Frequently Asked Questions about the MultiFAX System:

1) What Hardware/Software do I need?

This is a brief list of what's required. More information on all of these components is provided in detail below.

To receive the NOAA (US) and Meteor (Russia) polar orbiting satellites (VHF, 137-138 MHz) you will need:

To receive the GOES and Meteosat geostationary weather satellites (1691 MHz) in addition to the polar orbiters, you will have to add:

2) What's Included with the MultiFAX Demodulator?

MultiFAX demodulators are available in two versions. One version (the Internal demodulator) is to be installed in an empty 8 or 16-bit slot in your computer. The other version (the External demodulator) is connected to the parallel (printer) port of your computer. Both demodulators have exactly the same capabilities and specifications and use the same software (included). Neither demodulator uses any additional "interrupts" ("IRQs"). The external demodulator has the advantage of being powered by 12 volts DC (a 120 VAC adapter is included) and can work with any IBM compatible computer that has a printer port, such as laptops and notebooks as well as desktop computers. Both demodulators accept the audio signal from a satellite or HF receiver. This is a simple two wire hookup. Included is the latest MultiFAX software which works with the demodulator to track satellites, receive, store, display, print, grid, and manipulate the satellite pictures you record. In addition a Reference Audio Tape and complete 85 page User's Guide are included. Both MultiFAX demodulators are FCC class A and B certified.

3) What are the computer requirements?

  • An empty slot or parallel port:

    The internal card plugs into an 8 or 16 bit slot on your IBM compatible computer's motherboard - just like all of the other cards in your computer. The external demodulator connects to an unused parallel port (LPT1, LPT2, or LPT3).

  • 640 KB or more of computer memory:

    Extended or expanded memory is not required for a complete recording but can be used instead of a hard disk. See the section below on Hard Disks.

  • VGA or Super VGA (SVGA) card and VGA or SVGA monitor:

    A system with standard VGA capability will produce pictures with 16 shades of gray (or 16 false colors) with 640 pixels (picture elements) horizontally and 480 pixels vertically. A super VGA card and monitor used with the MultiFAX software will produce up to a 1024x768 pixel image with 64 shades of gray or 256 false colors. While any VGA or SVGA card will work in the 16 shade mode, most, but not all, SVGA cards are supported at this time for the 64 shade mode. This is because SVGA cards implement their capabilities differently and each card needs it's own driver written into the software to function at the SVGA level. Currently these SVGA cards are supported:

    Up to 1024x768 resolution:

    > Trident 8900C chip set
    > Cards based on the Tseng ET4000 chip set (Tseng, Orchid, Boca, CompuAdd, others)
    > Cards that support the VESA standard (virtually all cards today)

    640x480 and 800x600 resolution:

    All the above cards plus:
    > ATI VGA Wonder and Wonder XL cards
    > Video 7
    > Paradise
    > Cards based on the Tseng ET3000 chip set (Tseng, Orchid)

    All of the above cards must have at least 512 KB of memory installed to function in the 800x600 SVGA mode and 1 MB to support the 1024x768 SVGA mode.

    Note: A standard VGA monitor will produce 64 shades of gray in the 640x480 mode if you have one of the above SVGA cards. In other words, if you currently have a standard VGA system (16 shades) and want to upgrade to 64 shade capability in the 640x480 mode, only the video card needs to be replaced - the monitor will still be usable.

  • Hard disk or RAM disk with at least 4MB empty capacity:

    The image data received from the satellite is simultaneously displayed on the computer screen and saved to disk (or RAM disk) by the computer. Computer memory is not required for storing picture data--the data can be stored directly to your hard disk. This means that extended or expanded memory is not required to receive a full satellite image--a 12 minute NOAA pass with both the visual and IR pictures. Extended or expanded memory can be used to store the picture during recording if desired (see the information on RAM disks below).

    The data stored during the satellite recording is independent of the graphics card in your computer (VGA or SVGA). This means that any recordings saved with a VGA system still have the all the data stored to produce the full 64 gray shades (256 colors) if used on another PC with SVGA or the VGA system is upgraded to SVGA. The display on the screen during recording is primarily used for monitoring the picture as it is received and for adjusting the gain on the receiver to adjust the "brightness" of the picture.

