Wireless Telemetry Network for agriculture and weather variables. This project involved the complete design of wireless telemetry stations with PLL programmable frequencies from 300 to 500 MHz at 50KHz spacing and the data acquisition board. Solar panels and batteries feed these transmitters, and the data acquisition board is capable to allocate 32 sensor signals of several formats of voltage, current and frequency, that are converted into 16 bit digital words.

The project involved the design of the sensors for several variables, including relative humidity and air temperature, pyranometric and photometric solar radiation, wind vector, and a patented volumetric soil moisture sensor

(US PTO # 6,014,029) with a two-wire serial interface that can be buried at some 1000 feet distance from the telemetry station.

The project also involved the design of a high sensitivity receiver with PLL programmable channels from 300 - 500 MHz. The receiver, with about 95 dB dynamic range, sends the files to a computer with a graphic user interface to explore a cumulative histogram data base, and has mathematical analysis tools, developed by other members of the team.

Inside the main box of the transmitter station there are several circuit modules, the main one is a mother board capable to receive and convert into digital up to 32 sensors, each one generating signals in a variety of formats, say voltage, current loop, frequency coded, PWM coded, etc.

When large quantities of sensors are connected, and in winter when sun light is not strong enough all days, and when the RF link covers long distances, say 10 or 15 Km, and the UHF buffer must be adjusted to maximum power, it is possible to connect two batteries is parallel in order to store more energy for night hours.

Each installation site has different requirements and sensors. A special timer unit controls the sampling times, programmable with pseudo random sequences in order to minimize transmission collisions with other stations. The transmission burst of the 32 channel data frames takes just a few milliseconds, and the sampling rate can be programmed, say 60 or 120 or any number of average samples per hour.

In general, the variables to be sensed have slow variations, but the timing can be programmed for very fast sampling rates, up to 12 "Mega-channels per second". To the moment no need for fast sampling rates has been required.

These stations are part of a set of 5 stations, located strategically in a valley and surrounding hills of a private industrial agricultural company. The receiving station software, installed in a computer located in the offices of the company, is capable to interpolate and map over a wide zone the weather variables: Relative humidity and temperature of air are displayed as color contour curves over the map, and the wind speed and direction are displayed as a vector field that can be sampled with the mouse. The sun light cannot be averaged realistically because some clouds have sharp borders.

The soil moisture is considered as a concentrated variable, valid just around each sensor of the network around each telemetry station. Up to 32 soil moisture sensors can be installed up to 1000 feet (300 m) from the telemetry station.

I keep no images of the receiving station and the computers site, but it is not attractive, it is just like an office. The receiver looks like a modem with a cable connected to the antenna, and a RS-232 cable connected to the serial port of the computer. The antenna, an omidirectional monopole is installed outdoors on the roof of the office.

The receiving station, on receiving each frame, is capable to detect errors, and in some cases is capable to correct them, or discard damaged samples, and keep waiting for the next sample to confirm values, but this does not imply to reject a complete 32 channel frame, but just the damaged channels. Each complete frame is transmitted twice.