Deeter Wireless Sensor System
The Deeter Wireless system uses radio messages from a remote sensor unit to the base station. This replaces the traditional wiring used to connect sensors and switches with a radio link. Because the system uses very little energy the remote sensors can be battery powered making them truly wireless.
The Deeter Wireless system uses the IEEE 802.15.4 standard.
The IEEE standard 802.15.4 focuses on low-cost, low data-rate communication between nearby devices. It is very well suited to low power consumption in battery powered devices.
The Deeter wireless system operates in the unlicensed ISM (Industrial, Scientific and Medical) 2.4-GHz radio band which is available worldwide. This means that in most countries the user does not need an installation license from the local regulatory authorities.
The Deeter system uses the Jennic JN5139 high power RF module. This is FCC certified for the USA market and meets ETSI (Europe) and IC (Canada) standards.
For an IEEE 802.15.4-based radio link, the radio transmit power is limited by the local regulatory radio regulations. Jennic’s JN5139-based modules are designed to comply with these regulations and are available as “standard” and “high-power” modules. The transmit power of a high-power module is approximately 100 mW, a hundred times that of a standard module, which is 1 mW.
At the receive end of a radio link, the minimum power level that can be detected is approximately 10-9 mW. Thus, radio receivers require only a tiny amount of radio energy to discern a usable signal.
It is convenient to use a logarithmic scale to express signal levels. Transmitted power is measured relative to 1mW. Thus 1mW is 0dBm. The receiver is sensitive to signals of -90dBm.
The maximum allowed transmitted power is 20dBm (in USA and Canada).
The Deeter Wireless System uses external low-loss, dipole antenna connected to a co-axial RF connector on the Jennic RF module.
This type of antenna is about 2 to 4 times more efficient, achieving up to double the free-space range, than an integral ceramic type.
It is important to mount the antenna away from other metallic structures, obeying a 6-cm clearance rule.
Does the antenna transmit in an omni-directional signal? What is the radiation pattern?
The radiation pattern of a half-wave dipole antenna looks like a doughnut. The dipole radiates in a similar way to the isotropic case close to the horizontal, but has virtually no radiation at the vertical.
Antenna gain is simply the antenna directivity taking into account any inefficiency in the antenna, and is usually expressed in dBi (that is relative to isotopic). The antenna used in the Deeter system has a gain of 2.2dBi.
Antenna inefficiencies can originate in the antenna structure itself, as well as the RF feed and the cable to the antenna.