HOW TO RECEIVE APT PICTURES FROM THE NOAA SATELLITES ----------------------------------------------------So you have decided you want to receive the NOAA orbiters and you have a  radio  that receives 137.500 MHz and a computer. So now what do you do?  I  hope  this  short  dissertation  will steer you in the correct direction.
To  display a picture from the orbiting birds you need several things. First  you  need  to  'acquire' the satellite. This means you need the program to calculate its position at any time and determine if you can hear  the  signals from the 'bird'. The best place to get this program is  probably AMSAT-NA an organization dedicated to AMateur SATellites. They have several very good tracking programs for the IBM and also for Commodore  and  Apple as well. After you have acquired the program and have it running on your computer, you then need the Keplerian Elements for the NOAA satellites. These are available from the CELESTIAL RCP/M, run  by  TS  Kelso, at 512-892-4180 (Austin, TX)  and from the Weather Fax and Remote Imaging BBS run by Dr. Jeff Wallach, N5ITU as bulletins for some  50 + sets of satellite data. Another bulletin also tells you to  what the printed numbers correspond so you can enter them into the computer program. Use the newest elements you can find as the orbiting satellites are subject to forces which change their orbits. If you use old  data  the error is worse and your chances of hearing the bird are reduced.
Once you are tracking the birds you should hear them on your receiver. They  will  be  on 137.62 (NOAA-9), 137.500 (NOAA-10), 137.850 (Meteor 2-14,2-15)  and  137.4  (Meteor  2-16).  Now  comes  the  first  thing different  about  NOAA  orbiters.  The  frequency  deviation of the FM transmission  is  about  +/-18-20  kHz.  This  is  4  times the normal deviation  of  a police call and 1/3 the deviation of the FM broadcast band   FM   signal.   If   you  receive  the  signal  on  the  regular communications  width  of  the  scanner the light areas of the picture will be noisy and the signal will sound distorted and the picture will basically  be useless. If you use the FM broadcast bandwidth (assuming your  scanner  will let you), the signal will be weak and there may be too much background noise to see the picture. So what now ? Well there are  two ways to fix the problem, find a receiver with the proper I.F. bandwidth  filter  of  50  kHz,  or modify the I.F. of your scanner to about  50-80 kHz. The simplest mod which has been found to be workable is to remove the narrow communications I.F. filter and replace it with a  0.01 uFd capacitor. This provides for good Wefax pictures from GOES and  pretty  fair  NOAA  orbiter  pictures. It can of course result in retuning  the  radio,  voiding the warranty and making the squelch not work properly.
The  other  characteristic of the NOAA satellite transmissions is THEY ARE  WEAK.  To  get  good  pictures  over a large area we have found a pre-amplifier  to  be  essential. A GaAs-FET type can be obtained from various  sources at a reasonable price but still about 50-100 dollars. You  can  also build one for about 25 dollars from plans for a pre-amp for the 2-meter amateur band and tune it to 137.5 easily.
Lastly   but   importantly,  the  antenna  needs  to  be  of  an  omni directional,  uniform pattern type such as a turnstile antenna similar to  those  used  in  the FM broadcast reception business but of course tuned  to  137.5  MHz.  Mount  the pre-amp at the antenna if possible. Crooked  coathangers  on  broomsticks have been known to work with the pre-amps  mounted  on  the broomstick, so it is not difficult to build the antenna.
Now that you have a nice audio signal from the satellite, what happens next?	The  audio  tone of 2400 HZ which is the carrier tone that is
used to carry the picture information (video), must be removed and the video  data converted from analog to digital and then displayed on the computer monitor by the software. The software to do this is available from several sources with more coming along. Several stand-alone boxes are also available that produce some form of computer output either in printed  form  or  on the display. In addition the people on the Wefax BBS  may  also  have  some  data  to  share  with  you  regarding this equipment.
One  of  the  best  sources  for  information is the weather Satellite Handbook available from Dr. Ralph Taggart of Michigan State University at 602 S. Jefferson, Mason, MI 48854 for $12.50. Taggart also writes a monthly WEATHERSAT column which appears in '73 Magazine. A must is THE JOURNAL OF THE ENVIRONMENTAL SALELLITE AMATEUR USERS' GROUP - JESAUG which  is  published  quarterly.  It  is available for $12.00 from the editor, Greg Mengell, 2685 Ellenbrook Drive, Rancho Cordova, CA 95670. Back issurs of the 'Journal' are also available.
At  the  present  the  simplest  software  for  the  IBM  is the Elmer Schweittek MULTIFAX 2.0 software. A hardware kit is available from A&A Engineering  which  includes  the  video  dectector  circuit  and  A/D converter. Input to the PC is via the game port.
The  WEPIX(tm)  software  and hardware should be available from Encomm before  Christmas  time this year and it will produce pictures of 1200 lines  800  samples  of  each line displayed in 200 x 200 pixels in 16 shades  of  gray or 16 colors using an IBM PC with 640kB, EGA card and at least one 360k disk.