    The full 12 minute pass of a NOAA satellite requires 3.5 MB (3.5 million 8 bit pixels) of storage! This is much more data (pixels) than can be seen on the computer screen at any one time. The MultiFAX software allows you to "zoom" in on any area of the picture you have recorded up to a factor of 8X (64 times magnification of the area). Zooming from 1X to 4X allows more data to be placed on the screen at each stepÄthe pixel density stays essentially the same while you magnify. Therefore, zooming from 1X to 4X not only magnifies the picture but it also displays 16 times as much detail as the original 1X view. At 4X the pixels are displaying the maximum resolution, only about 2 miles on a side!

    If you plan to use a slow computer (10 MHz or less) and a slow hard drive (75 ms or greater) you may find that the hard drive has difficulty keeping up with the continuous 12 minute flow of data. This can cause the picture to "break" or have a step in the picture as it jumps sideways on the screen. One remedy for this problem is to defragment your hard disk with a utility such as DEFRAG (included with DOS 6.0 and later) before recording every picture. This is usually very effective at fixing the "breakage" in the picture.

    If you have extended or expanded memory the best way to record the picture is with a RAM disk. This reduces the wear and tear on the hard drive and there is no concern about the speed of the computer or the speed of the hard drive - the RAM drive is more than fast enough to keep up with the data rate. IBM DOS and Microsoft DOS have RAM disk software included with the DOS package. Of course you will need 4MB of expanded or extended RAM in addition to your normal 640 KB to use this approach.

    4) What type of signals does the MultiFAX system work with?

    There are three major sources of WEFAX signals that the MultiFAX card can capture:

  • HF fax ground transmissions

  • Polar orbiting weather satellites (NOAA, Meteor, Feng Yun) transmitting APT (Automatic Picture Transmission) signals in the VHF band (137 to 138 MHz),

  • Geostationary weather satellites (GOES) transmitting at 1.691 GHz.

    The majority of MultiFAX users primarily receive the polar orbiting satellite signals for two important reasons:

  • The equipment is relatively inexpensive to purchase, make, or modify, and

  • The images acquired from the polar orbiters have the highest resolution (2-3 miles) of the three signal sources. More details on the various receiving systems are given below.

    5) Where can I get a receiver for the polar orbiting satellites?

    There are two common methods for obtaining an APT receiver:

  • Purchase a receiver made specifically for receiving the polar orbiting satellites. This option will supply the highest quality images. MultiFAX sells the MF-R1--an excellent, high quality, low cost weather satellite receiver that can be used for both polar orbiters (NOAA, Meteor) and, in conjunction with a downconverter, the geostationary weather satellites (GOES, Meteosat). MultiFAX also sells the popular Vanguard WEPIX-2000 receiver.

  • Modify an off-the-shelf scanner. Many people have found this to be a low cost alternative for APT reception. Almost any scanner that can tune to the 137 to 138 MHz band can be simply modified to receive acceptable quality pictures. The modification requires the replacement of a filter with a 0.01 microFarad capacitor. Because all scanners are different, no one procedure can be presented that will work with them all--someone that is knowledgeable in electronics can easily find the component that should be replaced. One drawback to this method is that a scanner modified in this manner will not reproduce the image exactly as the satellite is sending it--this means that infrared temperature measurements are either fairly inaccurate or not possible.

    6) What about antennas for polar orbiters?

    There are two basic antenna choices for VHF reception of NOAA (USA), METEOR (Russia), and Feng Yun (China) satellites: turnstiles and Yagis. Turnstiles are relatively insensitive to direction (omnidirectional) and are generally fixed in location. Yagis, which resemble TV antennas, are more directional and are best used with rotators to track the satellite as it passes.

    The stationary turnstile antenna has the advantage of being fixed and "pointing straight up." The antenna accepts signals over a wide angle and will provide good pictures once the satellite is about 20 degrees above the horizon. Because there are no moving parts, installation and maintenance effort is minimal, and cost to purchase and setup are relatively low. Of course the antenna (like most antennas) should be mounted outdoors in a high place, such as the roof. The antenna is approximately 4 feet square, 3 feet high, and weighs about 3.5 pounds.

    One drawback to the turnstile antenna is that satellite passes near the horizon are typically noisy which degrades picture quality. In addition, because of the wide beam angle, extraneous noise signals are occasionally picked up along with the satellite signal.

    The crossed Yagi is the other popular form of polar orbiting satellite antenna. This antenna is physically larger than a turnstile (about the size of a TV antenna), has greater gain yielding stronger signals, and must be aimed towards the satellite as it passes. This requires two rotators (such as TV antenna rotators) to move the antenna in both altitude and azimuth.

