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AMATEUR RADIO BY GARRY CRATT, VK2YBX Receiving weather satellite signals - the hardware required Interested in receiving off-air pictures from the weather satellites? Here's a rundown on the equipment that you'll need & where you can obtain it. Ever since the advent of weather satellites , amateur radio enthusiasts have been involved in the reception of images from spacecraft. Apart from the meteorological aspects of weather satellite reception, there are a number of technical challenges to be overcome if successful reception is to be accomplished. Areas such as satellite antennas , receivers , data processing and storage techniques all add to the challenge of satellite reception. There are several levels of weather satellite transmissions that can be received and each level provides higher · resolution and more varied formats all at an increasing level of complication, as far as the receiving equipment is concerned. Some satellites produce high resolution imagery which is sent at high speed on microwave frequencies. Such signals require significant effort and investment to be received. Other satellites, such as the polar orbiting "birds", use a much slower rate of transmission, in the VHF bands, and can easily be decoded using relatively simple equipment. These satellites use APT (automatic picture transmission), a system devised to allow users in remote locations direct access to meteorological data at low cost. APT resolution is typically 2-3km, allowing definite identification of cities, rivers, lakes and other major land features and their proximity to cloud masses. APT transmissions are FM, with an audio subcarrier that has been amplitude modulated. The amplitude peaks on the subcarrier correspond to white areas, while the lowest amplitude corresponds to black. Pictures are transmitted at either 120 or 240 lines per minute. What's needed This German-made satellite receiver (model MR-137) & its companion decoder unit (model FX-666) are one way of receiving weather satellite signals. Other hardware options are discussed in the text. 42 SILICON CHIP In order to receive APT signals from a polar orbiting spacecraft, we need a suitable antenna, a receiver, a decoder and a display unit. These days, with the cost of PC-compatible computers reaching their lowest levels ever, most operators will choose this kind of hardware to handle the display and decoding functions. However, this still leaves the antenna and receiver, which must both have particular performance characteristics for good reception. · The antenna should be horizontally polarised and have a high angle of radiation to allow reception for the maximum amount of time as the satellite becomes "visible", then passes overhead and disappears over the horizon. We discussed the construction of a suitable turnstile antenna in the tained. Other frequencies sometimes. used are 137.06, 137.12, 137.15, 137.33, 137.45 and 138.8MHz. VHF APT transmissions from these polar orbiting spacecraft use wideband FM with no pre-emphasis. Because the maximum deviation (of NOAA spacecraft) is ±18kHz, the maximum modulating frequency is 4kHz and the maximum Doppler shift is ±3kHz, we need a receiver with an IF bandwidth of 50kHz. This will present a problem to anyone proposing to use a standard scanning receiver, as the typical NBFM bandwidth is 15kHz and the wideband FM bandwidth is 180kHz. Alternative receivers A J-pole antenna is ideal for weather satellite reception. You can either use a commercial unit, such as the unit pictured here, or build the design to be published in a forthcoming issue of SILICON CHIP. November 1991 issue of the magazine. The next requirement is for a good VHF FM receiver, capable of reception in the 136-138MHz band. Many enthusiasts use a suitable scanning receiver which, despite not having ideal IF bandwidth characteristics for weather satellite reception, can be used to produce fair results. Dedicated kit receivers are also available at moderate prices. Some older crystal locked 2-metre FM receivers could also be pressed into service, although the cost of crystals will often make the purchase of a scanning receiver a more attractive proposition. The accompanying table shows a list of current VHF channels and the spacecraft that use them. As can be seen, some satellites share the same frequency (one will be turned off by ground station command if there is any chance of interference), so that maximum frequency utilisation is ob- One solution, suggested by Paul Hayden VK4ZBV, is to use one of the old 60kHz crystal filters from an early commercial 2-way radio transceiver. He also suggests an alternative approach, which is to use a crystallocked converter in conjunction with a surplus ex-army transceiver, such as the C45/46 or PRC9/10. Both these transceivers have a receiver IF bandwidth of 50kHz and can be converted to solid state operation. It is also possible to purchase a custom made 10. 