Setting up your Satellite Data Acquisition system


1. Don't rush. Allow yourself plenty of time to familiarize yourself with the various components. Satellite data acquisition is not something you can just plug-in and expect to get instant results. Because it's more complex than any program you may have used and because the operation requires several components that must function properly, it's best to take it one step at a time.

2. The first thing to do is to make sure your computer doesn't radiate so much interference that it blocks out the satellites weak signal. All computers generate a very broad spectrum of interference. The FCC sets limits on this interference, however the allowable limits are much greater than the signal strength from the satellite. You will have to take precautions to prevent this interference from being picked up by the receiving equipment. The receiver is in a metal case and unless your computer is sending hash into the power line the receiver itself should not pick up any interference. Make this test to make sure. First turn on the receiver in the auto-scanning mode and for now do not connect an antenna or cable. Make sure the squelch is on according to the receiver instructions and that the LED indicators show that the receiver is scanning. Now turn the computer on. If the scanning stops it means the receiver has picked up an interfering signal from the computer. If this happens, move the receiver a few feet away from the computer. If you still pick up a signal you might have to plug your computer into an outlet box that has an RFI filter. These outlet boxes are also equipped with with a surge protector but not all surge protector boxes have RFI filters. Make sure you get one with an RFI filter. You can get one at Radio Shack or at many mail order supply houses. Do not plug the receiver's power adapter into the same outlet box as the computer. When the receiver scans continuously with the computer on or off you can go to the next step.

3. Now assemble the antenna. It's best not to assemble it indoors unless you plan to use it in your attic. It will work in an attic but reception will be affected when the roof is wet. You can assemble it and test it at ground level in a yard prior to mounting it on your roof. You may find that the antenna will have to be 100 feet away from the computer to keep from picking up interference from the computer, so start off with 100 feet. If you are using it on a boat 100 feet might be too much; in that case use as much as you can and hope for the best. Use RG-58/U cable as you will not gain anything by using the heavier RG-8/U. The cable will need a BNC male plug on both ends. If you can't buy a 100 foot length with the plugs already attached then make sure you do a good job. It's easy to get a short or open connection if you don't have experience. You can also use two 50 ft. lengths connected together with a UG/918 coupler.

4. Radio shack sells pre-assembled cables for CB use which will work fine with our antenna and receiver. Just make sure the cable is 50 Ohms as there is also a 75 Ohm variety. When you have the antenna assembled and the cable connected between the antenna and receiver repeat the test you did in paragraph #2. This time it's possible that the scanning may stop even with your computer off. You may actually be picking up a passing satellite which you can identify by a sort of beeping/ticking sound or you could be picking up an interfering signal from one of your neighbors electronic appliances.

5. In metropolitan areas the environment is jammed with electromagnetic signals so one has to learn to live with them. If you do get an interfering signal all you can do is hope it doesn't last. Whatever is causing it will usually go away in a period of time. At this point you are probably wondering why the receiver can't be more selective. Actually the receiver is extremely selective but if the interference falls right on the satellite frequency there is no way the receiver can be prevented from picking it up since they are both electromagnetic waves. Normally in radio and TV communications the problem is solved by overriding the interference with a strong signal. The satellite's signal however can sometimes be weaker than the interfering signal. Any attempt to amplify the satellite's signal will also amplify the interfering signal. While all this sounds discouraging, it's not really all that bad. Usually it's possible to find the source of interference. Once that is out of the way you should proceed to put the antenna in it's final position. The higher up you can put it the better. Keep it as far away as possible from TV antennas. They all radiate interfering signals. When in it's final position redo test #2. You might find you have to move the antenna to another spot on your roof.

6. Before trying to capture pictures, practice listening for the satellites. Use the satellite tracking program to determine when they will be within range. Check the accuracy of the timing and how long they stay within range. Familiarize yourself with every aspect of the tracking program. Make sure it has up-to-date Keplerian elements. If you don't know what they are, read up on them. If you get stuck, ask questions. There are several satellite bulletin boards throughout the country where you can get help.