    The satellite tracking function of the MFMAP software will provide you with maps and schedule output for predicting the rise and set of the satellites. The MFMAP software will also give you the information you need to track the satellite during image capture in azimuth (from 0 to 360 degrees) and elevation (0 to 90 degrees) when using a Yagi antenna. The antenna can be "pointed" manually using the rotator controls located near the receiver. In addition, the tracking can be done automatically using the MFMAP software and the Kansas City Tracker during the recording. The advantages of this type of antenna setup are that low satellite passes of high quality can be easily recorded. Satellites only a few degrees above the horizon can often be recorded with very little noise. This allows a full, high quality pass, nearly horizon to horizon (in other words, a picture 2940 miles long by about 1875 miles wide - over 5.5 million square miles with a resolution of about 2 to 3 miles). For a receiver in Florida that means from the northern part of South America to Hudson Bay! In addition, because of the narrow beam width, extraneous noise sources often do not interfere with the satellite signal.

    The obvious disadvantages of a controllable Yagi are complexity, higher maintenance, and cost. Many users find that the stationary turnstile antenna is perfectly adequate for their needs.

    A last note about antennas - many people find that using a preamp located at the antenna improves their picture quality significantly. In addition, the use of a preamp will compensate for signal losses that occur in the coax that connects the antenna and the receiver. If the use of a preamp is not contemplated then a high quality coaxial cable (low loss) is needed, for instance RG-8U. A preamp is strongly recommended when using an omnidirectional antenna such as a turnstile.

    7) What is this satellite tracking function mentioned above?

    Because the polar orbiting satellites are in low Earth orbit, they are constantly moving with respect to the observer. In order to predict when they will be "visible" to your antenna (and where to point the antenna if you are using a movable antenna) you will need satellite tracking capability. This tracking function is built right in to the MFMAP software so there is no need to purchase a separate satellite tracking package. Accurate tracking will require satellite orbital elements that should be updated every few weeks or so. These elements can be downloaded from several bulletin boards using a modem. To download up-to-date elements click here. Current elements can also be downloaded from the Celestial Web Site (

    The satellite tracking function of MFMAP can also be used for locating the position of the geostationary satellites.

    8) How often will I be able to receive a NOAA satellite?

    The NOAA and Meteor satellites are in near-polar orbits. That means that every location on the Earth is covered and can receive images at least twice in a 24 hour period (once in the daytime, once at night). Because of overlap on consecutive orbits, nearly all locations are imaged four times a day. In addition, even though your location may not be included in a picture because the satellite is not very high where you are, you still may be able to receive an excellent picture, especially with the Yagi antenna. That means that you may be able to receive an individual polar orbiting satellite up to six times a day (24 hours). Because there are several operational US NOAA satellites that means you can receive quite a few images a day - just from the US polar orbiters! The same holds true for the Russian Meteor satellites.

    9) What resolution can I expect from the MultiFAX system?

    Both MultiFAX demodulators sample the NOAA polar orbiting satellite signals 4800 times per second. This means that each sample, or pixel, is approximately 1.5 miles wide. The NOAA satellites can provide two to three mile resolution in the center of the imageÄthis means that the MultiFAX system captures ALL of the detail that the NOAA satellites can provide. This is important--many systems available today do not sample the image data often enough to provide full resolution.

    10) What is the audio tape for?

    The audio tape included with the demodulator contains actual recordings of a NOAA APT polar satellite pass, a Meteosat geostationary satellite transmission, and an HF fax signal. The tape can be used to get an idea of what these signals sound like when you actually start recording your own. In addition the two satellite recordings (not the HF) can actually be played back on a tape deck or portable tape player and recorded by your MultiFAX setup to produce an image with no need for antenna or receiver. The HF recording can also help you "gain an ear" for tuning the HF fax signals properly.

    11) Can I store satellite passes on my own audio tape recordings?

    Yes. Because of the PLL (Phase Locked Loop) circuitry employed in the MultiFAX demodulators, standard audio tape recordings of satellite passes can be used to store satellite images. There are several advantages to using an audio tape recording of a satellite pass rather than using the original satellite signal directly:

  • An archive of important or interesting (hurricanes, etc.) images can be easily and inexpensively assembled.

  • Recording an image from a tape is a perfect way to demonstrate your satellite image acquisition system when it is not convenient to work with the satellite schedule.