7MHz filter from Hy-Q Crystals in Melbourne. Considering the highest altitude a polar orbiting weather satellite is likely to attain is 3000km, and that the resultant path attenuation at 137MHz is likely to be in the order of -145dB or so, the receiver must be capable of producing 20dB of quieting for an input signal of0.5µV (based on the spacecraft transmit power of 5 watts). This level of performance is reasonably easy to obtain, particularly if using a FET preamplifier at the antenna. Users should be aware of the close proximity of TV channel 5A and the adverse affect such signals will have on VHF weather satellite reception. Software Because we have elected to use a computer and video monitor as the decoder and display (and memory) devices, the choice of a suitable software program is the next project to tackle. There is an enormous amount of weather satellite software available, ranging from barely adequate to brilliant. Computer programs to suit Amiga, IBM, Commodore 64 and STOCK SALE!! FANS 80 x 80 x 25mm 240VAC .... $16.84 120 x 120 x 38mm 240VAC $16.92 Fan Finger Guards for 80mm Fans .. ....... ....... ..... .. $1.43 Fan Finger Guards for 120mm Fans ..................... $2.12 MISCELLANEOUS Circuit Breakers 7.5A- Press To Reset ............................ $7.25 Mains Power Lead 10A 1.8m long ........................... $4.16 9V Battery Snaps .... ............ .. $0.20 2 x AA Battery Holder ....... ..... $0.28 12-Way terminal block 10A ... $1.60 SEMICONDUCTORS 1N4004 Diodes ..................... $0.07 1N4007 Diodes ................. .... $0.10 1N4148 Diodes ... .... .. ... ...... ... $0.04 MJ15003 Transistor ..... ... ...... $6.50 MJ 15004 Transistor .......... .... $6.50 MJ15024 Transistor ........... .. . $8.60 MJ 15025 Transistor ... .. ..... ... . $8.60 MJ13007 Transistor ......... ..... $4.87 MFR571 Transistor .. .. ....... .. .. $4.27 NE555 IC .. ... ... .. ............. ....... $0.30 TL494 IC .... .. .. ...... .... ... .. ..... ... $2.83 MC14514 IC .......................... $3.00 MC34063 IC ............ .............. $2.98 ALL ITEMS 10 PLUS 10% OFF HYCAL ELECTRONICS Unit 4, 62 Gt. Western Hwy, Parramatta, NSW 2150. Phone (02) 633 5477 Fax (02) 891 5640 Credit Cards Welcome APRIL 1992 43 terns, Wichambrook Newmarket CB8 8QA, England. Phone (0440) 82 0040 of fax (0440) 82 0281. Their US distributor is Spectrum International Inc, PO Box 1084, Concord, MA 01742, USA. Phone (508) 263 2145 or fax (508) 263 7008. A comprehensive range of receivers, decoders, antennas, and other hardware for both APT, GMS and HRPT reception is available from: Quorum Communications Inc, 1020 Main Street Suite A, Grapevine, TX 76051, USA. Phone (817) 488 4861 or fax 817 481 8983. For those sufficiently affluent, Mitsubishi Electric can supply a suitable Video Copy Processor, allowing black and white prints of any video screen to be made for posterity. Model P75E can produce high resolution prints at 640 X 580 dots resolution in handy 200 X 154mm print size - ideal for the family album! Next month, we will discuss hardware requirements for the reception of GMS and HRPT satellite signals. A turnstile antenna can also be used for weather satellite reception although the results are generally not as good as from a J-pole. This is a commercial unit but you could also use the build-it-yourself design published in the November 1991 issue of SILICON CHIP. Tandy COCO computers are available, and may also be for other types of computer. Perhaps the best way to evaluate available software is to contact a local user group or scan some of the available bulletin boards for information on such programs. Hopkins, 4 Handsworth Street, Capalaba, Qld 4157. The software is available from: Mr M. Delahunty, 42 Villiers Street, New Farm, Qld 4004. A complete weather satellite receiving system and all discrete components including software can be obtained from Timestep Weather Sys- Hardware guide A suitable weather satellite receiver kit is available from Stewart Electronic Components, phone (03) 543 3733 or fax (03) 543 7238. The kit was described in the February 1988 issue of "Australian Electronics Monthly" (which has now ceased publication). A complete standalone receiver and decoder is available from Mr Volker Wraase, Kronsberg 10 D-2300 Altenholz/Kiel, West Germany. The receiver model is "MR-137", while the decoder is the" FX-666". A suitable pre-assembled and tested 137MHz preamplifier is available from: (1) SCISAT Products, PO Box 307, Kenmore, Qld 4069. (2) Vanguard Electronic Labs, 196-23 Jamaica Avenue, Hollis NY 11423, USA. An IBM PC/XT/ AT plug-in decoder board is available from Mr David G. 44 SILICON CHIP VHF WEATHER SATELLITES Country Satellite Freq. (MHz) USA NOAA9 136.620 USA NOAA 10 137.500 USA NOAA 11 137.620 USA NOAA12 137.500 USSR Meteor 2-17 137.300 USSR Meteor 2-18 137.300 USSR Meteor 2-19 137.850 USSR Meteor 2-20 137.850 USSR Meteor 3-2 137.850 USSR Meteor 3-3 137.300 USSR Meteor 3-4 137.850 Further reading (1) Communications Satellites - A Monitors Guide. 3rd edition by Larry V. A. Horn. Published by Grove Enterprises, PO Box 98, Brasstown, N.C. 28902, USA. (2) US Department of Commerce, NOAA Technical Report NESDIS 44. NOAA Office of Constituent Affairs, Herbert C Hoover Building, Room 6815 A, 14th & Constitution Avenue, Washington DC 20230, USA. (3) "TIROS-N Series Direct Readout Services Users Guide" and "The WEFAX User's Guide"; both available from The Co-ordinator, Direct Readout Services, United States Department of Commerce, National Oceanic and Atmospheric Administration, National Earth Satellite Service, Washington DC 20233, USA. In addition, NOAA has a large range of technical publications (NESS61 to NESS115) relating to weather satellite reception. These can be obtained by 'Yriting to the National Technical Information Service, US Department of Commerce, Sills Building, 5285 Port Royal Road, Springfield, VA 22161, USA. Information on related subjects can be obtained from the Environmental Data Service, D822, 6009 Executive Boulevard, Rockville, MD 20852, USA. SC