| The James Madison University Wireless Experimenters'
Group, in conjunction with students in the JMU Renewable Energy program, maintain a simple weather station on the CISAT campus of James
Madison University. The instrumentation package consists of a Peet Brothers Ultimeter 800 basic station. The station transmits a wireless (radio) data packet once every five minutes on 145.510 MHz FM. The radio transmission is made using AX.25 protocol, at 1200 baud. The station transmitter operates under Part 97 of the FCC rules, and is licensed by the FCC under callsign WN4JMU. Station trustee is Dr. David R. Fordham, professor of accounting systems and information technology at JMU's College of Business. The instrumentation package collects wind and temperature data to determine the suitability of the site for a possible wind-generation (electrical power) station. The wind measurement project is under the direction of Dr. Jonathan Miles, professor of Energy Engineering at JMU's College of Integrated Science and Technology. The station is located on an 80-foot tower, at the northeastern corner of Commuter Parking Lot C-10. This tower is just northwest of the new University sports track, and southwest of the overpass of Reservoir Street over Interstate 81. The approximate coordinates are: N38-26.08 latitude, W78-51.50 longitude. Altitude is approximately 1375 feet above mean sea level. The tower is designed and engineered to ultimately hold a wind generator producing electrical power. For the time being, however, it holds only the weather station and its associated transmitting equipment. The anemometer is located at the top of the tower, along with the direction vane. The temperature sensor is located at the standard five-foot-above-ground level at the north side of the tower base. There is a second temperature sensor inside the electrical box. The box houses the weather console, TNC, and radio transmitter. At the present time, the station does not have a barometric pressure indicator, humidity sensor, or rain gauge. Although the station is within proximity to the licensed heliport atop Rockingham Memorial Hospital, its height is insufficient to fall under FAA rules governing aircraft warning lighting. However, for safety purposes, the top of the tower is illuminated with a steady red aircraft warning light 24 hours a day. The entire station operates off of 12-volt DC power provided by a battery bank, which is recharged daily from a set of photovoltaic solar panels mounted about 30 feet northwest of the station tower. The weather instrumentation is generating continuous data which feeds into the RS-232 port of a Kantronics PacketCommunicatorPlus KPC-3+ TNC. The TNC output drives an Alinco DJ-130 FM transceiver. The transmitter operates at one (1) watt of power, into 85 feet of Belden 9913 coaxial cable leading to a Diamond X50A antenna mounted at the 75-foot level on the southeast leg of the tower. The antenna exhibits a gain of 4.5dB and is omnidirectional. The transmitted signal is vertically polarized. This configuration should allow direct line-of-sight reception throughout most of Rockingham county, except for areas north of Island Ford & Elkton, or west of Little North Mountain. Reception might also be unavailable in certain areas shadowed by hills. Display of the weather data requires a standard AX.25 packet radio receiving station. Such a station consists of an FM receiver (standard 12.5 KHz narrow-band FM demodulation bandwidth) with its audio output to a 1200 baud AX.25 protocol terminal node controller (TNC), such as those available from MFJ, Kantronics, AEA TimeWave and Baypac. The output from the TNC is then fed into a serial port on a personal computer, and the received packet can be displayed using a standard windows terminal emulator, such as Microsoft WinTerm or HyperTerminal. (Alternatively, a receiving station could feed the audio output from the receiver into the "line-in" sound port of a personal computer loaded with any one of a number of sound-card-based digital packet radio terminal programs.) Data packets are transmitted once every five minutes, and consist of a 48-byte ASCII string preceded by the characters "!!", and followed by three carriage returns. Packets are identified as originating from FCC station WN4JMU, using unproto beacon type WX. The 48-byte string consists of twelve (12) four-byte fields, each containing a four-digit hexadecimal number. The field definitions can be found in an Adobe PDF document which can be downloaded HERE. Once you have the data packets, the easiest way of looking at the weather readings is to use a special Microsoft Excel Spreadsheet, available for free from HERE. Using the Microsoft Clipboard, copy and paste the data packet (starting with the two exclamation points!!) into cell A1 of the spreadsheet, then press Ctrl+w to execute a macro. The macro will parse the packet into the four-character fields, automatically convert the hex strings into decimal, and then calculate the following data fields and display them for you:
For the expermenters, a more tedious way to decode the data string is to manually break the 48-byte string into twelve fields, and type each field into the appropriate cell of a different Microsoft Excel spreadsheet which has been developed and which can be downloaded HERE. With this spreadsheet, you must manually enter the twelve four-character hex fields from the packet string, and the spreadsheet will automatically convert, calculate, and display the weather data. More information on this station can be obtained by contacting: Dr. David R. Fordham Click HERE for a picture of the tower. Click HERE for a photo of the solar panels.
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