7. Now you're ready for that exciting moment when the pictures will appear on your screen one line at a time. Since different programs and interfaces will have different procedures, read the manual or instructions thoroughly. Don't be discouraged if things go wrong. Not everyone understands instructions the same way. What's obvious to one person might not be to another. As long as you've made the correct electrical and mechanical connections any errors made will not cause any harm. Some possible causes for errors are as follows: setting a signal level that is to low or too high, selecting a NOAA capture mode while receiving a METEOR satellite and vice-verse, using an EGA monitor while using a VGA program mode and vice-verse. Using a color mode where you should be using gray scale. Go easy on colors. Too many colors create confusion. The satellites do not transmit in color. You create colors by assigning a gray level to a chosen color. Experiment to your hearts content and give yourself time, lots of time to gain hands-on experience. Satellites are here to stay and you can expect many more environmental type satellites in the future.

8. Now that you've received a few pictures the one thing that will come to mind is: what is it that you're looking at? You see land and sea but where is it? It becomes even more confusing if much of the area is covered by clouds. Here is where experience comes in and it will take time. Just as a radiologist makes sense of an X-Ray by years of training it also takes training to interpret a satellite picture Metrologists are particularly well trained for this but you can train yourself by making a few observations over a period of time. First you must check the satellite tracking program to see what path the satellite took and envision a swath 3000 KM wide. If it passed near the coast, look for some coastline features ( a map is helpful), If it passed inland look for large lakes, rivers and mountain ranges. After a few passes you will see a repetition of some landmarks and it will begin to make sense. Remember that the satellite is always transmitting one line at a time what it sees immediately in its line of vision as it spins. You, on the other hand are receiving what the satellite sees only when the satellite is in line of sight of your antenna. Since the satellite is hundreds of miles up it can see hundreds of miles in all directions.

9. Since cloud patterns are never the same and the satellites take a slightly different path each time it makes a pass within your receiving range, all the pictures you get will be different. All the NOAA satellites transmit both visible light pictures and infra-red pictures. Most capture programs give you a choice of viewing them side-by-side or separately. Infra-red pictures don't look like much to the untrained eye but contain valuable temperature information which is particularly useful to fishermen. The Meteor satellites do not transmit infra-red during daylight but since each scan line is devoted solely to visible light the pictures are twice as detailed as the NOAA satellites. Keep in mind that the satellite's picture resolution is limited by the sub-carrier frequency of 2500 Hertz. Since the sub-carrier cannot be modulated by more than 1/2 of its frequency before a distortion called aliasing becomes apparent, 1200 light variations per second is the most it can send .Since it sends 2 lines per second each line will have 600 light variations or pixels as they are called. This is very close to the VGA mode of computers and is a very acceptable picture. For the NOAA satellites each line actually contains 2 pictures - the visible light and the infra-red. If you choose from the viewing program to see just one or the other, half the data is thrown away and the remaining data is doubled to cover the width of the screen. The picture will be bigger but the resolution will still be the same - 1/2 the original 600 pixels. Remember that your screen resolution is independent of the captured data resolution. If you use the zoom feature of many picture capture programs all you will see is an enlargement of the pixels, not greater resolution. The zoom feature though will make it easier for you to see small details in the picture. Some weather fax boards sample the demodulated sub-carrier as high as 9600 Hz to get a more faithful reproduction of the demodulated signal but that still doesn't change the resolution. Some applications though, such as a digitized oscilloscope included with some fax boards benefit from a high sampling rate.

10. After a while, when you've got the operating procedure down pat, you will be able to set it up for automatic operation and be able to spend more of your time analyzing the pictures and debugging occasional problems. You might find after you've been successfully receiving pictures for some time that the quality of the pictures is deteriorating. Your first thought will be to blame the equipment. In all probability it will not be the equipment and you should not return anything for retesting unless you are certain beyond a doubt that a piece of equipment is at fault. Because testing is expensive we must charge for testing anything you return that is found to be in good working order. Many of the causes for deteriorating pictures are elusive. and often will clear themselves up after a while. Some causes are as follows. Sun spot activity, magnetic storms and interference from electronic devices particularly computers, printers and disk drives. The interference can originate in another location as a poorly installed piece of equipment can transmit interference for hundreds of feet. CB'ers can also cause interference as the 5th harmonic of 27.5 MHz falls right on 137.5 MHz.