The weather side of KC8FAY
someday there will
be a picture here
I got into weather satellite reception before I actually started the ham radio stuff. I currently receive the NOAA LEO satellites as well as the GOES WEFAX and 9600 baud EMWIN signals.
What is he talking about:
Part of the United States Department of Commerce (don't ask why), the National Oceanic and Atmospheric Administration (NOAA) which is the large government agency that has as one of its main functions the collection of data for the analysis and prediction of the world's weather. Branches of NOAA include:
The part of NOAA I am most interested in is NESDIS. NESDIS in association with NASA is responsible for designing, manufacturing and deploying both low earth orbiting satellites and geostationary satellite systems. Information on these systems can be found in detail at a sub-agency of NESDIS known as the Office of Satellite Operations (OSO).
Polar or Low Earth Orbiting Satellites (LEOs)
These satellites are usually referred to as the NOAA birds. They are orbiting our earth in a polar orbit (from pole to pole) and only about 500 to 600 miles up (hence, low earth orbiting). These satellites use an optical scanner to 'watch' everything that passes below them in both the visible light spectrum and the infrared spectrum. These pictures are transmitted in real time as the bird orbits the earth.
The Russians also have LEOs in orbit, and they are called the METEOR satellites or just MET. There is currently only MET 3-5 transmitting signals. The current generation of METs only have a visible light spectrum reader and do not transmit on the dark side of the earth to save power.
China also has a LEO in orbit called Fen-Yung (or something like that). We basically ignore this bird because it is very seldom sending a signal. I don't even know if it's operational anymore.
These sats have a designed lifespan of > 2 years. The life of a LEO satellite is a lonely and short one. The environment is very hostile to electronic and optical equipment.
Geostationary Satellites
NOAA currently operates three geostationary satellites; GOES-8, GOES-9, and GOES-10. What is GOES? How about: geostationary operational environmental satellites. A geostationary satellite is one that is placed in an orbit above the equator at a specific distance from the earth (about 25,000 miles) so that the speed of the satellite in orbit matches the speed of the earth turning below it - and so the satellite appears to 'hang' in the same place all the time. Almost all communication satellites are geostationary satellites. Since the geostationary satellites never move (relative to the earth), you can only 'see' them if you are on the right side of the earth. GOES-8 sits out above the atlantic (75 degrees West) and serves the atlantic side of the earth, with coverage well into the middle of the US. GOES-9 sits out above the pacific (135 degrees West) and serves the pacific side of the earth, with coverage well into the US. GOES-10 is actually a standby bird and will be moved to replace GOES-8 or 9 when the time comes, GOES-10 is also used in hurricane season. Click here to see coverage of these geostationary sats. These GOES birds transmit a whole slew of useful signals among the more popular ones WEFAX (weather fax), GVAR (GOES variable format), EMWIN (emergency managers weather information network). These formats are detailed later on.
Now that you know about what's out there collecting the data, we need to talk about how the data is sent back to earth and how to make sense of it. The current, most popular data sources are:
APT (automatic picture transmission)
These pictures have a resolution of about 4km and are transmitted in real time from both the NOAA and the MET birds. The NOAA birds transmit both a visible light and infrared picture, the MET only has a visible light picture and only transmits when its solar cells are illuminated.
The APT signal is transmitted in the 137MHz band and is readily receivable with any basic scanner. However, the transmitted signal is about 40khz wide and most scanners are only 15khz wide. So most scanners chop off most of the signal - so you need a special receiver or you need to modify a scanner so it is 40khz wide.
There are currently two NOAA birds actively sending APT, these are NOAA-12 and NOAA-14. NOAA-12 transmits APT on 137.50 MHz FM with an AM modulated signal. NOAA-14 transmits APT on 137.62MHz using the same signal. The Russian MET 3-5 is transmitting on 137.8MHz. A NOAA-15 bird is scheduled to launch in May of 1998.
HRPT (high resolution picture transmission)
The APT birds mentioned above also transmit another kind of signal called HRPT. This has a resolution of 1km and is transmitted around 1.7GHz. A tracking high-gain antenna is needed to receive these signals. They are well worth the work however, the pictures are spectacular.
I do not believe the Russian MET birds have HRPT capabilities.
WEFAX (weather fax)
Weather Fax is available on numerous ground based HF stations that you can pickup on any standard shortwave radio.