  • The full satellite pass can be replayed at anytime to "fine tune" the recording level to accentuate certain features captured in a recording.

  • A satellite pass can be recorded using just the antenna, receiver, and tape recorder. This means if a computer is not available (in a portable situation for instance) the pass can be recorded and input to the computer/demodulator later at the user's convenience.

    Many weather satellite systems currently available will not work with audio tape recordings. This is a critical feature for many users.

    12) What do I need to know about HF and GOES reception?


    The US Navy's fax stations on the east and west coast send weather charts and rebroadcast some satellite pictures to their ships at sea. These stations are often the best signal sources, though there are many HF Fax stations in all parts of the world sending both weather and picture information. The Navy stations broadcast 24 hours per day on several different frequencies throughout the HF range.

    Almost any HF (2-30 MHz) receiver is sensitive enough, however not all have sufficient frequency stability for HF Fax. Any receiver designed to receive SSB (Single Sideband) transmission, which is required, is more than sufficiently stable, as is any receiver that derives its frequencies by synthesizing them from a single crystal. Several current HF receivers sold at Radio Shack have sufficient stability for HF Fax.

    An outside dipole antenna cut to the frequency you receive best should be used for HF fax. If you already have a dipole antenna cut for some other frequency, give it a try. The fact that the stations broadcast on several frequencies make it likely that you will get reasonable reception on one of them.

    But HF fax differs from satellite fax. Satellite signals tend to be loud and clear when they are in view. HF signals can be subject to multi-path reception accompanied by considerable fading at times. Multi-path upsets timing and under these conditions chart lines can become blurred. Good reception is often possible, however, and HF fax is probably the least expensive way to copy facsimile.

    A typical HF picture from the Navy stations is composed of 1600 lines and requires 13.3 minutes to send. This fills one screen of your monitor.


    The GOES (Geostationary Operational Environmental Satellite) and Meteosat require the most sophisticated receiving system. Before attempting to get GOES fax, one should establish the reception of the polar orbiting satellites, since part of the same receiving equipment is used for both.

    The GOES satellites operate on 1691 MHz and send pictures almost continually - each picture requires only 200 seconds. This means that more weather pictures are available from GOES than any other source, and they are relayed to GOES from all parts of the earth. Each picture is made up of 800 lines.

    A dish antenna 6 feet in diameter or several loop Yagi antennas (9 feet long, 4 inches diameter) are normally required. Some of the newer GOES satellites (GOES 8) transmit at high power levels and a dish smaller than 6 feet may suffice. Also required is a downconverter which converts the 1691 MHz frequency to 137.50 MHz, which is one of the polar orbiting satellite frequencies. This means that the output of the down converter feeds directly into the input of the polar-orbiting satellite receiver. MultiFAX sells a high quality, low priced downconverter for this purpose.

    13) Does it take a lot of effort to get a system put together and running?

    Not at all. However (like anything worth doing), you should be aware that some minimal work is required on your part to install the hardware and understand some of the basics involved in this technology. The result will be better and more consistent satellite images. An antenna will have to be mounted in an appropriate location. This will require a mounting bracket or tripod of some sort - these are available at Radio Shack. The effort is not much different than installing a TV antenna. A coaxial cable connecting the antenna to the receiver will have to be installed: typically 50 feet or so of RG-58 (or better yet, RG-8U). This too can be purchased at Radio Shack. You'll find that the MultiFAX software is has a "point and shoot" graphical user interface with mouse support and very easy to learn.

    The Weather Satellite Handbook by Ralph Taggart (American Radio Relay League, 255 Main Street, Newington, CT 06111) is highly recommended. It is not required but it will give you a good idea of what results you can expect, some helpful tips on how to get those results, and was written by one of the pioneers in amateur weather satellite reception.

    14) What about a complete package?

    MultiFAX has put together complete hardware/software packages including an internal or external demodulator, the MultiFAX MF-R1 receiver, and an omnidirectional turnstile antenna with built in GaAs preamp. Of course these items can be purchased separately as well.

    The package prices offer approximately 7 to 10% savings over purchasing the components separately. Please refer to the price list for more details.

    15) How can I tell what the pictures will look like on my PC?

    To see how typical pictures will look on your PC, try our Demo Packages--they (as well as many other images and software) can be downloaded at no charge from the MultiFAX BBS (716-425-8759).

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