($120), but it was a really nice, though technologically
outdated, machine.  When he shipped it, he shipped it in pieces, over a
period of about a week, and I had to call him (not easy since he keeps
unusual hours) to find out what was going on, since I first received
part of a WEFAX machine and a very strange-looking desk, but no
electronics and no manual.  Then the manual arrived, then the
electronics, and, to my surprise, in the end it all fit together into
the desk.  The company has been in business a long time, and they have
an interesting catalog (although it also took 6 months to get the
catalog).  But buying anything from them is an exercise in extreme
patience.
--
Eric Roskos, IDA ([e-mail] or [e-mail])

"It is so self-conscious, so apparently moral, simply to step aside from the
 gaps where the creeks and winds pour down, saying, I never merited this grace,
 quite rightly, and then to sulk along the rest of your days on the edge of
 rage.  I won't have it."              --A. Dillard

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End of SPACE Digest V11 #523
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