The same weather fax format is also available from the GOES satellites. This is broadcast down at 1.691GHz almost constantly. It requires a high-gain fixed antenna (pointing at the fixed geostationary satellite).
EMWIN
EMWIN is Emergency Managers Weather Information Network. This is a 9600 baud datastream of assorted weather products ranging from text based bulletins to WEFAX pictures and all sorts of other neat stuff.
This signal is sent down also around 1.7GHz and requires a high-gain fixed antenna system (the same one used for the GOES WEFAX signal).
What do I do with the signal?
So, let's say you set up a dish in your backyard and point it at one of the GOES birds. What do you do with the wire coming into your house?
Well, most satellite dishes have what is called an LNA (low-noise amplifier). This is the thing that is suspended over the middle of the dish. Inside the LNA is usually a downconverter - this takes that 1.7GHz signal and converts it to a frequency that is easier to use, usually around 137MHz. Once downconverted, you can use much less expensive cable and equipment to process it.
So, now you've got this 137MHz signal coming in the house - now what? Send that signal into the back of a typical scanner and tune it to 137.5MHz (with most downconverters) - you should hear one of two things - silence (quiet-like dead carrier, not the standard empty FM hissing noise) or a very clear signal that sounds like a computer modem. If you get this signal you are hearing the WEFAX feed - this signal can be fed into your computer's sound card and decoded with software or sent to a dedicated demodulator and then processed with software.
The EMWIN downfeed is at 137.250 (with most downconverters) and you cannot hear it on your scanner. In fact, you must modify your scanner and tap off the discriminator output to get the 9600 signal. This signal then is sent to a 9600 baud demodulator and processed by software on a computer.
The final product in all these systems is a file that contains some sort of useful weather information, either text or graphics based.
6 foot loop yagi antenna
This antenna is tuned for 1.7GHz and provides a gain of about 20db. It is adequate for GOES reception but a dish is the preferred method and will produce much better results. My antenna was purchased in kit form from Spectrum International, the US marketer for TimeStep weather satellite products. I can highly recommend the TimeStep equipment and Spectrum Int. is quite good to work with.
35db HEMT amplifier
Once again, brought to you by TimeStep. 35db gain with less than 1db noise. I could have built the LNA but since I was already pushing my luck with the yagi, I wanted a rock solid high quality LNA.
Downconverter
This is the DEM1691CK purchased from Down East Microwave in kit form and converts my 1.691MHz WEFAX signal to 137.5MHz and also gives me the 9600 baud EMWIN signal at 137.250MHz. DEM also has a loop yagi available, the 1844LY which has a 9ft boom.
Uniden BC-560XLT scanner
This scanner is used for the EMWIN downlink. It has been modified to pick off the discriminator output and I also replace the stupid motorola antenna jack with a standard BNC connector.
9600 baud EMWIN demodulator and Weathernode Software
Both were puchased at the very friendly Skywalker Data Systems - give Jack a call, he's a very helpful guy.
TimeStep Scanning Weather Satellite Receiver
An 8 channel scanning weather satellite receiver. Very well made, high quality, high sensitivity scanning receiver. Timestep sells complete turnkey APT and GOES systems for those who just want to plug it in - but the parts are some of the best for those like me who want to mix and match. Hamtronics also makes a scanning receiver in kit form.
Woodhouse communications visual contrast enhancement system
Available in kit form only. Adds contrast to MET APT images (which basically are just black and white, very little shading).
Homebrew crossed dipole antenna system
PVC pipe is every antenna builder's best friend. Total cost of antenna is less than $20. Build it in about an hour. Details in the Weather Satellite Handbook available from the ARRL. This book is a must have.
Hamtronics 137MHz low noise amplifier
Mounted at the antenna for improved reception at low angles.
Multifax demodulator and MFMAP7 software
This is probably one of the best demod/software packages on the market today. Runs in DOS (which means you can go portable with a cheap laptop), completely unattended recording, automatic satellite tracking (with a Kansas City Tracker), does APT, GOES WEFAX, HF WEFAX. I use the external demodulator so I can go mobile with the laptop. An excellent system if your serious about this stuff. Timestep also has demods and software, Hamtronics sells them too, I'll be Jack at Skywalker datasystems has something as well.
